WHOOP Podcast - How Meal Timing Affects Sleep & Metabolism with Circadian Rhythm Expert Dr. Satchin Panda

Episode Date: August 20, 2025

In this episode of the WHOOP Podcast, WHOOP SVP of Research, Algorithms, and Data, Emily Capodilupo, sits down with renowned circadian rhythm researcher and expert, Dr. Satchin Panda, to explore how the timing of your daily habits, like light exposure, sleep, and meals, can transform your health. Dr. Panda explains why our body doesn’t just run on a single “master clock,” but on a network of clocks in nearly every cell—and how food timing plays a surprisingly powerful role in synchronizing these clocks. You’ll learn practical strategies for training your circadian rhythm, optimizing your nightly routine and light exposure for better sleep, and using time-restricted eating to improve metabolic health.(00:23) Rapid Fire Q’s with Dr. Satchin Panda(02:26) Decoding the Brain’s Master clock(08:12) How to Train Your Circadian Rhythm: What Factors Apply Most?(11:09) Importance of Light Exposure For Optimal Sleep(15:41) Time Restricted Eating: How Does It Help Circadian Rhythm?(18:56) What Time Restricted Eating Studies Tell Us(28:22) Benefits of Time Restricted: What Do We Know?(40:54) Practical Takeaways For Time Restricted Eating and Circadian AlignmentFollow Dr. Satchin PandaDr. Panda’s Salk ProfileDr. Panda’s InstagramWHOOP Blue Light Blocking Glasses:WHOOP ShopSupport the showFollow WHOOP: www.whoop.com Trial WHOOP for Free Instagram TikTok YouTube X Facebook LinkedIn Follow Will Ahmed: Instagram X LinkedIn Follow Kristen Holmes: Instagram LinkedIn Follow Emily Capodilupo: LinkedIn

If we have too much light at night, we stay awake. When we sleep less at night, then the next day morning, our control of our food deteriorates. Sleep actually helps us to make decisions. There are a lot of decisions we make throughout the day. Some of the decisions are what to eat, when to eat, how much do it, when to eat, when to stop eating. Light is still the primary driver for our subconscious decision to eat. Dr. Panda, we are so, so excited to have you here. Thank you so much for traveling all this way to be here.

I'm excited to be here, too. We're going to start with something a little bit fun. We're going to do a rapid-fire set of questions. I know it's super hard, but you can only answer true or false, and then we'll dig into the details over the next 45 minutes or so. True or false. The time of day you eat has no effect on your metabolism or long-term health. Okay, you knew that was an easy one.

A, true or false, exposure to blue light at night can disrupt your ability to fall asleep. True. True or false. hundreds of medications could be more effective if taken at specific times of day. True. True or false? Does restricting eating to an 8 to 12-hour window show benefits for both weight control and inflammation?

True. And then last one, true or false? All cells in your body run on the same clock regardless of external light cues. False. You looked like you had more to say there. What was the hesitation? Well, the thing is external timing queue, mostly in trends are part of the brain clock. But the rest of the body and rest of the brain, actually they work on timing of food clock.

So that's why you can have light driving part of your brain. And then if you eat at the wrong time, then the rest of the clock can be out of sync. So let's jump off here because I actually think this is one of the big contributions that your research has had to the field. And I think a lot of people, and Whoop certainly harps on this point, like circadian rhythm, sleep consistency. And I think most of our members really only appreciate circadian rhythm, sleep consistency. And your research is all about, uh-uh, there's a lot of different important behaviors. You've done fascinating research around physical activity and eating and how they relate to the circadian rhythm. So what do you mean that most

of our clocks go off of food? What are people not understanding? Yes, for a very long time, we thought that there is a master clock in the brain that makes us go to sleep and wake up, and that must be driving clocks in the rest of the body. And to step back one step, actually, if you dial back to 1980s and early 90s, people thought there is only one clock that's only in the brain and that clock ticks. And then towards the end of the last century, there was a big discovery that almost every cell in our body has its own clock. Even our skin cells has its own clock. So then the question became, well, if there are all these clocks all over the body, is there a master clock that actually, like a conductor of the orchestra that conducts this orchestra? And then people realized very quickly that it's the master circadian clock that's present. in only 20,000 neurons at the base of the brain.

