Feel Better, Live More with Dr Rangan Chatterjee - How to Sleep Better, Boost Gut Health and Get More Energy with Professor Satchin Panda #306

Episode Date: October 25, 2022

CAUTION: This podcast discusses fasting and its advice may not be suitable for anyone with an eating disorder. If you have an existing health condition or are taking medication, always consult your healthcare practitioner before going for prolonged periods without eating.   Ten years ago this week’s guest published a seminal paper on time-restricted feeding (TRF) and this research was hugely influential in kick-starting a global health phenomenon, now known as intermittent fasting. Professor Satchin Panda is a leading expert in the field of circadian rhythm research. He’s associate professor at the prestigious SALK institute, he’s recipient of the Dana Foundation Award in brain and immune system imaging and he’s also the author of two best-selling books The Circadian Code and The Circadian Diabetes Code.   Over the years, Satchin’s work has had a significant influence on the way I practise medicine and I’m delighted to welcome him back onto the podcast today for our second conversation so that he can update us on where we are with our understanding of this topic today. Research has shown that around 50% of us currently spread our meals and snacks across 15 or more hours of the day. But Satchin’s research suggests that 10 hours may well be the optimum window for eating for many of us. Having periods of time in every 24 hours where we are not eating is essential for repairing, resetting and rejuvenating all of our organs and tissues – and ultimately releasing anti-inflammatory signalling molecules that strengthen our immune system. We talk about the multiple benefits that people can experience when they compress their eating window. People sleep better, their digestion improves and their energy increases. Further proven benefits over time include weight loss, improved gut health and kidney function – not to mention some incredible results when it comes to reducing pre-diabetes and type 2 diabetes symptoms. And food, while important, is not all that counts when it comes to optimising our daily circadian rhythms. Satchin talks about the other simple lifestyle factors that are hugely important. He also shares some great advice on jet lag, shift work, ‘social hangovers’ and the optimum time for naps and exercise. It’s no exaggeration to say that Satchin’s work has revolutionised our understanding of health and wellbeing and it was a huge honour to speak to him again. I hope you enjoy listening. Support the podcast and enjoy Ad-Free episodes. Try FREE for 7 days on Apple Podcasts https://apple.co/feelbetterlivemore or https://fblm.supercast.com. Show notes https://drchatterjee.com/306 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.

It's a huge experiment and this is something that has never been done. We looked at all the genes in the genome to see what is actually going on during this fasting process. By tuning your timing and eating within 8 to 10 hours, the number one thing that we found is nearly 80 plus percent of the genes were changing what time they were turned on or off, or how high or low they were going up or down. So that means really by changing your eating time, you can be the master conductor of your whole genetic program. Hey guys, how you doing? Hope you're having a good week so far.

My name is Dr. Rangan Chatterjee and this is my podcast, Feel Better, Live More. and this is my podcast, Feel Better, Live More. Around 10 years ago, this week's guest published a seminal paper on something called time-restricted feeding and it's safe to say that this paper was hugely influential in kick-starting a global health phenomenon now widely known as intermittent fasting. Dr. Sachin Panda is a leading expert in the field of circadian rhythm research. He's associate professor at the prestigious Salk Institute. He's recipient of the Dana Foundation Award in brain and immune system imaging. And he's also the author of two bestselling books, The Circadian Code and The Circadian Diabetes Code. best-selling books, The Circadian Code and The Circadian Diabetes Code. Now over the years,

Sachin's work has had a significant influence on the way I practice medicine. And he first came on my show over four years ago now in June 2018. And I'm delighted to have him back for a second time so that he can update all of us on where we are with our understanding of this topic today. Now, research has shown that around 50% of us currently spread our meals and snacks across 15 or more hours of the day. But Satchin's research suggests that 10 hours may well be the optimum eating window for many of us. be the optimum eating window for many of us. Having periods of time in every 24 hours where we are not eating is essential for repairing, resetting and rejuvenating all of our organs and tissues and releasing anti-inflammatory signaling molecules that strengthen our immune system. Now during our conversation we cover the numerous benefits that people can experience when they compress their eating window. Better sleep, improved digestion, more energy.

Some studies have shown benefits for things like weight loss, improved gut health and kidney function. Not to mention some incredible results with pre-diabetes and type 2 diabetes, a topic brought to life in Sachin's latest book, The Circadian Diabetes Code. If you've listened to my show for a while, you will know that food, whilst very important, is not all that counts when it comes to optimising our daily circadian rhythms. And Sachin covers some of the other simple lifestyle factors that are hugely important. He also shares some great advice on jet lag, shift work, social hangovers, and the optimum time for naps and exercise. Now, it's no exaggeration to say that Sachin's work has revolutionized our collective understanding of health and well-being, it really was a huge honour to

speak to him again. I hope you enjoyed listening. Now, two quick things that's really important for me to say before we get started. Number one, this podcast talks about restricting our eating windows in order to gain potential health benefits. This advice may not be suitable for anyone suffering with or recovering from an eating disorder. Please, please do take this into account if you are listening. And secondly, if you have an existing health condition or are taking medication, for example, for type 2 diabetes, always consult your healthcare practitioner

before going for prolonged periods of time without eating. And now, my conversation with Professor Sachin Panda. You know, I think a really good place to start this conversation would be to really help us all understand what happens in our body when we have a period of time when we're not eating yeah so my research background is circadian rhythm or 24 hours rhythms which means that our body is actually designed to be at its peak performance whether it's metabolic, physical, biochemical, or intellectual performance peak performance at every hour of the 24 hours day. And we all evolved on this

planet with 24 hours light-dark cycle and eating fasting cycle so that's why we are designed to go through this at least 12 to 14 hours of fasting every day so now coming back to what happens during this period of time one thing is this fasting has to be consistent from one day to another consistently at the same time so that our body's internal program recognizes that fasting is going to occur. So there is a lot of preparation, internal preparation. The circadian rhythm does that preparation. So after your last bite of the dinner, for example, if it happens at six o'clock in the

evening, then although your mouth finished chewing the food and swallowing and that food is going to be digested for next five hours so the first five hours of your overnight fasting your body is actually not fasting it's digesting the food and then after five hours approximately five hours the food goes to intestine and then nutrient absorption happens for the next few hours and during this time the body is using most of the glucose and stored glycogen for fueling our system and then slowly when it runs low

On glycogen so which happens maybe seven eight hours or even ten hours on glycogen, so which happens maybe seven, eight hours or even 10 hours after our last meal, then it slowly begins to burn a little bit of fat. And when the fasting period aligns with your sleep, then there is another magic that happens, that is our gut lining and many parts of our body actually gets a lot of damage throughout the day and they have to be repaired and that repair process happens only when we are in our deep sleep and also we are fasting we don't have too much food to digest so

after nine to ten hours this is when if you're asleep then your pituitary gland will produce growth hormone that will travel to many parts of your body, including the gut lining, to trigger the repair process. So that's when a lot of the repair process will happen. Your gut lining will get repaired. Many other tissues will get repaired. And then after maybe 12 hours, 12 to 14 hours, that's when a body will produce enough, will break down enough fatty acids or stored fat to produce a little bit of ketone.

And this ketone now begins to fuel your body. And then ketone is also very recent discoveries suggest that ketones are anti-inflammatory because they affect the immune system. The immune cells also like ketone in many different ways. One is they can use it as fuel. Ketone is a fuel. And second is ketones are also signaling molecules. So that means they can instruct the cell to turn on different kind of programs.

So one of the programs they turn on is anti-inflammatory program. What we are also learning is this is just the tip of the iceberg because until now, no one has actually done a very systematic experiment, even in laboratory mice, to see what happens during this 14 to 16 hours of fast in different organs. As we all know, we have at least a couple of dozen different organs, and then our brain, different parts of the brain is also very different. So only recently we started doing that. We took the same mice, the same genotype, they were born to

the same mom with the same microbiome. One group of mice got to eat whenever they wanted, the other group of mice were given food eight to nine hours every night because mice are not enough. And then after a few weeks, we took out 20 plus different organs and brain regions from these mice in every two hours, over 24 hours, to see what is actually going on during this fasting process. And then we looked at all the genes in the genome. So that's 22,000 genes in each of these 20 plus organs at every time point in male and female mice. So it's a huge experiment and this is something that has never been done even in caloric restriction and other types of nutrient intervention. So the number

one thing that we found is by imposing a strong feeding fasting cycle we could see that nearly 80 plus percent of the genes were changing what time they were turned on or off or how high or low they're going up or down. Wow. So that means really by changing your eating time, you can be the master conductor of your whole genetic program. And that is amazing because in many previous studies,

people just look at one organ, say liver or the gut, or fat tissues or muscle, and they find a few hundred genes changing. But when you cast a wider net, so that means it impacts almost every organ in our body. This is huge. As a medical doctor, I'm always looking for a few things with my patients. First of all, I'm looking for what is the root cause of why this person's

come in? Not necessarily the symptom. The symptom is important to me, but it's more important for me to understand what's driving this in the first place. And I'm always looking to see how can I help my patient go further and further upstream, what's one change I can help them make that will have multiple downstream benefits. What I hear with this new research that you guys are doing is the timing of your food intake as you say can be this master conductor and can have multiple effects on genes, inflammation, immune system function, all kinds of things. And one thing that's always fascinated me about your work is the whole conversation around nutrition for many years, and even now, is still dominated by what

we should be eating. Should it be fat, carbs, protein, what proportion? And I'm not saying those things are not important, but your research beautifully demonstrates that timing a food intake is something we also need to pay a lot of attention to. Yeah, so it's very intuitive and it's very simple to follow as well. So for example, I don't know about you, but I cannot remember how many calories I ate yesterday and what fraction of that calorie was a simple versus complex carb, how much was protein, fat,

or carb. So for implementing in day-to-day life, although these are very important, quality and quantity of nutrition, the timing becomes very easy because we all know what time it is. We schedule our whole day around time. Another thing that we are finding is when people control the timing of their food then as I mentioned from our surprising discovery with gene expression data they also seem to sleep well and once their sleep improves then the repair process improves and once somebody sleeps well then the food craving and somebody sleeps well, then the food craving and craving for energy-dense diet, that also goes down. So that means by controlling timing, we can inadvertently change the nutrition quality and quantity. And that's now seen in many clinical trials with time-restricted eating or intermittent fasting. People, although they are asked to eat within 8, 9 or 10 hours window and

then leave the rest as fasting, when you go back to analyzing what they ate, then what we find is they modestly reduce their calorie intake by somewhere between 5 to 10 and some cases some people can reduce even by 20%, which is pretty good because intentional calorie restriction is very hard. For people to reduce calorie by even 10 to 20% every single day is very hard. So you're saying the side effect of people focusing on a particular eating window, whether it be 8 hours or 10 hours or 12 hours, whatever it might be, you're seeing side effects that actually people are also consuming less calories without actually trying to reduce their calories.

