Feel Better, Live More with Dr Rangan Chatterjee - How To Build Lasting Strength: What Hunter-Gatherers Can Teach Us About Movement, Exercise & Healthy Ageing with Professor Daniel Lieberman #514

Episode Date: January 22, 2025

Why do we find it so hard to exercise despite knowing how good it is for us? Is sitting really the new smoking? And what can we learn about movement from studying populations who live more traditional lifestyles?   My guest today is the brilliant Daniel Lieberman, Professor of Biological Science and Chair of the Department of Human Evolutionary Biology at Harvard University. His research studies how and why the human body is the way that it is, focusing on the evolution of physical activities such as walking and running and their relevance to health and disease. He has published more than 200 peer-reviewed papers and three books, including his most recent, Exercised: Why Something We Never Evolved To Do is Healthy and Rewarding.   In this conversation, we cover so many fascinating topics and explore the powerful idea that humans have not actually evolved to exercise.   We compare the sitting habits of modern humans with more traditional societies and Daniel shares why it may not be how long we sit for that is causing us problems, but more the way in which we choose to sit. We also talk about the profound importance of maintaining strength and activity as we age, the relationship between movement and cancer, the truth about barefoot running and minimalist shoes and the concept of 'mismatch diseases' - this idea that our modern environment is in direct conflict with our evolutionary design, and the impact this is having on our wellbeing.   Throughout the conversation, Daniel challenges many common beliefs that exist around health, and offers us evidence-based, practical strategies for building a healthier relationship with physical activity.    Whether you're interested in the science of movement, looking to build sustainable exercise habits into your life, or simply curious about how our ancestors lived, this is a truly wonderful conversation with one of the world’s most highly respected experts. I hope you enjoy listening.   Support the podcast and enjoy Ad-Free episodes. This January, try FREE for 30 days on Apple Podcasts https://apple.co/feelbetterlivemore. For other podcast platforms go to https://fblm.supercast.com.   Thanks to our sponsors: http://www.vivobarefoot.com/livemore https://thriva.co https://calm.com/livemore https://drinkag1.com/livemore   Show notes https://drchatterjee.com/514   DISCLAIMER: The content in the podcast and on this webpage is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or qualified healthcare provider. Never disregard professional medical advice or delay in seeking it because of something you have heard on the podcast or on my website.

There is no one number of steps to take per day. 10,000 steps a day came from there was this accelerometer that was created in Japan just before the Olympics in 64. The story is that apparently in this company they were sitting around deciding what to call it and apparently 10,000 is an auspicious number in Japanese and they said well let's call it the 10,000 steps meter. Look the evidence on exercise is pretty darn clear right? Anything is better than nothing right? If you're if you're completely sedentary, more steps a day, climbing the stairs, parking your car further away from the shopping, anything is better than nothing.

More is better. At a certain point, the. My name is Dr. Rangan Chatterjee, and this is my podcast, Feel Better, Live More. Why do we find it so hard to exercise despite knowing how good it is for us? Is sitting really the new smoking? And what can we learn about movement from studying populations who live more traditional lifestyles? Today's guest on my podcast is the brilliant Daniel Lieberman, Professor of Biological Science and Chair of the Department of Human Evolutionary Biology at Harvard University. Daniel's research studies how and why the human body is the way it is, focusing on the

evolution of physical activities such as walking and running, and their relevance to health and disease. He has published more than 200 peer-reviewed papers and three books, including his most recent, Exercised, why something we never evolved to do is healthy and rewarding. In this conversation, we cover so many fascinating topics and explore the powerful idea that we humans have not actually evolved to exercise. We compare the sitting habits of modern humans with more traditional societies, and Daniel

shares why it may not be how long we sit for that is causing us problems, but more the way in which we choose to sit. We also talk about the profound importance of maintaining strength and activity as we age, the relationship between movement and cancer, the truth about barefoot shoes and the concept of mismatched diseases, this idea that our modern environment is in direct conflict with our evolutionary design and the consequential impact this is having on our wellbeing. Throughout the conversation, Daniel challenges many common beliefs that exist

around health and offers us evidence-based, practical strategies for building a healthier relationship with physical activity. Whether you're interested in the science of movement, looking to build sustainable movement habits into your life, or simply curious about how our ancestors lived, this is a truly wonderful conversation with one of the world's most highly respected experts. I wanted to start with this apparent paradox, this idea that exercise is something that is really, really good for us on so many levels, yet at the same time, it's not necessarily something that we have evolved to want to do.

Oh, I would say we didn't evolve to do it at all. But yeah, that paradox is what really motivated my last book, Exercise. And maybe to answer your question, I'll give an anecdote, right? Which is, I use in the book, but I was just finishing up a previous book, The Story of the Human Body, and I was in Mexico doing some research, and we were studying, you know,

runners and people who run, and actually discovered that most of the Tarot Mara famous for running don't actually run very much. But anyway, there was this one elder fellow who was a famous runner, did these very long distance races. And I was being a good anthropologist and I was asking all kinds of questions. And I had asked all kinds of other people the exact same questions with a translator. And one of the questions was about training. And everybody had always struggled with this question because, and I was beginning to realize that my concept of training was kind of alien

to the Tarahumara. And this guy just looked at me and I could tell without even the translator saying anything, it's like, why would anybody run if they didn't have to? And I suddenly had this like, you know, this little epiphany, right? That our concept of exercise is alien to most people, right?

And of course I work in parts of the world where people are very physically active. that our concept of exercise is alien to most people. And of course I work in parts of the world where people are very physically active, they work hard. Here I was in a part of the world where people are hardworking farmers, they've got no machines, they've got no running water, they're doing everything by hand. They occasionally do these long distance races, which by the way are a form of prayer,

that's why they do them. But the idea of going for a five mile run in the morning is nuts, nobody does that. So I think, and I had this sudden like this moment that, yes, we evolved to be physically active, but the kind of what we call exercise, which I define as voluntary, discretional physical activity,

it's planned for the sake of health and fitness is a completely modern idea. And furthermore, if you're struggling, if you're a farmer or a hunter gatherer, of course we were hunter gatherers for most of our existence, if you're struggling to get enough energy, right? Struggling to feed your family,

going for a five mile run in the morning, which is about 500 calories is a terrible idea, right? Because those 500 calories is a terrible idea, right? Because those 500 calories is energy that you could use either on your own body or on your family, right? So the idea of doing unnecessary voluntary physical activity for no reason other than for your health and fitness when you're already very physically active is nuts.

So we evolved to avoid physical activity except for two reasons, for when it's necessary or when it's rewarding, right? So play is important and rewarding. Work is rewarding. A race might be rewarding, but getting on a treadmill in the morning, in a gym with fluorescent lights

in a room with no air, et cetera, working as hard as you can get getting absolutely nowhere. There's a reason people dislike it. We never evolved to do that. Yeah. I think that's a very powerful message today. Like we're having this conversation in 2024. Everyone listening, I'm sure has been hammered with the message that exercise, that physical activity is good for us, it's good for your body, it's good for your brain, it's good for your longevity, et cetera, et cetera, et cetera. So we've all got the knowledge that we possibly, probably should be moving more.

Yet despite having that knowledge, so many of us are simply unable to put that into action regularly and they start to blame themselves. They feel guilty, which is a huge problem that I see and have seen in practice for many years. And, you know, we're having this conversation in London. I'm rarely in London these days, but I came last week for a couple of days. And I think the underground station where I took a photo and posted on social media really illustrated your point, which was this beautiful flight of stairs. And on one side was an escalator going down,

the other side, an escalator going up. And literally there was nobody on the stairs and both sides of the escalators were full. And I posted it, the first thing I said is this is not a post about blame. But I thought it just beautifully illustrated the problem that we have in modern society, which is why would you choose to take the stairs if you don't have to?

It's an instinct, of course. It's an instinct to take the escalator. There are no escalators in the Stone Age. I think I can say that with definitive knowledge, right? There were no elevators, lifts, so you call them here in England, but it's an instinct to save energy when you can. The escalator scene that you described

has actually been studied. There are actually a series of papers that have been now done in many different countries. It's been done in the US and Sweden, Israel, Japan, I can't remember where else. And it doesn't matter where you are on the planet, when there's a staircase next to an escalator, only less than 5% of people take the staircase. And it doesn't matter what culture you are, it's a universal. Because it's an instinct to, if you can save energy, why wouldn't you? And I imagine that our hunter gatherer ancestors would also have taken the escalator had that

option been available to them. Of course. And it turns out, so some of my former students actually measured how much hunter gatherers sit. Turns out the average hunter gatherer, because we're always told that we sit too much, right? And that's, you know, our chairs are out to kill us and et cetera, et cetera. And that, you know, we're kind of an over-sitting society.

Hunter-gatherers sit about 10 hours a day. That's the same as most Americans and Brits, right? So, they're no different from us. When they can, they sit down. I mean, there's some differences in their sitting, which we can maybe talk about later on. But I think going back to your point, I think in addition to the fact that it's an instinct

not to exercise, right? Not to be physically active when it's neither necessary nor rewarding, that we also engage in this form of blame or shame, right? People are made to feel lazy. If you don't exercise, for some reason you're lazy. And you have to remember that we're asking people to overcome a very deep seated instinct, right?

And so, and then people feel bad about themselves because they feel that, sure, I mean, they wake up in the morning and they think, well, yeah, I should go for a run or I should do this or I should lift some weights or something. And they don't do it for one reason or another. And then they feel really bad, right? And then we made, and then they think that, well,

they're lazy, there's something wrong with them. They're actually normal, right? They're completely normal human beings. And we, I think our job is to try to figure out how to help people be physically active, maybe not even exercise, but how to be physically active in a way that doesn't cause

that kind of, you know, do it in a positive way rather than a negative way. And I think, and no offense, I know it because you're a physician, but you're a physician that cares seriously about prevention. But I think one of the problems is that we've medicalized exercise. We consider it a pill, right? And nobody likes to take pills. Nobody likes to, you know, it doesn't make it fun. It doesn't solve that particular problem

of overcoming that barrier. I mean, I'm sure you know that most medications, people don't take their medications either. So if people don't take their pills for diabetes or this, that, or the other, why are they gonna take the exercise pill? Yeah, because it's often called the magic pill, isn't it?

Exercise and, you know, anti-cancer, anti-aging, anti-mental health problems, anti-everything. So perhaps a new PR angle is needed around exercise. I love that definition. You know, I can't probably get it word for word, but you basically said some sort of structured, planned activity for the purpose of health and wellbeing. Yeah, I think the key word is discretionary.

You don't have to do it. Discretionary. It's discretionary physical activity for the sake of health and fitness. Yeah, it's interesting. The movements that our ancestors used to do regularly and you've detailed them in depth and exercised, but they're not doing those things

for the purpose of health and wellbeing. Like that's a byproduct of doing what they need to do in order to survive, right? So it's a side effect. So it is a side, I mean, you're right. They do it because they have to, right? If you want to have dinner that day, you have to go out, you have to be physically active to get food.

There's no Uber Eats in the Paleolithic. So you have to go out and get your food. You have to go out and find the plants you're gonna eat. You have to go hunt the animals you wanna eat, all of that. So it's true, physical activity was absolutely necessary. But I think that it's not just a side effect. I would argue that human beings, not only like every other animal, benefit from being

physically active, but there was special selection in human evolution for exercise to be unusually potent for enabling us to live long and healthy lives. And that's something that makes us different from every other organism. So to understand that, you have to recognize that we evolve from apes, and our closest living relatives are chimpanzees. And well, I've had the good fortune to go out and watch chimpanzees in the wild.

And let me tell you, you know those shows on TV where you watch chimpanzees and they're doing all kinds of amazing, wonderful things? They do that, but very rarely. Most of the time, chimpanzees just sit and eat. They're incredibly sessile. They're like plants. They do that, but very rarely. Most of the time chimpanzees just sit and eat. They're incredibly sessile. They're like plants. They just sit there.

They spend half of their day literally putting food in their mouth. Then they digest that food because it's full of fiber. And then occasionally do some wild, crazy things, have sex, run around, throw things, and then they go back to eating and digesting. And so chimpanzees turn out to be basically couch potatoes, they're incredibly inactive. Typical chimpanzee walks two to three kilometers a day, takes basically as many steps per day

as a sedentary American. And sleeps 12 hours a night. And that's kind of a chimpanzee life. And then we evolved for two things that are very special in this regard. One is that we evolved to be way more physically active. So we've got data on hunter-gatherers and citizens as farmers.

These people are taking 15 to 20,000 steps a day, way more than a chimpanzee. They're running, they're carrying, they're climbing, they're doing all kinds of things, right? So they're very physically active, way more so than chimpanzees. So we evolved to be extra active compared to our ape ancestors. they're climbing, they're doing all kinds of things, right? So they're very physically active, way more so than chimpanzees. So we evolved to be extra active

compared to our ape ancestors. That's one thing, but the other thing that's important is that we also evolved to live very long lives after we stopped reproducing. So almost every species on the planet stops, you know, basically doesn't last very long after they stop reproducing. That's because natural selection sadly cares

about only one thing and that's how many offspring we have. So once you stop having offspring, you enter what's called the selective shadow. I love that term. It means that you're basically irrelevant. There's no selection to keep you alive after you stop having babies. And humans are one of very few species

for which that's an exception. And that's because human grandparents actually play an important role in helping their children and their grandchildren. And what are they doing? Well, I mean, they're passing on knowledge and all that sort of thing, but they're also hunting and gathering.