And the technical term is suprachyasmatic nucleus. And if you take out those 20,000 neurons, then the mice or rats, they have no sense of time. So that's why people thought that that's the master clock, and that clock gets entrenched by light and dark. And then there are a series of studies showing that this master clock in the brain actually regulates body temperature.

So core body temperature rises during daytime, falls at night, and that temperature rhythm is enough to synchronize all the peripheral clocks. And similarly, there are many other ideas, for example, cortisol, which is stress hormone, that can also synchronize clock. So all this stuff was kind of coming out of famous laughs between, say, 2000 and 2010. And I had a curiosity like, well, this is for. for a mouse rat or anyone, wild animal that's out there because their sleep awake cycle and eating fasting cycles are governed by nature.

But we are the outlier. Humans are the true outlier because we are the only species that controls fire and light. So we stay awake and we truly have the freedom to eat at whatever time we want. So then we did a very simple experiment. and the experiment was to take even the night-eating mice, mice are night-eaters. So they stayed in light-dark cycle, just like day-night cycle, and instead of eating at night-time, we fed them during daytime. It's almost like night-sipped workers who are working at night and sleeping during daytime.

And then we asked, if the brain controls all the clocks, then the timing of food should not matter. because all the clocks will be the same, whether they're day feeding or night feeding. To our surprise, we found that everything in the liver was tracking when the mice ate. And that was kind of a very big discovery at that time. A lot of people didn't believe it because right before that there were publications saying that, well, there are some signals from brain that can still drive brain originating signal in the liver. But to our satisfaction, there are quite a few researchers from Europe and U.S., they validated our results.

Not only that, we looked at only liver. They went on looking at all the organs and even part of the brain, even a few millimeters away from the supra-cosmetic nucleus. All those brain regions were tracking food. So then it became very clear that actually, truly, that's when the light bulb went up. And I said, I used to work on light, and then I thought, light is the master controller of circadian rhythm, which I truly believe till now,

but then the challenge is we don't have control over lighting. I did not choose what kind of light will be in the studio, what intensity in which direction they will be falling. But I have the control over what I have in this glass of water, whether it's pure water or sugar water or whatever it is. I promise it's pure. So that's why we thought, well, then we can actually let people really control their circadian rhythm

because instead of the SCN being the passive conductor, they can be the conductor of their own circadian orchestra by just deciding when to eat and when to stop it. In some ways, what you're saying is very exciting because we're all kind of passive recipients of most of our light environment, right? When I'm home, I can control my light, certainly around evening and stuff like that. actually spend most of my waking hours here where it's above my pay grade. So you go home. Right. I go home and I can control my lights. Here I can't. Certainly can't control sunrise and sunset.

But I do have a lot of control over my eating. So, and I will say, it's, it's super fun to be having this conversation with you because I worked in one of these sleep labs that you're talking about, starting in 2010 when we were told that the SCN was the master clock. And I worked. with people who contributed to those findings. And I remember when some of your research and the research you're talking about started to come out and you're like, hmm. And I think that's what's so beautiful about science

is that willingness to learn that we're wrong and to realize that the story is a lot more complicated and in this way, more complicated in a really empowering way. We have more control than we realize. So is it the case that, I guess you would agree that light is still important? Oh, yeah. Yeah. Okay, great. Not at all disputed. Is it the case that eating is more important than light in terms of entraining the circadian rhythm?

I won't go there because, you know, it's like a tango, right? Both have to dance in synchrony. So you can't say that one dancer is more dominant than the other. And so I think the point is light still drives some of the eating behavior. So for example, if we have too much light at night, we stay awake. And then when we sleep less at night, then the next day of morning, our control of our food deteriorates. Sleep actually helps us to make decisions. Yeah.

