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Time Restricted Eating & Circadian Rhythms: Sleep, Metabolism, and Longevity with Dr. Satchin Panda

• Dr. Supatra Tovar • Season 1 • Episode 114

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Time restricted eating and circadian health are transforming how we understand weight, energy, and longevity. In this second half of the interview, Dr. Supatra Tovar and Dr. Panda dive into the science of meal timing—showing how aligning your eating window with your body’s natural rhythms can prevent disease, improve metabolism, and restore hormonal balance without calorie counting or extreme diets.

✨ What You’ll Learn in This Episode:

  • The difference between time restricted eating and calorie restriction
  • Groundbreaking research showing identical calories have different effects depending on timing
  • Why eating within 8–10 hours protects against obesity, diabetes, and metabolic disease
  • How meal timing influences hunger signals, taste preferences, and satiety hormones
  • Why breakfast and lunch should be larger meals, with lighter dinners for better sleep
  • The risks of extreme fasting (like OMAD) and how diet culture distorts circadian science
  • Practical strategies to align your daily eating, sleep, and light exposure for long-term health

 Timestamps

00:00 – Welcome back & introduction to Part Two
 01:00 – What time restricted eating really means
 03:00 – Groundbreaking mouse studies on fasting windows
 07:00 – Why “small snacks” can disrupt fasting benefits
 10:00 – How fasting resets taste buds and reduces cravings
 12:00 – The best time of day for larger meals
 16:00 – Why we eat more at night—and how to reset hunger patterns
 20:00 – Diet culture vs. true circadian science
 23:00 – Health risks of over-restricting food and over-exercising
 25:00 – Hunger as a healthy signal, not the enemy
 28:00 – How fasting supports ketones, liver health, and immunity
 30:00 – Why extreme calorie restriction backfires
 33:00 – How circadian rhythms restore satiety hormones naturally
 35:00 – Final takeaways and closing thoughts

 Continue Your Journey

Thank you for joining us on this journey to wellness. Remember, the insights and advice shared on the ANEW Body Insight Podcast are for educational and informational purposes only and do not constitute medical advice. Always consult with a healthcare professional before making any changes to your health routine. To learn more about the podcast and stay updated on new episodes, visit ANEW Body Insight Podcast at anew-insight.com. To watch this episode on YouTube, visit @my.anew.insight. Follow us on social media at @my.anew.insight on Facebook, Instagram, TikTok, and Threads for more updates and insights. Thank you for tuning in! Stay connected with us for more empowering stories and expert guidance. Until next time, stay well and keep evolving with ANEW Body Insight!

satchin_2_07-30-2025_114442:

Yeah, so that's a mouthful of, uh, term time restricted eating. But in popular media, this is also one for most popular form of intermittent fasting. There 13 years ago when we first published this result from this research, uh, we called it time restricted eating because we are not calorie restricting. There is no reduction in calorie. Um, there is no. There originally, there was no counting up calories, and the idea is instead of counting calories, if you just look at the count, the number of hours or number of minutes you are eating, there is, there will be few benefits. One is if that eating window is consistent, then that will sustain your circadian rhythm in physiology, hormones, metabolism. that means your body can metabolize or absorb nutrient much better, and also process the nutrient, use them properly, and during the fasting or overnight fasting period, uh, it'll also, the metabolism actually changes from building stuff to cleaning out or removing the toxins so your body has enough time remove these toxins that your body doesn't need and repair itself. So that was the whole idea. And then the idea came from, again, very foundational research in mice. And again, we are going back to this basic research because these are some of the questions that we cannot ask in humans. So the original experiment was very simple. We took, uh, mice that are young, they're born to the same parents in the same room. I think same gut microbiome, same genes. They add the same diet. Uh, we actually gave them a little bit unhealthy diet and they add the same number of calories. The only difference was one group was allowed to eat whenever they wanted, and the second group was allowed to eat the same number of calories from the same food within an eight hour window. So that means mice are nocturnal. So they're night active, they eat at nighttime unlike humans. So in the evening we would give them food, access to food. They would eat for eight hours. They catch up with what the, uh, other group was eating. And we did this for 18 weeks, which is I equivalent to feeding a human for 10 years or so roughly. And then after 18 weeks, uh, what we, surprisingly, what we found was the first group that ate whenever they wanted, they were obese, diabetic, they had high cholesterol. Uh, all the telltale signup, metabolic dysfunction, or they had metabolic disease. later on we also figured out that they were also more prone to cancer. But the second group that ate the same number of calories from the same unhealthy diet within eight hours were completely protected from all of these bad things, bad metabolic disorders. So that was the first experiment. And then in the second experiment, we took the fat mice. Those already had the disease. And we put them back into eight, nine or 10 hours of eating, even 12 hours of eating. What we found was when in case of mice between eight and 10 hours, they, if they eat within eight to 10 hours, even for five days out of seven days, even though the mice were allowed to cheat on weekend, they could still maintain their healthy body weight. I think same gut microbiome, same genes. They add the same diet. Uh, we actually gave them a little bit unhealthy diet and they add the same number of calories. The only difference was one group was allowed to eat whenever they wanted, and the second group was allowed to eat the same number of calories from the same food within an eight hour window. So that means mice are nocturnal. So they're night active, they eat at nighttime unlike humans. So in the evening we would give them food, access to food. They would eat for eight hours. They catch up with what the, uh, other group was eating. And we did this for 18 weeks, which is I equivalent to feeding a human for 10 years or so roughly. And then after 18 weeks, uh, what we, surprisingly, what we found was the first group that ate whenever they wanted, they were obese, diabetic, they had high cholesterol. Uh, all the telltale signup, metabolic dysfunction, or they had metabolic disease. later on we also figured out that they were also more prone to cancer. But the second group that ate the same number of calories from the same unhealthy diet within eight hours were completely protected from all of these bad things, bad metabolic disorders. So that was the first experiment. And then in the second experiment, we took the fat mice. Those already had the disease. And we put them back into eight, nine or 10 hours of eating, even 12 hours of eating. What we found was when in case of mice between eight and 10 hours, they, if they eat within eight to 10 hours, even for five days out of seven days, even though the mice were allowed to cheat on weekend, they could still maintain their healthy body weight. They could still get almost 80 to 90% of benefit of. Doing the eight hours every single day for seven days. And they also improve their muscle performance and sometimes the, at least the male mice could put on some extra muscle. So that was really surprising. We published those. And then in the intervening 15, 13 years or so, there are at least a thousand different research papers repeating the study in different conditions in different countries even. In different strains of mice, uh, rats now even in fruit flies and also in humans, the conclusion is very similar, that if mice, humans, or any animal can eat within eight to 10 hours consistently, at least for five to six days in a week, seven days is much better. Then they can. Prevent disease from happening. So at least those, um, maybe again, is a big con, big qualifier. Maybe because, you know, people are different. Some people might have different stages of cancer, different stages of, um, different types of, uh, drug. So, um, I was surprised the profound effect of this time restricted eating or time restricted feeding, in popular media, intermittent fasting on not only our metabolism, but also for some hormonal, uh, disorders for cancer, for even now for dementia and some of the psychiatric conditions. So this is also something interesting that although we might say, well, you can eat anything. But what we're finding is after maybe the first week is difficult. People typically eat over 12, 13 hours. Um, most people will say, uh, I eat within 10 hours because I have my breakfast at eight and then I finish eating, but my dinner at six.

dr--supatra-tovar_4_07-30-2025_114442:

is waking up the villains. Similarly,

satchin_2_07-30-2025_114442:

So they cannot, like I personally, even I, I could finish a donut several years ago, but not anymore. to trigger your brain to feel happy. So you can be happier even with the, with, uh, less food or less, um, sugar, salt, and fat. That is a, that's kind of a side effect that we see. There is a nice paper that, uh, came out from Geneva, one of my collaborators, and he did a study on time restricted eating in Lucerne and Geneva. The nice thing, the reason why it was interesting was, uh, those who are familiar with that part of the part of Europe, there are German speakers, English speakers, and French speakers.