They're foraging. Grandparents in hunter gather societies are out there every day. Grandmothers are digging up tubers and other sorts of things and bringing them back for their children and their grandchildren. Grandfathers are out there hunting and bringing back honey and all sorts of things like that.

They're physically active. And so we evolved to live long lives, not retiring, going to the beach and playing canasta or whatever it is. We evolved to live long lives to be physically active. And in turn, I believe that there's been selection in our evolutionary history for the effects of that physical activity to turn on the mechanisms

in our body that help us increase our health span, which means increases our lifespan. So physical activity isn't just something you do to get the food, it is, but the reason that exercise or physical activity isn't just something you do to get the food, it is. But the reason that exercise or physical activity is so healthy is that we've undergone selection for that physical activity to turn on all kinds of repair and maintenance mechanisms that keep us healthy.

And because we never evolved not to be physically active, we never evolved to turn them on to the same extent when we're in inactive. So instead of thinking of exercise as medicine, I would think of inactivity as being like poison or like not having air. Yeah. So it's not necessarily that exercise or physical activity is good for us. It's that the lack of doing it is really harmful. Exactly. We call that a mismatch in evolution. It's an evolutionary mismatch. Just like we never evolved not to breathe. Right? That's a problem. Right? We never evolved not to be physically active. And when we stop being physically active, everything goes wrong.

I mean, literally, because physical activity affects every system in our body. Yeah, it's so fascinating. In Exorcised, you write about, you know, grandmas and grandfathers being really active in these hunter-gatherer populations. I think this is a section where you were even writing about how a nursing mother, yes, she still does some gathering, I think, but you were sort of making the case that the grandmas are way more active. I thought that was really, really interesting because that's quite alien to the common belief, I would say, certainly in Western cultures that you can kind of slow down a bit as you get older. And we have this modern phenomena that's retirement, right? So speak to that a little bit, because that's really interesting.

Yeah, no, I mean, the literature is amazing, right? So there's an anthropologist at Utah named Kristen Hawks, and she did a study many years ago of Hadza hunter-gatherers, and she showed that the mothers are digging, you know, several hours a day, getting, because one of the mainstays of the diet there are these underground storage organs, tubers, right? So Kristen Hawks showed that mothers might spend

two to four hours a day, I think it was, I have to go back and look at the paper, but something like two to four hours a day. Grandmothers are basically twice as active. They're spending twice as much time digging, because why? Because they don't have to take care of the kids as much anymore, although the grandmothers

do help a lot with childcare. But they're not nursing and breastfeeding, are they? Yeah. So I guess they've got- Yeah, and also they're, you know, the kid's not clinging onto them as much, right? So they have more time. So they're out there spending more time every day,

digging up these underground storage organs, and then they're not eating them all themselves, they're bringing them back to camp. And by the way, how do they bring them back to camp? You carry them, right? So carrying, you know, today we have maybe little backpacks, et cetera, but we don't carry very

much anymore. But in the life in the Stone Age involved lots of carrying. So they're digging, they're carrying, they're walking. And all of that goes until you die, basically. There's no weekends, there's no bank holidays, there's no retirement, there's no social security or it's equivalent. This is what you do. And it's rewarding, of course, but it's also necessary.

And I think in turn, that physical activity helps them live to be grandparents in the first place. Think about it this way. In the West today, a lot of people as they get older become less active. We know that from lots and lots of studies and that we don't turn on those repair and maintenance mechanisms that keep us healthy.

So we're more likely to get heart disease and diabetes and osteoporosis and Alzheimer's and the list of various diseases is very long. But now we have medicine, people like you kind of keep them going, right? And so we can enable us to live, we have reasonably long lifespans, even with a lot of chronic disease.

So the average American, I think their lifespan is 78, 79. The average health span, the number of years that average American lives without entering a period of chronic disability is about 60 something, 63. So the average American spends 16 years before they die in a state of chronic disease. And how does that compare to these hunter-gatherer populations that you've spent so much time with? As far as we can tell, they don't have that at all. I mean, there's no evidence of diabetes really in these populations. There's heart disease, as far as we can tell, is essentially non-existent or very, very, very rare.

It's very hard to diagnose these diseases, obviously out in the field. Have you been to Kenya annually since you were in your twenties? Is that right? Oh gosh, I've been going to Kenya almost every year since 1987. I know, so a long time, and other countries in Africa.

You've been studying these populations, which gives you, I think, a rather unique insight and other countries in Africa, you've been studying these populations, which gives you, I think, a rather unique insight into movement and how we as humans have moved for much of our past. It's interesting that there's very little heart disease from what you can tell. And of course, there's multiple risk factors for heart disease. Lack of physical activity. And of course, there's multiple risk factors for heart disease, lack

of physical activity being one of them. But it's kind of fascinating to me that some of these populations, to my knowledge, at least, are eating sort of significant amounts of fat in their diets. We don't have that much data on hunter gatherer diets. But we just published an analysis last year, two years ago in the American Journal of Clinical Nutrition where we took all the data on every hunter gatherer population for which there is good dietary data.

Turns out there's only about 12 or 13 populations for which we have sufficiently high quality data to analyze their diets. And there is no such thing as a hunter gatherer diet. They are incredibly varied. Some of them eat a lot of meat and some of them eat very little meat. Some of the, and it's, there is no one paleo diet.

That's probably one of the problems with the paleo diet. But I would say that if you took an average, about 30% of the calories in a typical tropical subsistence population comes from meat. But also that meat is very different from the meat that we eat in the West. That meat has got lower levels of saturated fat. It's a different beast basically. So the meat is not even the same.

When we're talking about the movement patterns that these populations have had, it strikes me as though there's a unity when they move. Let's say you're walking and you're digging for tubers. That has a real purpose, doesn't it? Right? You're doing that because you know that's important for survival, for your daughter maybe who's nursing your grandchild back at the camp or whatever it might be. Whereas a lot of the ways we now move as modern humans living in urbanized settings is there's almost a lack of unity. And what I mean by that is, you know, we could be, let's say we've motivated ourselves to go to the gym, the treadmill in front of the fluorescent lights. Okay. Let's say someone has motivated themselves to do that. And good for them.

And good for them. Often it's such a tedious pastime for them to do that they will do anything they can to numb themselves away from the activity. Maybe they're watching this podcast. Yeah. Someone will probably be watching it now or listening to music or watching the news or whatever. Again, so the grandma, the hypothetical grandma who you have seen and spent time with, who walks and

then is chatting and is digging for maybe four to eight hours a day and doing that hard physical activity. There's a reason for that. Whereas it feels like we've kind of divorced our body and mind some of the time when we try and move in terms of, I know physical activity is good for me. I need to do it. I've got to this treadmill, but let me just numb out for the next hour, but I'm still going to get those physical benefits. It's not any validity to what I've just sort of hypothesized there. And do you see any potential consequence of that? that. Vivo Barefoot are one of the sponsors of today's show. Now I am a huge fan of Vivo Barefoot

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I mean, I could have spent my entire day doing almost nothing. And I'm sitting in a chair here. I could have taken the subway here, et cetera, et cetera. And the lift up and all that sort of stuff. So we now have created this weird thing called exercise because it's good for us. But when we do it, we're doing it,

there's no purpose for it other than for the sake of exercise. And that is a kind of weird thing. And so, and because it's not fun, we try to divert ourselves while we're doing it to decrease how unpleasant it is, right? Make it as minimally unpleasant as possible, right? And that, you know, we've industrialized it,

we've commodified it, we've medicalized it, we've, you know, we've, and there's nothing wrong with industrialization or medicalization or commodification, but that takes away the real kind of the purpose for it that could make it much more, I mean, I think it's why people enjoy sports, right? Because when you play a game of football or something, right? You now have a purpose that's,

and most people don't think of going for a walk with a friend or playing a game of sports. They don't always think of it as exercise, right? They think of it as you're playing a game of football, you're going for a walk with your friends, and that gives it purpose. And I think that's, I think one of the, I think one of the arguments,

one of the tricks that we should be using to try to help each other be more physically active, make it part of our lives. So go for a walk with somebody. Yeah, I'm not at all criticizing that. I myself will do that from time to time, right? So I get it. I just find it fascinating that throughout my career, I'm sure the same is with you.

You evolve. You sort of spiral around. You think you've cracked something and then you get some more information. You develop new insights. You come background against it, possibly where you were before. And I kind of think about this mind body separation a lot. And I think two things, I think we're a time-pressed society because of the way that we work often. And therefore we're trying to fit in our exercise and our meditation and our mindfulness and our breath work practice and all these things all take time. But actually, let's say someone, you mentioned before some tribes run as a form of like religious expression. It's a form of prayer. It's a form of prayer.

Right? So there's a real unity there. There's a real mind, body, spirit, if you want, like connection in terms of what they're doing. And you tell this beautiful story, I think in the chat, when walking and exercise about when you accompanied two handsome gentlemen on a hunt. I think you asked them if you could go on a hunt and it made me stop and laugh. They were very minimalist dress with their kind of sandals and you had your full gear on your waterproof trousers and your GPS and your backpack. And it really painted a wonderful image. But one of the things that really stood out to me

is that you were sort of saying that maybe it was a few hours of walking in silence where they are paying attention, listening, looking for footprints. And I kind of felt, have we lost something here where you could potentially, if you have a mindful walk in nature, let's say you're lucky enough to have nature near you and you go for a one hour walk in nature,

let's say with a friend or by yourself, but instead of listening to something, you pay attention to the birds singing, nature, the wind rustling. Like you're getting your mindfulness meditation, your movements all in one go. Absolutely, yeah. I mean, there's a wonderful argument actually

that the origins of science comes from tracking because you're making hypotheses. You're not only observing nature, right? Because you need to, right? You're trying to follow an animal, right? But you're also thinking, you're not only observing nature, right? Because you need to, right? You're trying to follow an animal, right? But you're also thinking, you're also trying, you're making guesses. So I think it went to the right.

Oh, let's see. How would I figure that out? Oh, there are some footprints. So I think that you're engaging your body and your mind together in an integrated way that is really kind of wonderful. And I think that's actually the origin of the runner's high because if you do really long-term aerobic exercise,

you get this wonderful thing called a runner's high. It's caused by basically endocannabinoids, right? Which are the same molecules that give us high when you have cannabis. And when you get high, right? What happens? You have an increased sensory perception. In fact, one of the first times

I got a really good runner's high was actually at the London Marathon, I remember, because I ran London many, many years ago, I ran the London Marathon. And I was at a conference and whatever, and I just had fun running it, and I just kind of ran it for fun. And at the end, I just had fun running it, and I just kind of ran it for fun.

And at the end, I remember going by Big Ben, because right by the end, and I remember saying to myself, wow, Big Ben is really big. And I was having like experiences like that. Everything was, the blues were bluer, and that person's butt was bigger, and all the things I was looking at.

And I remember I got to the finish line and I was talking to some of the folks from the medical tent, because I was working with some medics there. And I remember this guy named Dan Tonstel-Pito, who's the medical director of the marathon. He said, Dan, you need to be very careful on your way back to your hotel

because you've got a really serious runner's high. Right. It's like, oh yeah, I guess I do. But why do we have that runner's high? Because when you're running, you're tracking and you're picking up all this information and it's helping you get more, everything you're seeing is now heightened.

The sensory awareness is higher. And I think, so we actually have adaptations to increase exactly what you're just talking about. Because I guess the point of running, and I appreciate that you do mention that there are these long races that Tara Humara often do to, you know, celebrate or as a form of prayer, but generally speaking, the running is done for a purpose. Correct.

So therefore it makes sense that we would have heightened awareness and sensations and maybe sounds. Yeah, and everybody who runs knows that or does any kind of exercise, you know that you have this heightened sensitivity. And it can be fun to listen to. This morning I ran along the Thames and I had headphones and I listened to some very, very zippy playlist

and that was a lot of fun. But sometimes I often run without music and I find it's very, very zippy playlist and that was a lot of fun. But sometimes I run without, I often run without music and I find it's a form of meditation. And my mind wanders and I look at sites and all that. And that's really kind of wonderful too. I think when I spoke to Elida Kipchoge, the Kenya marathon runner a couple of years ago, the week after he broke the world record in Berlin,

from recollection, when he's running with his running team and his crew, no one's listening to anything. Never. But he said, I think when he's like doing some extra work on his indoor bike, I think he said that's when he'll put on music again, to sort of maybe dilute the tedium of something, which I find interesting. Then you've studied the biomechanics of human movement in a number of forms over the years.