And there are a lot of decisions we make throughout the day. And some of the decisions are what to it, when to eat, how much to eat, when to stop eating, what combinations to eat, with whom to eat, all those stuff. They go out the windows. So then, in that way,

light is still the primary driver for our unconscious or subconscious decision to eat. So this is an interesting nuance. The light-dark cycle impacts sleep, and sleep impacts eating, and eating impacts our circadian rhythm. And so everything's impacting everything else. Because light behaviors and light exposure,

and therefore sleep impacts so much of what we choose to eat, it's ultimate effect on the circadian rhythm, sort of hard to isolate. greater. Yeah. So that's why we have to control both light and food. So when it comes to controlling light, as we discussed, we have very little control over actual lighting.

And even we don't have control over, you know, the specifications for the light bulb. We may choose different light bulbs, but actually we are at the mercy of the Department of Energy that figures out how much light each water's of power should come. crank out. And those engineers for their job, they have very minimal knowledge or appreciation of the quality of light. And also there is technological limitation. So as you know, most of our modern LED lights are mostly driven by three LEDs, RGBs. And it's impossible to simulate daylight with these three LEDs. And if you want more power from every ward, then you just crank up the blue LED.

Most people who don't understand the color of the light or brightness of light, they want to buy the biggest, the brightest bulb for their buck. And when they buy that and then put it in their bedroom and living room, then actually they are making a mistake, but even if they dimmed down, they still have a lot of blue light. So I guess that's why food becomes an important story, but at the same time we should not give up our attempt to control light. So I want to tease apart two things that you're saying.

One is we're buying the wrong light bulb. For people listening, what light bulb should I have in my bedroom? And you don't need to get into a brand, but what should people be looking for in a sleep-friendly, circadian-friendly lighting choice? So for most of us, when we go to any store that sells light bulb, Light bulbs come in mostly in three different flavors or colors. One is pretty bright, and it has little tinge of blue, and that's the one that we most prefer during daytime.

We feel more a lot excited, and we're more also likely to buy that because we think that, huh, this is a bright bulb and then I should buy it. And then at the opposite spectrum is kind of the orange color light that mimics the old school candlelight and it's golden color and then some people like that and actually that's the light that has less blue light. So maybe that's the one one may prefer for bedside table lamp or somewhere where you sleep. That's one choice, one layer of choice and then the second layer of choice is your light switch. So most of us have flip switches at home. And so the next choice you can make is have dimmers.

that you can also dim down the light if you need. So these are two different things that everybody can do to reduce their light exposure at night. Right. So in terms of things that are good for your health, changing out your light bulbs, maybe adding a dimmer, are pretty accessible home upgrades. If somebody does that, what would they expect to see happen to their sleep? Well, so. Someone's listening and they're like, okay, it's better. Like, is it going to solve all my sleep problems? What's going to happen? These are some of the elements in your toolbox to improve sleep. Right. So just like, you know, you cannot have only one screwdriver to fix all the screws in your own house. Oh, no, of course. So similarly, this is one. So people who have

very bright light and they may not understand why they cannot sleep well or why they're so jazzed up even after dinner and after a long day. So they may benefit if they have very bright light, dimming down light or having an orange-sipped light bulb can help them to feel sleepy. And then in the extreme cases, if they want to filter out all the blue light, there are also blue filtering eyeglasses where you look cool. Either you can choose to be yellow, orange, or even some people wear red. No, we actually, we make our own, and we validated them in Loop Labs, which is our clinical research lab downstairs.

And then we did a sleep study. We did show that improved sleep architecture, reduced sleep onset latency, and improved recovery scores the next day. So big believer in the blue light blocking glasses. But it sounds like what you're saying is if you notice that you're feeling a little wired in the evening, this is a tool worth exploring, not necessarily going to make or break massive issues. Yeah, I mean, we brought up, you brought up this blue filtering glasses, and this is where, you know, personal control over light, you know, you can have a pair of blue filtering eyeglasses, and suppose you're traveling and you check into your hotel and that has the bad lighting, then, yes, those are some of the cases where you can have complete control over your light. I love the practical advice that you're giving here because, you know, in my own home, I can change the light bulb. when I travel probably a bit extreme to bring light bulbs with me and change hotel room lights. You're traveling right now away from home. And so, you know, blue light blocking glasses

