Leading Circadian Rhythm Expert Dr. Satchin Panda Shares 6 Secrets to Longevity

My guest today is Professor Sachin Panda, a world-renowned circadian rhythm researcher and leading authority in the field of chronobiology. You might also know the concept of time-restricted eating, AKA intermittent fasting—work that came out of his lab. With a passion for understanding the impact of our internal clocks on health and well-being, Dr. Panda has dedicated his career to unraveling the intricate relationship between circadian rhythms, sleep, and overall human physiology. Through his groundbreaking research, he has shed light on the effects of disrupted sleep-wake cycles and artificial light on our health, offering practical strategies to optimize our daily routines. He is a professor at the Salk Institute and founding executive member of the Center for Circadian Biology at the University of California, San Diego. Please enjoy our talk today on optimizing your health and longevity using circadian rhythms.

Welcome to the Longevity and Lifestyle Podcast, Professor Dr. Sain. Such a pleasure to have you on today.

Yeah, happy to be with you on this podcast. So I'm very excited to have you on. Obviously, I've been following your work for several years, and being in this space, I heard you present last year at the Health Optimization Summit in London. But I really wanted—and I'm I'm delighted that we could make this this time—to really bring the concept of your work and what it's doing and the implication, because it is just so important for every single person to understand better, um, out to the world. So let's start with the concept. Um, as you were the the world leader in circadian rhythm, can you explain exactly what the circadian rhythm is and why is it so important for our health and well-being?

Yes, so the word circadian actually literally means near 24 hours. So that means anything that we experience or our body goes through once in every 24 hours, um, is considered as circadian rhythms. And we always think of—we always told that—well, our DNA holds the blueprint for our bodies, just like any blueprint for a building. The DNA sets everything, but what we forget is, um, when we build the building, whether it's an office building, whether it's a school, uh, it's not a dry building; it actually has life into it. So something happens during the day, something happens at night. And you look at any building that has specific tasks happening at specific times of the day. So, for example, before the office starts, the custodian staff would come in and clean up the place, and then the cafeteria people, and then they will come and brew the coffee, and then people will show up, and the shipping and receiving would come. So similarly, what happens is in our body, um, a body is not static. And we know that, um, what I am in the middle of the day and who I am in the middle of the night are very different. So the basic concept is just under this, uh, seemingly sleep-wake cycle, our body actually goes through a huge number of changes between day and night. And if we think of every hormone, every brain chemical, every immune response or immune modulator, every enzyme, digestive or anything else, even every single gene turns on and off at a specific time of the day or night. So that, uh, then the question is why are these rhythms? These rhythms essentially do a few things: one is to consolidate similar tasks. Like, for example, when when you are awake, your muscle tone should be better, so that we go running. Just imagine if your muscle tone is much better in the middle of the night, then you would be acting up all your dreams and you'll be kicking and kicking around the place. Yeah. So, and then the second is, um, separating incompatible processes. Um, same thing as I said, uh, your muscle tone should be compatible with the daytime, not with the nighttime. Similarly, bowel movement should be in the first half of the day after we wake up and clean up our bowel so that we are ready for food. Uh, so even at a very complex level like genes and proteins, we do see these things. And then the third one is anticipation. So, for example, in anticipating waking up, your heart rate begins to increase; your body temperature begins