ZOE Science & Nutrition - The science of weight loss – and why calories don’t count! | Prof. Giles Yeo

Episode Date: January 16, 2025

Think weight loss is all about eating less and moving more? Think again. In this episode, Prof. Giles Yeo reveals why calorie counting isn’t just inaccurate—it could actually make weight management harder. He explains why the popular “calories in, calories out” method doesn’t add up and explores how factors like genetics, brain signals, and gut health play a major role in shaping our weight. Giles Yeo is a Professor of Molecular Neuroendocrinology at the University of Cambridge and Honorary President of the British Dietetic Association. His research focuses on the influence of genes on feeding behaviour and body weight. Giles is also the author of ‘Gene Eating’ and ‘Why Calories Don’t Count’. Giles shares the surprising impact of ultra-processed foods on how we process calories and why losing weight often feels like a battle against our own biology. With decades of research in his back pocket, Giles shares science-backed advice to help you break free from yo-yo dieting, read calorie labels smarter, and embrace a more balanced, plant-rich diet for long-term health. 🥑 Make smarter food choices. Become a member at zoe.com - 10% off with code PODCAST 🌱 Try our new plant based wholefood supplement - Daily 30+ Follow ZOE on Instagram. Timecodes 01:17 The quickfire round on weight myths 02:05 The biggest weight loss myth revealed 03:07 What are calories, really? 04:08 Burning poop: a bizarre calorie experiment 08:05 The woman who invented calorie counting 11:41 How calories became a diet obsession 15:00 Why calorie counting doesn’t work 18:56 Why food quality matters more 20:05 The blindspot of calorie labels 23:13 We eat food, not calories 27:02 Stress eating vs. stress starving 31:00 Why we always have room for dessert 38:22 How your gut controls your hunger 45:17 Why pizza makes your brain light up 49:41 Ultra-processed foods hijack your appetite 📚Books by our ZOE Scientists The Food For Life Cookbook Every Body Should Know This by Dr Federica Amati Food For Life by Prof. Tim Spector Free resources from ZOE Live Healthier: Top 10 Tips From ZOE Science & Nutrition Gut Guide - For a Healthier Microbiome in Weeks  Mentioned in today's episode Long-term weight-loss maintenance: a meta-analysis of US studies, 2001, published in American Journal of Clinical Nutrition How dieting might make some fatter: modeling weight cycling toward obesity from a perspective of body composition autoregulation, 2020, published in International Journal of Obesity Weight-loss outcomes: a systematic review and meta-analysis of weight-loss clinical trials with a minimum 1-year follow-up, 2007, published in Journal of the American Dietetic Association Diet or Exercise Interventions vs Combined Behavioral Weight Management Programs: A Systematic Review and Meta-Analysis of Direct Comparisons, 2014, published in Journal of the Academy of Nutrition and Dietetics Diet, exercise or diet with exercise: comparing the effectiveness of treatment options for weight-loss and changes in fitness for adults (18–65 years old) who are overfat, or obese; systematic review and meta-analysis, 2015, published in Journal of Diabetes & Metabolic Disorders  Is regular exercise an effective strategy for weight loss maintenance?, 2019, Physiology & Behavior Have feedback or a topic you'd like us to cover? Let us know here. Episode transcripts are available here.

Welcome to ZOE Science and Nutrition, where world-leading scientists explain how their research can improve your health. You may have heard that weight loss is about restriction, right? Eat fewer calories, spend Friday night at the gym, and when dessert comes round, just say no. But what if weight loss could actually mean saying yes? Yes to whole foods. Yes to more vegetables and fiber. Yes to a diverse diet. And when it comes to calories, saying yes

to understanding what these numbers can really tell us and what they can't. Today's guest, Giles Yeoh, is a professor at the University of Cambridge. For over 20 years, Giles has been researching obesity and the truth behind why we gain weight. He's also written three books that debunk everything we thought we knew about weight loss. In this episode, you'll learn a new way to think about weight loss and you'll walk away with science-backed tools that can help you sustain a healthy weight. Giles, thank you for joining me today.

Yeah. I don't know if I'm going to regret this. Hello. Thank you for having me too. So we have a tradition here at Zoey and we always start the podcast with a quick fire round of questions from our listeners. I'm nervous already. You should because it's designed to be really hard for professors because you're

only allowed to say yes or no, or if you absolutely have to, you can give us a one sentence answer, but it's basically a fail. Are you willing to give it a go? Yeah, let's go for this. All right. Will counting calories help me lose weight? No. Are calorie labels giving you the truth?

No. Could ultra processed foods be causing my cravings? Maybe. That's a fail. I just have never failed already. It's terrible. Is gaining weight each year just a natural part of aging? Yes.

Is there a sustainable way to maintain a healthy weight? Yes, but it's difficult. I'm going to give you a whole sentence now. I can see you really wanted one. Let me give you a whole sentence. Yeah. What is the biggest myth when it comes to weight management? That there is one magical solution for all people.

Brilliant. When we told our listeners about this episode, we got one question over and over and over again. How do I avoid gaining weight as I age? I love this question because I had exactly the same question eight years ago when I started Zoey. I was 40 at the time and I was distinctly aware that I needed to buy jeans with a bigger waist size. I'd spent my whole life basically thinking I'm really skinny and I can't put on any

weight at all. And I bet that there's quite a lot of listeners who can relate to this. So I'm really excited that you're going to be sharing like what's the latest science about sustainable weight management and talking about how a lot of what we've learned are basically just myths. Now you've written multiple books that debunk diet culture and your most recent book, Why Calories Don't Count, basically argues that calorie counts are lying to us. So we're going to get into all of that, but let's begin with what are calories? The original concept of calorie came in the way of measuring heat. Actually, it was sort of like a 18th century thing, actually, of measuring heat. And a heat calorie, and I'll

come to the food calorie in a bit, is the amount of energy it takes to raise one mill, one milliliter of water, one degree Celsius at sea level. That's a small sea calorie rather than a big sea calorie. I'll explain that in a second as well. The food calories we're talking about, however, it's not this. It is the amount of energy it takes to raise one liter of water, one degree Celsius at sea level. So it's 1000 small sea calories. And actually the nomenclature for it, it's spelt with a big C in the United States at any rate. Okay. Or sometimes people call it a kilo calorie, a Kcal, if you look at a bag of packs, because it's 1000 small C calories. So that is what a food calorie is. A calorie is a unit of heat