Yeah, that's my day job really. Yeah, and so, from what you have seen, and there's a gorgeous section in the introduction where you said you've played barefoot cricket in India, you've raised horses on foot in Mexico, you've tracked oxen and kudu in Tanzania, you've run and carried water over your head in Kenya. I thought what a rich life you have led. You've studied all these populations as well, but what are some of the key things you've learned from these more natural populations about human movement that we perhaps have got wrong

in terms of how we understand human movement here in the West? Well, first of all, I think what I've learned the most from, I've been very fortunate, I agree, and I have the best job on the planet, I think, and I'm incredibly lucky. But I think. And I have the best job on the planet, I think. And I'm incredibly lucky. But I think what I've learned the most is that

these folks are just ordinary everyday folks. They're like everybody, right? And they have the same goals and wishes and desires. They're trying to do better for their children. And they're working hard, just like people in London are working really hard, but they're just working hard in a different way. And there's nothing really special about them.

It's just that, but I think the thing that I've learned the most, but I've learned to really, I don't think of them as more natural populations. I just think of them as just human beings who just live a less industrial life. Yeah.

But I think what I've learned the most is that it's changed the way I think of what's normal, right? We think it's like yesterday, I got in an airplane and flew from Boston to London. And this morning, I, you know, my hotel, I had breakfast cereal that came in a box. And I had milk that came from a thing. And then when I wanted water this morning,

I just turned a faucet and out it came and all that. We think that's normal. And I think what I've learned the most is that the lives that we live today in many parts of the world, especially cities and high income countries, they're not normal, right? And just perceiving that, thinking about that

is been eye-opening. Everything from the footwear that we wear, like wearing cushion shoes with high heels and all that kind of stuff, to the foods that we eat, the physical activities that we do, they're not normal. There's not no one normal way of doing it, but what we're doing is very abnormal. And sometimes that's good.

I mean, antibiotics are good. Refrigeration is good. There's, you know, brushing your teeth is good. There's lots of things that I do that are not normal that are good for me, but there's also a lot of things I do that are not normal that are bad for me. And I think the experiences I've had

have helped me think a lot more about just what's normal and also think about variation because there's an enormous amount of variation out there in the world. If you go to populations in the Arctic versus the tropic and you know, the wetter tropics and the drier tropics, et cetera, the variation is stunning. It's stunning. You mentioned footwear then. You probably regarded, I think, as one of the godfathers of the minimalist shoe movements. The barefoot professor. Yeah, I don't know how that sits with you,

but let's go there. You do mention it quite a bit in exercise as well about the footwear that these less industrialized populations routinely wear. You know, many things in life have got, they're a trade-off, so there's pros and there's cons. What are some of the benefits, do you think, of those populations and potentially us wearing kind of less cushioned shoes or for want of a're back to minimalist shoes. Well, I think the word that you used, trade-offs, is the operative word, right?

There are benefits and costs to everything, just about everything on the planet. There might be a few exceptions, but they're hard to think of. And shoes are one of them, right? So shoes, the big benefit of shoes, apart from the fact that they can look sexy or nice or all that kind of stuff, is that they protect your foot.

They protect the sole of your foot from damage. And the other thing that we look for in shoes today in high industrial, wealthy populations is for comfort. So we wear shoes because they look good, they protect our feet and they're comfortable. But the trade-off is that, that is really the most the trade-off is that, that is really the most important trade-off is that they make our feet weak.

So what a shoe does is it kind of does some of the work for you that the muscles in your foot would otherwise do. If you have a shoe that has this, like if you've ever gone for a walk on the beach, which I'm sure you have, or gone for a run on the beach, after a day of running or walking on the beach, your feet are kind of tired.

Why is that? Because when you're pushing off from the sand of the beach, after a day of running or walking on the beach, your feet are kind of tired. Why is that? Because when you're pushing off from the sand or the beach, that's a compliant surface and now you have to use your foot muscles, have to work harder to generate force. And you're talking about walking on the beach without shoes on? Without barefoot. Thank you. But if you were to wear shoes, it's a lot easier because you've now made the surface now stiff. And so you can push, you have this old expression in America, you can't fire a cannon from a canoe, right? If you push off from a stiff shoe, right? You're now, your foot muscles have to do less work.

And your muscles in your feet are like the muscles on any other part of your body. If you use them more, they're stronger and they're larger. And so by having shoes that are stiff, but also having arch supports in them and toe springs and all the fancy schmancy features that we have in our shoes, enable the foot muscles in our feet to atrophy

or not grow to the extent that they normally would have grown and be as strong. So we've published studies where we've taken out into the field, just an ultrasound, you know, now we can get these really cheap ultrasounds that work on a tablet. It's amazing, the technology. So we can go out and ultrasound people's feet in Kenya

and places like that in Mexico. And people who don't wear shoes have much stronger foot muscles. That's the best way to measure foot strength, is the cross-sectional muscles. And we can look at people from the same population who live in the city, who wear shoes all the time, and they have smaller, weaker feet.

They also have a much higher percentage of flat feet. So actually out in the areas where people are habitually barefoot, we don't see flat feet at all. I mean, it's non-existent. Whereas you go into the city, you see the same percentage of flat feet as we see in America or in England.

So I think the big effect is that people's feet have become weak and you go to the gym and you watch people work out, right? I go to the gym sometimes too. And people are working on their biceps and their legs and their whatever, but the one bit they're not working out is their feet because they're now encased

in these supportive cushioned shoes that have effects. So that's one thing. There's one more thing though, which is that when you have cushioned shoes, it also changes how you run. So barefoot people don't land hard on their heels. They have to land softly and gently because it hurts.

And now we have these shoes that have all this cushioning and that not only that changes the mechanics of how we run. And when that does that, we end up not feeling the impacts, but the impacts are there, because they're just slowed down. That actually increases the impulse. That's the area under the curve.

It's the integral of that. And that actually shoots up to our knee. And that causes, we think that causes a lot of knee injury. So shoes make your feet weak, and they also, I think, change the way we walk and run and that can have negative effects. Okay. I've got so many questions.

That's a long, long answer, sorry. No, no, no, not at all. I mean, regular listeners to this podcast will know what a fan I am of minimalist shoes. I personally have been wearing them since 2012 now. So 12, almost 13 years, like pretty much exclusively. I see you've got some Vivo barefoot on like I have at the moment.

But I just want to go back to what you said about strength. So let's make the case to someone who goes, well, but why do I need foot strength? Like, for example, they may see the merit in, I don't know, going to the gym. Let's say they're a young guy in their 20s. They might fancy the idea of some bigger biceps, right? So they can see, oh, if I work on my biceps in the gym,

my biceps are gonna get bigger, which might look good, and also potentially gonna help me carry things, right? So there's a reason that they might want to go and work on their biceps. They might also be thinking, Dan, yeah, but why do I need my foot to be strong? What benefits is that going to have for me? Well, if your feet hurt,

you're not going to be a happy individual, right? And having weak feet can cause a wide range of problems. The biggest one is, I think, plantar fasciitis. So the plantar fascia is this connective tissue that runs underneath your foot. It goes from your heel and it's like a, it's this very avascular, but highly innervated. So there's lots of nerves in it,

but very few blood vessels. That runs from your heel and it wraps around underneath your toes, right? And it's, we've actually studied the evolution of the plantar fascia. It's an old feature that evolved long ago, but in humans, it's taken on a new role. And that role is to act as another layer of the foot

that helps us stiffen our feet when we push off. So humans, unlike, one of the unique things about humans is we have an arch in our feet. Chimpanzees, other animals don't have that arch in their feet. Actually we have several arches in our feet. There's a transverse and a longitudinal. Anyway, that fascia helps stabilize that arch when we push off.

But the problem is that it didn't evolve to do it very much because there are also four layers of muscles in your feet. And those are the ones that really, their job is to stiffen the foot. And what happens is that when those muscles are weak, the fascia ends up doing a job it never evolved to really do, which is to take over the job

that the muscles should be doing. And then what happens is you get, you stretch that fascia, it gets angry and you get plantar fasciitis, which I'm sure you know, and I'm sure many of the listeners know, is one of the worst things can happen. It's awful. Plantar fasciitis sucks.

I've had plantar fasciitis. That's actually what got me interested in a lot of this. I was, you know, I'm a runner and I used to, if I didn't change my running shoes fast enough, I would had plantar fasciitis. That's actually what got me interested in a lot of this. I was a runner and I used to, if I didn't change my running shoes fast enough, I would get plantar fasciitis. And then I would, I got to the point where I was like buying running shoes constantly to avoid plantar fasciitis.

Now that I've switched to minimal shoes, cause I started, cause we published the big barefoot running paper in 2010. It was the cover of nature. But I started sort of studying this in the, I was sort of doing it maybe 2007, 2008. I haven't had, I can't even imagine having plantar fasciitis anymore

because I have much stronger feet. So if you want to avoid plantar fasciitis, you want a strong foot. If you want to avoid having a fallen arch, collapsed arch is no fun either. People develop an arch the first few years of life, babies are born with a flat foot. You develop it as you start using your foot.

And then people, if they stop using, you know, those muscles in their feet, the bones of the feet, those muscles get weak and your foot collapses again. So again, people who have strong feet and who don't wear shoes, they don't have fallen arches. They don't have flat feet. So those are two good reasons to avoid a flat foot, avoid falling arches.

And I think there's a third reason, which is that it's a proxy, right? For using your body as we evolved to use it. And there are all kinds of muscles in our bodies we don't use very much anymore. And having strong feet, strong legs, strong, everything is just part of being a normal human being. And when one bit gets weak, it's like a weak link in a chain. Right? Everything is connected. Everything is connected. You can't, you can't just strengthen this and

not strengthen that. Everything should be strong. Yeah. If I just share my own experience with transitioning from regular modern cushion shoes, I remember when I first went into minimalist shoes in 2012, it takes you a little bit, you just start getting used to it. But there was a very noticeable impact on my back for the better straight away. Like a lot of that stiffness just, just went as a consequence of wearing them. Um, when I started wearing them, people told me I had flat feet, podiatrist diagnosed

me with flat foot. You could see that I had flat feet. I don't anymore. Exactly. Okay. And this is what I think people sometimes don't understand, it's like, oh, now that I'm using my foot muscles, well, guess what, my arch is coming back. This happens over and over and over again. We published some data on this.

I mean, you know, this is considered anathema to many podiatrists, but it's true. By strengthening your foot, you can actually, you can restore an arch. And you know, there are a lot of podiatrists out there who say you can't do that, but that's a lot of podiatrists out there who say, you can't do that, but that's just not true. Yeah.

It's another example of where I feel in medicine, for all the things that we do well, one of the problems I've always had in my profession is that I feel much of my training and focus is to deal with the downstream symptom. Oh, absolutely. So my previous book, The Story of the Human Body, I came up with a term for this.

I call it what I call dis-evolution. What happens is that we treat the symptoms rather than the causes of problems that are mismatches, like not using, you know, having strong feet. And then we, by treating the symptoms rather than preventing the causes, we allow the things to get worse, right? So more and more people get flat feet,

more and more people get diabetes, more and more people get, I mean, obviously there's no flat feet and diabetes are very different levels of things. Yeah, but the principle is that. But the principle is the same, but I do wanna back up a little bit because it's also true that when we medicalize

and commercialize these treatments or these preventive treatments, sometimes we overdo it too. So when that book, Born to Run came out, which started arguably in my lab, but a lot of people read that book and they thought, I'll have to switch to minimal shoes, go barefoot, and all my problems will be solved.

My teeth will be whiter, girls will like me more, whatever, right? I'll be able to run a two hour marathon. And what happened was that people went crazy. They went, they did it too far, too fast. You have to build up strength. You have to learn, if you've been running one way your entire life

and you have to learn to run differently, you can't just do it overnight. You have to be gradual. So I think we also sometimes oversell sometimes these treatments. And I remember my wife, who also likes, my wife has ever since she was a kid loves to go barefoot and she loves still walking barefoot.

She walks around Cambridge, Massachusetts barefoot all the time. But she went to a podiatrist or an orthopedist at the Harvard Medical Service. And he was like, he was upset about me. And so he knew that she was really my wife. And he started saying, well, you know, I'm seeing all these patients now are getting injured

because of these minimalist shoes, these common barefoot shoes. I don't like the term because you're wearing a shoe, you're not barefoot. But anyway, and she pointed out to him, she said, well, that's true. And some of these people are overdoing it, but you're not counting all the people

who are also wearing the shoes who you're not seeing. Yeah. And he's like, oh, I never thought about that. It's a good point, isn't it? Yeah. But it's also that I think when we talk about this topic, we need to be really careful what we're talking about, right? So for example, my current view based upon what

I've seen and what I've studied, a lot of it being your research, is that a lot of the benefits come when people start living their regular daily life in minimalist shoes, right? So they're off issue, they go to the shops and then they're, you know, I think most people, a lot of people do really, really well when they make that transition. I do think for some people, look, some people can run in cushioned shoes and having no problems. They're running fine. And if they broke, don't fix it. Yeah. So I get that. So I think, I think the whole minimalist shoes thing gets conflated with running and I think running is sure. Like I run in, in minimalist shoes and I'd be wearing

them for 12 years now and I've been gradually doing stuff. Right. But I think, I don't think you necessarily have to run in there. No, of course not. Actually, that's one of the things that's mystified me. So when we published the Barefoot Running Paper, it was the cover of Nature and had a big deal and it's, you know, it got a lot of publicity. And I thought, okay, this is fun, but you know what? What's the most fundamental form of physical activity? It's not running, it's walking. And I expected to see people start applying the tools that we put, you know, the arguments that we published

and the methods that we published and the ideas that we published to start working on walking. And yet there's now been thousands of papers in the literature on barefoot running. It's been great for my, you know, citation index, but I was like, why aren't you guys studying walking? Walking is actually more important. So we've started doing a lot of work on barefoot walking,

published another paper in Nature. And what does it show? So here's one of the really cool things that we found was that when you walk barefoot, of course you develop calluses and calluses are the natural shoe. And one of the reasons we wear shoes is to protect our feet, right?