to rise up slightly. So it prepares our body for the next act in the day. And if we're not prepared, just imagine if you're not prepared for your for your exam, if you're not prepared to go to the doctor's office. Yeah. So, so we prepare all of this. So then the bigger question for everybody: so what, why should we pay attention to it? And this is so—what thing actually relates to why we cannot live a long, healthy life? I mean, if we're designed to have this DNA to give us this perfect body and mind, and why we cannot live—the reason why we can't live a long, healthy life relates to four major types of disease: uh, first one is infectious disease; everybody can relate because we all came out of COVID, but there are many more infectious diseases, um, that make us sick. And second is the metabolic disease: obesity, diabetes, um, starting from there to cancer; all of these are, um, affecting millions and billions of people these days. And almost one in two adults in the US, in the Western country, is going to experience, um, at least diabetes. One and two is going to experience high blood pressure; four out of 10 will be diagnosed with cancer. All of these bad things are going to happen. Then the third one is brain health. Um, the statistics is very different because at any given time, 5 to 15% of people may be experiencing depression, anxiety, but in our lifetime, if you take the entire lifetime, 85% of us will experience or have experienced some kind of depression, anxiety, which is clinically significant clinical depression, anxiety, or PTSD, all of this. And then the fourth category that I say is injuries. We know that, for example, I just crossed 50 a couple of years ago, and the reason why I cannot run as fast as I could or I want to, or why I cannot lift certain things is because I have certain injuries. And as we get older, we accumulate injuries, and that also reduces our performance. So getting injured and coming back to full play is what we need. So what is interesting is over the last 20, 25 years, scientists all over the world—there are very few scientists who actually work on them, but they're really smart scientists—and they—we figured out that circadian rhythm actually optimizes our health, so that a body can better fight infectious disease. And second, it can actually—if we have good, strong circadian rhythms, this day-night cycle, then we are also more likely to prevent chronic disease, from diabetes, obesity, all the way to cancer, even dementia. We can even combine the principle of circadian rhythm with whatever treatment you are doing right now to accelerate cure and come back to full play. And similarly, it's becoming very clear that certain principles of circadian rhythm, for example, sleep, maintaining proper sleep-work cycle, maintaining enough light exposure during daytime, avoiding light at night, and combining that with proper timing of nutrition, etc., can also reduce the severity of depression, anxiety, and brain—improve brain health, improve mental performance, and, um, just recently, we're beginning to understand that many of the injuries and prevention—prevention of injury, um, and then coming back to full play, whether it's bone injury, whether it's muscle injury, all of these injuries—having a strong circadian rhythm also helps us to better repair ourselves. And having a strong circadian rhythm and having physical activity at the optimum time also prevents injury. So that's why I'm looking at almost every health concern for everyone through the lens of—the reason is this is such a powerful concept, and it doesn't cost anything to adopt this into our life. Of course, you can spend a little bit of money to optimize your circadian rhythm, but this is something that we can—the solution is now; it's right now. And if we just understand how these rhythms are regulated or how we are the master conductor of these rhythms, uh, through when we eat, when we fast, when we sleep, when we wake up, uh, when we get exposure to light, and when we exercise—a few simple things—then we can actually leverage the power of the circadian rhythm. And I'll give you some specific examples where these simple attention to circadian rhythm is even more powerful than the best medication available.