Yeah, because previously we thought some nutritionists had imagined that when people are going through long period of fasting, they might gorge and eat more. But we find exactly the opposite. People reduce their calorie. Second thing is since they're sleeping well, then they also improve their nutrition choice. So in almost every study, we find people reduce their alcohol intake. Of course, there is less opportunity to drink alcohol. And then they also reduce processed food. And we don't know why, but it may be because they're sleeping well, because a sleep-deprived

brain actually looks for highly processed food, nutrient-dense diet, and when people sleep well, then they can take that decision. I think everyone intuitively knows that, even if they don't understand the science. I think everyone knows that experience when they haven't slept well. Yes, you can talk to the science of leptin and ghrelin, and the hunger hormone goes through the roof, and your satiety hormone goes down. But actually, I think we all know when we haven't slept well, we want more caffeine. We crave more food. This happened to me a few days ago. Hungry all the time and you're not craving healthy whole foods at that time. You're craving sugar, high energy dense foods. Yeah, because your brain actually gets confused how long it will stay awake.

And since brain consumes a huge amount of energy per unit mass, that's why it kind of programs you to eat more because it doesn't know how long it will stay awake. So that's one side effect that we see. By tuning your timing and eating within 8 to 10 hours, you can also reduce calorie and improve nutrition quality. So that's where, although quality and quantity of nutrition are very important, by focusing on timing, one can improve those two aspects too. So let's go into timing. Lots of things happen in the body when we have a period of time without foods.

Ketone production, reduction in inflammation, change in genetic expression, ability to repair and rejuvenate better. But I guess there's an ideal body clock that if the modern world didn't drive us to do certain things at certain times that we could all beautifully follow. And then there's real life for many people. So let's start off by going, what does an ideal body clock look like for someone? Let's say they wake up. i know you're a big fan of saying that we should try not to eat for the first hour after waking up is that true and if so why is that um so most of us when we wake up we we're waking up to an alarm clock or um we have to go to office or do something

or take care of the children so that's why we're waking up in the morning. So that means our sleep hormones are still high. Although we just dragged ourselves out of the bed, our hormones, particularly melatonin, is still pretty high. And that takes an hour or two to go down. And within 45 minutes of waking up up our stress hormone cortisol reaches its peak so this is the time when you can say changing of the guards that happens in the morning so the sleep hormones are coming down the stress hormones are going up and your body is actually

not ready to digest food and assimilate nutrient perfectly because melatonin inhibits glucose-induced insulin release from the pancreas. So that means within an hour of waking up, most of us still have pretty high level of melatonin, which can inhibit this insulin release. So if we eat something or drink tea with milk and sugar, to process that, a body has to produce and release a sufficient amount of insulin, which may not happen properly in the first one hour. So in the first hour, I love this changing of the garden analogy, particularly as you're in London at the moment. So I think that's a very practical tip that everyone, no matter what diet they choose to

follow, no matter what culture they're from, no matter what country they live in, that seems like quite a good universal principle for all of us. Whenever you wake up for the first hour, for all of us, whenever you wake up for the first hour, don't eat any food. But you're also saying no coffee or tea with milk and or sugar. So does that mean, according to this model, a black coffee or a black tea is okay at that time? Or would you still advise that gets pushed a bit forward as well? Well, many people ask me why can't they have one small teaspoon of sugar or a little bit of milk. So for an average sized person like me, if you drain all of my blood, you'll get around five liters of blood. And since the glucose concentration in my blood should be below 100 milligram per deciliter, that means you'll get maximum five gram of sugar from my blood.

So that means even if I drink a tea or coffee with half a teaspoon of sugar, so that's 2.2 grams of sugar, if that's not processed properly, then my blood sugar level will shoot up to 140 or 160, around that. Wow. So that's why even- And you're saying at that time, you're not going to be able to, or you're unlikely to be able to process it properly. Properly.

Because you've still got these sleep hormones, things like melatonin, and the stress on the cortisol are kicking around the system still, which is potentially going to interfere with the way that you process that sugar so if you do want to have a hot drink when you wake up like many people do yeah you would advise keep it black basically keep it black and uh or herbal tea or something tea and yeah because some people just need that hot drink to to start their day and initially i was a little skeptical because this is an experiment we can never do in mice we cannot wake up mice and give little herbal tea and see what happens um but if if somebody really needs coffee or tea to begin the day because he or she is sleepy, then that's also a warning sign that

the person is not sleeping well. So you may have to kind of interpret that you may have to go to sleep a little bit earlier. So I used to say that there are three exceptions to the coffee rule in the morning. So one is if your job depends on it. So for example, you're a physician, you're going to see patients and you should be alert because if you make a mistake, then that can be quite deadly, literally. Second is for public safety. If you're driving, and we know in the US, one in three drivers in the morning is sleep-deprived and needs coffee and the third one is if that's the only love in your life then we're not going to deprive you yeah i think that's those

three really beautiful because there's a real practical element to that isn't there there's like there's optimal yeah there's what ideally for our biology to live in harmony with our circadian biology there's a way to live but there's also a practicality depending on your life. And I think that third one is a really nice one. You know, if that is your real love in life or that's something, because of whatever's going on in your life, that that is something

that's really important to you, then that has to be taken into consideration. Would you say ideally, if you could, that in that one hour after waking you would ideally avoid any caffeine as well? Has any of your research looked at that or not? There are other circadian researchers who have beautifully shown that caffeine actually resets our clock. It's almost the effect of caffeine on resetting or synchronizing our clock to the outside world or to coffee drinking is as good as getting strong exposure to light.

But I won't go to that extent because light has many other benefits that caffeine cannot do. So in a way, caffeine is pretty good to For many people for some people it can be a little bit tricky those who have acid reflux having a strong black coffee Can exaggerate that and people may? See more serious acid reflux problem But if you for example, if you go back to the history of breakfast

breakfast actually, people are not eating breakfast in the old days. If you go back to the history of coffee, for example, in Turkey. And in Turkey, when people started drinking coffee in Istanbul in the morning, and strong coffee, a lot of them, they started experiencing this morning acid reflux and to reduce that acid reflux they had little food with coffee and that food with coffee became breakfast if you look at the turkish name for breakfast that essentially means the food before your coffee before your coffee to reduce the acid reflux effect of coffee. Yeah.

Okay, so morning time, one hour, no food if possible. If you can have a drink, tea or coffee, keep it black. What else should we be thinking about doing at the start of the day to help us robustly support this natural circadian clock that we have inside us? support this natural circadian clock that we have inside us. Yeah, so another thing is light because our body clock is entrenched or synchronized by food, but our brain clock is actually synchronized by light. And light also reduces sleepiness. We all know that because it's very hard to fall asleep in a lighted room and in the morning if you want to wake up your children then just open your windows and they are more likely to wake up

and this is very important because many of us most of us actually don't get enough light in the morning to synchronize our brain circadian clock and to reduce sleepiness and depression so light is a strong anti-depression and it has been documented in many many studies so if you have the chance to go outside to the balcony or even open all the windows in your room you'll get good amount of light and'll get a good amount of light. And when I say a good amount of light, you need around 1,000 lux of light for 30 minutes to an hour to synchronize your clock and to reduce sleepiness and depression. Even on a cloudy day in England, you get 5,000 to 10,000 lux of light outdoor.

And if you're sitting right next to the window, sipping your coffee or tea or drinking your or eating your breakfast or reading your newspaper, then you're getting around 800 to 1,000 lux of light. So that's one thing that you can do during this one hour time. Or if you have to get ready, if you're in the bathroom, and if you have a dimmable bathroom light, crank it up. Crank it up. And if you have those modern bathroom mirrors that have the light integrated, then that's actually pretty good because light falls straight into your eye,

and you can crank it up to 800 to 1000 lux at full strength and that's a good way to get the morning light. What about movements at this time? How does that fit into our body's natural clocks? So exercise is always good. I mean most of the time. You don't have to exercise in the middle of the night, but any exercise is better than no exercise. So you can combine exercise with light exposure by going for a light walk or morning run outdoor, or if you're going to a gym,

also choose a place that gets a lot of light. So you can combine both light and exercise. Exercise and circadian clock, they reciprocally interact with each other. So that means exercise has some impact, not as much impact as food or light. But the clock has a lot of impact on when is the perfect time for you to exercise. And we'll get to that as we move towards afternoon. Yeah. Okay, so what I like about that initial morning recommendation is that you can actually hit all three bases in one go. So if you are able to go for a walk in the morning and you don't take a drink with you,

and you don't take a snack with you, then number one, you're not going to be eating or drinking. You're going to be getting exposure to natural light and you're going to be moving your body. So that's a really powerful thing that we can do. One thing that has multiple benefits on our physiology and on our circadian clock. Before we move beyond that, you mentioned something that I found fascinating. Food helps us reset our body clock. Light helps reset our brain's clock. Can you explain what is the difference between our body clock and our brain clock? Just taking a quick break to give a shout out to AG1, one of the sponsors of today's show. Now, if you're looking for something at this time of year

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And when we say clock, one thing that comes to our mind is sleep. Because we go to sleep every night and then wake up. And if we think what happens during sleep, during sleep many things happen to our brain. And that can be summarized into three things one is repair reset and rejuvenation our brain repairs itself we know that the brain takes out its um its trust and that has been shown recently and rejuvenation so the brain's cells connect with each other much better synaptic strengthening, and it resets

itself for the next day. So similarly, every cell in our body has to repair itself and go through this. So now, all these clocks have to also be synchronized with each other. So that means our liver clock should be in sync with our gut clock so that our gut has its own timing when the digestive juice is produced. And it also has a better time when it can absorb all the nutrients and the liver has to process. So liver also has a peak time or preferred time when it can process all the nutrients. So all these clocks have to be synchronized with each other. Liver also has a peak time or preferred time when it can process all the nutrients so all these clocks have to be synchronized with each other and

What we find is if somebody decides to eat in the middle of the night wakes up Tim light and it's some food then all these clocks they will think all the body clock. They'll think huh? Maybe this person moved to a different time zone. So they'll try to reset themselves, anticipating that next day this person will also eat in the middle of the night. But the brain clock doesn't reset to that food cue. So this is why consistency is so important. Because actually, so I'll tell you what happened a few nights ago.