and it's what it takes to actually raise one liter of water, one Celsius at sea level. So you completely lost me already because what does any of like making water hotter got to do with whether I'm going to put on weight if I eat some food? Yeah, no, exactly. So people were measuring heat using this calorie item. And that has been in the late 1800s where then some German agricultural scientists realized actually we can measure the amount of energy in food. And they were feeding it to cattle, they were feeding it to chickens, you know. And what happens there is farmers, agricultural scientists are interested in, well, how much

do you feed and therefore how much product, meat, eggs you actually get out the other side. And so what they did was they realized that if you burnt the food and measured how much product, meat, eggs, you actually get out the other side. And so what they did was they realized that if you burnt the food and measured how much heat was given off, then you could say, well, how much energy was in there. Then if you fed the food to the animals and measured what came out the other side, then you can see, well, how much food was absorbed by the animal. And so hence this whole concept of calorie is a unit of heat. I'd like to share something exciting. Back in March 2022, we started this podcast

to uncover how the latest research can help us live longer and healthier lives. We've spoken to leading scientists around the world doing amazing research. And across hundreds of hours of conversations, they've revealed key insights that can help you to improve your health. If you don't have hundreds of hours to spare,

no need to worry. At the request of many of you, our team has created a guide that contains 10 of the most impactful discoveries from the podcast that you can apply to your life. And you can get it for free. Simply go to zoe.com slash free guide or click the link in the show notes and do let me know what you think of it.

Okay, back to the show. And so does that mean that to figure out what's going on inside when I eat something, I can just look at this unit of calories and that tells me, as you said, like how much I absorb and that's basically how I put on weight, helped me to... So, you know, I can just look at this unit of calories. And that tells me, as you said, like how much I absorb. And that's basically how I put on weight, helped me to.

So what happens was that was the way of that people will figure out how much total calories they were stuck in a food, whatever food you're talking about, celery, an apple, a steak, whatever it is, whatever is in there. But then the agricultural scientists, you know scientists figured out that, well, actually animals don't absorb all the food they eat. They eat the food, sometimes something comes out the other side, and so animals only ever absorb a proportion of the food that they're eating, depending on what they're eating. Then a chap named Atwater, Wilbur Olin Atwater, who was a professor of biochemistry from Wesleyan

University which is in Connecticut in the United States in the late 1800s, was a sabbatical in Germany learning about this technique. When he went back to the United States, he decided, well, if they're doing it to farm animals, if they're figuring out how much hay and straw and grain, whatever it is those animals are eating, can we do the same thing for humans? Can we actually go and measure human food, meat and chickens and whatever it is we're eating, and figure out how much of the food we're actually absorbing? I'll give you an example. Okay, if you take sweet corn, corn on the cob, and you actually eat sweet corn, and

then the next day you sort of look in the loo, it's quite clear that you haven't absorbed all the sweet corn because you can still see bits of it. And so Atwater realized this thing. And so what he did, he then spent 20 years of his life between 1880 and 1900 burning lots of food to figure out how much heat was given off, feeding said food to human beings, and then burning people's poop. So now you know what went in, now you know what came out and he then began to realize,

oh, okay, well then the rest is what's being absorbed. And he worked out all the numbers and at that point he then came up with these at water general factors they're called. And you may have remembered it if you're studying in a high school or GCSE or what have you and that is four calories for every gram of carbohydrate, four calories for every gram of protein and nine calories for every gram of fat and incidentally if you're interested about alcohol is seven calories for a gram of alcohol but we'll leave that alone and so he then worked out these factors of when you actually ate something. So in terms of protein, carbs, or what have you, that was how Atwater then calculated the

amount of calories he ate. So it was a very long, drawn out process. I mean, 20 years of burning poop. You have to be very dedicated to nutritional science to do that. And this is what Atwater figured out. And so all the calories on the side of the pack that is based on Atwater's numbers from burning poop. This guy in the 19th century spent 20 years burning food, and feeding it to people, collecting all their poop, and then burning that as well. Figuring out the difference between these

somehow must've gone into your body. Just because it went into my body. How does that link into weight gain? I mean, couldn't I have just used that to walk around or do something else? So you could, you do it to walk around clearly because if we consider calories, therefore, as this energy. So Atwater, when he was actually doing this, was not thinking about it from a weight gain

or weight loss perspective. He was literally trying to understand, you know, how much, you know, he was a nutritional scientist, how much food people was absorbing. So just to be clear, he actually wasn't really focused on weight, he was just trying to understand, like, what the hell is going on when you eat food? And he was sort of discovering, oh, wow, there are these like macronutrients and some of

them give more energy than less. And also by the way, it sounds like you're saying we don't absorb all the food that we eat because presumably he wouldn't need to burn the poo if nothing was coming out the other side. So he was also interested in like what was like not being picked up and what was being used. Yeah, I mean, he was interested in really the nutritional density of foods. In other words, what foods were better for you than others, okay, in terms of the amount of energy and how digestible specific foods were.

And he was doing it from not from any judgmental perspective. I mean, he published everything. I mean, he did reams and reams and reams. He can go and actually Google it now and get it for dirt cheap from, you know, an online bookstore where he actually have these lists of things. It was actually quite an interesting read because this was done between 1880 and 1900. It is sort of like a peak behind, into like Victorian period food.

And it's really quite interesting. Mutton, I mean, many other places eat mutton. We don't eat a lot of mutton in this country. Pilchards, and it's just really quite an interesting read. I have to ask, what was the weirdest foods that he made his poor participants eat that you have now discovered looking through this? Actually mostly organs.

I think a lot of organ meat was eaten more than we do today, you know, like tongue and you know, obviously tripe and gizzards. He literally has different calorie weights for whether it's like your heart or your lungs or your skin or he's got it all calculated. Absolutely. It's slightly weird in Frankenstein. It's slightly weird in Frankenstein, It's slightly weird in Frankenstein, but because of when he did it, they tended to be whole foods. He did some tin foods,

but in terms of what was available at the time, but they were whole foods because we're talking 1880, 1890, 1900s. So it wasn't what we would see typically today if we, for example, went into a supermarket. That is not the kind of foods that he necessarily would have been burning. They didn't exist at the time. That's interesting. None of the like ultra processed foods or even processed foods that we might think about today, it was all like raw ingredients that someone would cook up. That's fascinating. So how do we jump from this story 120 years ago of like, oh, I'm curious about how much energy there is in food to how we think about calories today where they are sort of like

this secret of how you're supposed to manage your weight in a world where it seems like we have to manage our weight because otherwise we all put on weight. So there was another brief history and then I promise I'll stop with the history lesson. There was a doctor actually in just around the World War I period called Lulu Hunt Peters and she was a woman doctor, a female doctor, which was unusual enough in the early 1900s and she was by all accounts a larger lady shall we say. But because she was a doctor and she was by all accounts a larger lady, shall we say. But because she was a doctor, she was a scientist, she then caught up and she became acquainted with Atwater's publications about these things. And she began to realize that, well, hang on a second, there must be some physics involved.