Yeah, and I'd love to hear those. And and what you just said is just so powerful that not only can it help to optimize, but it can reverse so many of these, um, chronic diseases that are affecting so many people, um, and everyone I think has some connection to one. My mother has dementia; my father has cancer; relatives have issues, um, and you know the beauty is is that when you've understood this model—and I'd love to hear some use cases as well of that you've seen some transformations—but I'd love to break it down: um, how does one master the rhythms, as you were saying? You know, how does one a) understand if they're off-balance, and b) what is the right time for the individual, because we are all different?

Yeah, I guess you are asking a very fundamental question: what are these rhythms, and how our lifestyle or what we do affect these rhythms? So it all boils down to one fundamental reason why we have these rhythms. For the last 200,000 years, we humans have been living on this planet, and for almost a billion years, other life forms are on this planet. And over the last billion years, you may argue, okay, so there is global warming, there is global cooling, and all that stuff, but—and seasonal changes—but there's only one constant through that billion years: that is, the sun came up and went down, and exactly approximately after 24 hours, the sun came up again. So it's a very powerful cycle of light and darkness, and with light and darkness can warmer temperature and cooler temperature at night, and also access to food. Um, for diurnal, active animals like us, access to food during the day and and mostly fasting at night. And then for people—for animals and humans who are day-active, they have to run back at the end of the day to go to safe places to hide or run home. Um, so these very fundamental rhythms: in getting exposed to light during the day, minimal light or darkness at night—that's one rhythm. Second: eating mostly during our wakeful hours during the day, because in the old days there was no, um, processed food and preservation and maintaining overnight fast at night, um, then having all this—a lot of physical activity towards the end of the day—those were the only constants that actually happened for the last 200,000 years for humans. So, as a result, our genome, our physiology, our metabolism, our brain function, everything is tuned to this cycle. And just imagine, we cannot live outside this modern world for a few days. Imagine if we—I cannot imagine if you drop me in the middle of some wilderness where there is no modern amenities—I can survive there? Yeah, I cannot survive there for even more than a week or month. And just imagine our ancestors; they lived up to say 20, 25, 40, sometimes 40, 45 years, um, because they built up that resilience against disease, against injuries, against all the metabolic, uh, disease that we're talking about. And also, they have to be alert; they cannot be depressed; the lion will come and kill them. So, so all these things were there. So now the question is, we cannot go back to that ancestral life, because our modern life, our modern way of living involves—actually forces us to be—be active at night, to be more exposed to light at night, and we have access to food all the time, and we are sedentary. So now the question is, we can't give up the life of the modern world and creating wealth, um, goes synonymous with breaking our circadian rhythm. You cannot expect to make a lot of money and be rich or or bring enough, uh, for your living—to to pay for your family—by just going to bed at 7:00 in the evening and working, unless you get up at 4:00 a.m., maybe. And so, yeah, so the point is, how do we manage this? And then who is it—who is getting disrupted, and how do you understand that you are disrupted? So let's begin with a very simple thing: like, if you're sleeping less than 7 hours, you already have a problem with circadian rhythm disruption. So many of us can relate that—if you sleep for—for kids, for toddlers, for young adults, it's even 9 to 10 hours; those of you who have a kid, you know that—the night the kid did not sleep for more than eight or nine hours, the next day you will know that there's disruption. So that's very simple: that when we don't sleep enough, we have immediate signs that something went wrong. Because when we sleep, that's when the combined action of sleep and circadian rhythm—they help detoxify our brain; literally detoxify, because many of the toxins, many of the breakdown products, byproducts that are not necessary for our brain are actually drained out during our sleep. Second thing that happens is during sleep, our brain cells or neurons, they strengthen connections between them. And then the question is why this is important: when our brain cells talk to each other and strengthen connection, then our brain can take information correctly, process it correctly, and also spit out the reaction correctly. So the reason why the kid becomes cranky is—cannot process the information coming in correctly or cannot process the, um, information that's given, and instead of smiling, starts acting out. And the same thing happens to all of us. And in fact, if we go back to a very simple thing that almost every adult experiences: that is conflict between couples, between loved ones; if you think carefully, you'll often find that at least one of the partners either did not sleep enough, I've been traveling a lot, and so it affects not only your brain health, it actually affects even your family. So that's one—second note to anyone listening with relationship issues: just note if you or your partner have slept enough. And if not, maybe park it until you're both well-rested. So exactly scientific proof. So my rule of thumb is: I never argue with my wife after 11:00 p.m. at night, because I know that this is the time when my brain is loaded with toxins, has not drained it, and I'll be making—when we say emotional, what does it mean? It means irrational, because my brain is not processing information. So he kind of has an understanding that okay, that's not a better time. Exactly. And if—and we also know that if we haven't slept enough, if I'm coming back after long travel and all that stuff, I'm also irrational. So this is a very telltale sign that you want to see whether you are circadian disruption. Just—so this is one. Second is, um, in these days, we have a lot of light. And when you're exposed to a lot of light in the evening hours, so we have two problems: one is too much light in the evening. So a lot of light in the evening, and these days even we go out and buy those very brightly lit, um, LED lights, because we want to feel more alert in the evening, we—because everybody is coming back home very tired, and they just—but still, after coming home, we have to enjoy the evening time, because the life after sunset is very different from the life before sunset. Life before sunset or life before evening is all about—for an average person who is doing a day job—is all about working, uh, making enough earning so that the person can enjoy. And life after evening is very different: we want to socialize, we want to share our thoughts, we want—want to entertain ourselves, we want to care for each other, we want to share a meal, and we want to feel energized to do that. And then we turn on all the lights to be energized to do all of this or watch TV. And then the problem is that bright light can suppress many nightly hormones, including, um, melatonin, that actually helps us to sleep. So, um, in that way, we have another circadian rhythm disruption. If you see that you cannot easily fall asleep, even though you try, even though you're tired, your hormones—your melatonin—is not high enough; it's not telling your brain that hey, it's time to sleep, rather than—it's actually telling you, maybe tired, it's okay, but I don't see any sign that night has arrived and you can sleep. So that conflict happens. So there are a lot of people that say, I'm tired, but I cannot sleep; that's another sign that your circadian rhythm disruption has happened.