So it's Thursday morning as we record this. Now, normally for me, I have a consistent lifestyle. And usually, my rhythm is that I will go to bed at 9 p.m., maybe sometimes before. But roughly, I'll be in the bedroom from 9pm a bit before or asleep then, and I'll wake up around five. That is, I'm at my best when I do that. I have sort of rhythms around my life and my work that help me stick to that. Now, on Tuesday night, I came down to London and I was doing my very first live podcast event on stage in the evening. So the event started at 8pm, you know, this is with lights on me and my guest on

stage. By the time I left the venue, it was probably about 11.15pm and I had eaten early, but I got back to my hotel room. I was still wired mentally. Really had a wonderful evening, and I had some healthy kind of food in my hotel room. I had some cashew nuts. I think I had some dried mango slice as well, which we can argue whether that's healthy or not. And even though I know your research, even though I've written books referencing your research, I'm a human being and I thought, I'll just have a little bit. So I was just unwinding with that. So I was probably eating at around midnight, right? Yeah. I still woke up the next day at five, even though I didn't want to, I didn't have to be up,

at five, even though I didn't want to, I didn't have to be up, but it's like clockwork in my body. I wake up at five, no alarm clock. I felt exhausted the following day, all day, obviously I had less sleep. I was hungry all the time, at times when I wouldn't normally be hungry. And so I really struggled on Wednesday, this is yesterday. I just wasn't with it, and I still don't feel recovered today,

even though I had a pretty good night's sleep last night. So maybe you can unpick that a little bit for me. Yeah, so a few things happened. One was your body clock was not ready to get that food. So when you ate, your digestive system had already gone to sleep. Although you didn't sleep, your brain did not go to sleep. Your body's, all the other clocks have already thought that it's time to sleep. The kitchen had closed, so they were going to sleep.

So when you ate that food, that was not easily digested because the gut was not producing enough acid and then the nutrient absorption didn't happen. And you woke up with food hangover yeah because that's what i call it as well you literally hangover but at the same time when they when all these organs are woken up by food it's not that they will just leave the food like that they'll try to digest and at the same time they they'll think that, okay, maybe from tomorrow Rangan is going to eat at midnight. So let's try to reset ourselves.

So the next day they're trying to reset themselves. At the same time, your brain is producing other hormones that help all these other organs. So there is a what we call producing other hormones that help all these other organs. So there is what we call desynchronized clocks. Your brain clock and your body clocks are in different time zones and they're trying to figure out what will be your next day's schedule.

So that's why you're feeling that discomfort on Wednesday. Yeah. And I know you've got two brilliant books out there. The new one, The Circadian Diabetes Codes. In this one, there's something I highlighted, which is if you eat or if you behave out of sync with your clock, it can take you quite a few days to recover. That's kind of what I'm feeling at the moment. I feel that one aberration, right? Which even though it was kind of healthy whole foods, and I think this is really key.

It's not just what you're eating, it's when you're eating as well. This is a key message from your work. I'm still struggling today because of what I did in that, I wouldn't say a moment of weakness, but maybe, maybe a moment of weakness on Tuesday nights. Can you explain it? Because I think a lot of us are doing this without realizing it. We think, ah, you know, a little bit of this now.

But actually, it can take us quite a bit of time to recover. Yeah. So two things. One is your story clearly demonstrated timing can make healthy food junk Timing makes or miss timing can make healthy food junk So by eating that healthy food in the middle of the night when your body was not expecting it Your body reacted as if you had some junk food It's very similar to your best friend knocking on your door in the middle of the night for

a friendly chat, not even anything. I don't think you'll be friendly with that person too much. So that's one. And then the second thing is those who are doing shift work or who travel quite a few time zones, two to three time zones, it's very normal for them to understand that when you change time zone it can take three to four days and even sometimes seven days to adjust your sleep-wake cycle to the new time zone. So the rule of thumb is it takes one day to reset your sleep-wake cycle by one hour. So that means if you're traveling

three time zones, then it can take up to three hours. So in your case, if you are eating, say, In your case, if you are eating, say, if your dinner is usually at 6 or 7 p.m. I'm done by 7. 7. I'm normally by 6, 6.30, I'm done. Yeah. Oh, man, so that's like six time zones. Six time zones.

So that's what your body felt like you have traveled six time zones. So it will try to readjust itself for the next six days. But the good thing is you came back to your previous schedule so you can reduce that jet lag. We call it social jet lag because it's not real jet lag. You're not doing jet travel, but your body thought because of social obligations and social events, you at the wrong time so it's called social jet lag. This idea that you can turn healthy food into junk food by eating at the wrong time I think is really really powerful and it's a message that I hope spreads far and wide because this timing piece is it's arguably for me one of the big missing pieces

when we are trying to help people change their health. It's like what to do, but we don't tell people, we don't advise people when to do these things. And since I've shifted my whole lifestyle and work patterns, everything to suit a rhythm that I can consistently do. And I'm lucky to be able to do that. I appreciate not everyone can do that, especially if you're doing shift work and it's changing from day to day or every three days you're on a different pattern. And we'll hopefully get to that later in the conversation. Every part of my life gets better. Gut function is better.

Energy is better. I rarely get sick. All kinds of things start to happen. One of the most powerful things I think about the work that your lab has done is it shows that when you really pay attention to the timing of multiple things, but let's say food and light, but let's say even just foods, there's benefits for weight loss, there's benefits for immune function, for reducing inflammation, for gut function. Kidney function, we're finding. Kidney function. Yeah. Yeah. Instead of trying to do something for your gut and something for your kidney and something for inflammation, it's like, well, hold on a minute. Why don't we just

work on an eating window that's going to work for you? let's go there to an eating window. You published your first seminal paper almost 10 years ago to the date, which basically sparked off this phenomena around the world, which has gone into multiple different directions of intermittent fasting. In the last 10 years, from all the research you've done, from all the research you've seen being done around the world, with the understanding that everyone's unique and everyone's different, do you think you have a universal recommendation like this kind of eating window is going to work for most people? Do you know what would you have a number that you would recommend? Yes, that's a little tough. It is a tough one, yeah. So let's start from, we started the conversation from the morning and we said one hour we should not eat and then when should we eat. So the breakfast or the first meal that breaks your fast because let's redefine breakfast.

Breakfast is actually the first meal that breaks your fast okay not the morning not necessarily the morning meal that you have to eat so you have to eat your breakfast at a consistent time because of this its effect on body clock because the breakfast time actually is most powerful in resynchronizing all your clocks and then telling, okay, so I'm in the same time zone, let's start the day. And then the question is, should somebody eat within four hours, six hours, eight hours,

10 hours, or 12 hours, or more? So we can do some simple math, and then we'll reach what would be the ideal one. Okay. Okay. So we know that after we eat, after we finish our dinner for the next five hours, it's not actually fasting, it's digesting our food and the stomach. So that means we should have those five hours set aside.

And then we should actually sleep for, we should be in bed for eight hours. So even if you, suppose you finish your dinner at 6 p.m., you're not going to sleep right away because your stomach is digesting food, your core body temperature is high because blood is flowing to the stomach to absorb that nutrient. So you need two to three hours after your dinner to get ready for your sleep. So now we'll take two to three hours after your last meal and then add eight hours of being in bed. So eight hours plus two hours, so that's 10 hours. So now in the morning you got to wait for an hour, so that's 11 hours.

So that leaves 13 hours window within which one can choose to eat for X number of hours. So nobody should eat for more than 13 hours, necessarily, according to this math. So now if we come back to clinical studies, there are some studies where people were asked to eat everything within 12 hours every single day. But unfortunately, we didn't see much benefit. So 12 hours every single day is not a good idea.

When you say not a good idea, let's say, I know your app has shown that a lot of people are eating over 15 hours. 15 hours. Right? Yeah. And a lot of people don't realize they're doing that. Yeah. Because that includes, of course, sugar in their coffee or a little snack in front of the TV at night. So if you are currently consuming over 15 hours or 14 hours, moving to only doing it over 12 hours presumably is a good thing.

So it's a good thing to some extent. But what happens is people who are, So it's a good thing to some extent, but what happens is if someone is eating over 16 hours and now moves to 12 hours, that person will get some benefit because that four hours delta, the change in reducing eating window by four hours, will benefit that person. And many different types of benefits may improve nutrition quality and then we don't know whether it will help to reduce calorie intake significantly to the point that the person will see some benefit. So there's some benefit there but you're saying some of the research when you took people and put them in a 12-hour eating window, so 12 hours in 24 where they're not eating, hopefully they're

sleeping for seven or eight hours of those, you're saying you didn't get many benefits? No, so again, these are clinical trials with a lot of people. So we are comparing the averages, but there are some people in those groups who actually saw benefit. But if we average all of them, then we don't see that. So from a clinical trial point of view, we have to always do the stats. I'm just going to pause you. That's such an important point because one almost universal recommendation I have with most of my patients is let's at least start off making sure you're eating all of your food within a 12-hour window maximum. Yes. Right? So that's often my starting point. And a lot of people, if they can't do that, or they say that they struggle, I say, okay, you should be able to do that. So let me help you

get to a point where you can do that. Because sometimes if they have their blood sugar imbalances or hormonal imbalance sometimes, or it's just conditioning. Okay. So in the 12 hours, some people saw benefit, but overall, you couldn't say that there was a huge benefit. Now, I guess let's dial back because every clinical trial also has inclusion-exclusion criteria. So that means what type of people were studied. And in this study, we didn't have people who had any chronic disease. So they were just overweight or obese.

They didn't have too much complications. They didn't have high blood pressure consistently or high blood glucose. Even in my new book, The Circadian Diabetes Code, I also tell that just try 12 hours for the first two weeks. And then you see whether you can even do 12 hours. If you can do 12 hours, then you can try to- And start experimenting with less, yeah, exactly. Yeah, so there are all these caveats to clinical trials.

So it's important to know what is the inclusion-exclusion criteria? What type of people were studied? Second, what was the baseline eating habit? Because if they're starting from, say, 13 hours or 14 hours eating window and they're trying to shrink it to 12 hours, you may not see too much. Dr. Panna, what you're talking about is nuance and perspectives and context, something that is fast becoming a thing of the past, certainly on social media.

Because this is important, isn't it? Instead of seeing the headline of the past, certainly on social media. Because this is important, isn't it? Instead of us seeing the headline of the study, this doesn't work, this does work. It's like, well, hold on a minute. Hold on a minute. Let's just say this average didn't work. For who? What kind of people?