Calluses, people can be barefoot and they can walk on the most amazing stuff if you have a proper callus and you don't feel, you know, you don't hurt yourself. But what's really cool is like unlike a shoe. So when you're wearing a shoe, you don't feel what's under the ground. You can't tell what temperature the ground is.

You can't feel the pebble that you stepped on, et cetera. But when I started running barefoot, I suddenly realized that I could run over an acorn or something like that and not hurt me. When you when I started running barefoot, I suddenly realized that I could run over an acorn or something like that and not hurt me. When you say you were running barefoot, do you mean with minimalist shoes or completely barefoot? Completely barefoot. Okay, so real barefoot.

When I say barefoot, I mean barefoot, right? And so I built up calluses. So I had this tradition, I would run the Boston Marathon, which is in April, and then I'd start taking my shoes off. And by the end of the summer, I had really nice thick calluses. And I put my shoes on again in the winter, right?

And I realized that I could run over surfaces that would otherwise hurt me. But it wasn't that I didn't feel the ground underneath me, it's just that it didn't hurt me. So what calluses, because calluses are made out of keratin. It's like what makes your fingernail or your hair, right? It's stiff, but it's protective. And so when you run on calluses,

you're like a hair, like a fingernail. It's protecting your feet remarkably well, but with no loss of sensory perception. That's amazing. And so we did these studies in Kenya. We looked at people who had thick calluses because they never wore a shoe in their life. And we measured their sensory perception. And we ultrasounded their feet

so we knew how thick their calluses were. And they could feel just as well what somebody who had almost no calluses had, but they had all that protection. And so one of the things that's abnormal about our world, we were talking earlier, is having no calluses on your feet. And I remember when I was doing a lot of barefoot running,

I don't run barefoot very much anymore, because I've just kind of, I don't know, moved on. But I remember one morning I was, there was this, to get to the Charles River from my house, so there's a few streets I run down. And I often in the morning, I would see this woman who was, she had two beautiful dogs. I remember I would see her all the time,

because they were gorgeous, beautiful dogs. And I remember one morning as I was running by her, she looked at me and she said, you're not wearing shoes. And as I went whizzing by her, I said, nor are your dogs. And she was like, the look of shock on her face, like her dogs are not wearing shoes, oh my God, right? But it's normal not to wear shoes, and it's normal to have calluses,

but we think it's now weird people buy pumice stones to get rid of their calluses, right? And so that's just one more way in which our world is abnormal. Yeah, I remember as a kid, we'd go every other summer, we'd go to India because that's where mom and dad's family, my family, that's where they all stayed. So we'd go for six weeks every other summer. And you know, some of my fondest memories are like when I was playing with my cousins

and about 4pm every day in this block of flats, you'd be like, oh, you know, it's kind of playtime downstairs. And so I was a oh, you know, it's kind of play time downstairs. And so I was a kid, I wanted to go and play and they're all playing football barefoot. And I'm used to wearing shoes, you know, in the UK and you just go, all right. And you know, the first day or two it probably hurts a little bit.

I think you're totally used to it. And you're like, oh, you can totally play the same level and the same ferocity, but everyone's barefoot. Actually, you have to play better because I played barefoot football with the kids and because we work a lot in schools and you can't kick a ball in a sloppy way. Yeah, exactly.

Because the shoe enables you to be really sloppy. But when you're barefoot, you learn good technique, right? It's the same with running, isn't it? If the sole of your foot can't feel what's happening when you interact with the ground, you could probably be very sloppy with your mechanics because it's kind of hiding it from you. I think, yeah, I think the key skill in running

is to run lightly and gently and not overstride. I mean, that's like 90% of the game. And if you go barefoot, it's pretty hard to overstride and it's pretty hard to overstride and it's pretty hard to hit the ground like an elephant. What would your advice be then to people who think, okay, well, that's really interesting, Dan. I'm interested in maybe not wearing my thick cushion shoes or my high heels or whatever it might be so much. What do you encourage them to do?

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to take advantage of this limited time offer, all you have to do is go to drinkag1.com forward slash live more. That's drinkag1.com forward slash live more. That's drinkag1.com forward slash live more. I think you can benefit from, first of all, walking around your house barefoot. I mean, many people do that because it's cleanly, you know, like shoes running around in the house anyway. That's barefoot walking. It depends on how much you may not do that because it's cleanly, you know, like shoes running around in the house anyway. That's barefoot walking. It depends on how much, you may not do that much.

But if you want to try, you know, try a pair of minimal shoes, but if you do use them, you have to build up, right? You can't go from zero to a hundred overnight and see how you like them. And if you like them and your feet feel better and it's gonna take some time, wear them more. There are some other nice things about minimal shoes. You have a nice wide toe box.

Your feet toes aren't scrunched together. And there are other things that I think are nice about them too. And there are now quite a few companies out there that make them. And some of them are really kind of sexy and nice and all that. So, but if you have plantar fasciitis-

Don't go straight into them now. No, I mean, you need to, actually that's a good time to wear a shoe, that to provide you some support so that you can actually take the pressure off your, so if you're worried, so being barefoot and having stronger feet is going to help prevent the next bout of plantar fasciitis, but it's not going to treat, it's actually going to, it's going to aggravate a current case of plantar fasciitis. Yeah, so the short term versus the long term.

So you need to be careful about it too. Okay, so you mentioned that these hunds of other populations sit for comparable amounts of time to Western urbanized populations. We have been told that sitting is the new smoking over the last few years. What's your take on sitting? Well, again, it's completely normal to sit, right?

I mean, cows in the field sit, you know, moose sit, chickens sit, birds sit, everybody sits, and humans are no different, right? And so when Dave Reichlin and Herman Ponzer and Brian Wood measured sitting among the Hadza, which are a population of hunter-gatherers that are, you know, the most studied because they're the easiest to study,

they sit 10 hours a day. So the idea that, you know, sitting is this modern Western scourge is just not true. That said, there are important differences between how we evolved to sit and how people now sit today. Now, right now we're having this lengthy conversation and I'm kind of glued to this chair. But so what we sit now in the West,

we may sit a long periods of time, but we tend to live, we also tend to sit for long uninterrupted bouts, hours at a time without getting up. But if you look at populations that don't have chairs, they interrupt their sitting bouts constantly. They get up to turn the fire, to go pick up a kid, to do a little bit of this, to do a little bit of that. And so-

Is that always to do stuff or is it sometimes because if you don't have a chair, you might be sitting in a- Oh, absolutely. Position that becomes uncomfortable after 20 minutes. I think it's a combination of the two. Yeah, exactly. So they don't sit for long uninterrupted bouts.

That's one difference. And the other difference is that they don't have, like this chair I'm sitting in, I'm now leaning against the back, right? It's now, the chair has been designed to, you know, for ergonomically to have the least amount of work that my body's doing, right? And so that means that I'm not turning on a single muscle

in my body now, except for I'm gesticulating and I'm using my mouth, right? Whereas, you know, the modern chair with a seat back didn't become common until the industrial revolution. Actually, the first mass produced chair was produced in 1859, an important year for evolutionary biologists because that's the year that

The Origin of Species was published, right? And so Tone, a guy in Germany, produced the first, you know, the cafe chair with those bent, that was the first industrialized chair. And now of course, chairs with backs are omnipresent. You go anywhere in the world, those plastic chairs, you name it,

you go anywhere on the planet, people have chairs, right? But that this chair I'm sitting in and that you're sitting in now, we no longer have to use any back muscles to keep up our upper body. We're not squatting or sitting on the ground. So we're not using any of the muscles in our legs. And when you, even that little bit of muscle effort changes

and also getting up every once in a while. So intermittent, you know, sitting for, you know, getting up every once in a while and also using chairs. More active sitting positions. Exactly, and also, you know, having to use your back to stabilize yourself or your quads or your hamstrings, et cetera, to squat or sit on the ground, all of that's turning on your muscles.

And you're not using a lot of energy, right? It's not gonna help you lose weight, but just turning on your muscles turns on all these genes, et cetera. You're using up fat in your bloodstream, you're using up glucose in your bloodstream, you're doing all kinds of other things that makes that sitting much less harmful.

So I think for me, Dan, isn't that really the key take home from your work, which is let's study these populations, let's observe what they're doing, that can give us an insight into perhaps how we have evolved to live and move and eat and all these other things. But we're not going to go back to that world, most of us.

So what can we learn from them and then apply in our modern urban environment? And so what came to mind as you were describing that is about three years ago or so, we're in London at the moment, but in my own podcast studio, I've got, I don't know, you call it a chair, it's called a Moveman. And it's the best thing I ever bought

because it's basically, there's no back to it. I think it's not one of those medicine balls, but with a stable base essentially. So I'm sitting there having these long two hour conversations and I feel my back feels amazing at the end of it because if I have to constant, my muscles are having to do something to keep myself upright.

Constantly, exactly. And I don't give it, I don't have one for my guests. They've got an ergonomic chair because I'm like, well, if they're not used to that, they may be going all over the place and not be on the mic, right? So I'm like, okay, well, I'll give them a normal chair, a really nice ergonomic chair, but that has been transformed so we can learn

from the research that you and your colleagues do and go, okay, well, could we have sitting positions that are less, it's not making them uncomfortable because who wants to sit at a desk in an uncomfortable way, but using, having to use your back muscles whilst you're sitting at your computer typing, well even that would make a difference. Sure. So I agree. I mean, that's, that's one of the reasons I'm interested in this, but I'm also interested in not just people like you and me, but I'm also interested and concerned about the transition that's going on around the world as people transition from being subsistence farmers to living in cities

and to help them not make the mistakes that we've made. So as people, we call this the physical activity transition. So for example, we have a project in Rwanda now. We're looking at people as they move from being farmers out in the rural areas where they have no machines and no running water and no electricity. And then they move to Kigali, the big city,

and all of a sudden their lives change overnight, right? How can we help that transition occur in a better way, right? Because I think this has global implications because so this is not just for people in England, this is for people for everywhere. And if we can avoid these mismatches, again, we don't have to go back to, you don't have to be a hunter gatherer,

but just a simple thing, like just changing the way you sit can be important or having a little, your watch telling you to get up every once in a while, to remind you just to get up or make a cup of tea or go use the bathroom or whatever. All of that is good. Are people receptive? Like in those populations, you're saying that you'd love to help them

not make some of the mistakes that we have made. Well, right now we're mostly studying what's going on. Okay. And then hopefully having an impact in terms of public health, right? So, for example, in Kenya, working with the Kenya National Museum to do an exhibit on this sort of thing that's in the of public health, right? So, for example, in Kenya, working with the Kenya National Museum to do an exhibit on this sort of thing

that's in the Kenya National Museum, which is the big museum system in Kenya, to try to actually use the enthusiasm for running in Kenya, kind of give a public health message about physical activity. You don't have to be like Elliot Kipchoge or whatever and run and win the London Marathon

or the Boston Marathon or whatever, just going out for a jog can be a great thing or just other aspects of physical activity. So we're, yeah, so that's, yeah, this is an important message that the whole world needs to know. In terms of walking, there's a, you know, maxim isn't there that we should aim to have

around 10,000 steps per day. What's your take on that? Oh, well, you know, that's a kind of a funny story. I'm not sure if you've covered that on this on your podcast before, but you know, that 10,000 steps a day came from, there was this accelerometer that was created for the, in Japan just before the Olympics in 64.

And the story is that apparently in this company, they were sitting around the table and deciding what to call it. And apparently 10,000 is an auspicious number in Japanese. And they said, well, let's call it the 10,000 steps meter. And turns out it's actually not that bad, right? It's a, you know. It's not bad as a recommendation.

It turns out to be okay. So if that'll help you get more steps in, so if you have one of those watches that makes sure you get 10,000 steps every day, fine. But again, we've kind of medicalized it, right? We've turned it into a prescription. And we often talk about optimizing health or whatever. Well, it doesn't work that way, right?