Can I ask a question around that? So to interrupt, um, because you've done work around blue light and how it affects in the in the retina, and I'd love to just dig into that for people to understand exactly, and and the differences also between that blue light—junk light—and then like more warmer tone light. Like, is there an implication or a big contrast between them? Like, is there a good light versus the blue light, which we know is the junk light? But can you just break down the science a little bit: like what's happening that the light is affecting melatonin production?

Yeah, so this is where I would also bring up another thing: that light is not good or junk; it's the mistiming of light that makes it good or bad. Okay? So people always say blue light is junk light, like you said, but it's actually, uh, the evening excessive blue light is what disrupts our circadian rhythm. So coming back to—it's good that you pointed out this very important discovery from 22 years ago—let's step back and then talk about light. So, uh, if we think carefully—if you're not living right at the equator, um, for example, you are in London, and if you look up now your sunrise and sunset time, you'll see that the sunrise to sunrise time is not exactly 24 hours, because of the tilt of the planet of our planet and the rotation. So that's why it's not exactly 24 hours. So that means every day our circadian rhythm must—sleep-wake cycle—if you're not exp—means in the modern world it's different though, but our ancestors, they had to adjust their circadian rhythm every single day, because it's not 24 hours—the sun—depending on whether it's summer to winter or winter to summer transition, either the sun comes up slightly later or earlier. So then how does this sunlight or daylight signal get into the clock, and, um, for almost 75 years, starting from the 1920s, scientists knew that all the light information to our clock—circadian clock—goes exclusively through the retina, at least for humans and mice, not for birds and other animals. For humans and mice and rats, all light information that is required to reset our sleep-wake cycle clock or circadian rhythm clock goes through the retina. But here is a twist: there are many animals and there are many humans who are blind because of some genetic disease or something happened, they—or due to a—they—they're blind; they cannot see anything; they cannot read anything, and everything is dark for them. But still, they could reset their circadian rhythm just like normal people. And there was this conundrum: you need the eye. Why? People knew that they need the eye, because there are many, many, many people who went to war; they lost both the eyes, or they had cancer in both the eyes; the eyes were completely removed, and they could not reset their clock to this day-night cycle. So they would drift. So then, in 2001, three different labs, including—I was the first author in that paper—we discovered that there is a blue light-sensing protein called melanopsin. And this melanopsin protein senses the blue spectrum of light. And you might say, well, I don't see any blue light, but you—we all know that this daylight has all the seven colors, so that's why we have the rainbow colors. So daylight is actually the richest source of blue light; there is nothing else; there is nothing that we have designed so far that or any other light source that can exceed what the daylight or sunlight can produce in terms of blue light. So this blue light-sensing protein senses daylight, um, sunlight, and us to reset our clock every morning. And in the evening, all the ancestors lighted off some fire, um, and grilled something or begged something, whatever they did; there was some light coming out of this ember or fire. That firelight was mostly orange color, because there is no—there's not much blue light there. And this melanopsin protein was not sensitive to blue light—sorry, to orange light. So that's why, even though there was orange light, even though people could actually see each other, uh, sing and dance or talk stories to each other, um, that light was not very effective. And as a result, by 9:00 or 10:00, these people would get tired and go to sleep. And in fact, even these days, some of my, um, very heroic scientific colleagues who have traveled to, uh, very few parts of the world where there is no electricity—now you know you can imagine that it's not easy to access those places—they go there and then study people who have no access to light—electrical lighting; they have firelight. And they literally—they—they switch flips between 9:30 and 10:00; all of them would go to sleep. And then exactly at dawn, when there is twilight, they would all wake up, just like there's an alarm clock went all over the village; they all wake up and become active. So that used to happen. So now, with the new bright LED light that we have indoors—this LED light, particularly the white-blue-enriched LED—if you have any confusion, just walk to any grocery store or drugstore anywhere in the world; there are all blue and white LEDs. It's not a very flattering light either.

Yeah.