Was it a man? Was it a woman? Did they have chronic disease? Did they not? And that's often missing in the kind of discourse around this stuff. Did they have chronic disease? Did they not? And that's often missing in the kind of discourse around this stuff. Yeah, so that's why I think anyone who is reading the headline has to ask these questions. Which type of people are studied? What is the baseline characteristic, habit, and health condition?

What did they try to do? Could they actually do that? Because in many studies, if I was just asked to eat within eight hours and i never kept any record and i came back after 12 weeks and i said hey i didn't see any benefit but i don't have any record to say that i actually tried this then that's also flawed so these three or four things we have to keep in mind. The baseline characteristic, what type of people are studied, and whether there is monitoring.

So for example, in many calorie restriction studies, where people are asked to reduce calories, people are also asked to diligently record all their food, portion size, so scientists can figure out whether they reduced calorie so similarly in many of the time-restricted feeding start eating studies or intermittent fasting studies we have to look for those things like where they monitored did they really reduce their eating time and how much they reduced what was their baseline characteristic and

was the reduced, what was the baseline characteristic, and what kind of benefits they found. So going back to 12 hours, what we find is, yes, people can start with 12 hours. And as we did the math, there's only 13 hours available to you to choose a window. And if you can do 12 hours, then that's a good starting point. In all of our clinical studies what we do is we ask people to choose a 10-hour window that suits their lifestyle and this is very important because we are not asking people to start eating breakfast at 8 o'clock or 9 o'clock or 7 o'clock or we are not even asking to skip breakfast or skip dinner we just ask them

a very simple idea that try to eat within 10 hours with some caveat that your first meal should be at least an hour after waking up and your last meal should be two to three hours before going to bed so within that window you're going to choose that 10 hours that works for you. And in both mouse studies and in human studies, what we're finding is if people can do this 10 hours for five days in a week or six days in a week, and they can have one cheat day where they can go a little bit outside the eating window, we still see many benefits in people who have one or multiple items of metabolic syndrome.

So that means they have obesity plus high blood pressure, high triglyceride, or high blood sugar, even multiple of these conditions. And what we find is if they can do 10 hours for 12 weeks, then we do see improvement in almost all of these elements of metabolic syndrome. Some are more profound and some take a little bit longer time, particularly blood triglyceride takes a little bit more time. Blood pressure improvement happens within six to eight weeks. Blood sugar also improves in 10 to 12 weeks, if they do 10 hours. It's also important to remember that many people

who have obesity with metabolic disease, they're so used to eating over a long window of time that it becomes very difficult for them to shrink that eating window to 12 then 10 and shrinking that to eight hours becomes very difficult to for a lot of people in fact in some of couple of our studies where our collaborators wanted people to eat within eight hours although they started with hours, towards the end of the experiment, 12 weeks, when we look at the real data, we found that they were mostly drifting towards 10 hours.

So 10 hours seems to be a number that many people can adapt their eating window. And it's also, it gives them a sweet spot that they can still have their social life and enjoy life and improve their health. Yeah, a couple of things there for me. I agree, some people really struggle initially. But actually, some people also find it quite liberating. I found there is a subsection of my patients who, in the past, I found that they find like an eight hour window where they're eating very liberating. And once they get used to it, they actually find that they've got more energy, less hunger. It speaks to this idea that we can maybe train our circadian biology to a certain degree by having a consistent pattern. And as we have this conversation, I've been in clinical practice

for over 20 years, right? And I've learned that very few things apply for every single person. And you have to take into account a person's lifestyle, their previous history, their job, what their family are doing, all these kinds of things. And so I have these recommendations, but I'm loosely attached to them because I realize that people have to be able to personalize them. You know, you've done a lot of science on this, right? Which is clearly in the times in which we live, a lot of people need that science to persuade them that this is something I should be doing. But if we just zoom out for a minute and look back at our evolutionary history as humans,

actually, it's hard to make the case that we would have been eating consistently over 13, 14, 15 hours in every 24 hours. We would have naturally had these long periods where we didn't eat in every 24 hours. So yes, there's science to support it, but there's also, if we look at our lives through an evolutionary lens, it kind of works as well, doesn't it? Yeah, it does. And in fact, our ancestors, hunter-gatherers or farmers, they didn't have access to plenty of food. And another thing was they didn't have access to processed food. So food was not ready for consumption any time of the day. So in the morning, people typically spend

time gathering food or preparing for cooking. And the first substantial meal was maybe around lunchtime. And then in the evening, after everybody came back home, that evening time was very important, and it's still important. And if we think about human history, what we do in the first six hours of the evening after we get home, that actually determines every aspect of our life. Because after we come home, our hunter gatherer, ancestors or farmers, they lighted a fire. And they cooked or grilled food

or whatever they had gathered, and then they shared that food. So there was social aspect of eating. And then that's the time when people feel liberated from their daily life. So you have come home, you are not working for a bus and that freedom time two to three hours after dinner is very important for a lot of people. And our ancestors hunter-gatherers, that's the time when life changed. So daytime people thought about how to work to bring food to the table.

And after dinner, they became more creative. That's when people started singing, dancing, talking about philosophy and science and politics. So that's the cradle of civilization is actually in that evening time. So we should not forget that. So we have to keep in mind that people have to come back and in their lifestyle, they have to socialize and do certain things. And that dinner time is very important. So going back to your question that people have to relate not only to science, but also to society and culture and how we have evolved on this planet, they can keep that in context

and maybe delay the breakfast in the morning because that's what our ancestors did. And that also aligns with our physiology because when people are in experiments, when people are isolated inside laboratory without any cue what time of the day or night it is, what we have found is our hunger, subjective hunger actually reaches its peak in the evening, not in the morning.

And that makes sense because a lot of people actually will say that they don't feel that hungry in the morning. But almost everybody would say that they have some hunger in late afternoon or evening. So we are programmed to be hungry towards the end of the day and that hunger, since it's universal, everybody feels that. That's also is a basis for

that socializing and consuming food in a gathering and then discussing something other than how to how to make money to bring food to the table how does this fit with there's quite a lot of research that i've read which is showing that if we consume the bulk of our calories in the first half of our day compared to the second half of the day, that can have powerful effects on our circadian clock, on weight, on sleep, on immune function, all kinds of things. There's obviously't there? Breakfast like a king, lunch like a prince, dinner like a pauper, which I think works really well for a lot of people, actually. But how does that fit in with what you've just said, which is that we are wired to maybe feel hungry later on in the day, maybe late afternoon or the evening, because on the

face of it, it might seem as though these things are quite opposing yeah so when i say that it's not that we are saying that people should just consume food in the evening okay they'll still it's true that in the first half of the day uh a blood sugar control is much better and um as, you might have seen that if you do an oral glucose tolerance test, which is looking at blood glucose X number of hours after a bowl of sugary drink, then the same person may look normal in the morning when the glucose tolerance test is done. But in the evening, that person's glucose will shoot up, or late night it will shoot up,

and you may diagnose that person as diabetic. So there is this aspect of how glucose regulation, particularly insulin-producing cells, have their own clock so that blood glucose level shoots up in the evening. So that brings up what we should eat at different time of the day. And the analogy that I gave, again,

another thing is our hunter-gatherers, when they were lighting up the fire, they're not lighting a fire to actually eat berries. They're lighting a fire to eat meat or complex carb that needed little bit of cooking so that that would become palatable they were not actually lighting fire to warm up their chips and ice cream to eat. Yeah that's a good point. So that means the biology and the social aspect still holds good that in the first half of the day they're more likely eating food that was easily palatable which already had a lot of

simple sugar or easily digestible food which typically raises our blood glucose so that our insulin producing cells can manage that whereas the late night or late evening whatever they were eating, they were mostly food that was rich in fat and maybe protein. And that would help them to go through the long period of fasting overnight. Yeah. That makes a lot of sense, actually. It also brings up this idea that when we're trying to compare modern humans with our evolutionary biology and hunter-gatherers, there's another big piece that we miss, which is many of us these days have broken metabolism.

If you look at the numbers in terms of how many people, yes, are type 2 diabetic, but also pre-diabetic, which means fundamentally we have issues already with our ability to maintain our blood sugar and our body's not functioning optimally. I can't remember what the stats are now, but I don't know. So in the US now, almost half of the adults are pre-diabetic or type 2 diabetic. Do you know what it is in the UK? I think it might be. It might be similar because it's, yeah. Very similar. So therefore, if we're trying to make a comparison, it's like, yeah, wait a minute though. Yeah maybe they were hungry early evening and maybe there was a big part of their culture

and community around that. But if you are someone who is already struggling with blood sugar, so you will not like those hunter-gatherers, then actually what you're saying from your research is that we're much more efficient at managing our blood sugar earlier on in the day than later on in the day. So this is where we have to be a bit cleverer with our recommendations. Do you know what I mean? Use history to help us, but not to completely kind of enslave us to saying this is what they did, so this is what we should do no actually yeah so we should we should break that comparison because you know our hunter-gatherer ancestors they lived to the life of say 35 or 40 years old because life expectancy was

less than 45 years although a lot of people will say that's because of high infant mortality. Yeah, so high infant mortality. But anyways, the point is, yes, in the first half of the day, our ability to handle glucose is much better. So that means for the first half, particularly you can plan your breakfast in a way that you can have your sweet treat or a little bit of complex carb and a balanced breakfast. Then as you move towards dinner, you can actually plan to have a little bit more protein and fat to help you go through the nightly fast and also to help you live with your own physiology that your insulin response is pretty bad.

Can you summarize? If most people, if anyone listening to this or watching this goes, okay, I'm going to now try and eat all of my foods that I'm going to consume, whatever diet that might be, within a 10-hour eating window. So first thing I want to clarify, well, within a 10-hour eating window, can you list what are some of the benefits they may get? Before we get back to this week's episode, I just wanted to let you know that I am doing my very first national UK theatre tour. I am planning a really special evening where I share how you can break free from the habits that are holding you back and make meaningful changes in your life that truly last.

It is called the Thrive Tour. Be the architect of your health and happiness. So many people tell me that health feels really complicated, but it really doesn't need to be. In my live event, I'm going to simplify health and together we're going to learn the skill of happiness, the secrets to optimal health, how to break free from the habits that are holding you back in your life, and I'm going to teach you how to make changes that actually last. Sound good? All you have to do is go to drchatterjee.com forward slash tour, and I can't wait to see you there. This episode is also brought to you by the Three Question Journal, the journal that I designed

and created in partnership with Intelligent Change. Now, journaling is something that I've been recommending to my patients for years. It can help improve sleep, lead to better decision making and reduce symptoms of anxiety and depression. It's also been shown to decrease emotional stress, make it easier to turn new behaviours into long-term habits and improve our relationships. There are of course many different ways to journal and as with most, it's important that you find the method that works best for you. One method that you may want to consider is the one that I outline in the three question journal. In it, you will find a really simple and structured way of answering the three most impactful questions I believe that we can all ask ourselves every morning and every

evening. Answering these questions will take you less than five minutes, but the practice of answering them regularly will be transformative. Since the journal was published in January, I have received hundreds of messages from people telling me how much it has helped them and how much more in control of their lives they now feel. Now, if you already have a journal or you don't actually want to buy a journal, that is completely fine.