something you can easily throw in your suitcase and bring with you. And so I love that tip. What's up, folks, if you are enjoying this podcast or if you care about health, performance, fitness, you may really enjoy getting a whoop. That's right. You can check out whoop at whoop.com. It measures everything around sleep, recovery, strain, and you can now sign up for free for 30 days. So you'll literally get the high performance wearable in the mail for free. You get to try it for 30 days, see whether you want to be a member. And that is just at whoop.com. Back to the guests. I think people are going to really find this fascinating. So I want to make sure we do this area justice. But you talked a lot about eating. And you've pioneered a ton of fascinating research around

time-restricted eating, which is the idea of sort of eating in alignment with your circadian clock. What are the principles here? What does it look like to follow time-restricted eating and why does it matter? Yeah, so the time-restricted eating, which is now popular as intermittent fasting, it started from our lab. The idea was very simple because for many, many years, for decades, all the labs that work on metabolism, obesity, diabetes, and all these bad diseases that happened to us. They used to give mice, fatty, sugary food, and then they would give the food and disappear for a few days,

and then mice will have all the freedom to eat, what, when, and how much they eat. And actually, this is a cool discovery from one of my circadian colleagues, Joe Bass, at Northwestern University. He just measured when mice actually eat this unhealthy food. And he found that mice, instead of eating most, of their food at night time, they start to nibble more during daytime.

So then during daytime, they're not fasting as much as they're supposed to, and at nighttime they're still eating. So they published that, and then it kind of triggered my thinking. I thought, well, if it is so, how much of the disease that we see when we, or mice eat on healthy food, gaining weight and becoming diabetes is due to the bad diet or mis-timing of the diet. because now the mice are eating when they're not supposed to eat. Right, and I think this is what's so fascinating about so much of your research, right? It's this idea that, like, I think there's so many people that want you to believe it's like calories in, calories out,

and all that matters is like how much food do you eat, period. And that there's something like very nice and easy to turn into an app about that idea. But the reality is that like if our microbiome is active on a certain circadian rhythm, If our pancreas is active on a certain circadian rhythm, if, you know, our body's sort of, you know, activity levels follow a certain circadian rhythm, it feels absurd to think that it wouldn't matter. And I think it is so cool that you thought to ask that question, felt like it needed to be asked. Why don't you talk about what you found? Yeah, so just step back because you brought up that like calories, a calories, a calorie. But the point is, if you simplify it, for example, in your Oop office, there are say 100 employees coming to work.

and an employee is their employee, it doesn't matter. Which is crazy. It doesn't matter when they show up, right? Wrong, because if your security guy doesn't show up at the right time to unlock the gate, then nobody else can get in. And similarly, so that's why the timing does matter in every aspect of her life. Even your best friend, if she or she comes and knocks on your door at 2 o'clock in the morning, that person will never be a best friend again.

Or at least you receive them very differently. Very different. So that's why healthy food at the wrong time can be junk. So here, that was the idea. So then we took this mice and then they're all born from the same parents in the same room. They had the same, got a microbiome. One group got to eat whenever they wanted, just like 10,000 other experiments done. And then the other group was given food only for eight hours.

and it was not a magic number eight hours. We decided eight hours because mice actually eat the same number of calories as the mice within eight hours as the mice that have access to food 24 hours. Right. And making that an isochloric experiment feels important. Yeah. Because unless you equalize calories and the quality of food, you can't make an interpretation from timing. So we did that.

And to our surprise, the mice that were eating within eight hours were completely healthy. And they didn't look like the obese, diabetic mice with high cholesterol and fatty liver as the mice that ate the same diet throughout 24 hours. So this is, I think, like, just absolutely fascinating. And I think our listeners are going to be saying, wait, what did he just say? So I want to say it again. If you eat the exact same food, just as much, same quality, but over eight hours, is spread out over 24. Doing it in eight hours resulted in less disease than doing it over 24.