dr--supatra-tovar_4_07-30-2025_114442:

just because you're giving your body the chance to remove toxins. And you know, if you're eating a lot of highly ultra processed foods, you're getting a lot of, uh, additives and preservatives and strange chemical concoctions. And if you give yourself enough time to, uh, release those from their body, uh, they may not hold such an addictive quality anymore, which I think is really.

satchin_2_07-30-2025_114442:

Yeah, so as, uh, we have circadian cloud that does different things at different time of the day. Um, there are a few things that you touched off on. One is what happens in the morning. So, for example, in the morning, as you can imagine, your body has rested for 12 plus hours. So that means your digestive juice are primed your stomach can digest a good chunk of food. And your insulin response is also much better. This because the better cells that produce insulin, they're also primed, they also have a circadian clock. Um, they respond to food much better. So as a result in the first half of the day, it's not only like right after waking up in the first half of the day, um, say six to eight hours after wake up, up to that time, your body is much better in digesting processing food and controlling blood glucose. Uh, so that's why having a bigger meal in the fast half of the day, uh, is better for your body. the day progresses, your insulin response goes down slightly so that you can even do the experiment yourself. Uh, yes, it may be better to have bigger meal towards the fast half of the day, but then there is another caveat. Our body kind of plays, tricks with us. One is, you know. If we dial back more than 200 years ago, we didn't have food available to us 24 7. Even fire was not 24 7 keeping fire going in the house was very expensive because you had to bond coal or food through 24 7. So that's why. In the ancestral population, what was happening was people would come back from hunting or agriculture and there was no refrigerator. So even if you hunted and you got a rabbit or um, or some meat, you cannot store it overnight. You have to cook it. So that means in the evening, the community or the family would light up a fire and then cook, grill, whatever it is, and then would share the meal. So as a result, what has happened is we humans also have another interesting phenomena that is we are more likely to feel hungry in the evening. And so that means we are feeling more hungry in the evening, but our insulin response is much better in the morning. Why is that? Because in the morning you're not going to go kill a rabbit and eat it in the morning. You're more likely to go and find some ripe fruit or vegetables, which has a lot of carbohydrate, and that's what we are designed to eat during the daytime or in the past hour. Whereas in the evening when you come back and you know, in most cases you are grilling some. Meat, um, uh, or protein, and that doesn't need too much of insulin response. and also another thing is, you know, and if you go back to many, 200 years ago, it was not that every night somebody is killing a deer or bringing a big animal. It was a little bit of food that was shared among many people, and they. You know, in a family there would be six or seven kids, and then the grandparents and the uncle, and then the, people who are sick, everybody has to share the same meal.

Just like going to bed at a consistent time is good for your mental health. Having the breakfast at a consistent time is also good for metabolic health. And after suppose, say you wake up at seven, you are waiting for a couple of hours, your breakfast is at nine, and in case you cannot have breakfast at home because your commute time is long, you can always bring your breakfast back at breakfast, eat at work, and then suppose, say you count eight, nine, or 10 hours, then from nine o'clock, 10 hours is 7:

00 PM So that means if you're back home around 6, 6 30, then you can have your dinner. And that's when you'll close your kitchen. So I thought, so that would be an ideal, uh, way where you can balance everything. You are still having breakfast, you're having a light lunch so that you build up enough appetite for a good dinner with your family, and then supposed, say you're finishing dinner at seven, most people go to bed after 10 o'clock anyway, so you will have three hours of good fasting before going to bed, because this three hours of, uh, evening fast actually helps you to digest food so that your core body temperature can go down and your melatonin builds up and it's not in interfering your blood glucose regulation so that you can have a good night's sleep. 00 PM So that means if you're back home around 6, 6 30, then you can have your dinner. And that's when you'll close your kitchen. So I thought, so that would be an ideal, uh, way where you can balance everything. You are still having breakfast, you're having a light lunch so that you build up enough appetite for a good dinner with your family, and then supposed, say you're finishing dinner at seven, most people go to bed after 10 o'clock anyway, so you will have three hours of good fasting before going to bed, because this three hours of, uh, evening fast actually helps you to digest food so that your core body temperature can go down and your melatonin builds up and it's not in interfering your blood glucose regulation so that you can have a good night's sleep. Um, and especially, you know, when I am very conscious about, uh, the health status of my food keeping it more on the healthful and whole foods, plants, that whole deal. Um. I, I know that I operate, um, so much better. My energy's better. Mental health is better. I really honestly can't remember the last time I was depressed. So what we see, so what we see is this like, um, adherence to intermittent fasting as a diet. And a lot of people make their windows very short or they will hold their eating until like as long as humanly possible until they're about to pass out and then start their dieting. So can you address that at all?