I go through in detail all of the questions within the three-question journal completely free on episode 413 of this podcast. But if you are keen to check it out, all you have to do is go to drchatterjee.com forward slash journal or click on the link in your podcast app. Yeah, so once people eat within 10 hours eating window, what we find is within few days, that may be two to three weeks, they may find their sleep will improve. And this is something that we find in many of our patients

who self-report how is their sleep. It may not increase the number of hours they sleep, but it may just improve their sleep satisfaction. They might actually get into a better sleep, quality of sleep will improve. Then those who have acid reflux, I don't know the numbers in the UK, but in the US, there are 65 million prescriptions for acid reflux every year. And there is a lot of over-the-counter acid reflux medication. So that means almost more than half

of the adult population experiences some kind of acid reflux or stomach issues every week. So we also hear that people have much better gut health within two to four weeks, they will feel that. gut health within two to four weeks, they will feel that. So, sleeping better and then having better gut health will also improve the sense of energy in the morning and throughout the day. So these are the, we think that these three benefits

are the positive feedback loop that helps people to sustain with eight hours or 10 hours eating window. Then those who have preddiabetes or type two diabetes with minimal medication, for example, metformin, they may also find that blood sugar control will improve, particularly the nighttime or the time period in which they are fasting. At least in that period, 14 hours or 16 hours,

the blood sugar will remain much better under control. Then surprisingly, many studies, although we haven't connected how it works, we find that people with hypertension, they improve both their systolic blood pressure and diastolic blood pressure. And that can happen between six to eight weeks after trying this regimen. So the flip side is if people are already on hypertensive drugs, then after four to

six weeks, they should actually check their blood pressure to make sure that they should do some mid-dosis adjustment. I think we should pause there because I think this is an important point. There are all these incredible benefits on the other side of this. One of my cautions with patients, and again, I'd caution anyone listening or watching, if you have type 2 diabetes or if you are on any blood sugar lowering medication from your doctor, you might want to just have a chat first because your blood sugar starts to come down, you may not need that. What I've always done is I would stop something like Gliklazine, for example,

which can drop blood sugar. I would usually stop that when we're transitioning over and then revisit this in a few weeks to see, or a, or a few months, you know, what do we need now? Metformin usually is okay, I've found, but blood pressure medicines, you would agree with that, be cautious with those, talk to your doctor first. So if you have some health issues, there are benefits, right? But what about that person listening who goes, well, actually, you know, I feel, there are benefits, right? But what about that person listening who goes, well, actually, I kind of feel okay. I haven't got pre-diabetes. I haven't got much of a weight issue. What are the benefits for me, Dr. Panda, of eating all my food within a 10 hour eating window? I think everybody would agree that they need a little bit more energy.

Yeah. And they may not have other health issues, but almost many of us, we have a little joint problem, we feel a little pain. And overall, other things that we are finding biochemically and with all the gene expression analysis, what we're finding is the kidney function improves. Our muscle repair also improves. There are now new studies showing that circadian clock is involved in repairing tendons and ligaments. So injuries. Injuries, particularly recovery from injuries. And if we think about it, actually every day we injure some of our joints, ligaments, and muscles. We are on a continuous rejuvenation process. And that's why I say that just like our

brain, when it sleeps, it resets, rejuvenates, and repairs itself. Almost every tissue in our system repairs itself. And whether you're an athlete or elite athlete or just recreational athlete it also helps to repair or recover from injuries. What about athletic performance? Do we have anything on that? Yeah so athletic performance at least our mice are more athletic. So mice become more athletic? Yeah. When you restrict the mice's eating window, they become more athletic. Yeah. So in mice, it's very profound.

So 10 years ago, when we published this paper, one question was, well, since these mice are eating within 8 to 9 hours, are they actually, is their muscle weak so that they cannot perform well. So we had to put these mice on treadmill to measure how long they can be on treadmill before they become exhausted and cannot run anymore. So normal mouse in the treadmill condition, the inclination and resistance that we applied, normal mouse would run around 60 minutes

on treadmill and then if the mouse is eating on healthy diet, that would run around 45 minutes. And these mice that ate within eight hours, surprisingly they could stay on the treadmill for 120 minutes, so twice longer than regular mice that were eating normal healthy diet, but whenever they wanted. So that was really eye-opening for us to see their exercise performance improve that much. So coming back to humans, although elite athletes and people who are training pretty well,

they have already maximized, optimized their lifestyle. But what we find is even among them, they do see some improvement in their athletic performance, whether it's strength training or endurance training. And this is very important because if you're competitive, then a fraction of a second actually makes the difference. So this is something that if you combine your optimum nutrition, optimum sleep, with optimum nutrition timing, that can actually help. And for many bodybuilders, they're asked to eat in every two to three hours.

And I have heard that a lot of them actually put a certain alarm to wake up in the middle of the night and eat. And some of them, when they start doing this timeless today eating or intermittent fasting with optimum nutrition, first thing they report is the acid reflux. They thought that acid reflux is so common that it must be normal, but it's not. That acid reflux goes away and they actually feel more energetic because there are many bodybuilders who don't feel that full of energy throughout the day. Yeah, I mean, I find this whole area fascinating because I believe that live in harmony with your circadian biology as much as you can. And frankly, there's very few areas in your life that won't

improve as a consequence, whether we talk about health or beyond health. I really passionately have seen that with patients. I've experienced it myself. To the point where, you know, it's interesting. I rarely come to London anymore to do podcasts, right? But for whatever reason, I'm here this week and I've got, you know, a busy day. And I know I'm aiming to get a train home tonight from Euston Station at around 7pm, which kind of means I probably won't walk into my house till 9.30. Now, that means I've got two options. One option is I can wait till I get home and have a really nice kind of healthy meal that technically you would say is better for me. You know, I know the ingredients, I know what's in it.

Maybe it's something my wife cooked earlier for her and the kids that I can eat when I get it back. I've done that before, but I realised for me, either I skip dinner, but if I'm hungry, I'm better getting something as healthy as I can at Euston Station, eating it on the train and finishing eating by about 7, 7.15, something like that. And I found, for me, I can have a... And this really speaks to this idea you said before that you can make healthy foods junk by eating at the wrong times. I've realized, for me,

I'm better off getting something where I compromise on, let's say, nutrient quality a little bit and have it at 6.45, 7 p.m. rather than wait and have a better whole food meal later in the evening, which I think really speaks to the point that you're making. The other thing I wanted to comment on is my son's 11. And one thing me and him do most Saturday mornings, if not every Saturday mornings, go to the local park run which is a 5k run around the local park right which you know these apartments are transforming communities and people's people's lives in so many ways and what I'm trying to do with my kids is help them start to pay attention to what happens when they do certain things for

example oh I feel tired and sluggish I don't want want to go. Oh, now that we've gone, how do you feel now? Rather than, you know, daddy telling him, it's like, oh yeah, I've got more energy now. Even though I didn't want to come, I've got more energy. And I've also asked him, we used to say, just pay attention now to what time we eat the night before and how you're doing and how your time is on a Saturday morning. And I think he's already started to draw the comparison. And when we stick to the early meals on a Friday evening, my sleep's better and I'm running better on a Saturday compared to, do you know what I mean? So I'm, I'm taking your science and I'm trying to actually, instead of teach it to my son, I'm trying to just help him start to pay attention to, oh, do you know what I mean?

No, actually this is, you're doing the right thing because this is a time, particularly teenage time, that's when the kids, after they get into late middle school and high school, this is when all of our security and disruption happens. Right. Because that's when they get a lot of homework. They have to stay up late into the night. And when they stay up late into the night, they think, and often they're also told, that your brain cannot function unless you have a late-night snack. And they get used to that late-night snack and staying up late in the night.

And in the morning morning they are sleep deprived and they have to rush to the school and i don't know what is this school start time here but in the u.s for example most of the school start time used to be 7 30 in the morning before the pandemic started so um in collaboration with Horacio de Iglesias, who is a professor in Seattle, he did a very simple study. What he did was he was looking at sleep. And we know that many teenagers, starting from middle school to high school and college, they're sleep deprived.

And that's also the time when their circadian clock tells them to wake up a little later than adults and also toddlers. So the experiment was to delay the school start time by an hour and to track the students before and after the school start time was delayed. So we tracked nearly 200 students in two different schools, their sleep habit, their activity, and their academic performance. And when school start time was delayed by an hour,

these kids got 35 minutes more sleep, extra sleep. And when they got that 35 minutes extra sleep, then many parents would think that now kids are sleeping more, so they're not doing their homework. And that 35 minutes is coming from their homework time, so their grades might go down. But actually, what we found was their grades improved by 4%. And a 4% grade improvement can be pretty big for people who are struggling, or those who are getting B grade, they can go to A grade. So this is an example where small change,

starting from middle school or high school, can have a huge impact, not only on their health, but also on their academic performance. And if we go back to now, actually in the pandemic, quite a few things happened. One was the kids were, at least in the US, many kids were always on Zoom, and they lost track of that regularity in their life. They didn't have access to a lot of bright light. There was social isolation and

and they're also watching a lot of TV and eating late into the night. So now this has become and also since there was online education a lot the time at which people had to resubmit their homework also inadvertently now has become midnight. So in high school and colleges, at least in the US, the deadline for submitting your homework is midnight. So that means it's now institutionalized that students should stay awake until midnight to finish their homework and submit it. And this is... This is circadian chaos. This is circadian chaos, which is now institutionalized,

at least in the US, for all high school and colleges. So this is something that, I've got to be honest, I find incredibly frustrating, particularly with schools, but it applies to adults as well. Which is also what happened over the last two or three years is that schools that weren't really using technology that much with their kids, now everyone's on technology. And even though a lot of schools now, well in the UK are completely back to normal, the screens have stayed. So they're now in and they're not going back. And a lot of the homework that's now being given is on screens, whereas three years ago it wasn't been. And I don't think

a lot of schools realise the disruption. I speak in a lot of schools, I get asked to speak about stress and resilience and what people can do. Why are so many kids now depressed and anxious? And I'm thinking the problem is, well, A, there's too much pressure on kids at an early age. That's a slightly separate issue in my view. But the way they're being asked to work now is fundamentally going to mean that most of them are going to become sleep deprived. Yeah. Even if they're not sleep deprived technically in terms of the amount of hours, most of them will have been looking at screens probably in the last hour before bed. Yeah. So therefore, even if they are falling asleep,

they're not going to get the same depth and quality of sleep. Can you make me speak to that? Because a lot of adults are actually doing that as well. You know, 20, 30 years ago, you couldn't do that after dinner. Most of you couldn't really work. Now we can get back on the emails and keep going until late. Yeah. So we mentioned food.