I need to lose weight, I'm a larger lady. And so what she then began to do was to say that, well, I am going to, instead of thinking about eating less food in order to lose weight, I am now going to put a number on it. I am going to quantify the food. She then now takes Atwater's lists, which were by all accounts quite dry, aside from the fact that you can look at all these organ weights and things, but converted all of them into calories. So obviously, she used imperial numbers. What would be three ounces of bacon, for example, in terms in calories? And she then converted all of these lists into two, three, four ounces, whatever a serving

size someone might have eaten in the early 1900s, and then converted those into calories. And now all her writings, and she became a syndicated columnist for the New York Times and what have you. So she put this into newspapers. And so directed to ladies, she was targeting this to as ladies. And so she would say, ladies, what you need to do is to make, if you want to lose weight, what you need to do, you know, is to make, if you want to lose weight, what you need to do is you need to eat three ounces of this and what four ounces of that. Don't think about a slice of pie. Don't think about a ratio of bacon.

Think about the number of calories of pie. Think of the number of calories of bacon. So Giles, she was like the original MyFitnessPal with her lists and her thing that like, if you just count your calories and eat less, then you're going to lose weight. Correct. That's where this all starts.

She also came up with her own version of the BMI. It was a lot more complicated than a BMI. We can debate BMI later. But she then had some way of saying, well, what should your ideal weight be? It was a early proto BMI thing. So she was the first person to weaponize the calorie. In fact, I would argue that she is probably the mother of the diet industry, because from there, she then converted all of these columns into a book, and then she published it. And then in the meantime, she then went to post World War I

to the Crimea. She was a doctor. So she worked for the Red Cross for four years, OK, in wherever she was in the Balkans. And she came back and realized that in the intervening four years, her book, her calorie counting book, had topped the New York Times bestseller list four years in a row.

So we've been obsessed about calorie counting for a really long time. I thought about that as a sort of 1960s on or something, but you're actually saying that for a hundred years, we've been obsessed with the idea that if you count calories, that's the secret to losing weight and like looking better and all these other things. And it is unusual thing about it because we think of obesity, overweight, metabolic diseases, you know, what we're talking about today, as a relatively contemporary problem, certainly at least at the scale it is, and that is true to an extent. But what this little vignette of a story tells us, this little history lesson tells us that, okay, she was a privileged lady, obviously,

okay, and the United States was not stuck in a war at the time. So there was a growing middle-class and there was a growing concern about looks, I would say, and, and, and, and weight gain between 1910 and 1920. Calorie counting was born. And Giles, you said something that I want to pick up on. Tell me. You said she weaponized the calories. She did.

Which is like a very strong statement. Could you explain? She formalized how to measure the energy in food for someone who was trying to lose weight. When I mean weaponize, I mean she took the esoteric, slightly esoteric science of at water, of calories, of macronutrients, of stuff, you know, and then boiled it down into really actionable information that an average educated American

woman in the early 1900s could say, okay, so I now need to eat this much less bacon, this much less eggs in order to do it. That's what I mean by weaponized. I think that the toxicity of the diet industry comes a bit later when more and more people, I think started jumping on the bandwagon and then all the food companies start jumping on. I think that's a later thing,

but she definitely did action calories for food in terms and for weight. She was definitely the first person that did that. So lots of people will be listening to this and saying, what's the problem here Giles? Everybody knows that you need to count your calories. There's a certain number of calories that you're supposed to eat. And as long as you eat less than that, you'll lose weight. And if you eat like one calorie more than that,

you'll put on weight. And like she set us on this brilliant path to understanding what was going on. I think there's some complexity here. Clearly what were they eating in the past? There is that. She did argue for, if you read her writings, she did argue for a balanced diet

and a balanced way of actually doing these calories. So what she did not say was to, okay, you need to eat less calories, but hang it, you can eat whatever the hell you want. She did not say that. She did say in her language, and she was quite a funny writer to say that you need to be balanced, you need to make sure you have enough of this and that. Whenever I talk about calories, people think I'm anti-physics. I'm not anti-physics. I understand that 200 calories of chips, potato chips or chip chips, are twice the portion of 100 calories of chips. Of course, I understand that. I do understand that. But so is 200 grams

of chips, twice the portion of 100 grams of chips. And no one is trying to compare 200 grams of chips to 200 grams of carrots. And put simply, that is the problem. So calories do give you the amount of food, particularly if you're talking about the amount of one type of food. The issue comes when you're trying to compare different types of foods using the calorie. The moment you do that, the whole shooting match falls apart. How's Antoine Assange who's never heard anything about this before. So they're just in the world that it sounds like this rather amazing early scientist you're describing,

that we're living in this world where like counting calories is the way that we understand what happens and the calorie number is what determines our weight. I think you're saying that's not correct. It's not correct if you deal with it the way we do today. In order to lose weight, you need to eat less. Let's just, if you want to debunk anything, because that's got to be true. Okay. So when you say we open and you said there was calorie deficit, you need an energy deficit

in your food if you want to lose weight. And there is no if, ands, and buts about that because it's a function of physics. So in other words, if you now have a meal, let's call it a balanced meal, whatever you might actually look at. And if you then suddenly took that meal and says, well, instead of eating all of it, I'm going to eat two thirds of it or half of it in a balanced way in which I want to have the carrots and and halve the steak and halve the potatoes and actually eat that, then ultimately, yes, you will lose weight. So if you calorie count in a perfectly balanced way, yeah, you can actually, you can and you will lose weight.