Yes. And that's the light that you want to avoid, because of course, in business, for example, you don't want the pharmacist in a pharmacy to fall asleep and make a mistake. So that's why it's okay to have that bright light in pharmacies and drugstores. Same thing when you go to a grocery store: two things happen; they want you to be awake and grab as many items as possible; it's good for business, and the checkout. So the point is, you don't need that kind of light in your in your bedroom, in your living room. So that's why you have to pay attention. The good news is there are two solutions: one is, instead of light switches, you can, um, install dimmers—light dimmers—so that you can dim down the light, irrespective of what light you have, you can just dim them down. Because another property of this melanopsin protein or melanopsin blue light-sensing sensor is it cannot actually sense too much of dim light. What is dim light? For example, if you're old school, um, if you had access to a 40-watt light bulb, and the equivalent will be a 40-watt equivalent LED light, and if that light is kind of in the ceiling, um, in a big room, say 3 m by 3 m or 12 ft x 12—yeah, something like that—10 ft x 10 ft, something like that. So then that 40-watt light bulb in a in that kind of room will give you what is considered dim enough light so that it doesn't activate your melanopsin as much as—but there is a caveat—but if you're sitting in there and then you have your eye—if you have your tablet or PC or laptop with full glare, that will also disrupt your circadian rhythm. So that's why it becomes important to kind of pay attention to lighting. So rule number one: don't put—put too much LED—blue LED light—in your living room or bedroom. And if you do—because I—I'll tell you why you sometimes—then instead of flipping the light switch—the old-style light switch—put a dimmer, so that in the evening you can actually dim them down. Or if you have more money, you can actually have a programmable timer that will dim down the light. So that's about controlling—purchasing the light and controlling it. Second is: we get a lot of light exposure from rectangular pieces of glowing objects, whether it's your phone, whether it's your laptop, whether it's your tablet. And fortunately, all of them have inbuilt features to what is called a night-save feature, um, so you can turn that on. So depending on what is your preference—maybe 8:00 or 9:00—they will all dim down or change their spectra to orange color light. So that's half of the story: how you should manage light in the evening. During daytime, the story is very different, because for most of us, we spend most of our time in dimly lit classrooms—for high school, college students—or in offices. You know, only when you are a top-notch executive you'll get that corner office or access to a large window. But for most—most people, they actually stuck in an interior office with very little access to windows, uh, and even though you have a bright light, you think it's bright enough—that light, in most cases, is not bright enough to fully activate your melanopsin—a blue light sensor—during daytime, so that you feel more alert, you can actually take—you are happier. So that's why during daytime, you need to be exposed to at least 30 minutes of daylight. When I say daylight, you don't have to go out and look for the sun and stare at the sun. Means even in London, in a cloudy day, you get sufficient—you get 5 to 10,000 lux of light, and 5 to 10,000 lux is a—a lot more, because in the evening, if you walk into a drugstore or grocery store, you are getting only 1,000 lux of light. So a cloudy day in London is at least 5 to 10 times brighter than your bright drugstore that you can work in.

Yeah, if it's cloudy though, do you need to increase the time? So say it's a sunny day, you want to aim for—is it just 30 minutes a day to get that exposure? And then ideally in the morning would you say? Or if it's cloudy, does it need to be an hour or two hours to be equivalent?

It kind of reaches saturation around, um, 4 to 5,000 lux. So it doesn't matter, but okay, what we feel is there is some more benefit of even super bright light, like for example, a daylight with with full sun in London will be 100 to 200,000 lux.

Wow.

And we know that there are—now there are also infrared light coming, and then there is UV light. So we have to be careful about, um, but there are also new violet light sensors—there are many new light sensors that are being discovered these days, uh, which suggest that there are other functions of light that may be going through your skin and, um, not directly related to circadian rhythm, but for other reasons, like for example, vitamin D. If you want to avoid taking a vitamin D3 pill, then of course you have to be exposed to more light. But when it comes to just regular people who are not depressed and they want to get some enough light, the morning light is better, because our executive function is much better in the first half of the day. We're already programmed to be more happier, a lot, and have the ability to take on complex tasks. And on top of that, if you actually get this blue light spike, then that helps to have that high performance for the first half of the day. When it comes to people who are feeling low, depressed, whether they are on medication or not, it doesn't matter—any bright light during the day is extremely important for their brain health. And this is something that we always have to keep in mind. I mean, we always say that well, there's so many kids who are these days going through depression—almost one in—depending on the stats, where how you look at it—one in three, um, college-going female students and one in four college-going male students may be experiencing depression. And we talk about a lot of things about social support and other stuff; we never talk about one thing: are the dorms lighted enough? Are they spending too much time in front of the computer, so that they're actually not going outdoors? So when the issue of mental health comes in, I always tell—if you want to care for somebody, just take them out for a walk in a during the day—doesn't matter whether there is bright light, dim light, cloudy day, or whatever—just take them out for a walk; they will get your company, they will get some physical activity, and they will get light. And light—daylight—is the best antidepressant; it's plentiful and free; you just have to step outside. But when you're depressed, you may not feel the urge to go outside. And that's why your best service for somebody you care for who is depressed is to take them out for a walk during the day. So this is the story about more light during the day, and for depression, most researchers agree that you have to get that daylight for at least an hour—30 minutes—not cut it; an hour is better. And if you cannot go out, then at least—if you're living with someone who is going through depression or feeling low—at least open all the curtains in the room. And if you have even extra light, as I said—LED light—this is where the LED light or the bright light comes into play: they should be in a brightly lit room with large windows and a lot of lights should be coming in, and that will help a lot.