We're mentioning light as big drivers of our body's circadian rhythm. You mentioned light in the morning, how important that is for your brain's clock. What's going on with light in the evening and what can we do to kind of mitigate that, both for children but also adults? Yes, light is extremely important when it comes to brain clock. And in the morning, you've got to resynchronize a brain clock to day-night cycle, and it reduces depression, brings alertness.

And for the last 200,000 years, humans never saw too much bright light after sunset. The light, the firelight or the candle light is very dim and it also doesn't have too much blue light. Yeah. So we are designed to see only dim light or orange color light in the evening. And even if you go back to the history of light in the UK in 1850, between 1850 and 1900, the cost for lighting of an average-sized UK home for two to three hours every evening was substantially high. It used to consume almost a week's worth of income. So people actually didn't, light was expensive.

of income. So people actually didn't... light was expensive. So only in the last several last 50 years or so the cost of lighting, I'm not talking about your entire gas bill and all this bills, just lighting is less than 1% and actually less than 0.5% of an average household's income. So we have plenty of light. And in fact, now we all want bright light. So light pollution in our house has become a big deal. Second is the screen time. We are essentially looking at rectangular pieces

of glowing objects until from the time we wake up until we go to fall asleep yeah and so what what a what a time to be alive hey of course there are many benefits i'm just you know having a joke yeah yeah and uh you know we are also talking now we are thinking about metaverse where the light will be actually attached to our head. Looking at rectangular pieces is not enough. We have to actually attach it. So this is kind of the silent epidemic that has begun.

And I think from circadian point of view, we are at the same point as what used to be the, what I call the late and the bestest moment. So this is a time when we realize when you're beginning to realize what is the widespread health impact or disruption of circadian rhythm disruption by having exposure to too much light ambient light and also and also screen time, and reducing sleep or reducing sleep quality and eating at the wrong time. All of these three are converging. But just like smoking suggestion or lead and asbestos took almost a generation to correct, I guess we are at the very beginning of that correction phase. And it will take us

almost a generation. But at least a few things that we can begin to implement in every family, and you are doing pretty good. Awesome setting an example for your kids is to come up with simple rules that two to three hours before bedtime, there should not be any bright light exposure so at home for example now is a good time to put almost all all your lights in dimmer so that you can dim the light not flip switch it on or off and then use indirect light so that means light that doesn't illuminate your face but actually the workspace um table lamps, for example, in the old days. So those kind of lights. And also for all of your devices,

make sure that all your devices are set to the minimum brightness. Because if that is your default setting, then during daytime, of course, most of the devices will crank up their brightness to compensate for the ambient light but at night time at least they will go back to the minimum brightness. So you mean that so go into your computer or your phone and change the setting so that it automatically starts low or are there settings you're talking about where it it changes according to the ambient light? Yeah so most of the devices now will change according to ambient light,

but they will always come back to, in the dark, they'll come back to your default setting. So make your default setting really low. And then almost all rectangular pieces of glowing objects also have night shift feature. And this is really gratifying for me personally, because 20 years ago, in 2002, December, actually we published this paper demonstrating that this blue light receptor called melanopsin is important for resetting our clock and also important for sleep regulation,

alertness and depression, all that stuff. And seeing that being translated to billions of devices is very gratifying. But so now you can go back to all your devices and set the night shift or night light, whatever feature it is. So that means it will actually change the color composition of your screen from white balance to a little bit orange in color. So even if you are working at night on your computer, your job requires you to, even if your kids have to do homework at that time,

their school requires them to, you're saying that by doing this, we can mitigate the effect that that's going to have on our sleep quality and our sort of circadian rhythm. Yeah. So at least, you know, just like for waking up, we have an alarm clock. For going to bed, these are the nudges

that will come in automatically, that our screen will become a little darker and change its color. So at least for me personally, I feel like, okay, so it's time to wind down and prepare for bed. And for kids. It must be really gratifying for you because I guess one of the reasons, I guess from having spoken to you before,

to become a scientist was to really help create change in the world. And how phenomenal that you've been involved with research 20 years ago with the discovery that you and other labs made about melanopsin. And now you're seeing this widespread adoption into devices. It must be incredible to see work in the lab now being translated to real life, which is incredible. I want to really acknowledge you for that because it's no small feat to be able to do that. That has a massive impact on people's lives. On that, you previously said,

I know there's science on this, that blind people, even though they're not, well, blind people can still detect when there is bright outside light. What's going on there? That was the mystery for a very long time, that the majority of blind people, they cannot read the newspaper, they cannot find their ways, but they can actually sense when they're next to a window or when they're outdoor or indoors, so they can sense that brightness of light. And even blind mice, mice that have genetic mutations that make them blind, they cannot navigate through a maze, but they could actually sense light. In the sense, if you change the light-dark cycle, then the circadian clock would track

the new light-dark cycle. And blind people also, when they travel, most of them can readjust to the new light-dark cycle. So how are they doing that? So that was the mystery and that's what we saw that there is this melanopsin. And the reason why it is called melanopsin is this is an opsin. These are light sensing proteins and typically called opsin. And this opsin was initially found in the melanosome or the pigment producing cells in the frog skin.

So this was discovered in 1998 or around that time. So this is a clear example that basic research into how a frog adapts its skin darkness in response to daylight or sunlight led to the discovery of this melanopsin present in frog. And then when the human genome was sequenced, then we also found the same gene to be present in humans. And subsequently, other groups, other scientists actually showed that this particular melanopsin gene is turned on in very few cells in the retina. And these cells actually survive the genetic blindness that affect a lot of blind people and blind mice.

So that set the stage for us. Science is always a communal activity, and it always builds on previous research. So I won't say that I take full credit for it, but the stage was set to ask this very simple question, is melanopsin present in very few cells in human retina or in mouse retina responsible for the light perception that was already documented for almost 75 years and that happens in blind people and blind mice so that's what we discovered in 2002 that yes, this melanopsin is the Light sensing protein that resets our clock and that's present in very few cells so for example in a human retina, we have 14 million rod and cone cells that give give us the

outside view, whereas melanopsin is present in maximum 5,000 cells. And another interesting fact is since 2002, people have been studying this melanopsin in mouse retina or rat retina. And based on that, we have devised all these night shift feature, brightness setting, all this stuff. But only two to three years ago, for the first time, we could actually measure what these melanopsin cells look like or how they sense light in human retina.

For the first time, only three years ago. So this is also another example how the honest taxpayers money that goes to research actually helps make discoveries in weird animals like frog skin or mouse in a laboratory and that can have a huge impact on how we live long before even way before when we

can do those experiments in human retina so melanopsin is just present in retinal cells so not on the skin no not in the skin so people who are blind yeah although they can't see you know that's a um i guess that's an oversimplification, but that they're basically still. Can sense light. Can sense the light and set their body's circadian rhythm. That's really powerful, isn't it? Yeah. It's really, really powerful. Yeah. Just to close off then the evenings, right, Because there's a really nice symmetry where you want at the start of the day, one hour without eating, get some light, get some movement if you can. Those things are great. At the end of the day, you're saying two to three hours before bed,

not to eat. So you almost kind of start and the end are quite similar in some ways, but very different in other ways in terms of, instead of bright lights in the morning, you now want dim lights in the evening, candlelight, firelight. If you are on your screens, change that. One thing we've also done at home, which has made a massive difference, I have these low blue light bulbs now in all the bedside lamps. You can feel it. Actually, once we ran out recently and we changed it to a normal low wattage bulb, I couldn't believe how bright it was. I thought, wow, for years, this was what it was. It makes such a difference. You feel more relaxed. I think, again, that's a very simple thing that people can do that will make a difference. Go out to eating windows.

Okay, so we've said 10 hours appears to be a pretty good universal recommendation that most people tend to find works around social life, work life, and what they're able to do. Now, there's a huge trend these days in the low-carb keto community to skip breakfast and maybe go even more aggressive, like eight hours. Maybe first meal at 12, finish eating by 8 p.m. Or I know some people go even later. They use coffee to get them through in the morning. And they don't feel hungry at all.

So often it'll be 2 or 3 p.m. they start, but they'll eat quite late, or let's say 10 p.m. So they've actually got a compressed eating window, but it's towards the end of the day. So I just want to get into some of the subtleties here. Compared to what most people are doing, which is eating across 15 hours, we want to reduce that. Great. Let's say 12-hour minimum. You're showing a lot of benefits if people can get to 10 hours. Okay, fantastic. Are there increased benefits for some people when they go even lower to, let's say, an eight-hour eating window or a six-hour eating window? I guess that's the first part of the question.

And the second part of the question is, what do you think about, yes, we have to personalize it to our life, but if we have an eating window that's... My understanding of the science is that eating windows that tend to be earlier in the day tend to be more in harmony with our circadian biology. But I have also seen people get benefits even though they're doing it late into the evening so can you maybe put some of that together for us yeah so compressing eating window to a narrow interval is almost like exercise any exercise at any time of the day is always better than no exercise so similarly compressing eating window to eight hours if you can do or six hours and eating healthy nutrition within that eating window is also pretty very important and we have to stick to that because sometimes what we have seen through our public facing app my circadian clock or the research is some people tend to

compress that eating window too short, maybe four hours or six hours. At the same time, they try to improve their nutrition quality, so they're eating only salad or they reduce their calories. And they may be eating less protein or less fat. And particularly for women, that can—and they're also more active. So that can trigger something, what we call relative energy deficit in sports. So many athletes, particularly women athletes, they report this, that most athletes who do

triathlon or marathon runners, women, they become amenorrheic. They don't cycle anymore. And they feel that it's so widespread that it's normal, which is not true. So that shows that by reducing calorie or eating within a very short time, and at the same time not paying attention to nutrition quality can put you into this state where your neuroendocrine system can malfunction. But if you're doing well with nutrition quality then we haven't seen any study and that compared this very short eating window with longer eating window. So what we have seen is for people who are obese, diabetic or

pre-diabetic, overweight, if you put them on six hours or four hours eating window then they have a lot of adverse event so for example they can feel dizzy they can feel extremely low energy and sometimes even nausea those kind of stuff can happen but those who are adapting to it they have to pay attention to nutrition quality we cannot look at longevity or overall health comprehensively in humans. But there was a study that just got published a couple of weeks ago in Science magazine. It's not even in full print. It's only online.