The issue is that is not the way life functions and people begin to sort of take it to extremes and sort of worship the calorie and use the calorie as the only piece of information there. Because ultimately, I think in order to lose weight, you need to continue eating a balanced diet but eat less of it. The problem with calorie counting is it takes away the nuance of it and you start to just count the calorie. And a calorie does tell you how much food that is there, but that's all it and you start to just count the calorie and a calorie does tell you how much

food that is there, but that's all it tells you. It is completely nutrient blind. It doesn't tell you how much fat is in there. It doesn't tell you about sugar content, about fiber, about salt, about anything. Anything about that either makes the food taste good or bad or is good for you or not so good for you. The calorie cannot tell you any of that information. So I think we need to, I guess my point here is that the calorie is one dimensional, literally is one dimensional when you're referring to a meal.

Whereas that wasn't what Lulu hunt Peter's original intention was because she was preaching, you know, eating less of everything, not just counting the calorie, even though she did, you know, push and say, don't think about a slice of pie. Think about it in terms of how many calories are for pie. What's the reality that happens then for people who are following calorie counting? Because I think, again, a lot of people are listening is that, well, surely if you do follow calorie counting, then you will lose weight. And the only reason it doesn't work is because you've got poor willpower

and you can't stick with it. And therefore it's all your own fault. And that was definitely what I grew up with. So does counting calories work? So imagine if you were saying that you want some diet, whatever the diet is, and this particular diet prescribes that you only have 300 calories for lunch, just as an example. These diets exist. Now if you therefore walk into a store because you're working or what have you, and you purely

look at that, well then in theory, you could buy 300 calories of a chocolate bar or 300 Now, if you therefore walk into a store because you're working or what have you and you purely look at that, well then in theory, you could buy 300 calories of a chocolate bar or 300 calories of a salad or 300 calories of a ready meal or whatever or 300 calories of soda. Okay. And if you do that and think about it, well then it does make a difference what you're eating and the calorie counting is just a really not a very smart thing to do because you can say, well, I did have 300 calories, I just consumed it all as soda, which is slightly extreme, but not that extreme because people do to decide that that's the

amount of calories I'm eating, particularly if you're plugging it into your app. And so in that sense, it is not very useful because you could be having more calories but eating something different, carrots, steak, something else compared to drinking 300 calories of a soda and it makes a big difference. So I think because of the one dimensionality of the calorie, it is not very useful and if you're focused just on one number and you're looking at the back and you're seeing that number then that's all'll, that's all you'll focus on. It's easier. I grant you, but it's, it's, I would argue that it's very, very meaningless.

I think what we want to do is improve the quality of our food. Even as we eat less, we need to eat less. Yes. But actually eat less, but probably eat better quality food. The calories are completely useless number. And Giles, is this just like your opinion or is there any actual science behind what you're talking about there? There is science behind it. I mean, I didn't make this up I didn't I didn't you know invent it and you know and called it the yo diet and or anything like that

It is true because okay people say yeah, but all calories are equal They are once they're in you as a little poof of energy, poof. And I think ultimately we have to remember, okay, the mantra, let's go with a mantra. This mantra you can say is from me. We eat food, we do not eat calories. And depending on what we eat, our body has to work harder or less hard to extract the calories from the food. Sweet corn is an example where clearly we can eat 100

calories of sweet corn, but we don't absorb anywhere close to 100 calories of sweet corn. Then our body extracts the calories from the food. And depending what you eat, you can extract differing amounts of energy from the foods we actually eat. So I think you're saying something that I've heard often on this podcast and from others that the body weight is not as simple as just sort of calories in versus energy out. And maybe it would be if we were like some sort of simple machine, but we're not. We're human beings. Our system is a lot more complex. What are the key things to know about how our body manages weight? And I think a lot of people listening to this will be immediately thinking about appetite because of course, there's been all of this noise in the last couple of years about these new drugs that have this amazing impact on appetite that seem to have nothing to do with calorie counting

and seem to be achieving like outcomes that, achieving outcomes that seem sort of impossible, I would say, until a couple of years ago. So what's actually going on inside us, Giles? And how do we know that? Let me just stress again, we do need to go into energy deficit to lose weight. And that's because it's physics, it's a function of physics. How you get there really depends on who you are. Clearly, there is an energy balance equation, and that is true. The complexity is not in the physics of it. The complexity is because that's the how, how you get to where you are. The complexity in terms of weight loss, weight maintenance is in the why. So why do some people eat more than others, for example, or why do some people appear to be more efficient with their food

in terms of burning versus storage versus how fast you would actually burn the food? Let me give you an example. Why do some people stop eating when they're stressed, like work stress or what have you, whereas other people start eating when they're stressed? So for example, I'm a comfort eater. If I'm stressed, suddenly my face is in a bowl of noodles. I don't want to back myself into a stereotype, but that's what I do. My wife, however, is someone who, the moment she's stressed at work or something like that,

she goes, I have no appetite. It's literally diametrically opposite, but it's the same hormone that goes up, the stress hormone, cortisol goes up, but yet we behave entirely differently. That is just one behavior and the world is split into those who eat after stress and those who don't eat after stress. So that's an example of the why, right? Other people, why do some people appear to be hungrier than others all the time? And you know, or how come some people take more to get full?

And these are not imagined behaviors. They're just not. Okay, where, yes, clearly they're gonna be cultural, sociological underpinnings about why, where, how much, and what we eat, clearly. But there are also huge biological underpinnings driving our appetite, driving what we eat, driving who we like to eat with, driving where, when, all these things. And all of that integrates eventually into some form of energy excess or energy deficit.

And so you either gain weight or lose weight depending on these innate drives, myriad of different reasons about why you end up eating more or eating or eating less. Hi, I have a small favour to ask. We want this podcast to reach as many people as possible as we continue our mission to improve the health of millions. And watching this show grow is what motivates the whole team at Zoey to keep up the really hard work of creating new episodes each week. So right now, if you could share a link to the show with one friend who would benefit

from today's information, it would mean a great deal to me. Thank you. That's really interesting. I never thought about the idea that, you know, some people might be a comfort eater and some people might turn off. I think if I'm really stressed, I often want to eat less, actually. Exactly. Don't even talk about food. Whereas I do eat. I'll sit there and it comforts me. And so I know that I do it and you try and organize your life so you don't do it, but

sometimes you just do it. Could you tell us a bit about the science of appetite? Because one of the things I'm really struck, you know, with my journey with Zoe over the last eight years is that I ate a completely typical like British or American diet eight years ago. And one of the interesting things, you know, having followed sort of my diet now for quite a few years is that it feels as though my appetite has changed

a lot and that I don't have the same level of, I don't quite know how to even describe it, like sudden hunger bursts in the same way. But what's going on there, Charles? So appetite is an interesting term because it's actually quite a, we sort of understand it. We talk about appetite, but it's actually quite a complex concept because it's an integrated concept. What I mean by this, in my head, I simplify appetite into sort of a triangle. Okay. Of which there are three points. Um, one is hunger.