Yes. Okay. So my... That was my next question. Mice. I am not a mouse. Does this apply to me? Yeah. So let's get back to here, our mouse. And then, you know, this was the first experiment. It was very surprising and shocking. So I had to repeat it two three times. And then we did it eight hours, nine hours, ten hours. And we figured out that mice can eat within eight to ten hours. And we can be healthy. One point is, these mice are getting really unhealthy diet, like 60% calories from fat and 20% from really simple sugar, which will be equivalent to us eating all of our calories from nachos ice cream. So in real life, very few people would eat that kind of food. Although doesn't that kind of sound like the standard American diet to you, or you think

it's like maps to something worse than that? It's worse, because the standard of American diet is around 35 to 40 percent fat. Okay, that's helpful context. So it's significantly worse than that. The first experiment was 61 or 63% fat, and that too unhealthy fat. But nonetheless, the sort of eight-hour eating window mice didn't develop these diseases, or they just developed them in a lower rate? No, we did the experiment only for 18 weeks, which will be equivalent to maybe 8 to 10 years of human life.

and these mice were young. So if we look at human population, suppose a young person is eating on healthy food but eating within a constant hours, then maybe for a few years, maybe that person may not develop disease, but in the long run, that person might develop disease. So we haven't done the experiment lifelong on the same bad diet.

Not on humans, but in the mice, were young over those 18 weeks, the ones that had access to food for 24 hours, they did develop? They did develop a lot of disease. Yeah. So that's pretty profound. That's very profound. And in that case, then the question was, well, if you do it in humans, then what happens? Yeah.

So I guess at that time, if I dial back, the paper was published in 2012 May or June, and it was very difficult to publish that paper because the nutrition field thought calories are calories and they were suspecting. I must have made some mistake and I have done this experiment three times. So it took us two years to publish that paper and then I thought that's it. I'm never going to work on it again. And then within six months, there are books out there, eight-hour diet. So the point is we did a study where we prevented disease and we prevented obesity. Prevention is not same as treatment. So for example, if I stop smoking, I am protected from my chance of getting lung cancer is reduced. But once I have lung cancer, it doesn't matter anymore. Even if I stop smoking,

it's not going to cure me. So it was little embarrassing and shocking that people are now publishing this eight-hour diet book and then there are bloggers and influencers, they're saying as if this is a thing in human. And there was some bogus clinical trial. I don't know how people could do a six-month clinical trial in three months. There are actually bogus clinical trials that were cited in some of these books. So that prompted me to think, okay, so we have to go back and do the right experiment. We pattern up the mice first and then put them in eight, nine, ten hour. Or we ask, well, can mice just eat for five days in eight hours and then have two days of cheat day? And what happens? So luckily, I had an awesome postdoc, Amundin Che, who came to

love and she was ready to do all these experiments. And she had like 600 mice and she tried all combinations of food, all combinations of timing. And the bottom line is, yes, if you fatten of the mice, the mice already have fatty liver disease, diabetes, obesity, et cetera, and then put them on nine hours or 10 hours time restricted eating, then mice will lose some weight and they will improve their health. That's an incredibly important finding that not only can this, you know, eating behavior prevent disease, but if you are already in a disease related to excess eating, following this diet does seem to show some effects of reversing those condition. So there's a lot of hope out there because so many Americans are living with these

conditions. There's not all those conditions. In the same experiment, what we did, we actually put the mice on treadmill. Then we asked, can you exercise? And we also asked them, we tested grip strength in mice, and mice had to do grip strength, and then this treadmill. And then they had to run on a rotating drum to do their motor coordination. And what we found was once mice did time ratio eating for several weeks, then all three factors improved. Their motor coordination was improved so they could stay on a rotating drum

so they could be the circus mice. We can do all this stuff. And why this is important is motor coordination is a very complex phenomenon because the mice have to visually or based on their feet, the tactile input, has to go to their brain

to process how fast the drum is rotating. And then the brain has to send the right command to the hand and leg to make sure that they actually step with the right speed not to fall off the drum. So in that way, it actually showed that the effect is even much bigger beyond the body. It's inside the brain. So that was exciting. And then the second exciting thing was if you look at most weight loss study and nutrition weight loss study, it's given that when you lose weight or anything that prevents you from gaining too much weight that also affects impairs your muscle function. So people who quickly lose weight, they actually lose a lot of muscle.