That's powerful advice, especially coming out of the pandemic and obviously where people were spending a lot of time indoors. And I remember reading research that the average American and the average UK citizen spends up to 90% of their days indoors. So already there, that's, you know, just getting outside more often, ideally moving, ideally in nature if possible, will just totally shift so many different balances and and support the circadian rhythm as well. So that's really great advice; thank you for sharing that. Regarding sleep, you were saying, you know, timing is so important. So there's the the quantity, but then the question is: some people are like, well, I'm a night owl, um, I work really well in the evening, or you know, I wake up at 4:00 a.m.—like people have different rhythms, if you will. So how does one understand circadian rhythms when, you know, there's a couple—one goes to bed early, one goes to bed late—and they—they sort of function that way? Like, how can one think about optimizing circadian rhythms for sleep with different schedules?

Yeah, so here is a tricky question, because everybody wants to feel special; everybody wants to feel unique, uh, but now let's—let's dial back and go back to my—you know—yeah, the researchers who went to study this ancestral population who are living without light. And the question is very simple: are there also night owls and early birds among this population? The answer is no. So that means the genetic contribution or how our genes are designed to make us late night owls or early birds—it's still there; there are undeniably—there are some people who really cannot stay awake after, says, 8:00 p.m., if the sunset is happening at 6:00, for example. And they clearly—some people who cannot go to bed—they—they don't feel sleepy even up to one or two. So those people exist, but they're not as frequently found as we often think; there are one in a few hundreds or sometimes one in a few thousand. Um, so now the question is, well, why we always—help describe some of us, particularly night owls; many people say that they're night owls—they just function much better in the evening, and they're more creative, they feel more energetic in the second half of the day, etc. We don't have a clear, uh, objective way to measure that. What we have seen—this is where anecdotal data and personal experience also comes in—I was like—I used to go to bed at 3:00 in the morning, um, I used to work in the lab, and I would feel really energetic; I would come back around one or two, and then still relax a little bit or catch up on some like email or phone calls, and then go—then I realized that well, I was having five or six Diet Cokes throughout the day.

Oh my goodness.