So how hungry do you feel? I think we understand what that means. One is how full are you now? That is not the same thing. How hungry you and how full you are are different circuits within the brain and the reward elements of food. How nice or lovely does the food taste to you? Now those three all speak to each other.

They're not mutually exclusive and they involve different parts of the brain. And if you tug on one side of the triangle, the shape of the triangle changes, correct? And so in other words, if you are more hungry, for example, you're going to take more food to get fulled up. And if you're more hungry, the food has to be less rewarding for you to enjoy the food. If you're really, really, really starving, a bit of bread, a bit of cheese, a bit of rice, okay, it's like the simplest foods are the best. If you are not hungry, suddenly the rewarding element of the food has to be really, really big for you to

continue eating. It is the concept of the dessert tummy, where why after a full meal, you're never going to order another steak after a meal or whatever it is you're eating, but chocolate comes and you eat it. My son has explained that he's got a separate, you know, ice cream stomach for the last decade. Yes, and he's right. He's right, is he? He is right.

Where is it in, he thinks it's in his legs, or at least when he was six he did. I think now, I mean, he's 16, I think, he probably doesn't think. Where is his dessert stomach and how does that work? So the dessert stomach is this integrated concept where the fuller you are, okay, the more rewarding the food has to be.

So let me give you an example from an evolutionary perspective, okay? Take the grizzly bear, okay? Pacific Northwest, Oregon, Washington area, hitting the salmon run, preparing fibrination. And Josh, just, Washington area, hitting the salmon run, preparing for hibernation. And Josh, just to be clear, the salmon run isn't like a running race or a ski race. The salmon run is... Is when the salmon are swimming up the river in order to spawning their spawning grounds.

And the grizzlies know this. And so they kind of park themselves in between the spawning ground and where the salmon are coming and eat the salmon. At the beginning of the salmon run, the bear eats the whole salmon down to the bone. Okay? Just eats it and you can see there's just a whole pile of bones. Okay? But as the bear gets fuller and fuller and fatter and fatter because he's trying to gain

fat, the bear only eats the skin of the salmon and the fat underneath the skin of the salmon. Why? Because this is calorically wise, calorie wise, or even though they don't count, is the densest part of the fish. And you can do this. And this is what the bear does. Because he is trying to make sure

that he can continue stuffing he or she, is trying to continue to stuff as many calories into his body as possible, even when he's now completely full of salmon. So he's like eating the really fatty bits because that doesn't take up as much space with your calories you were talking about before. Exactly. So it's like bear chocolate.

It's bear chocolate. Now clearly desserts are a human specific cultural underpinning. So the bear is not having dessert. But this concept of which the fuller we become, the more dense the food we want to eat before we actually will bother doing it, before it tickles the reward parts of it, is a conserved thing. So this is not a human, your dessert tummy is not a human specific thing. It is a conserved behavior. So it's got to be high in energy density.

And so what are foods that are naturally, so in other words, that for every given gram of food you eat, you get more energy in it. So what are those? Those are going to be foods that are high in sugar, free sugars, or high in fat. And what are foods that are high in sugar and fat? They're desserts. And so that primarily is the big driver. So fatty foods or sugary foods, you know, 50,000 years ago

on the savanna, you know, we're not going to be eating a tart or citron and a muscat, but it might be honey. It could be a really ripe fruit. It could be making sure you eat the fat bit of the, you know, of your steak or bison or venison or whatever it is you're actually eating. Today, it's a tart or citron. Okay. But the whole it is you're actually eating. Today, it's a tarte au citron, okay? But the whole thing is you're looking for something high in fat and high in sugar, so that you can continue stuffing food into all the nooks and crannies,

even after you've eaten 2000 calories with a venison. Because you have to remember that, aside for the past 30 or 40 years of human history, most of the time we never had enough food, broadly speaking. And so the primary driver, the existential driver, is to make sure you ate when the food was there because we are designed for a feast famine environment. That's the natural way of it of sometimes there was antelope, sometimes there's no antelope,

sometimes you found the turnip, other times you didn't find the turnip. Even with agriculture, it was a scrabbling existence. Our drive has always been to make sure you continue eating when the food was there. The main issue today is that while we are designed for a feast famine environment, we are living in a feast famine environment, we are living in

a feast feast environment. And I think ultimately that is probably the main problem. What happens in our body when we start to lose weight, given what you were just saying that like we're used to a world where maybe you suddenly didn't have any antelope and a turnip or whatever it is. So your appetite is driven by the brain. It's a top-down control which then directs your body to act, the motivation therefore to actually drive you towards food.

So it hates it. Your brain absolutely hates it when you begin to lose weight, because it considers it a big red flag that you are less likely to survive. Put simplistically, okay, so in your brain, the moment you start to lose weight, and it doesn't matter really whether or not you've just lost five pounds

or whether or not you've lost 50 pounds. Your brain senses it and going, oh, and so what it does is it then begins to put all kinds of mechanisms in place, which are completely subconscious, I want to point out, to drag yourself kicking and screaming back up to where you were before you tried to lose weight. This is a natural biological driver. There are mechanism circuits.

This is what I actually study as my day job. What these circuits are, how do they turn on when you're actually eating too much or eating too little. So your brain makes you feel hungrier. So anyone who's gone on any type of diet, just by eating less, the moment you lose, yeah, the first few pounds are easy. Oh, it's wonderful, it's fantastic. And then suddenly you plateau and then suddenly you're thinking, jeez, I'm hungry. So we don't know every single circuit and hormone and molecule that's there, but we know a lot. So we know certainly far more than we did say 10 or 15 years ago about these molecular changes within

the brain, which happen. And subconsciously, it's not like I'm sitting there willing this hormone to go down in my brain, to go down, go down, make me feel less hungry. It won't because these are natural responses that happen in response to you losing weight. Just to be clear, however, not everyone will respond exactly the same way. So for example, the molecules in your brain might change, same as mine, but yours may change a little bit more, a little bit less than me, which means that we may very well behave differently to a specific diet or a specific type of food.