And that's why people who are taking this new GLP1 receptor drugs, they lose a lot of weight. Some of that is muscle loss. Their athletic performance deteriorate. So then we had the question, well, these mice are losing wet and not getting wet. How is them athletic performance and muscle strength? So that's why we did those studies, and then what we found were surprised was mice on time-restuted feeding actually gain muscle mass, and they returned that increased muscle mass late into the Middle-Ais. So we have done this experiment now to the equivalent of humans living to 50s, and, you know,

I'm selfish, so I did that. and then we also put them on treadmill and for surprise these mice that are eating on healthy diet actually in this experiment they were eating I think 45% fat slightly more unhealthy than the average American diet but they actually outrun mice that eat healthy diet but whenever they want because see mice that eat healthy diet they still nibble a little bit 15% of their food they eat during daytime in the middle of their sleep. So that's fascinating. So an unhealthy diet, restricted to eight hours a day, seems to be more geroprotective

than a healthy diet sort of eaten around the clock. I don't go to that extent because it's only mouse and then. In mice. In mice. And also, you know, we took it to equivalent of mouse year of 50. Sure. Partly what you said is true. Yeah.

So I'd love it if we could jump from mice to people. What do we know in people? So in people, the challenge is people actually eat very randomly. And a few years ago, when we were trying to start human experiments, we didn't know when people eat. Because just one day of food record is not sufficient to figure out when they eat and how consistent is they eating. Because in mouse experiment, we have also seen women's other people in the field. They have done very careful experiment where they feed mice, but then they change their light, dark cycle by eight hours or six hours. So as if the mice are going from one time zone to another time zone, even within the same week.

So in that case, the mice change their eating pattern from one day to another, and those mice are also prone to, more prone to metabolic disease and liver disease. So along that line, somebody may be eating, say, between 8 a.m. and 5.m. 4 p.m. today, 8 hours. And tomorrow that person may be eating from noon to 8 p.m. Also 8 hours. And then day after tomorrow may come back to 8 p.m. to 4 p.m. So a standard nutrition science student would take the average of this window and say, this person is eating 8 hours windows. So it should be fine. But no, that's not fine because the consistency is important. Right. So that says it's not merely about consolidating your eating window, but it's about doing it at a certain consistent circadian phase.

Yeah. So when we monitor people, and we have to monitor for two to three weeks using our app, my circadian clock, when we did that in the first study, we had 156 people. They had to log everything they ate or drank within three weeks. So log means they had just had to take a picture of food or drink whatever they were doing. And then we would look at the picture and decide whether it looks like water, then we'll say, no, it's not a calorie-containing food. Or if it was black coffee or diet soda, then we did not consider them as food.

But if we put just the food and the timing of food, then what we found was an average person was likely to eat within 14 hours, 45 minutes window. If we consider all the eating that happens within three weeks, then that's 14 hours, 45 minutes, less than 10% of people actually ate within 12 hours or less. This was in 2015. So this was long before intermittent fasting or time eating was popular. So less than 10% for eating in 12 hours or less. We're not talking about even 10 hours or 8 hours.

So that's the data. And then meanwhile, people try to go back to large-scale. data collected through enhance, which is a massive data collection process, happens every two years. Nearly 2,000 people are interviewed about their food habit for one or two days. And as I said, these enhanced data is absolutely never reliable for determining eating duration or eating pattern. Anyone reflect, self-reflects their own life, if they randomly take two days, that's not going to represent their life for the year. Forget about projecting for the next five years, seven years or ten years. So far, unfortunately, there is no other data collection that have gone beyond, say, a few hundred people.

But all the data collections, that data that have been published, dozens to hundreds of people, they come to the same conclusion, we are more likely to eat more randomly, and a lot of us actually eat all of our food in a window that's at least larger than 12 hours. You're invited to join the waitlist for WOOP Advanced Labs. Advanced Labs delivers clinician-reviewed lab results right into your WOOP app for the most complete view of your biomarkers and biometrics and the most comprehensive understanding of your health. Unlike other tests, whoop integrates your lab results. with your WOOP data.

See how your habits and behaviors influence your biomarkers and get clear guidance on what to change to improve your results. To join the wait list, visit our website or the Health tab in the Woop app. Okay, so most people are eating over the course of 14, 15 hours, which like you could kind of see it. That's like if you have breakfast at 8 a.m., 7 a.m.,

then like you're finishing eating in that 9, 10 p.m. window, which I think we all know loads of people who do that if we don't do that ourselves. What do we know about the harm of doing that versus if those people got into that eight-hour window or even 10? Yeah. So I think most of the time when we talk to people, people will say that they eat within 10 hours. And then if we ask, well, what time you eat breakfast?