satchin_2_07-30-2025_114442:

Yeah, I mean, um, it's, it's a little bit extreme and particularly for young adults or anyone say before the age of 60, they are typically having a work. They have to go to work, they're doing a lot of stuff. They're taking a lot of, uh, complex decision throughout the day and. What we find is even, I've talked to some people who do this one meal. What we find is what they do is they try to hold up the hunger by drinking a lot of black coffee or black tea throughout the day. And, uh, towards late afternoon, they're kind of hangry. No, actually I have, I have heard the confession that some, uh, people are very hangry and, um, but then they still take the badge upon that they can hold off until evening and then they eat that, lot big meal and then they go into food, coma and sleep. So, uh, that's. One way people are dealing with it. And what we see is most of them actually cannot hold on to doing this for a very long time. They might do it for a month two, and then they will realize, um, how uh, you know, sometimes they're not eating with their family, sometimes they're not socializing with anybody and they realize that this is not a healthy way mentally, emotionally, and also physically. So then they will revert back to maybe eating within eight or 10 hours. For women. We have seen quite a few women, they want to do everything perfectly. So they will try to eat within eight hours. They'll go for five miles, run every single day, and then they'll try to eat a lot of salad and reduce their total food intake. So then what happens is they get into what we call relative energy deficit in sports. So this is a mouthful. But actually nearly 40% of athletes, even Olympic level athletes, um, you know, Boston marathon runners and even weekend athletes and college eight athletes, the, uh, varsity athletes, high school athletes, nearly 40% four out of 10 are doing this. No, actually I have, I have heard the confession that some, uh, people are very hangry and, um, but then they still take the badge upon that they can hold off until evening and then they eat that, lot big meal and then they go into food, coma and sleep. So, uh, that's. One way people are dealing with it. And what we see is most of them actually cannot hold on to doing this for a very long time. They might do it for a month two, and then they will realize, um, how uh, you know, sometimes they're not eating with their family, sometimes they're not socializing with anybody and they realize that this is not a healthy way mentally, emotionally, and also physically. So then they will revert back to maybe eating within eight or 10 hours. For women. We have seen quite a few women, they want to do everything perfectly. So they will try to eat within eight hours. They'll go for five miles, run every single day, and then they'll try to eat a lot of salad and reduce their total food intake. So then what happens is they get into what we call relative energy deficit in sports. So this is a mouthful. But actually nearly 40% of athletes, even Olympic level athletes, um, you know, Boston marathon runners and even weekend athletes and college eight athletes, the, uh, varsity athletes, high school athletes, nearly 40% four out of 10 are doing this. They're eating less and they're exercising more. And they might feel better because they're slim and trim.. They have a good physi, but actually internally, their organs are suffering because when you have less food available, then your body will eat itself. So, so that happens. How it eats itself is, um, the bone mineral density goes down so that they can have high risk for bone stress injury for women, the telltale sign is the, the menstrual cycle will become irregular or then become amenorrheic. And in fact, you might have heard many um, athletes, they would say that they are  amenorrheic or irregular menstrual cycle. And the thing that being an athlete, and having this is. So common that it may be normal, but what is common is not normal always. So, um, if they see that their menstrual cycle is changing and becoming more irregular or amenorrheic then that's a good sign that they are eating less and pushing their body to the extreme. And I, I'm always trying to tell people that hunger is not bad. Hunger is a very important signal. Can you explain to people why it is so important and it is important to heed it? It's important to feed ourselves when we are hungry. No, you don't know what is starvation, sorry. Most people don't know what starve is. And then reaction is you should reach out and grab that energy bar or something to feed yourself. But if you are, um, for a regular person, you know, if you had a good meal in the morning, um, it takes roughly five hours for that breakfast to get digested in your stomach to go to intestine. yeah. Theoretically that's what, that, that's how much reserve we have. Um, so that's why you'll hear all this news when, you know, after a natural disaster, after a earthquake or something, somebody was trapped under, uh, some building for seven days and they found him alive because, you know, the body was using that reserve. the bottom line is when you start that hunger, that means the body has either depleted, it's easily available carbohydrate, and is looking for that storage. And let it look for the storage, let it take out that stored fat that we have been storing, run it off a little bit. And in fact, you know, when you're delaying that meal. literally your body can, will be perfectly fine with three meals or two meals even, in a day and in between if you're feeling hungry, that's just a sign that the body is switching from one energy mode to another energy mode. And when it switches that, then it's actually good thing because. When we use energy, from carbohydrate or fat, we also, our body also produces different types of molecules that are used in building our body or repairing our body. yeah. Theoretically that's what, that, that's how much reserve we have. Um, so that's why you'll hear all this news when, you know, after a natural disaster, after a earthquake or something, somebody was trapped under, uh, some building for seven days and they found him alive because, you know, the body was using that reserve. the bottom line is when you start that hunger, that means the body has either depleted, it's easily available carbohydrate, and is looking for that storage. And let it look for the storage, let it take out that stored fat that we have been storing, run it off a little bit. And in fact, you know, when you're delaying that meal. literally your body can, will be perfectly fine with three meals or two meals even, in a day and in between if you're feeling hungry, that's just a sign that the body is switching from one energy mode to another energy mode. And when it switches that, then it's actually good thing because. When we use energy, from carbohydrate or fat, we also, our body also produces different types of molecules that are used in building our body or repairing our body. Uh, you're doing, uh, your body is doing at least two or three good things when you burn that liver fat, then you are protecting yourself against fatty liver disease that's going to affect one in three adults in this country. Second is that ketone is going to power your heart and many other, uh, organs because some, some of our organs actually love ketones than sugar. The third is some of the ton actually are good for our immune system because they make our immune system more efficient in finding, say, tumors or baby tumors or tiny tumors or even fighting bacteria and other things.