Your brain, broadly speaking, needs to know two pieces of information in order to influence your feed and take. Third, if it's how nice it actually makes you feel, but too broadly, it needs to know how much fat you're carrying, okay? How much fat, it needs to know how much fat you're carrying. Okay? How much fat you're carrying?

Because how much fat you're carrying is how long you would last without any food. So if your food sources stop today, how long would you live for? Okay? That's your long-term energy stores. Your brain also needs to know what you are currently eating and what you have just eaten. Okay? Those signals are going to come from your stomach and your intestines. Okay?

As the food go, every mouthful of food we eat, depending on what we eat, goes down. The further down the gut it goes, different hormones from the guts get released. Your brain senses these long-term signals from fat, short-term signals from the gut, and then interacts, integrates, and influences your next interaction with a refrigerator or with a menu. So where the differences come in is primarily really in the gut hormone section of it, because the fat is the long-term energy source. That happens a little bit later.

Because depending on what we eat, I guess there's some simple rules that we can follow. The longer something takes to digest, the farther down the gut it goes, and different hormones are then released, and gut hormones tend to make you feel fuller. And so they tend to. There are 20 different gut hormones that we know about from the intestines, 18 of them make you feel fuller. And they change depending on how much protein or carbs or fat or fiber that you might be eating. The signals then go to your brain and your brain senses,

I'm still hungry, I'm full now, stop eating, you know, what have you. And so the type of food we eat really influences how your gut responds, what hormones are released, and so how you might then behave differently to different types of meals. And interestingly, how you and I might behave differently to exactly the same meal that we're eating based on how our personal guts may actually respond to it. So Giles, this being Zoe, I have to obviously, now you've brought up gut hormones, I'm going to have to ask the follow on question, which is, is our gut microbiome involved in what you just said, like there's

a 20 hormones, 18 of them make you feel fuller. Is my microbiome involved in that? It is the frontline, right? Because obviously it's what our food hits first before it gets to the intestinal wall and before it gets absorbed. So yes, the gut microbiome will always play a huge role in how the food that we're eating is being digested and hence absorbed. And hence the hormonal milieu, the hormonal secretion

is going to differ depending on the type of bugs we have in our gut. You know, I was brought up, it's just like, it's the amount of calories. And now I'm in this world where it seems that there's this huge shift to the focus on the quality of the food, but this is, you know, we haven't talked a lot about appetite on this show. Like, is that, there's this link here to appetite and...

I think the microbiome definitely plays a role. I think that it's not the, I would have thought it's not the actual primary driver of the pandemic of diet related illnesses we actually have today, but undoubtedly it has played a role because your microbiome is immensely sensitive to the environment in which we live in, which includes the type of foods we eat. And if you don't keep it happy, if you don't give it enough nice and fiber and things to keep it nice and diverse, then you begin to change the microbiome and ultimately it does begin to change some of the... It certainly influences the hormonal release and therefore will influence your appetite if you don't have a microbiome that's healthy.

So, Jars, I'd love to sort of switch out of all of this to therefore sort of what you can do. I'd quite like to pull back to like the bear story that you're talking about at the beginning, which I'm now really thinking about, like just eating the fatty salmon and the equivalent for me of my special stomach that works for chocolate. It makes me immediately think about like ultra processed foods and all these sorts of foods that we sort of know we can't stop eating. Does that tie into this appetite you're talking about? And what therefore should we be wary of? And what should we be thinking that we can change that might adjust this appetite control

that you're saying is so important? We've just focused here on weight loss. There's many different reasons why people change their diet, but let's, for the sake of here, let's talk about weight loss. So what is the easiest way to lose weight? The easiest way to lose weight is just to eat less. That's difficult. What's the easiest way to eat less?

The easiest way to eat less is to feel fuller. And so ultimately, what strategies do we have in play, both from a diet perspective or a pharmaceutical perspective, but we're here talking about food, can we actually do to make us feel fuller? Now, if you remember what I said about the fact that the longer something takes to digest, the farther down the gut it goes, and therefore gut hormones get released and you feel fuller. I think if you use that as a principle to explain what is going on in our world today, I think it begins to make some

degree of sense. So clearly, if you ate whole foods, the macronutrient that takes the longest to digest just happens to be protein. It is chemically the most complex compared to fat, compared to carbs in that order. Okay, so a calorie with all the weaknesses we're talking about, but a calorie of protein makes you feel fuller than a calorie of fat, than a calorie of carb, largely because of the amount of time it takes to digest. Second, the amount of energy it takes to metabolize each of those, okay, and for that. So if you actually thought about that, then foods that are higher in protein and higher in fiber, because fiber comes out the other side, we don't digest it at all, will naturally

have a certain repertoire of gut hormones that are released and naturally make you feel fuller. The issue with ultra-processed foods is that because of the ultra-processing that has gone into the food, it is naturally lower in protein and or fiber, depending on, depending, fiber only comes from plants. So depending on what you're actually eating. Hence, it's actually very, very easy to absorb the calories within ultra-processed food, the energy in ultra-processed foods, because it doesn't have a lot of protein, it doesn't

have a lot of fiber, so it digests very very quickly. It also doesn't have a lot of flavor because it's been ultra processed, right? And where does flavor come from? Flavor comes from the holy trinity, sugar, salt, fat. So because it doesn't have flavor, you have to add in flavor, which is sugar, salt, fat. So ultra processed foods, not all of them, but most of them are typically low in fiber and protein and high in sugar, salt, fat, which means that it's a flavor bomb and it's very quick to digest.

And so this does end up driving appetite and end up having you to eat more because you're feeling less full when you eat ultra processed foods. Because one way to think about it is just it's sort of passively less filling than other things. But another way to think about it, which I guess I've been starting to think about it more is it's somehow almost like hacking into some of these responses. And I was thinking about your description of the bear only eating the salmon and like there's these hard, you were saying like these sort of hardwired things you're looking for. Is there anything going on there with this ultra processed food or is it just simply

that it's easy to digest? So there's two things, it's easier to digest. So that is a more visceral effect, shall we say. A colleague of mine, Dana Small, she did this work when she was at Yale. She's now at McGill in Canada, but she did this, I thought, really quite interesting study. She works on human beings. She's a brain imager. Just to quickly summarize the experiment, what she did was she took human beings and

she got them to try and predict how many calories, what the energy content of something that was high in carb, something that was high in protein, and something that was high in fat. And what happened there was that people were actually quite good at trying to judge how many calories there are in fat, something that was high in fat. Less good at how many calories were there in carbs, less good. The moment, however, you mix the fat and the carbs together, and if you think about it, everything delicious is a mix of fat and the carbs together, and if you think about it, everything delicious is a mix of fat and carbs.