So my colleague, Iman Li at Harvard has done a lot of work on step counts in health. And if you look at some of the graphs that she's published, for example, first of all, there's a lot of error around the mean, but if you're interested in say heart disease, the more steps you take, the better. 3000 steps is better than 0,000 steps and 5,000 steps is better than 3000 steps and 7,000 steps is better, et cetera, et take, the better. 3000 steps is better than 0,000 steps

and 5,000 steps is better than 3000 steps and 7,000 steps is better, et cetera, et cetera, et cetera. Is there an upper limit? So far, I don't think she sees a limit for steps. It's just walking, right? So like if you could get to 15,000 or 20,000 steps, it's currently from what we know, we think that's gonna help decrease

your risk of heart disease. That's what her data show. But again, there's a lot of error variation around the mean. So what happened, what your benefit might not be the same as my benefit. Of course. There's a lot of variance around that mean. But if you look at the data on step counts

and say all cause mortality, it kind of evens out starting around 7,000 steps. So once you're hitting 7,000 steps a day, it's kind of like, look, you've got most of the benefits. Yeah, and if you did diabetes, you'd get a different curve, et cetera, et cetera. But again, there's a mean, but there's also incredible variance around the mean.

So what might be good for you is not gonna be the same thing as for me, or if you're 50 versus if you're 20, or if you've had knee injury, or I could go on, right? So we prescribe it like, you know, how many or I could go on, right? So we prescribe it like, you know, how many aspirin you should take or how many milligrams of such and such you should take. And it doesn't work that way. Right. So maybe that helps some people, but I think other people makes them confused and agitated and, and, and stressed, right?

It's yet another source of stress in their life. Did you say before that some of these hunter gatherer populations that you have studied, they're taking what 15 to 20,000 steps a day-ish? That's correct. Yeah, but again, that doesn't mean that that's best for them, right? Just because hunter gatherers do something doesn't mean we should do it.

It's not a prescription, right? Hunter gatherers also don't brush their teeth. Hunter gatherers don't sleep on nice mattresses. Are you going to give up your mattress, right, and you sleep on the ground. Hunter gatherers don't get on airplanes. Hunter gatherers don't have refrigerators. Hunter gatherers don't use vaccines.

Hunter gatherers, I mean, I could go on, right? So we call this a paleo fantasy, the idea that what hunter gatherers do is a prescription for modern life. Instead, it's that by studying hunter-gatherers and also farmers, most of my work is actually with subsistence farmers. Subsistence farmers are people who tend to have no machines, they don't have to do their work for them, they don't have tractors, they don't have generators, they don't have electricity,

they don't have running water. These are people who are growing the food that they subsist on. That's why we call them subsistence farmers. And which country are you studying these populations in? We've studied them in Mexico, we've studied them in Rwanda, we've studied them in Kenya. That's where the three main places we've done this kind of work. Anyway, so just because hunter gatherers

take X number of steps per day doesn't mean that's the number of steps you should take. Just because hunter gatherers eat something doesn't mean that's what you should eat. Just because hunter gatherers don't do something doesn't mean that's what you should eat. Just because hunter-gatherers don't do something doesn't mean you shouldn't do it either. Instead, these are populations that tell us about the normal range of human variation

and how our world has changed, enabling us to now understand what's a mismatch, right? What is it that we're not adapted for, right? Because a mismatch disease is a disease that is more common or more severe because our bodies are inadequately or imperfectly adapted for this novel environment. And so these are ways of helping us identify

the mismatches in our world and then addressing them. So there is no one number of steps to take per day. Look, the evidence on exercise is pretty darn clear, right? Which is that, or physical activity, I should say, right? If anything is better than nothing, right? If you're completely sedentary, just taking a few steps, more steps a day, climbing the stairs, parking your car further away from the shopping, anything is better than nothing. More is better. And at a certain point, the benefits seem to tail off, right?

But trying to come up with a number, an optimum is not only impossible, I think it actually sends an incorrect message, right? That it's like a medicine which you can prescribe in a particular dose. It just doesn't work that way. And I think, and we also get this idea, it's like this magic pill, right?

I mean, exercise is good for you. There's no question about it. Physical activity is good for you because if you don't do it, it's bad for you, but it won't prevent all disease, it decreases your vulnerability. So people who are physically active are much less likely to get breast cancer

and many other kinds of cancer, colon cancer, the list is very long. They're much less likely to get breast cancer and many other kinds of cancer, colon cancer, the list is very long. They're much less likely to get heart disease. They're much less likely to get diabetes. They're much less likely to get COVID, right? But they're not prevented from getting them. You can still get diabetes if you exercise. You can still get heart disease if you exercise.

You can still get all these diseases. It's about reducing risk. It reduces your risk. I would say it reduces your, that's the medical term. The evolutionary term is it reduces your vulnerability. Right? Your vulnerability. So risk is a statistical measure,

but it doesn't really work that way for you and me. Yeah. Many people are becoming aware these days of the importance of strength and lean muscle mass, particularly as they're getting older. I think that certainly is a public health message, at least in the online podcast world, it's getting out there that it's important. It's incredibly important.

Yeah. So can you explain why you think it's so important based upon what you've seen? So one of the, you know, as people live longer, right? Actually, we're not living all that much longer. The data for how the hunter gathers, by the way, is that if they survive childhood, their mean age of mortality of death is between about 68 and 78. 78, by the way, is the life expectancy

of Americans today, right? So it's not dissimilar. No, it's pretty similar, right? But the difference is that they're not getting a lot of these chronic diseases that we get today in the Western world. So they're maybe living to similar ages, but free from these afflictions

that reduce quality of life for so many people these days. And the term we use is health span, right? So health span is the number of years you live without any serious disease or disability, right? And so their health span is basically the same as their lifespan, because there's no medicine to keep them going, right? Once they get sick, they die, right?

So we evolved to have a long health span, which means therefore to have a long lifespan. And one of the ways to extend your health span is to stay strong. What happens is that, you know, people, if they, you know, muscles are a use it or lose it tissue, right? They're metabolically expensive, but well, you're clearly stronger than I am.

But so most people are about 30 to 40% muscle. People who do a lot of weights might be a little bit higher, right? But muscle's really expensive tissue. You have to eat a lot more calories per day because of all your muscle, right? We get to pay for that extra muscle. So we evolved to have muscle when we need it.

So when you exercise, do strength training exercise, you build up muscle. We also evolved to lose it when we don't need it because it's energy that could go towards something else. Reproduction is what evolution cares about. So that's why it's a use it or lose it system. So as people become less active in high-income countries because they've got electric can openers

and running water and elevator lifts, they don't have to carry anything. Go to the supermarket, you have a shopping cart instead of carrying the food around, et cetera. We have prems for the carrying your children, right? I could go on, right? Because we don't do much strength anymore, we're losing, we lose muscle rapidly as we age.

And that creates a condition that you know only too well called sarcopenia. That's a medical jargon, but it's a good one because sarco is the Greek word for flesh and penia is loss. It's flesh loss. I love the term because it really makes you think about it, right?

So people become sarcopenic, they lose muscle mass. And that sets in motion a vicious circle because when you're frail from loss of muscle, you suddenly lose the ability to do all kinds of things like get out of a chair, right? Or it gets harder and harder because you lose power, you lose strength. And then you end up doing less of other things

and it sets in motion this, again, this vicious circle that makes you less and less active, which then sets in motion all kinds of other consequences of physical inactivity. So healthy aging requires you to maintain your strength. It's really important. And the populations that you said, you mentioned before how grandfathers and grandmothers

stay remarkably active compared to modern Western populations. They're not specifically doing, they're not doing their cardio and then their strength training and then their high intensity training, are they? They're sort of, how, have you seen that them maintaining their strength as they age? Well, we're trying to measure that now. There's actually very few studies of this. So there's

some grip strength studies out there, right? Cause that's easy to measure. And yes, their grip strength stays pretty good and grip strength is not bad. It's kind of a reasonable proxy for overall strength. But we're actually trying to study this phenomenon more carefully with sensors from looking at other aspects of the body. But yeah, I mean, there's no question. They stay pretty strong as they live, as they age. And that strength of course helps them age better.

But the mismatch, and again, because it's a user to lose it system. So if they're using it, so they're not losing it or they're not losing it as fast. I mean, they're still, they're still aging and they're not as strong in their 70s and 80s as they were in their 30s, right? But they're still, as far as we can tell,

generally a lot stronger than the average, you know, American in their 70s or 80s. And so that's helping maintain their health span. I've often thought about the cost of muscle. And yes, we talk about maintaining strength and putting on muscle. You don't need to become a bodybuilder and have massively huge muscles. If you want to, nothing against that. I'm just saying that's not necessarily what we're talking about. The cost of muscle, like if you're out and energy and food is scarce, you don't have

big refrigerators and freezers and store covers with loads of foods. If you put on loads and loads of muscle, you have to feed that muscle, which means you have to acquire more and more foods. So I think it's quite costly muscle, isn't it, to have it on your body? Very, yeah. So, and you also need extra protein and all that. So, yeah, we evolved to be, we evolved to be economical, right? And by that, I mean to have enough, but not too much, right? So you want enough muscle so that you can, and you want, also you want varied muscle, right?

We have muscle fibers that are good for endurance, but they don't produce a lot of power. Those are the slow twitch fibers. We have muscles that are good for power and speed, but they're not good for endurance. And those are the type, those are the fast twitch. And we have the kind of intermediate muscle fiber types and you need a good mix, right?

You need mostly slow twitch for aerobic long distance endurance for the walking, the running, et cetera. But you also need some fast twitch muscles too, right? And you also want to wire up your nervous system to your muscles kind of properly. And one of the things that physical activity does, exercise, sports, training, all that does is that you learn that you can actually turn on more muscle fibers

with a nerve than before. You can train your nervous system to be more efficient in how you use your muscles. It's all kind of a mix. But again, you're quite right. Bodybuilding, that kind of stuff, is actually deleterious, right? Having more muscle than you need is actually a cost.

Everything's a trade-off, right? So too much muscle is actually a problem, as is too little. There's a balance, right? Is too much muscle only a problem when you can't feed it with enough calories? That's right, yeah. So which was normal until very, very recently. when you can't feed it with enough calories. That's right. Yeah.

So which is, which was normal until very, very recently. So I tend to think in evolutionary terms. Yeah. So, so, you know, one of the things a lot of the longevity movement is kind of trying to educate people on is this idea that you, you know, your muscle mass is going to go down after the age of 30, unless you do something significant about it. Okay. If you're not paying attention and doing something, it's going to start declining. Can you slow down the rate of decline?

Yeah. And the good news is easy. You just do weights a few times a week. Yeah. You don't have to do that much. But I guess, let's say you go and really, really take this to heart and go, right, I'm going to put on loads and loads of muscle. I was thinking, you know, every time you eat foods, depending on what you eat, there is some sort of cost to the body. There is a bolus of inflammation to a certain degree, which your body has to manage, right? So then you're also turning on an anabolism, catabolism, you're, you know, I'm sorry, there's

a jargon, but you're, you're but you're going back and forth between building tissue and using energy and yeah, it's complicated. So I kind of think, because I feel we can, as you mentioned, you publish this paper in Nature in 2010 on minimalist shoes or barefoot walking and running, right? And then people take it to an extreme and they start trying to do marathons or barefoot walking and running, right? And then people take it to an extreme and they start trying to do marathons and barefoot shoes having never been in them before, right? I guess what I'm trying to get to is are we potentially at risk of taking the message? I've got to be very careful how I phrase this because sockapenia is real and it's causing a

lot of problems. So clearly it's better for people to focus on putting on muscle, but are there some people who perhaps are overdoing it and therefore having to overeat and turn on all those mechanisms every time they eat, which potentially could become problematic for their longevity. So it's a hypothetical point. I think it's a really interesting hypothesis.

I don't know any data on it. Certainly in terms of the endurance part, there are data on that, right? I've seen data on people who do ultra marathons and the question is, can you exercise too much? And most of that study is on aerobic exercise, right? Cardio. And the answer is, so far there's very little evidence

that you can't, right? There was actually a study done here in the UK on the UK biobank study. Where they actually looked at a few people in the biobank who did crazy ultra stuff. Now, remember these are very small numbers, right? So the statistics aren't great because they're not that many people who do ultra marathons. Even though it's a growing sport,

it's still, you know, a tiny fraction of the population. But so far there's really no good compelling evidence that they're doing themselves any harm in terms of their lifespan and stuff like that. I've not seen data on bodybuilding, but there is one trade-off that is, I think, very important and worth discussing, which is that people who do only strength training

and don't do cardio. So this is something that we've published on, my colleagues, Aaron Baggish and Rob Shave and I, because our cardiovascular systems evolved. There is a trade-off in how your heart works. So your heart's a pump, right? And it's pumping blood throughout your body. And sometimes when you're doing cardio,

what you're trying to maximize is this cardiac output, how much blood you're sending through your body at any one given time. So each time your heart pumps, how much blood is leaving the ventricle, the heart, right? And then flowing throughout your body, right? That's your cardiac output. And for cardio, that's what you're doing.

You're trying to increase cardiac output. When I'm lifting weights, now I'm doing something very different. Now my heart is pushing. I don't need as much energy from my body, but it's now pushing that blood through muscles that are contracting, lots of muscles that are contracting, and that's high pressure, right?