And I think that relates to this question. So this is a very simple calorie restriction study in mice. We know that when you reduce calorie in mice by 20 to 40 percent then these mice typically live longer than those who eat normal food and within reasonable nutrition quality. But the question was so but there was a caveat to all the calorie restriction studies done in mice. That is not clearly mentioned in many of the studies. That is, in calorie restriction studies, usually the mice that are put on calorie restriction,

they're given 20 to 40% less calorie, but only one meal. And mice usually finish that meal within three to four hours. And in many cases they can finish it within two hours. So that means they're eating within two hours to two to four hours and fasting for 20 to 22 hours every single day. Whereas the ad libitum, the control group, has access to healthy nutrition throughout 24 hours. So now the question was whether the life extension effect of calorie restriction is due to calorie restriction or due to long fasting.

Or how do we disentangle these two? So this is a study that's very well thought out and well planned. It also needed some technological advances where food can be delivered to mice at any specific time and in specific quantities. So they had the control group that had access to food anytime, and then the calorie restriction group was divided into multiple groups. One group got only calorie restriction and no fasting. So that means the reduced calorie food

was even split into very tiny pellets and these mice got those tiny pellets in every two hours. So in a long eating window. So yeah, so in every two hours they're eating something, they're not actually fasting much. Yeah. They're just reducing calorie, but no fasting. So compared to the control,

this group increased their lifespan by 10%, which is pretty good. I mean, 10% lifespan extension in mice is very good. So now the same calorie restricted diet was given within 12 hours. And when it was given within 12 hours, so that means same number of meals, but compressed into 12 hours,

so in every 60 minutes or so, these mice were getting a little bit of food, but they were going through 12 hours of fasting. And all these mice that ate within 12 hours, they got another 10% lifespan extension. On top of the other 10%. On the top of 10%. So now they're living 20% longer

by combining caloric restriction and some time restriction. So now, even they went one step further. They made that 12 hours fasting during daytime when mice are supposed to fast because mice are nocturnal, or nighttime. So that means these mice were eating during daytime when they're not supposed to eat and they're fasting during night. So the mice that fasted during nighttime so that is eating at the wrong time can be a restriction. So those are the ones that extended lifespan by 20% but the mice that ate at nighttime and fasted during the daytime, they actually lived 35% longer.

Wow. Okay, so now they went one step further. They said, okay, so what if we give all the food within two hours versus 12 hours? And the increase in lifespan was negligible. It was less than 1%. So whether it was 35% versus 36% or 25% versus 26%. So the bottom line is at least in mice reducing the eating interval to two hours or three hours did not give too much benefit in terms of lifespan and they went to see the cause of death because at the end anyways the mice were dying the cause of death was not different among any of these groups

they all died of the same causes which was mostly different types of cancer in this particular set of mice. So at least the mouse experiment has given us one answer, that whether we are reducing calorie or eating whatever you're eating, any duration of fasting is better than no fasting. But if you want to optimize, there is better to eat within your active period.

For humans, it will be finishing your dinner by six or seven p.m. And that will give you the best benefit. But at the same time, we have to keep in mind that in the pursuit of perfection, we should not forget what is practical and what suits your life. You should try to do that.

Yeah, I mean, thank you. That is so beautifully explained because there's a real practicality there. You know, there's optimum. You know, for the biohackers who want to optimise everything, great, it's good to know that. But for a lot of people who just want to lose a bit of weight, more energy, better gut function,

yeah, live longer, sure, whatever. It's like, well, look, increasing the amount of time where your body is not consuming foods, for most of us, is probably going to be a good thing and have multiple benefits. Because the truth is, you know, some people will say they've gone to one meal a day and they're thriving. And I don't think you would say to them, don't do that, or would you? My only advice would be, make sure that you have a balanced diet. Yeah. Because if you're eating only that one meal

and you're not mixing the right proportion of micronutrients and micronutrients then. Yeah. And again, it depends what your starting point is. Are you someone who's carrying a lot of excess weight, has got a lot of problems, and then maybe you're thriving on this? Yeah.

And I think there is a nuance there that we have to figure out. And one of the criticisms, I think, that would be leveled at this entire movement is that, well, a lot of the studies, and I guess this was more relevant a few years ago, a lot of the studies are done in mice. What's the relevance to humans? As someone who's literally at the forefront of this research, what do you say to those people?

I guess even in the beginning, when I used to give scientific talks, people used to tell me the same thing. Maybe it relates to mice. And in fact, for the first few years, I was never funded. I didn't get any federal funding because the reviewers of my grant made that comment that, you know, this may relate to mice. And we know that humans don't eat like mice, so it may not have any significance. So that actually forced me to go back and ask when people eat. And this was a very simple question that had never been asked objectively. So we made this app MyCecadianClock and where people had to just take pictures of their food, didn't have to enter what they ate, didn't have to type in anything, and the first

generation of that app and that's when we figured out we found that nearly 50% of adults in the US were not even shift workers. They were eating for 14 hours, 45 minutes, we rounded up to 15 hours and say that 50% of adults eat for 15 hours or longer. That's when many human studies started and the question was can people who are already eating at 15 or 16 hours change their behavior and try to eat within 10 hours because i can come up with a discovery that eating xyz for example maybe avocado with tomato every single day is good for everybody, but people

may not change their behavior. So that was a big question. Can people change behavior? And what we found was, yes, it was possible. People could change behavior and there are some positive feedback loops. So for example, the gut health, the sense of energy and sleep, we think those three actually drive people to sustain this behavior. And then there are a lot of small studies and these are, this is the way translation works. You go from mice and then you do a small feasibility study to see whether it's feasible. In humans.

In humans. And these are typically small because you don't want to put too many people at risk by doing something that can even cause harm. So that first phase went through the different types of studies and also it was gratifying to see studies were done in US, Europe, Asia, Australia, in all these continents, small group, male and female, younger and older, people with obesity or diabetes or metabolic syndrome. And universally, in most of the studies, we saw benefit. And these studies are also important because they define what benefit we are going to see

and what is the magnitude so that when you design large randomized control study then you can power them appropriately. So now we are going through that phase where the large randomized control studies are being done and also results are coming out. But there is one thing that we have to keep in mind that in any nutrition intervention study if you're going to change something then you should be able to monitor whether people are making that change and when you're doing small studies it's easier because you have handful of people maybe 20 or 30 people and you can monitor when they're eating and you can also teach them how to comply

with the intervention. But when you go to large study, that's the challenge. Can you actually monitor when people are eating? And if you cannot monitor, then it becomes very difficult to interpret the results. The second thing is we know that people with obesity, diabetes, and all this metabolic disease, they have adopted a lifestyle or habit

That suits them and they're used to eating over a long period of time So they need extra support. They're not the they're not the Bleeding as biohackers who are ready to do anything and can take little bit of discomfort and pain so you need some support, education, and you have to do that in the last trial. And that can become difficult. So that's why we have to keep those in mind now. Those eating patterns monitored objectively and whether they were given the right type of support to adapt to this

time-restricted eating or intermittent fasting. Well, one of the things I love in your latest book, The Circadian Diabetes Code, is there's a step-by-step plan and you go through common problems people have, whether it's headaches or compliance or energy and how they can deal with that, which I think is really, really helpful. And, you know, although the title of the book is The Circadian Diabetes Code, as I read it, it's like, well, this book will help you whether you have diabetes or not. It's a good recipe for how to live your life. Yeah. And something I'm passionate about as a medical doctor, and I wonder about your view on this, given that you're a scientist. Science has always interested me, but I've never felt enslaved by the science.

Science, I've always used as a way of guiding me, rather than telling me exactly what I should do with my patients. So my real life experience of time-restricted eating, probably since 2015, 2014 is probably the sort of time when I started to implement it based on your really... Mouthful. Mouthful, yeah. But as a doctor, it's like, okay, well, let's be intelligent about this. What is the likelihood of harm here by asking one of my patients to only eat within 12 hours or 11 hours or 10 hours? It doesn't appear to be like much risk of harm here, particularly if they're not on any medications or anything, right? So I think, okay, very, very low risk of harm,

high potential for huge benefits. Okay, I'm okay with that sort of risk-benefit ratio. potential for huge benefits. Okay, I'm okay with that sort of risk-benefit ratio. And I would, you know, counsel people. And I saw, like your researchers now show, like the human studies are starting to show, but I have seen with hundreds, maybe thousands of patients, that when people compress their eating windows, and I agree, 10 hours, I think, is a very sustainable and achievable window for most people. You see benefits across the board. Weight loss, blood sugar, energy, sleep quality. IBS, irritable bowel syndrome, oh man, this is a big one for me. The gut function just starts to normalize. All the IBS stuff out there tends to be about, oh, this diet or avoid these foods or these foods. I get it. But for me, the two big things in IBS that out there tends to be about, oh, this diet or avoid these foods or these foods.

I get it. But for me, the two big things in IBS that I deal with before anything else are stress and eating windows. Because I find if you go for those upstream levers, there are lots of downstream benefits. So I'm a passionate advocate of your work, and I've been using it with real-life people, including in my BBC One show in 2015. I used time-restricted eating with a family. Huge benefits. They all did it together as well, which was really lovely. So I just wanted to share that because I know sometimes people go mice, be human.

I think the human studies are coming, but that's my real life experience. Yeah. I guess going back to your comment about diabetes score, the reason why I wrote about diabetes is almost everybody knows someone, either a close friend or a family relative, or even within the same family, or maybe the same person who may be pre-diabetic or has type 2 diabetes. It's true. And we don't take it seriously because it's not like a heart attack or heart failure or another stuff. But we know that diabetes is the entryway

to heart disease. Living with diabetes is almost like living with having experienced at least one heart attack. Yeah. So that's why, and also now the stats is nearly half of the adults in the US are either pre-diabetic or type 2 diabetic. And just like you said, we have barriers to good lifestyle.