dr--supatra-tovar_4_07-30-2025_114442:

I think that's hard for people. I think that, you know, it's habit, you know, with, with what they eat and how much they eat. And certainly I think allowing the body to be a little bit hungry, um, you know, in getting to a certain point is good. But I think diet culture just takes that to a whole new extreme and we're seeing that. um, that's why people weight cycle as soon as they go off of something that's hyper calorically restrictive.

satchin_2_07-30-2025_114442:

you know, there is, uh, some data that, well, one or two days of calorie restriction may be good, but then beyond that it canwreck havoc by eating away your body. uh, yes, I agree that there is a fine balance there. And as you mentioned, for some people, when they feel hungry, they immediately have to eat. And that's why some of these new drugs, uh, like Ozempic, Wegovy and all of these, uh, they're helpful for people who cannot tolerate that hunger because it's essentially, uh, reducing that signal so that people feel full even with a small meal. And the idea is, it's almost like when you are trying to learn that bicycle, this is the third wheel. You are given this third wheel to gain back control over, over your hunger and satiety. uh, this is also an opportunity when you have the third wheel, gotta start riding your bicycle much better so that you don't need that third wheel after a while. So. Yeah. I mean, that's why I said that when people start doing time restricted or intermittent fasting the first few days, they feel hungry at bedtime. But then after a week or two, they don't feel hungry anymore because the body actually learns to produce or reduce that hunger hormone at bedtime and increase, um, satiety hormone so that people can go, um, 14 hours, 12 to 14 hours of fasting without feeling hungry. We eat slowly enough so that our body can, you know, take time with it and, and register all of this food in our stomach. We listen to that moment when we're no longer hungry. And we follow this clock, we can have our optimal health without doing anything, especially when it comes to restrictive dieting. Dr.​

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