So that's what we call a resistance or a pressure challenge. So when you're doing cardio, it's a volume challenge, but when you're doing weights, it's called a resistance challenge. And some of that's good, right? But our cardiovascular systems involved such that if we don't engage in cardio, we don't develop, we don't fight the kinds of problems that occur

in our arterial system that cause hypertension that prevent us from having cardiovascular disease. And resistance physical activity, which is fine, strength training is good, but if strength training in the absence of cardio leads to hearts and cardiovascular systems that don't get that benefit. So people who do strength training, fine,

but don't skip the cardio, you need both. And what do you mean by cardio? Cardio is any kind of physical activity that requires you to increase your volume, your output. So swimming, walking, running, volleyball, game of soccer, all that. And some sports are mixed, like rowing, for example. I recently bought a rowing machine and I absolutely love it.

It's like my favorite new form of cross training, right? Rowing is kind of a mix of both aerobic, but also there's some strength involved, right? That's one of the reasons why I love it. So there's a famous study that was done on Finnish athletes. So Finland's one of those countries where they have fantastic national healthcare system and they have data on everybody in the whole country.

And they looked at the aging of Finnish athletes who were strength athletes versus weightlifters versus like cross-country skiers and runners, Finland is famous for both obviously, versus the average everyday Finns. And it turns out that the weightlifters who didn't do much cardio actually had as worse or sometimes worse health outcomes as sedentary fins. They weren't getting the benefit of the cardio

that the aerobic athletes, the endurance athletes were getting. And there are other studies which kind of showed the same thing. So again, nothing wrong with strength training, but don't, the trade-off is don't only do strength training and not do some cardio. You need to do both. And then I think looking back to what you've been saying throughout this conversation, the case you make in exercised, like we've evolved to move every day, right? We've evolved

to, as you say, these populations walking 15 to 20,000 steps a day. Again, you've made the point, it doesn't mean that we have to do that same level, but it's hard to think that we can get away without doing some degree of kind of walking, significant walking every day. And it's certainly fine. If I just reflect on, you know, you look at things through the lens of evolution, I look at things through the lens of what have I seen in practice over two decades? And you know, yes, the research supports this, but time and time again, like, you know, the people who do well from a whole variety of different conditions, whether they be physical health or mental wellbeing, you know, a commonality is that they're moving regularly. And if they're

not increasing it makes a big difference. I've seen it time and time again. And so- Evolution explains why. Evolution explains why. So you have the data and the experience, but you know, we have this old, this famous expression, you know, nothing makes sense in biology except in the light of evolution. You could actually say So you have the data and the experience, but we have this famous expression, nothing makes sense in biology except in the light of evolution. You could actually say nothing makes sense

except in the light of evolution. And so it's the evolutionary story which explains why this is the case. And I think that the evolutionary perspective also helps us think creatively about it too. Yeah. You mentioned about, is there an upper limit to exercise and that some of this data on

ultra marathon runners doesn't appear to suggest that there is from that data at least. And you acknowledge that there's small sample sizes. But again, just as with sitting where you said, yes, although the Hadza tribe are sitting, you know, similar amounts to what we are sitting each day, the way in which they're sitting is fundamentally different. You can make the same case when we're trying to study exercise. And, you know, are marathons harmful?

Right, for example, if someone was to pose that question, because some people have saying, you know, a marathon's too much, right? But the point I'm trying to make is that let's say, what does running a marathon mean? Well, it means you're completing 26.2 miles, okay? You can do that in a variety of different ways. You can be hell for leather the whole time. You may struggle, but you could be in one of those top heart rate zones, or you could be doing it in a very, you could in theory do it in a low cardiac

sort of fitness zone under your lactate threshold where you're probably putting minimal stress on your body or at least less stress. So we, although both people have completed a marathon, you could make the case that while the impact on their body is gonna be completely different because of how they've done it. Absolutely, you know what?

I've run a lot of marathons, right? And I can tell you, it's so much more fun to be at the end of the pack, right? The guys who are, you know, and the women who are like trying to win, right? They're not having any fun at all. They're looking at their watches all the time. They're looking at their splits.

They're worrying about their gels and their hydration and this, that and the other. They're, you know what? If you're just like running to finish it, maybe because you're running for a charity, because it gives you a purpose, which I think is also a wonderful thing about the modern marathon.

I mean, the London Marathon is the biggest single day charity event in the world. It is a wonderful party. I've been to it twice. It's just amazing, right? So these people having a great time. And you watch the guys at the beginning and the women at the beginning,

walk across the finish line, because I've also sat at the finish line. They're stone-faced. They're like, you know, they're just relieved. They're like, ah, they did it. You watch the charity runners that come in and they're just, they're the happiest people on the planet, right?

They're having a great time and they did it, they made it. No, no, the more fundamental question is, do you need to run a marathon to get those health benefits? And the answer is most definitely not. Yeah, I agree. Marathons are a challenge. That's why they're such a big deal. It's hard to run.

And the training is really the hard part, right? Training to run 26.2 mile. And it does put a toll on your body. You have this cardiac troponin breakdown and I could go on all the technical details. Yeah, it's a stress on your body. But you know, there's no evidence that it's bad for you, but do you need to do it?

Absolutely not. And I think we have this idea that you have to swim the English Channel or run a marathon or do a full triathlon, you know, Ironman, et cetera. Absolutely not necessary. Again, some exercise is better than none. More is generally better, but the benefits tail off.

And there's always a trade off. And I think the biggest trade off for like marathons or triathlons is the toll on your family, right? You know, all that time out training was, you know, time that you don't spend with your loved ones or whatever. So there can be, you know, everything has a trade off and extreme endurance sports are no exception. Let's talk about another mismatch disease, cancer.

You call this mismatch disease and you specifically say that it's a disease of high energy. What do you mean by that? So cancers are, so I'm an evolutionary biologist, right? So I think of cancer from an evolutionary perspective. And for me, cancers are a kind of evolution that's gone wrong in the body. It's a kind of natural selection

when a group of cells suddenly acquires a set of mutations, more than one, that now enable them to out-compete other cells. They don't turn themselves off. They take energy from other cells. They're now competing with the other cells in your body. It's a form of natural selection in the body that doesn't benefit the host,

but it's benefiting those particular cells. And what is it that makes those cells able to do that? Well, it's generally more energy. So think about the causes, the things that we know are help fight cancer or the things that we know that cause cancer. Well, high levels of body fat, right? People with obesity are much more likely to get cancer.

People who have high levels of circulating insulin. Insulin is a hormone that makes things, turns things on. Cancer is about the on switch is off way more than the off switch. That's basically what's going on. Hormones, again, hormones like estrogen, progesterone, testosterone,

they're turning the on switch on, right? Cancer, the on switch is on so much that these cells are producing molecules that are caused damage, you get more mutations. They're, you know, I don't know if you've talked about mTOR and rapamycin on the show really, but that's the molecular mechanism, that's the off switch, right? So when we look at populations that move

from low energy environments to high energy environments, cancer rates go up. And we can see the mechanisms and think about physical activity that turns down cancer rates amazingly. Women who get just basic levels of physical activity, 150 minutes a week, the estimates are there's 30 to 50% lower lifetime risk

of breast cancer. Let me say that again. 30 to 50% lower lifetime risk of breast cancer from just basic levels of physical activity. Why don't more of us know this important statistic? Colon cancer, it looks like 60% decrease in incidence rate for people who are more physically active. I could go on, right?

And why is it? Because physical activity is essentially turning the off switch, right? But again, flipping it like you did before, yes, technically physical activity is decreasing those levels of cancer, but you could also look at it the other way and go, we've evolved to move when we don't move,

we increase our rate of cancer. Exactly, exactly. Yeah, I mean, that's exactly the, you're absolutely right. So the mismatch is not being physically active and we're not physically active. Again, remember what's life all about? It's about taking in energy and having babies. So when we have extra energy,

our bodies are gonna use that for building, for making babies, for building tissues, for whatever. So we, you know, so women, for example, who are sedentary, they all of a sudden have this extra energy they're not using on physical activity. So what do they do? They increase their estrogen and progesterone levels. Those experiments were first done

by my colleague, Peter Ellison at Harvard, who showed that women who ran 20 kilometers a week, so they're spending 180 calories a day, this is not high levels of running, right? Had 50% lower rates of progesterone and estrogen during the second half of the menstrual cycle. Now these women were not infertile. They were not having trouble conceiving.

You could say, exercise is lowering their progesterone levels. But I would actually say it's the reverse. Being inactive so that the body says, oh, I've got all this extra energy. I'm gonna shunt that energy towards reproduction. And because after all, that's what it's all about, right? So, and now you have higher levels of estrogen,

higher levels of progesterone, those increase cancer rates. And physical activity also, again, we've talked about repair and maintenance, right? The energy that you allocate when you're physically active, after I exercise, right? I energy that you allocate when you're physically active. After I exercise, right? I ran this morning around the Thames. I did probably about eight miles, right?

My body's metabolism is still elevated from that morning run for sure. It's probably three, 4% higher now than it would be if I hadn't gone for that run. And what's that higher metabolism doing? It's not, I'm not replacing the energy that I spent running. I'm turning on all kinds of mechanisms throughout my body that are repair and maintenance mechanisms.

One of the things I've done is I've increased the number of natural killer cells in my body, right? Now, natural killer cells, I love the term, right? It's very more like, right? But natural killer cells are part of our immune system that are all, they're swimming around my body all the time. And one of the things they do is they look for cells that have cancer and they identify

and get rid of cells with cancer. So I've turned up my immune system to help fight among other things, cancer in my body. But it wasn't that the exercise, you know, again, we evolved to do that, right? So it's, if the other way of thinking about is that not being physically active means that I have a depleted abnormally low level of natural killer cells, which are swimming around my body right now,

looking for cells that have cancer. So I'm not, that surveillance mechanism is now turned down and I could go on, there are many, many other antioxidants. You know, when you exercise, your mitochondria are producing all this energy for your body, but the mitochondria are spewing out what's called reactive oxygen species. These are molecules with unpaired electrons that can,

they rust, just like rust is called by oxidation or when your apple, you know, turns brown, that's exactly the same happening in every tissue throughout your body. But of course, exercise isn't bad for us, physical activity is not bad for us because our cells are producing antioxidants in abundance. And, but we never evolved to turn those antioxidants on

as much without being physically active because we never evolved not to be physically active. We're turning on enzymes that repair our DNA. Another thing that's important for cancer, right? Repairing mutations in our DNA prevents cancer. We're turning on glucagon, which is this hormone, it's the opposite of insulin. High levels of insulin are unquestionably related to cancer.

This morning when I ran around the Thames, my glucagon levels went up. Guess what glucagon does? It turns insulin off. So there are all kinds of factors that are involved in physical activity that have to do with energy that decrease the mechanisms that either cause cancer or increase the mechanisms that help prevent or repair the damage that causes cancer. What about the number of menstrual cycles a woman has? That's another example.

That's again, it's about energy, right? Because menstrual cycles, typical in a natural fertility population, by which I mean, people aren't using contraceptives. Women will get pregnant, then they'll nurse for a long period of time. by which I mean people aren't using contraceptives, women will get pregnant, then they'll nurse for a long period of time. The nursing, the energy it costs for nursing keeps their levels of reproductive hormones down,

which prevent them from getting pregnant again until their energy levels go back up again. Yeah, they're not having periods. That's right. They're not having periods because it's because of energy. Right? Now, so typical woman who's in a natural fertility population will have maybe 150 menstrual cycles in her life.

Now with contraception and fewer offspring, women I think get an average about 400 menstrual cycles. That's 250 more big massive pulses of estrogen and progesterone that are important for reproduction, but there's a trade off, everything has a trade off. They also increase the rates of some cancers, including breast cancer. Yeah, I don't think many people think

about things like that. When they're thinking about cancer, they're not thinking about the number of menstrual cycles. Cause it's fascinating that 150 versus 400, let's say on average, that is a huge difference. Yeah. Over the course of a life. Yeah, absolutely.

Or insulin levels, the people walking around today that we see in the streets of London, the estimates that we have, or the data we have, that everybody's walking around with higher levels of insulin than people who are walking the same streets a few generations ago. It's because we have so much more energy available to us. We're not going through those cycles of positive

and negative energy balance. I think that's one of the reasons why intermittent fasting or being careful about your caloric intake is beneficial because it's basically keeping those insulin levels down, also not eating too much sugar as well. What did you see in relation to fasting in some of these hunter gatherer or more traditional populations?

Well, they just don't eat all the time. I mean, look, in my building, right? There's a snack machine, and there's right at the bottom of the stairs. This is in Boston. Yeah, my building in Harvard, right? So if I'm hungry and I'm like, you know, I'm working on a paper or, you know,

something, you know, upset by my colleagues or whatever, and I get, you know, I'm stressed, get, I'm stressed, stress makes you hungry, cortisol makes you hungry, right? I can just run down to that machine and get all kinds of crap, right? All kinds of ultra processed junk, right? Full of sugar and whatever. And satisfy my craving.