They will say, well, I eat breakfast at 9 o'clock. And then if you ask more carefully, okay, so you wake up at 6. and you're eating breakfast at nine, there's nothing in between? I'll say, no. And actually, this is a real conversation I had with a professor a few days ago. He said, no, I don't eat anything. I said, okay, so what do you do then? I go to the gym, so you go to the gym, empty stomach and do a workout and come back?

Yes, I do empty stomach, and if I'm a little low in energy, then maybe I'll have half a glass of electrolyte, that's fine. And then he said, and after I finish my workout, I have a protein drink, protein shake. I said, but that has calories. He said, no, it's protein. Of course, he's not a nutrition or biological science professor. Okay, so I'm trying to play this out my own schedule. Water doesn't count when you talk about this window.

Okay, great. Black coffee doesn't count. Black coffee doesn't count. So calories. We're literally talking about calories in any form. Calories should happen inside of 12 hours. Yeah, so the bottom line. Mine is this. So for example, suppose I eat or drink anything that has five gram of sugar.

So let's go back one step. Suppose say you decide to bleed me to death and take all my blood. You'll find only five liters of blood and sorry, you'll have less than five gram of sugar because my fasting blood sugar is around 90 to 100 milligram per deciliter. So only five gram of sugar. That's what is circulating in my blood. That means when I take just one gram of sugar and my stomach immediately absorbs that and sends to the blood circulation, so then my blood sugar will go up to 120 from 100. And then it will wake up. So once I, instead of water, if I'm drinking even with one or two grams of sugar, it's waking

up my stomach to do its work, that is to absorb nutrient, send it to liver. Because all the, everything goes through liver, the liver junction sees, uh-huh, there is something coming in and decides whether to use some of it. And then it touches the pancreas, pancreas wakes up, max insulin. Insulin goes and unlocks the dot in muscle and many other organs. So just by drinking or eating something that has one or two or three grams of, just carbohydrate, simple carbohydrate, you are waking up the entire village. to do the work.

Okay, so this is like a fascinating way to put this into perspective. So there's about five grams of sugar. And for context, what could I eat? That's about five grams of sugar. That's like... One teaspoon of sugar. One teaspoon. Okay, so very little, like less than half an apple.

Yeah. And that is going to have about the amount of sugar that's in my entire blood. And we know, because we've seen, you know, CGM data and whatnot, that my blood sugar is not actually going to double. Instead, I'm waking up the whole apparatus of deal with sugar to keep blood sugar stable. And once I've woken up the village, as you said, they're up. They're doing their thing, fast broken, to help us really understand this point. Why is that a bad thing?

When you call it waking up the village sounds bad, but does the village go right back to sleep? Yeah, so I'm just giving the analogy, but then we don't stop at Hath, than apple. Sure. So the thing is, we're talking about now, actually, what happens when Belize wakes up. So, for example, insulin receptor gets engaged, and that will trigger mTOR cascade, and then mTOR will phosphorylate, among other things, some of the clock components, and that can likely trigger resetting of the clock in some cells. Right. So this is the important point that we started with. So somehow waking up the village

tells your whole body that it's actually a different time than it thought. And your circadian rhythm shifts. Why is that bad? Because the clock gets confused. It's almost like a jet lag. So just imagine when you fly from here to California, you're changing the time zone by three hours. And just that three hours wrecks havoc on some people. And we feel it because it affects our sleep wake cycle. And the thing is, the bad thing is we don't actually feel the clock in our gut. In most cases, we don't feel how bad it is. Right, because there isn't something as like painful as I can't fall asleep when I want to the way we feel it with sleep. Yeah. But what I think is so fascinating about your research is you're saying that secretly, that exact same snack

even if it's a bad-for-you snack is going to have very different damaging effects to my liver, to my metabolic health, simply based on whether or not my body was in a circadian phase in which it was prepared to receive food. Yeah, so that's one aspect. Then the other aspect is, suppose I have gone through 10 hours of fasting, I stopped, say, eating at 6 p.m. Then this is 4 o'clock in the morning. I woke up to catch a plan and then I decide to eat something, you know,

in the early morning, that long line next to the coffee shop, people are having that cappuccino. So then what happens is after maybe eight to nine hours of fasting, my liver is barely starting to make some ketone bodies, just barely. The process is just starting. And then that cup of coffee with cream and sugar that I really need before I get on the plan, puts a sledgehammer on the ketone-making mechanism. So that's another aspect that happens.