Human beings have no concept of how many calories are there. None. It's a big, you know, there is no regression line, nothing. She did this, but then she fed these items of food in a brain scanner, okay? And then looked at the brains of these people. And so clearly, carbs, ooh, and the little part of the brain that's reward goes, lights up. Fat, ooh, the moment you mix fat

and carbs together, whoop, whoop, your brain suddenly lights up because it then hijacks the systems coming up. And really from a, not only does it make you feel hungrier or less full, pardon me, it's a different thing, but it also really lights up the brain the part of the brain which says oh food is delicious And lights it up like a Christmas tree. That's crazy So you're saying you're literally I can you can put my brain in a scanner? And it has like a bit of a response to some like a cob and a bit of a response to some Fat like a piece of cheese, but once you the two like pizza, my brain goes wild for that. And on top of that, we are terrible at trying to predict from a natural perspective, imagine

you're in the wild, in trying to predict how many calories they might be in their pizza. There is an, okay, why might this be the case? So clearly, why does the brain respond in this way? It's always useful to sort of go back to evolution and think about what this this be the case? So clearly, why does the brain respond in this way? It's always useful to sort of go back to evolution and think about what this might be the case. And I guess an issue here is that there are very, very, very few foods that are naturally high in both fat and carbs mixed together. Okay, very, very, very few. Yes, you can have a roast potato, but that is potatoes sympathetically introduced to

fat. That's very different. You've put it together. Pretty much the only or one of the very few ubiquitous items of food that is high in sugar and fat is milk. And we are baby mammals, so what happens when we're born? What is our prime aim? To grow as quickly as possible to avoid becoming tiger food, correct?

And so you latch on to the closest source of food, which is obviously the boob. And the sugar that's there is lactose, rather than necessarily any other kind of sugar, but it's high in lactose and it's high in fat, which is what milk is. And so there is a hypothesis, difficult to prove, that part of this circuit is to make sure that the hard wiring is there to Really make sure we drive and go towards the milk and drink it the moment we come out latch on and that's still true today And so this is one of the hypothesis I'm not saying it's difficult to test obviously, but this is one of the evolutionary explanations that are out there

But why this mix of fat and carbs? is so, you know, why lights your brain up like a Christmas tree. It's fascinating. We've had a few podcasts talking about sort of this really recent research looking at how ultra processed food can affect your microbiome and some really interesting studies about this.

But what you're talking about is that you can actually measure these responses in the brain where it's just really responding differently to these sorts of foods than anything else in explaining, which I hadn't appreciated before, that this sort of mix that you're getting in these ultra-processed foods, it's not something that we normally get. It's not some food that you can pull off a tree or dig out of the ground or even like an animal that you eat that has that mix of fat and carbs. Very, very few coconuts, but that is very geographically specific. Maybe an overripe avocado, you know, but generally speaking, you have foods that are high in protein,

you have foods that are high in fat. Fat and protein because they come in an animal together, but carbs tend to come from fruit, which has no fat in it at all, largely speaking, or honey. And once again, there's no fat in there either, right? In terms of natural sources that are actually out there, if you eat a potato, it's got no fat in it either. So the whole concept of fat and carbs is something which is a human intervention to cook something in fat.

The term ultra processed foods, I still think is too broad a church. I think it's too, there are a lot of foods I think we should eat less of. But I think the umbrella is so big, it sort of sweeps in a bunch of foods that are probably don't need to be there. I mean, we'll go to the yogurt example, okay, where, okay, natural yogurt. But if you put natural yogurt with a bit of jam in it, suddenly it becomes ultra processed

Now they are completely ultra processed constructed from from foods But I think there are some foods that sort of slip in under under the net The other thing famously and I'm on the record for saying this where supermarket bread, okay Taste aside is still made largely of you know, flour salt and yeast and some water and Taste aside is probably not as bad for you as some people make out to be. It is more calorie dense, et cetera, et cetera. So I think we do need to be careful in a sense where we want to make sure we eat less of certain things and we want to quantify that better so that we don't demonize all the foods

which were there. But undoubtedly it is true that the majority of ultra processed foods, we should be eating less of. Do you know someone who's always counting calories? Maybe they're disciplined, but having listened to this, focusing on the wrong things? Why not share this episode with them right now and give them the science-backed tools to sustain a healthy weight long-term? I'm sure they'll thank you. That makes sense.

We're actually doing a lot of research at the moment to try and better define these gradations of ultra-processed food because there's really interesting data that we're collecting through this huge number of people who are Zoé members and see with a microbiome because this is quite new science, right? And I think for people listening, one of the things that I've discovered is, this is a process, isn't it? Like you discover something new,

a bit like you were telling the story 100 years ago, right? Of understanding better what's going on with calories and sort of understanding better what ultra processed food is. It's not just like anything that has anything, any processing is bad. There's clearly a scale. And it seems to me pretty clear now, there's quite a few foods in the grocery store

that I don't want to eat, and I don't really want anyone else to eat. The issue is that there's still pretty much the cheapest foods you can get in the supermarket because of their shelf life and because of their industrial processes. So here is the issue. How do we therefore improve the diets of people in addition to your Zoe customers, equitably?

Because at the moment, the healthiest foods are not the cheapest foods. So how are we actually going to fix this problem? So the other thing which I'm slightly uncomfortable with, even though I understand the problems of ultra-processed foods is how do we avoid, if we don't make healthier food cheaper and the ultra-processed foods are available, how do we avoid demonizing people who can't afford the healthier food at the moment when they're eating? I think there needs to be an adult, non-historical discussion about how we improve the food environment we're in, but in an equitable fashion. I just thought I'd have to say that.

I think that's right. And one of the reasons we do this podcast, among other things is that we believe a lot of that starts with demand. I think it's not as true really, that it's not possible to make food that is whole and healthy at prices that can work. I agree with you.