It's not gonna, it's gonna make me hungrier later on. But if you're in a subsistence population or if you're a hunter gatherer and you're hungry, you have to either find the food that you're going to eat. Or if you're a farmer, you have to go and cook it and prepare it and whatever and get it from the silo or whatever. You're just not surrounded by food and You're not surrounded by high energy food. So you didn't see them necessarily practice a form of fasting or restricted eating when they were one day a week

where they would reduce their calorie intake, nothing like that. It was more, it was kind of inbuilt. They have no choice, right? Yeah. Look, if they could eat as much as we do, they would. Absolutely. The populations I work with, people are always hungry

and they're always asking for food. Let me tell you a funny anecdote. So once I work with, people are always hungry and they're always asking for food. I'm gonna tell you a funny anecdote. So once I spent about seven or eight days with a group of hunter-gatherers, with some colleagues. Where was this? This is in Tanzania. And we had, you know, we came with a few jeeps and you're full of food, et cetera.

And we spent a wonderful time with these wonderful, these folks and they were very kind and whatever. And the last night we thought, let's have a party. And we cooked everything that was left that we had, all the food left, because we were just heading back to town, right? And so we had this cook with us and he made, he boiled every bit of rice that we had

and he made some cakes, which he smeared with jam. And he had, I mean, it was like, it was an amazing feast. And I've never seen people eat so much. I mean, and it was like a paleo diet nightmare. They ate so much rice and cake and whatever. And they went back for seconds and thirds. There was nothing left at the end. Why? Because they're hungry.

And all of a sudden they had this bounty of food, whereas you and I might like, okay, I don't need to eat thirds, right? But they were happy. And then we danced for hours and hours later, right? But, you know, when you're in a situation where food is always in short supply, you're always gonna eat what's available to you,

but you're only gonna eat the food that is available to you. Like breakfast, right? They often don't have breakfast, not because they're trying to intermittent fast and trying to skip a meal so that they can, turn off mTOR, et cetera, et cetera. They're doing it because there's no food at camp. They have to go out and find it.

Yeah, that's also what a lot of these modern practices are about. For me, at least, they're a way of navigating the modern world. That sort of point about energy, which you were talking about in relation to cancer, but there's a broader point. Many of us are living in a world of energy excess. We're exposed to lots and lots of energy that if we're not careful, we'll end up in our mouths and on our bodies. And that is why some people, some people don't like the word rules, some people don't like the words restriction. And I get that, but we're all different. We all need our own strategy to navigate the modern world. Oh, it's, it's, it's, it's a nightmare.

But some people find something like a time restricted eating protocol where they don't eat after 7 PM, for example, they find that really helpful because it just stops their evening snacking. It may work for them, it may not work for someone else. It's like why some people find a low carb diet or a low fat diet or whatever it might be useful because for them, that's their framework, which allows them to navigate this modern food environment. I totally agree.

Whereas last summer I was in Kenya for four weeks and I was bending the ear off this, this young Masai chap. I was asking, can you tell me what time do you guys eat? But he said, yeah, we'll have a bit of meat in the morning at seven. I said, okay. And then what do you do? Then he says, we're out with the cattle in the day. And he says, we don't really eat, but we'll sort of take, you know, if we're hungry, I'll just snack on some berries

or whatever. I might come across and then we'll eat again. I said, what time? He says, maybe around seven or so when we're back, it'll be more meat then. Right. So again, this is one person sharing what he and his tribe do, but it was fascinating for me because I thought, well, we kind of talk about this 12 hour window in every 24 hours where we don't eat as a modern way of trying to replicate things, but that's kind of what they're doing naturally. Well, so the mussels are pastoralists, right? They're herders.

And so they go out for the day and they, especially the men and our kids as well, watching the animals. Hunter gatherers populations that I've seen, but also mostly read about, cause of course I've only, you know, there's more to read about than to see. They snack constantly. If they dig up tubers, they eat them, right?

They're in the field, right? They're not saving them all for dinner. Guys, I think you read the description about those guys who they've, you know, when we went out hunting, they failed to hunt that particular day. So what did they do? We went from hive to hive to hive to hive, getting honey. They didn't bring a single ounce of honey home back to camp.

They ate it all themselves. They must have had a massive sugar overdose that day. I love that. That's, it was such beautiful writing. It was so evocative when you went on this hunt with these guys. And yeah, I think he talks about, you know, you heard an arrow being pulled,

but he came out looking disappointed. The arrow missed, but then the birds helped guide you to all the honey basically. The honey guides, yeah. So just so no one's interpreting that as, oh, my evolutionary ancestors would gorge on honey, let me go to the supermarket and buy big tubs of honey to gorge on as well. Hopefully no one will do that. But should we just be really clear?

You're saying some of them snack quiteorge on as well. Hopefully no one will do that. But should we just be really clear? You're saying some of them snack quite a lot as well. Is it not then the take home that in an environment of limited energy, people are gonna snack, they're gonna take honey, they're gonna take whatever they can when it's available. Whereas in an environment of energy surplus, we need to be careful with things like snacking and eating late and that sort of stuff. Yeah, we have to be careful with things like snacking and eating late and that

sort of stuff. Yeah, we have to do something really weird. We have to now not eat the food that's around us. That never happened for human evolution. I go to the supermarket and I go to a buffet. When it's somebody's birthday, everybody brings in cake, et cetera. Before this, I went for a coffee shop with some folks and all of a sudden there were these, you know,

lovely sugary, flowery things to eat in front of me that I hadn't ordered, right? And I ate one because it's delicious and you know, it's very hard. You have to work, we have to work, we have to, we actually sometimes pay extra money for food that has less nutrients in it, less sugar in it, because it's more expensive.

That's how crazy, no wonder people are struggling. So we have to, we're now in a world where we have to actually do something that's fundamentally unnatural, fundamentally against basic instinct, which is to use willpower to not eat the abundance for which we are surrounded. And the abundance is often full of all kinds of toxins

and poisons and whatever. That's, I mean, and that is a problem that, and then, of course people are gonna struggle, right? And that's why it's a problem that's not just an individual issue. This is a social, political, larger question than any one individual. And we need to help to help ourselves.

This goes back to how we started this conversation about the escalator and how, you know what? It's gonna take a certain type of person to actively choose the stairs when there's an escalator there, right? No blame, no guilt, it's just who we are. Kind of the same thing with food, right? It's like if there's energy-dense tasty food there,

all our wiring from a long, long time, hundreds of thousands of years, is to eat that food. Millions and millions and millions and millions of years. Exactly. Look, I want to take the escalator just as much as everybody else, but do you know why I take the stairs? I also take the escalator just as much as everybody else, but do you know why I take the stairs? I also take the stairs, but go on, give me your reason. Do you know why?

Because if anybody sees me, and I've written books on exercise, I'm a hypocrite. The number one reason I take the stairs is not because, because I get less exercise because I'm afraid of being caught out and being, I'm sorry, it's embarrassing, but it's actually true. It's good to be honest. Look, I mean, that is a partial reason for me as well in this country.

But the real point for me is that, again, I'm aware that everyone likes the word rules, but I feel that I've seen this with many patients. I've seen this with myself, that there are certain things that are very helpful. So I have an internal rule that is I always take the stairs unless in exceptional circumstances. That's a rule that I've now internalized. It's the norm for me. That helps me navigate this modern world where the temptation is to outsource my movement to electronic things

and lifts and escalators and all these contraptions, right? So it means unless I've got an injury or I've got a ton of suitcases and I physically can't do it or whatever it might be, I will take the stairs. And that's great. And that works for me, but I know across the population, that's going to be very hard to persuade everyone to do. Yeah, no, no, I agree with you, but I think there's another dimension to this,

which is that, yes, we create these rules, we create these ideas or suggestions. But the other thing I was going to say is that a lot of them are all geared towards weight. A lot of people are told to not eat this or do eat this because it'll prevent you from gaining weight or help you lose weight. There's this big debate now about exercise

and weight loss, right? And I've heard people say, oh, well, you know, actually I don't need, you know, taking the stairs isn't so important for me because it's not gonna help me lose weight. So I might as well take the escalator. I've heard this from people, right? When we're talking about this afterburn, right?

After the physical activity, the entire literature on how exercise raises your metabolism is primarily about whether or not that extra energy that you burn will help you lose weight. You know, not about all the other benefits that come from that elevated metabolism. So by seeing everything through the lens of weight loss and weight gain, and weight is not health, weight is related to health, but it is not health. By tying

everything to weight, people forget what the other benefits and important reasons for being physically active are, or discount certain activities because it's all viewed through this weight, weight,'s all viewed through this, wait, wait, wait, wait, wait, wait, wait. I completely agree. I mean, what is your take on the exercise and weight loss issue, which is, I mean, it's one of those hot controversial topics.

I mean, I'll share my view in a minute, but I'd love to know your perspective. Well, I think one thing is completely uncontroversial, I hope, which is that there's no question that physical activity is crucial in preventing weight gain. Study after study after study after study after study shows that people are more physically active, regardless of what they're eating,

that actually helps prevent weight gain. And sometimes you'll read, oh yeah, but you know, physical activity, exercise makes you hungry so you can eat more. That's just been debunked. That's not true. You do eat a little bit more, but you don't eat as much as you spend.

So I think that's uncontroversial. In fact, and we often talk about diet versus exercise for weight loss. That's a strange opposition. It should be diet and exercise. Why would you not do the two together, right? Although it's a harder exercise. And if you're overweight or have obesity, right?

It's like carrying weights on your body, right? It's, you know, walking as a person with obesity, right? It's like carrying weights on your body, right? It's, you know, walking, as a person with obesity, walking the same distance as somebody without it is spending 14% more energy. It's hard, right? It's difficult, right? So it's challenging and generally you're unfit and so you get less reward.

I think there's also compelling evidence that exercise can help you lose weight. But the issue is that it doesn't help you lose a lot of weight rapidly. I think there are careful, well-designed, randomized control, prospective studies where they weigh everything going in and weigh everything going out,

showing that people who get more than a moderate amount of exercise, you need at least 300 minutes a week, you can and will lose weight, but you're not gonna lose a lot. So if you wanna lose a lot of weight fast, there's no question dieting is better. But if you want to lose some weight,

there's no question that exercise can help, but it's not gonna be a huge amount. But what it's really gonna help you do is that once you lose that weight, because dieting, the problem with dieting is not that people don't lose weight when they diet, they do, the problem is it comes bouncing back, right? It comes rebounding, right?

And then often you're not getting muscle, you're just gaining fat. And so you get this yo-yo effect. The way to prevent that is to stay exercising, to stay physically active. That has an incredibly important role and it should be part of every weight strategy. Yeah, I really, I do agree with that actually. And I think, you know, there's no question that

people can lose weight without paying much attention to physical activity or exercise it. Because I've seen it over and over again, people will report that. Of course it's possible. And many people do it, but most people stroke all people who are trying to lose weight and not trying to do it for four to six weeks. They're trying to make it a significant part of their life. They're trying to transform their life. They want it to be long-term, not just for January or January, February or for the wedding or the beach or whatever it might be, right? They want it beyond that. And this is where I've always had a slight issue with some of these studies, or at least how they're reported. And you know, it was all blowing up on YouTube last year in the health

sphere on this exercise, nothing to do with weight loss and all this sort of stuff. And it's like, I just, I don't, first of all, I don't see how, how that's that helpful for people. And it sort of, it makes things very one dimensional. Yes, about weight when there's so many more benefits, but even if we are talking about weight, let's look at it another way. Whether exercise helps you to lose weight or not is not just in my view about the direct effect on calories from what you're burning off. Right. And let me explain what I mean by that. People who are struggling with their health

and are trying to, let's say, lose weight or make changes, there's all kinds of things to tackle. So if their mood is low, they're less likely to go out and move. They're going to sit at home. They're going to possibly more likely to come for eat, binge watch things on TV, accumulate stress, have less optimal sleep, which again will make them more hungry the following day because of the changes in hormones. So for me, it's like, you know what? If you're someone who can walk 30 minutes a day, whether it directly burns enough

calories to justify it for your weight loss plan, it will improve your moods, your self-esteem, it will help you lower stress, you'll feel better about yourself and your place in the world. These are real things for human beings. You cannot just look at it through the lens of how many calories were burned here. That's useful to know, but this is my bias as... No, I vigorously agree. I could not agree more.

I've seen so many patients, it's like you can't just look at one thing. You have to look at the totality of all the inputs into this person's life. And moving more for most people makes them feel better. Yeah, and it also does have energetic effects too. Of course it does. It's a combination.

And, but we tend to be, again, by looking just through this one lens of calories in, calories out or whatever, we're missing. What is it that actually moves energy around in our bodies? It's hormones, right? So just as one example of what you just said, just one example, right? People who are more physically active

have lower basal levels of cortisol. What does cortisol do? It's the arousal stress hormone. And guess what? When my cortisol levels go up, like when I'm stressed about this, that or the other, I'm more likely to eat. So it's just one of this complicated,

interconnected, integrated system. And chronically elevated cortisol, the primary stress hormone, or you could argue the primary stress hormone, encourages belly fat. Exactly. Right? Rather than subcutaneous fat.