It's not only clock. It also happens to our body's own ability to produce this ketone bodies during long fast that has many benefit for our brain, for our heart, and also it has some anti-inflammatory benefits. So the story goes on and on and on because what you are dealing with is three different things. One is the fasting is breaking,

So the related pathways that are important for ketone formation or maybe autophagy somebody has gone through a lot of fasting, those are strophying. And then second circadian clock is getting confused whether it's on or off. And then the third thing is the body was actually not ready for eating food. So although we are saying that the body will process food the same way, it doesn't. It actually doesn't absorb food the same way, cannot process it. for example, if I'm eating that food at 4 o'clock in the morning a big meal, then my stomach is not ready to digest and my intestine is not ready to move that digested food down the tubes. Yeah, so I think there's an important practical takeaway here. And I think, you know, as we get

ready to wrap up, I want to make sure that we wrap up the really practical takeaways for people. In that first hour that I'm up, my body is not ready. I haven't sort of begun the preparatory. processes to receive food. So we've heard that an eight-hour eating window might be ideal, and that that eating window should be at a consistent time, but it actually also matters what that time is. So what time of day, when to when, should I optimally plan my eight-hour window? Okay, let's go back, put all this together. Sure.

Because we talked about light, we talked about sleep. So actually, our day begins the night before. Of course. That's why the first thing is try to go to bed at a consistent time and be in bed for eight hours so that you can get your restorative six and a half to seven and a half hours of sleep. Then after waking up, wait for an hour or two so that your cortisol, the stress hormone is not too high, your melatonin is not halfway down. So both of them are down in one to two hours because both of them. them are not good friends for our food. So then after one or two hours, again, just like going to

bed at a consistent time, breaking your fast or breakfast at a consistent time is important for the clock. And then after you break your fast, so that's one to two hours after waking up, then you count eight, nine, ten, or maximum 12 hours window for your food. Because if you go beyond 12 hours, then your last meal becomes within three hours of going to bed, which is also bed. So that's why the maximum allowable window is 12, because if you think about a teenager or a 10 year old, they may not be able to do eight hours, but they can easily eat within 12 hours. So I like that. That's actually fairly user-friendly. So it's at least an hour after you wake up through no later than three hours before you're going to bed. And if you're going to,

so that's sort of four hours lost to padding on either side, if you're going to give. say seven hours to sleep, you're already, you know, at 11. So then not a ton of buffer to kind of find that 12 hours in the middle where you're eating. And that actually feels doable. Yeah, that's doable. It's only a few things. All the bad things happen after sunset. So between 6 p.m. and midnight, that's the challenging time. Because we evolved as social animal. We want to socialize. That's why it becomes very difficult to stay away from food for three hours before bedtime. And that's where having the mindset and coming up with some tricks to avoid food and enjoy maybe some sparkling water all the way to adopt high-restritating and to improve health.

Amazing. Well, I found this incredibly interesting and I imagine our listeners will as well. So thank you so much again for being here with us today. Thank you so much. Have a four-fax Acadian. If you enjoyed this episode of the WOOP podcast, please leave a rating or review. Check us out on social at Woop at Will Ahmed. If you have a question what's answered on the podcast, email us, podcast to Woop.com. Call us 508-443-4952. If you think about joining Woop, you can visit Woop.com. Sign up for a free 30-day trial membership. New members to use the code will W-I-L to get a $60 credit on WOOP accessories when you enter the code at checkup. That's a wrap, folks.

Thank you all for listening. We'll catch you next week on the WOOP podcast. As always, stay healthy and stay in the green.