But if there's no demand for it, then it doesn't matter. So hopefully some people are listening to this and it will have some impact on how they think about what they should do as they're thinking about, you know, we talk this mix between weight loss and weight management. I think there's a lot of people who like me suddenly realize, well, I've got to make a change or otherwise I'm going to just keep putting on this weight. And I have found in fact, since I met Tim, interestingly, my weight has been really stable for the last seven years, I guess, without worrying about it. Is there any other actionable advice you'd want to give for people who are looking to lose weight or maintain weight better other than that. Okay, I think there are three numbers that I would think that people think about. The first is 16.

And this is the percentage in terms of energy of protein that you should be consuming. And there is a sweet spot for the amount of protein to eat, unless you're an Olympian or unless you are ill and ITU. If you're a relatively healthy human being here, you should be aiming for 16% of protein in your diet. Too much, your liver and kidneys begin to stress out. Too little, you don't get enough. And I'm not only talking steak, just to be clear, tofu, beans, any source of protein,

vegetables or animals will work. So 16. 30, the next number. This is the grams of fiber we should be aiming to consume in our diet. At the moment, on average, in this country, in the United States, we're looking at maybe only 15 at the stretch, 20 grams of fiber a day. We need to double the amount of fiber we're eating. Fiber only comes from plants and from fruits. So I mean, eat more fruits and vegetables. And the third number is five.

And this is the percent that we've got to keep under of the free sugars in our diet. So free sugars are sugars that are not tied up in fiber. So eat as much fruit as you want, okay, please, because it's tied up in the fiber. I'm talking about anything that's been extracted. So yes, the white powdered stuff, honey, al-Gav nectar, maple syrup, and yes, they're all the same thing,

even though they taste differently. We want to keep this added sugar to 5% or less. To my mind, those are the three numbers to think about. 16% for protein, 30 grams for fiber, 5% or less for free sugars. Apply that to whatever dietary approach, whatever church you worship of the diets of the dietary gods. And I think that's going to be good for you. Giles, that's amazing. Thank you. And I love your little like pricey at the end for your rules. Everyone has some, you know, Tim has his six, you know, that's all the rest of

it. Zoe, we obviously have our own. Can I try and do a quick summary of what I heard and then you correct me when I get it wrong. Okay, let's do that. So, you know, I think we started by basically explaining calorie counting doesn't work. And you described this wonderful lady, was it Lulu? Lulu Hunt Peters. Lulu Hunt. Google her.

Lulu Hunt Peters. I will be Googling her after this, who basically created the first ever MyFitnessPal. Pretty much. Had a four year New York Times best seller, and basically invented this idea that here are all the calories and you should count them. And if you reduce them, that's the secret to losing weight.

And basically we've been talking about this for a hundred years, but it doesn't work. And what you said is the easiest way to lose weight is to feel fuller, right? So the reverse of counting calories, forget about that, it's like, how can you feel fuller? And what that means is you need to change the sort of food that you're eating.

And what it also means is it switches this focus suddenly to the brain. And what you're saying also is like, you and your colleagues like have literally imaging these brains and seeing what's going on appetite is this real thing in your brain you are like figuring out the particular circuits of how this works and it's very complicated because you talked about how there's hunger but also how full you are but also how like delicious it tastes and

basically the food that we're eating now is sort of messing with all of this over time and causing these problems. And I know we didn't really get into these new, you know, drugs like Azempic, but you can, I guess you can see how, you know, over time, this is, leads us to a point that the, the brain is like so damaged that you end with this. But interestingly, I think I took away two things. The first is my dessert tummy and my son's dessert tummy is real, but it only works for particular sorts of food. And this is not like something we've invented in the last 100 years. We're

giving this brilliant example of like bears have the dessert tummy as well, but it works for particular sorts of food. And the reason why I crave chocolate, I guess, at the end of the evening is it's one of those foods which has got sugar and fat. And you said to me, the only thing in real life that has that was like my mother's milk. So I'm like built to like that from a small child. But all of this modern ultra processed food triggers this. And so you're saying my brain goes off like a Christmas tree when I see it and it's not

supposed to happen. And so this like explains why, you know, in a sense it's not your fault you want this stuff, right? This stuff has been built to overcome your natural desires. And then I think the other thing you talked about is that sort of the gut hormones have this huge impact on how hungry you feel. And so it's not just that you want to eat this stuff more because of the sort of food. If you aren't eating this food that has lots of fiber that is sort of supporting the right microbiome that is going down into your gut, then basically you're not getting, you said these 16 different gut hormones that...

18. 18, I'm sorry, 18 gut hormones that come off and into your brain that sort of affect your hunger. And so, you know, another example of just how important sort of the gut is on the way that you feel. And that in a sense, we should all be a bit easier on ourselves because, you know, the final thing I guess I remember is you're saying, you know, as soon as I start to lose any weight, like a big red alarm goes off in my brain that's just basically pushing me to eat more because, you know, I soon as I start to lose any weight, like a big red alarm goes off in my brain, that's just basically pushing me to eat more because, you know, I might be going to starve to death.

And so this whole thing is just very, very different from what, you know, Coca-Cola taught me when I was at school about, you know, it's just simply like kick the ball, it's just the energy in, calories in and calories out, completely different thing than we had understood 25 years ago. Man, it's like you've done this before. Yes, correct. Giles, thank you so much for coming in. I really enjoyed that. I hope we can tempt you to come back again in the future. Absolutely. Thank you for having me on your platform. It's a pleasure. Now, if you listen to the show regularly, you already believe that changing

how you eat can transform your health, but you can only do so much with general advice from a weekly podcast. If you want to feel much better now and be on the path to live many more healthy years, you need something more. And that's why more than a hundred thousand members trust Zoe each day to help them make the smartest food choices. Combining our world-leading science with your Zoe test results, Zoe is your daily companion to better health for life. So how does it work? Zoe membership starts with at-home testing to understand your unique body.

Then Zoe's app is your health coach using weekly check-ins and daily guidance to help you shift your food choices to steadily improve your health. I rely on Zoe's advice every day, and truly it has transformed how I feel. Will you give Zoe a try? The first step is easy. Take our free quiz to find out what Zoe membership could do for you. Simply go to zoe.com slash podcast, where as a podcast listener, you'll get 10% off. As always, I'm your host, Jonathan Wolff. Zoë Science and Nutrition is produced by Julie Pinero, Sam Durham and Richard Willem.

The Zoë Science and Nutrition podcast is not medical advice and if you have any medical concerns, please consult your doctor. See you next time. Thanks for watching!