And that's the, that's the inflammatory fat. Yeah. So it's, it's all these things together. I mean, what did you see in some of these populations and in terms of, I don't know if you measured it or not, but what was your perception of levels of stress in hunter-gatherer populations? Ooh, good question. First of all, most of the research I've done

as an assistant farmer is in hunter-gatherers, but I mean, I visited hunter-gatherers, but we've never measured that, but there are studies where they look at, again, so cortisol is a complicated hormone in that cortisol doesn't cause stress. Cortisol goes up when you are stressed, right? So people have measured cortisol in some of these populations

and the levels tend to be low, but again, that could be because of physical activity. I don't know of any good studies that measure psychosocial stress in any of these populations. And I would say that their lives are not easy. Just like in our lives, there are problems, right? They're worried about food.

There's conflict between individuals. There's climate change. There's all kinds of things going on in their world that makes them like the rest of us, stressed. But I think that their life is slower. You know, they're not getting a 24 seven newsfeed. You know, there is a, I'm certainly calmer when I'm out there, right? Because I'm disconnected from all that crap

that's going on normally in my life that can make me arouse and stressed. And I think it's a reasonable hypothesis that just general levels of stress are lower, not that they're absent, they're not. They said these are not, you know, Rousseau's noble savages, right? That's not what we're seeing.

But I do think that the world we live in today, look, the average hunter gatherer, as far as we know, maybe meets 250 people in an entire lifetime. Today, just getting to the studio, I met, I didn't interact with them mostly, but thousands and thousands of people, right? And some of those, most of those were perfectly harmless interactions,

but there's just, our lives are just intense, right? In this modern, wonderful, crazy, but also stressful environment that we live in today. And you know, I was checking my phone today and you know, what's the news, et cetera, and all that kind of stuff. And I have to figure out, I have to get to my flight tomorrow, what time and how do I get to the, you know, whatever.

These are real, these are, this era of bombardment of information, whether it be news or emails or flight check-ins or whatever, they're all significant. Yeah, they add up. They add up. Absolutely. Each one in isolation is no biggie, but you put them one after the other,

throw a bit of jet lag in for you and all sorts of, you know, it does add up, doesn't it? I agree. So I don't know good data on stress levels, but I would be very surprised if they weren't lower. What about sleep? I know you bust the eight hour sleep myth in your book. You feel free to sort of explain that,

but I'm really interested as to what sort of, what did you observe in terms of, you know, sleeping patterns and sleeping duration? So I've never collected data on that, but I've read the literature on that. But my impression is that people just sleep, you know, they, you know, when they're tired, they sleep. And when they're not tired, they don't sleep.

And it's just not a big deal. Is it one prolonged go? So the literature is again, I've never measured this, but others have. And in general, so there's a researcher at the University of UCLA, who's done a lot of these sleep studies. So he put sleep monitors on three populations,

the Hadza, the San and the Kalahari, and Aceh in the Amazon. There's also studies now from people in Madagascar and other populations in the world where people aren't connected 24 seven to the world. They have no electricity. So they don't have phones, they have lights, TV, all the things that were supposedly robbing us of sleep.

You know, the idea that Ederson was the killed sleep, right? They sleep, I think 6.7 hours an evening, 6.5, I can't remember. They don't get eight hours. They rarely nap. They tend to sleep more when it's cold and a little bit less when it's hot. And they seem to be just fine.

And furthermore, when you look at big epidemiological studies in the West, right? Where you look at hours of sleep on the X axis and some health outcome on the Y axis, like cardiovascular disease or something like that. It's always a U-shaped curve with lots of variation around the mean. And the bottom of that U-shaped curve,

i.e. the sleep number, the hours of sleep that are associated with best health is about seven, not too far off from what our ancestors did. That's quantity though, isn't it? We don't know quality? No, we have no idea. It's very hard to measure that. One of the arguments might be that, and I've seen this a lot over the years where on the outside patients are sleeping, let's say seven, eight hours, but they're still waking up feeling exhausted.

There could be many reasons for that, but I've certainly seen enough times where people are chronically stressed and stimulated in the evening before they go to bed. It may seem as though they're sleeping for the same amount of time, but I, you know, again, I don't have a sleep lab, but it seems very much that the quality of that sleep wasn't as significant. And, and psychosocial stress turns up cortisol. Yeah. Cortisol doesn't make you stressed. Cortisol goes up when you are stressed. Cortisol is the arousal hormone.

It's the hormone that helps us get energy, again, back to energy to help us run away from the lion or whatever it is, right? So when you fall asleep, right, you go through four different stages of non-REM sleep. You slowly, slowly become less and less aware of the outside world. So that first you can hear the outside world, but et cetera.

And then finally you go to the non-REM period and then you cycle back and forth, right? Cortisol slows that and also it prevents you from getting into the non-REM and you're more in the less serious, the less REM parts of sleep. So if you're stressed, your sleep is not gonna be as good.

I mean, and we know that. And it's funny if you think about it, like you did ask me about my experiences. I will say one thing about sleep in these places. It's bedlam, right? Nobody goes to sleep in a quiet dark room on a soft mattress with the curtains closed and no sound. And you know, like, think about like how

so many of us sleep, right? We're in this like isolation chamber, right? And that's not how it is in any of these camps. There's always somebody up and about, you can hear stuff, you can hear the hyenas in the distance. I mean, there's all this stuff going on, right? And it's chaos. And, but because people aren't bothered by it

because that's just normal, right? They don't, they're not irritated by it. They just fall asleep, right? But we have this like, we get stressed partly because the neighbors playing their music, right? Or there's an ambulance on the street or whatever. And we have this idea that, oh, we have to have this perfect, quiet, dark, comfortable,

they're sleeping on the ground, they don't have mattresses, right? So we actually make ourselves by having this idea of like how we're supposed to sleep. And then when it's not perfect, we then get stressed about it, which then makes our sleep worse. So I think, and this,

and what I call the sleep industrial complex, there are all these people out there and companies out there trying to make us stressed about their sleep, about our sleep so that we buy their products or their book or whatever. They're also making us stressed about our sleep. And so that is the enemy of proper sleep. So I always point out, I ask people, you know, can you sleep on an airplane? Oh, yeah, I fall asleep on airplanes. And then they tell me they have problems sleeping. It's like, if you can sleep on an airplane, you can sleep on a horse probably. You can sleep anywhere, right? So that's proof to you that you actually can fall asleep in all kinds of environments. It's just that you're on the airplane.

You expect this noise, it's normal. You don't expect an airplane to be quiet, et cetera. So you fall asleep, right? So, or for me, it was when I was in college, I would go to the library and I'd fall asleep in the library. And the library is not super quiet. It's just that I was exhausted

because I hadn't slept a night before. You can fall asleep in all kinds of environments. It's just that we make ourselves stressed about sleep and stress is the enemy of sleep. Is myopia a mismatch? Oh, absolutely, yeah. So- So short-sightedness, I should say,

needing glasses or contact lenses. Yeah, I mean, there's a wonderful study that was done here in London many, many years ago. Done, I think it was the first study of myopia. You know, the Queen's Guard, those people with the, was it bearskin? This one's kind of fur on their heads. It was a study that was done in the early 19th century,

I believe, or the mid 19th century, where they showed that the common soldiers in the Queen's Guard, none of them, or very few of them had myopia, but their officers had a high percentage of myopia. And that was the first time somebody thought, oh my God, there's some environmental component to myopia. And then people started studying it around the world.

There's also studies where they've looked at Inuit populations in the Arctic, right? And they've looked at multi-generational families and that the grandparents have perfect eyes, right? And the grandchildren now have very high rates of myopia, right? So what's going on? Well, myopia is caused by an eyeball that's the wrong length, right? So if your eyeball is too long, when you refract the light, you can only refract the light so much. And so it's focused, it can't get focused on the cells in the back of your eye.

And so you can't see, you're nearsighted, right? So, and what's causing that is again, the eyeball is just too long. So what causes the eyeball to be too long? Well, I won't go into all the details of the experiments, but it turns out that people used to think it was reading, right, you know, close work, people who read too much, but it turns out it's not the reading,

it's actually just being indoors in environments that don't have a lot of complex visual stimulus, that affects the expression of genes in the eye as the eye is developing that don't, that control the growth of the eyeball. There's a few genes that have been identified. And so you end up growing an overly long eyeball and you're stuck with myopia.

So myopia is caused by spending too much time indoors. And there are elegant experiments on animals where they test this. And we can see this in populations where they've, actually Singapore is a place where they've done a lot of really cool research on this. So, myopia is much more common today because of, you know, we're not evolved to grow up and spend so much time indoors, which is why it's correlated with reading. And hence we develop overly long eyeballs.

Yeah, it's fascinating. I've seen some research suggesting that children, we want them outside for at least two hours a day. I think there's a correlation between kids who are outside for less than two hours a day and... Exactly. ...rates of myopia. Exactly. I think also one of the downsides of these phones and screens and homework being given on screens in the evenings, there's many potential downsides.

One of them, I think also is it encourages them to stay inside, but then also have that kind of narrow concentric sort of vision. But you're saying it's more outdoors than actually that the acts of just being focused on that near screen. That's the evidence that I've seen. Yeah. So it was, it was, it was, it was thought that, you know, when when you focus on near skins, you're pulling the little tiny ciliary muscles that are pulling on the lens, create tension in the eyeball that increase pressure.

But I think that's been mostly debunked from my understanding. I'm not an ophthalmologist, so I'm not a deep, deep, deep, deep into literature. But when my last exploration of that literature was really more the complexity of visual stimuli from being outside turns on genes that are important for regulation of eyeball growth. But I guess, you know, you're usually reading or on a screen, I would say, inside. Anyway, aren't you? So it's that will be playing into as well.

Hey, Daniel, it's always fun talking to you. We'll be playing into it as well. Hey, Daniel, it's always fun talking to you. Honestly, like the book exercise is so good. Thank you. It's such a fun read as well. In terms of practical advice then on the back of all the research you did, obviously in your conclusion, you finished off the book with some,

I think it's 23 sort of succinct words. Can I read it out? Sure, please do. Make exercise necessary and fun. Do mostly cardio, but also some weights. Some is better than none. Keep it up as you age. If you were writing that book today, would you change any of those words? No. And if you were writing exercise today, because it's been out now for a few years, what would be in it that isn't currently in it? Oh, good grief.

I actually haven't thought about that. I think I'd have to do more on mental health. I have a little bit in the book on mental health, but I've become more and more interested in the role of physical activity and how our brains function and anxiety, depression, other mood disorders. I think I would, because I think if you look around the world today, we not only have a crisis of physical health, we have a real serious mental health crisis. So I think what I would, I really want to delve more deeply into those mechanisms and

the data and the evidence because I think that's just as important as physical health. And finally, you grew up in the United States and you were a professor at Harvard University. Very esteemed, very prestigious. You've also spent a lot of time with populations who maybe didn't have access to the sort of things you had growing up. Of course, we've covered a lot of the things that you've learned throughout this conversation, and there's plenty more in your book. But guess what I'm really, really fascinated about is having spent time with a lot of these non-industrial populations, what has being with them taught you about life and the meaning

of life and what it means to be a human on this planet? I think the more time I spend with people who live lives that are very different from mine, the more I realized that what really matters is your friends and your family and the things that, you know, what are the things that we really care about, right? And their struggles are not that different from our struggles. It's just that in my world, I've got all this extra crap I also have to deal with. All of that is detracting my energy and my time from the things that I really actually care about,

which is the people I love and also trying to make the world a better place. And I think that's what most people try to do. And we've got this crazy world now that some of us live in. And I'm very fortunate. I love the fact that I get to get on airplanes and go to interesting parts of the world and try different kinds of foods.

But also what I really love is meeting people and seeing their lives. And I think, and it's really the commonality of the human experience, I think, that I find most moving. People who are, I'm fortunate, right? I don't lack for food, right? But seeing people work so hard

to get food for their families, right? That's what motivates them, right? And, or trying to help their kids who are sick, or, you know, that's what, and that's what motivates them, right? Or trying to help their kids who are sick or, you know, that's what keeps me going because, you know, in the long run, it's not about the papers I publish or how much money is in my bank account or how many people watch a video or something.

It's really, you know, when I die, none of that's going to matter, right? What really matters is the impact that I've had on people in my life and the impact that they've had on me. Yeah. Beautiful answer. Daniel, you've had a huge impact on me. I think the book's wonderful. I can't wait to see what you come out with next. Thank you so much for coming on the show. It's been my pleasure. Thank you. with next. Thank you so much for coming on the show. It's been my pleasure. Thank you. Really hope you enjoyed that conversation. Do think about one thing that you can take away and apply into your own life. And also have a think about one thing from this conversation

that you can teach to somebody else. Remember when you teach someone, it not only helps them, it also helps you learn and retain the information. Now before you go, just wanted to let you know about Friday 5. It's my free weekly email containing five simple ideas to improve your health and happiness. In that email, I share exclusive insights that I do not share anywhere else, including health advice, how to manage your time better, interesting articles or videos that I've been consuming and quotes that have caused me to stop and reflect. I have to say in a world of endless emails, it really is delightful that many of you tell me it is one of the only weekly emails that you actively look forward to receiving. So if that sounds like something

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