And one of the barriers can be being around with family members who want to have late night dinner or eating anytime. So that's why the book is actually for everybody because if you don't have diabetes, at least you are caring for somebody who has diabetes. And then the best gift that you can do right now is to help that other person to live a healthy lifestyle by paying attention to circadian rhythm, eating, compressing a window, paying attention to sleep, and then a little bit of attention to exercise and light. Yeah. And just to clarify, when we say diabetes, of course, we're talking about type 2 diabetes as opposed to type 1. Just to finish off, Sachin, there's three areas I wonder if we could just briefly touch on, shift work, naps, and jet lag. One of the things that struck

me yesterday when I text you, and I know you've only within the last couple of days landed from America, which of course is, you're on the West Coast, so there's an eight hour time difference between what your body clock is used to and what we're on in the UK. Of course, we've been trying to juggle the time of this conversation, right? I remember texting you yesterday saying, are you sure 8am is not too early for you? Because I'm aware that that's like midnight for your body clock. Won't you be jet lagged? And you said something like, no, I'm not suffering from jet lag. I was like, okay, that's interesting because I'm someone who has very much struggled. So why are you not suffering from jet lag? And in your view, what are the key things that we can do to reduce the likelihood that we're going to be floored by it?

that we can do to reduce the likelihood that we're going to be floored by it? Yes, a jet lag is when your brain clock is still thinking you're in the old time zone and your body clock is also thinking in a different time zone. So essentially your clocks are desynchronized from whatever time zone you are in. And as we have learned that light resets our brain clock and food resets the rest of the body clock, then we can use that to reset ourselves to the new time zone. So that means when I travel US to Europe, most of the flights leave US in the evening or late afternoon and reach Europe in the morning so that means that should be the usual fasting time for everybody so no food in flight so you don't eat on the flights yeah no food in flight and if it is short flight like this was a short flight for me because it was maximum eight hours flying so that means even I had to finish my dinner or last meal before even

boarding the plane. And then in-flight, you should not get too much light exposure. So that means the only thing that you should be doing in-flight is trying to sleep. So I not only try to sleep, I actually carry an eye mask or sleeping mask so that really cut out all the light exposure. So no watching television and not even very little or minimal reading, only books or something with light falling on the book and trying to sleep. And then after I reached here again, the flight reaches at 6.45 or seven in the morning. By the time you check into the hotel, it's 8.30 or nine. So your breakfast is around 10 o'clock in the morning.

So I already had a long fasting followed by this very nice big breakfast that reset up my body clock. So food can do that. It can help literally reset your body clock and so food can do that it can just it can help literally reset your body clock body clock and then of course i had a long drive from the airport to the hotel and as i said even if you're just looking outside it was a it was a rainy day in london but still that much light is enough to keep me awake and reset. So basically you're paying attention to light and food to help you when you come this way

and I guess when you go back from the UK to the US the flight will probably be in the daytime the morning or lunchtime from here. I've done that many times in the past, not for the last two or three years having said that. But it's almost the opposite. Well, would you eat on the plane this time when you go back? Yeah, so this time I'll eat my meal in plane. But then when I land, since I'm landing in the evening, I actually don't need that evening meal. So I can go to the next morning and that will give me that long fast followed by the breakfast next morning. Well, whatever you're doing is working because two days into your trip, having no jet lag and doing an early conversation with me where you're sounding completely on your game, I think just speaks to the power of what you're doing. That's jet lag. Can we just briefly,

because we said at the start, there's but the reality is many people they go yeah that sounds great but I'm a shift worker or I have to work late into the evening are there any tips I can use and I know in your books you've written about many tips for shift workers which is super helpful can you just give us a sort of brief overview on the sorts of things that shift workers can do to help them yeah so, shift work comes in many different flavors, different types of shift, and then how they change the shift. We have specifically worked on one type of shift work, that's 24-hour shifts that firefighters do in the US.

I don't know about 24-hour shift in UK. And in our study, which hopefully will come out this year, what we found is firefighters who do 24 hour shift, they could adapt to 10 hours time-restricted eating. And we asked them to self-select that 10 hours. And what we found is most of the firefighters, they selected a daytime time-restricted eating window that ended somewhere between 7 and 9 pm so they could all eat during daytime this is when they're off for 24 hours 24 hours but they still had enough energy to go through the overnight calls and this was risky for the fire department and also for us because we thought, well, if they cannot do their job, this is a civic duty, this is a civic safety.

It's not only for their own safety. They cannot respond to a fire. If they cannot respond to an accident, then that's actually too much risk for us. And we're pleasantly surprised that they could actually do that. And during that time, we also found out that they felt that by not eating during their shift, they felt more light and full of energy when they responded to the call. And when they came back from the call, they could actually go back to sleep much quicker. And on their off days, they could maintain that sleep and they could get the recovery sleep much better. So that was surprising. So now going back to other shifts,

12-hour shifts or eight-hour shifts, of course this is challenging because if they're changing their shift too frequently then it will become a challenge. But we have also seen other shift workers where this shift changes once every two months or three months. And typically what they do is they try to align their eating with their shift so that when they're not on the shift walk, they can have enough sleep and fasting combined so that they can benefit. So if you're, let's say you're a nurse or a doctor on a night shift and you're doing, let's say, an 8 p 8 p.m till 8 a.m or something like that you might try and encourage them to eat during that time window even though it's the night

yeah so there is a caveat when they're doing this 12 hours shift at night and doctors and nurses they usually have i don't know in the uk in the US, nurses typically have four days a week. They don't actually work all seven days, four or five. They get their hours in in a particular, yeah. Because they're doing 12 hours, four days, they're getting 48 hours almost. So in those cases, this is again what I call anecdata because we haven't done clinical trials, but what we have seen is what nurses can adapt to what they can do is they try to have an eating window that starts from say noon or

two o'clock and then goes till 10 o'clock at night um so in that way they can maintain that same eating window on their own days and off days yeah i get it so that's really yeah it's really clever isn't it so you're not switching too much yeah so they keep that same eating window and it's again personal so they can find their own sweet spot but the same time when they come off the shift in the morning if they're driving then they still need that black coffee or black tea to make sure that they are safe, they're driving safe. And it can interfere with their sleep, so that's something that they have to work on to see whether they can just have a warm decaffeinated tea or something just to get them home.

Or if they're taking public transport, actually the good thing in the UK is people can take public transport that don't need to be caffeinatedinated and they can get home and get that restorative sleep. Yeah, that's super helpful. Just finally then, naps. In looking at circadian biology and how important a robust circadian biology is for everything we've spoken about, weights, types of diabetes, inflammation, but also mood, depression, these sort of things. Absolutely really important to have a good circadian rhythm.

In your view, can naps help us if we need them? Yeah, actually, if we go back to the history of humans on this planet, we are not fully diurnal. What we call, we are crepuscular.

So that means we are more active in the morning and evening, and we're designed to take a nap after lunch, so early afternoon, right afternoon. So that's when, if you think about it, although we have access to now air conditioning and cooling, but our ancestors didn't have that access. So it used to be very hard to go outside, outdoor. And for most of the human history, only in the last 35,000 years,

humans moved away from the equator to go north or south. But equator, that area used to be pretty hard. So we are designed to take the nap, early afternoon nap. So it's already imprinted in our genome to take a nap. For me, I'm a fan of naps. I appreciate, for many of our jobs, we're unable to, but certainly at weekends, man, I love a nap. I'll get up early, but I also like

an early afternoon post-lunch nap. I guess culturally, I grew up with seeing my dad doing it. When we'd go to India every other summer, I'd see my family take naps after lunch. or when we'd go to India every other summer, I'd see my family take naps after lunch. So I kind of, it's ingrained in me. And if it's early enough, and I've been recommending naps. I know there's a lot of controversy around naps.

I personally find that as long as the nap isn't taken too late, where it can impact the evening, I think that can be incredibly helpful. And there's a ton of science now on what it does for concentration, learning creativity yeah those kind of things so you're you're pro naps basically yeah i mean we're designed for naps yeah and of course you said we should not take it too late uh like yeah no napping after say 3 p.m or 4 p.m um sachin i've i've just so enjoyed chatting with you. You know, you're involved with science and

you have been for many years now that is changing the fabric of how many people live their lives. You know, yes, I've also preferred the term time-restricted eating, but it is commonly adopted as intermittent fasting, right? Because I've always found intermittent fasting confusing as a term. I thought, what does it mean? Whereas time-restricted eating for me made, it was very clear. It's like, you know, you restrict your eating window. You eat within this period of time. But the truth is you and now many other scientists also, of course, are helping, but you and your lab has been really a big player in putting this on the map a way of living and eating that many people around the world are trying i want to acknowledge you for that thank you i always find you very humble with your research and says what you've done

um but but i think it is really really impactful and you know i could sit here for another two hours and chat to you about so many other things. But, you know, we've got to call it a close at some point. The books are brilliant. I think the books could help a load of people. This podcast is called Feel Better, Live More. When we feel better in ourselves, we get more out of life. Just at the end here now,

for people who feel inspired by what you said, they think, yeah, you know what? I think I want to give this a try. Do you have any final kind of top tips to share with people, to leave them with, so they can take your work and use it to improve the quality of their lives? Yeah, so there are six tips.

Okay, love it. Okay, so number one, go to bed at consistent time and try to be in bed for eight hours so that you can get seven hours of sleep. And then number two, in the morning, wait for at least an hour after waking up because that's the changing of the guards. The night hormones are going down, the day hormones are coming up, and your body is not ready to digest and assimilate nutrient.

The number three is to have again consistent time for breakfast and then eat for the next eight, nine, 10 or maximum 12 hours, not beyond that. Then number four is try to be outdoor for at least 30 minutes under daylight, even if it's a cloudy day, because light synchronizes our brain clock. It's an antidepressant, reduces sleepiness, improve our executive function. Any time of the day or specifically the morning? If you can do in the morning, that's better. If you can do any other time of the day,

then that's also good. Okay. So then number five is exercise. Physical activity, if you're compressed for time, then afternoon physical activity is much better than any other time of the day because that's when your muscles are ready, your flexibility is better,

and so your risk for injury is low and afternoon exercise is much better in reducing blood glucose than morning exercise of same time and duration. And then number six is two to three hours before bedtime. It's again changing of the guards. The day hormones are going down and the night hormones are coming up. So for two to three hours before bedtime, no food and no bright light. So those are the six.

Super simple. You've explained all the science. It's just been wonderful chatting to you. Thank you so much. And maybe in a few years again, we can revisit this to see where we're up to date with the research. Thank you so much. And maybe in a few years again, we can revisit this to see where we're up to date with the research. Thank you so much. Thank you, Rangan. Have a perfect circadian day. I will do. Really hope you enjoyed that conversation. As always, do have a think about one thing that you can take away and start applying into your own life. Now, before you go, just want to let you know about Friday Five. It's my free weekly email containing five simple ideas to improve your health and happiness. I share exclusive insights in this email that I do not share anywhere else, including health advice, interesting articles or videos that I've

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