And we know that the caffeine—means I knew that the caffeine affects a lot. So then, when I took care of my caffeine and light exposure, uh, when I do—even these days—for one month, I said, okay, so I'll—I'll not go on caffeine; I'm completely out of caffeine, and I feel like I haven't slept for a month or two. The first two or three days, of course, you have to be hydrated enough, uh, um, to avoid the caffeine withdrawal headache. And when I do that, there is no way I can stay awake beyond 10:00 at night; I become that one of those ancestral persons who used to go to sleep after the fire died at 10:00. And in my own family, I've seen my mom always complained that she could not sleep beyond before 11:00. I mean, she—she lives in India, so I call sometimes and then like, oh, I'm wide awake. And then now she's visiting me for 3 to 4 months, and then I realized that she has afternoon tea around 4:00 or 5:00 p.m., and then I said, no, you can have only tea up to 12 noon. Of course, the first one or two days she's like complaining, hey, my son is depriving me of the simple joy of life, and how can you do that? I raided you. I said, no, let's try this experiment. It went on like three, four weeks. Of course, she didn't tell me anything, but the other day I was listening to her, and then she was giving advice to her sister back in India that, hey, you know, you should stop drinking tea after 12:00; it works. I did this, and I have no problem going to bed around 10:00. So wow—this is some example that I—now, if you think about it now, all the listeners who are thinking that they're die-hard night owls, pay a few attention: one is when is your last sip of coffee, tea, and you know, Diet Coke—anything that has caffeine. The problem is, in these days, there are many drinks, many foods where we don't recognize that there is caffeine or there is—for example, dark chocolate also has elements that can keep you awake. And there are also some personal food interactions, like for example, I'm extremely sensitive to hot chocolate; means if I have hot chocolate, even four, five sips in the evening, for some reason, I cannot sleep. But is it the sugar—the sugar in it? No, it's not the sugar; it's not the sugar. So, and sometimes I, you know, I have friends who bring this German hot chocolate that has no sugar, and it's—it's very good to drink, but I know that I have to drink that in the morning. So there are some food interactions that also affect our sleep. And then the third—another one is light; we don't pay attention to light. A lot of people are exposed to light in the evening. And then the last part is sleep. So, for example, those who are night owls, they are already into a spiral, because they go to sleep very late, and for many of them, the day still starts at 8:00 or 9:00 in the morning, because they have a day job. So they're sleep-deprived for the first half of the day; they are struggling; they're drinking coffee to keep them awake; and then towards late afternoon, their sleep pressure is reduced, then they feel that they're more energetic; it's not because the circadian clock is like that; because of their sleep deprivation. So if you're really fighting off

Only 2025 blocks of light, very dim light. M. Surprisingly, these premies, premature babies, were exposed to light/dark simulation. They were released from hospital on an average 13 days earlier. Wow. Then P is work on constant light W. There's not even a single drug in this entire world that can have this much impact.

The reason why they were released 13 days earlier is because the growth accelerated. They said they met all the milestone growth, and they, the doctors, felt they are now okay; they can control their body temperature; they can be just like normal babies. And this is so powerful. There's not even a single drug anywhere in the world that's in clinical trial or anywhere that will actually accelerate the growth of a premature baby this much. So that's the power of light and darkness; that's really incredible.

Is this now standard practice? And I hope you're going to say yes. In all, not in the US, but in Mexico City, yes. You need to share this information, please. Um, you know, you can just imagine for the parents how distressing it is as well, so to get a baby, a newborn baby, home quicker than that, with 13 days, that's incredible. Wow. So this is very—because yeah, because in the US right now, on an average, one in 10 live births is actually a premature baby. One in 10. So in the US, 3.8 million babies are born, so that means 380,000 babies are born premature. MH. And I guess I don't know about the UK and EO; it may be very similar, 1 in 10 to 1 in 12 something. And that b—so that means almost every listener might know someone, might have had a premature baby. Feel free to share with people listening, with doctors in the hospitals, and have them listen to this as well. What a Game Changer! And it's not medication, and that's what I love about your work, is that it's not a prescription of "have to take a 100 supplements, and you have to do this." These are all free things that are naturally available, and it's actually going back to the way the body was developed for hundreds of thousands of years. So um, it's really beautiful.

I have one question: with the detoxification at night, is there a certain standard cycle um that happens? So um, I think with melatonin production, there's certain waves, right, when it when it happens as well, and detoxification. So is there a chance if someone goes to bed too late that they miss one of the detoxification cycles? Can you talk a bit about that?

Yeah, so this is a um really a groundbreaking discovery that happened in the last 10 years. Um, a scientist, Mik Nard, who made this discovery, that in nighttime, when we sleep, there's this thing called the glymphatic system, just like the lymphatic system in the periphery. Um, so this glymphatic system in the brain actually takes out the garbage. And as you can imagine, this is a very difficult experiment to do because people have to come to the clinic; they have to sleep; they have to be connected with different tubes, so that it's not only—you're not actually sampling blood because blood sampling is relatively easy because people can sleep; you can still put a line and draw some blood, but it's um even more complicated than a spinal tap. Like, for example, almost every woman who has had an epidural, they know how that is done. So it's similar, slightly more complicated actually. So plus you're supposed to stay asleep, right? I mean, while you are asleep. That's why—without medication, without medication, right, without medication. So that's why it's so difficult to know whether there are certain stages of sleep where this thing happens. The bottom line is, it is a very slow process, and it happens throughout our sleep. So it doesn't matter—just sleep as much, like at least 6 and a half to 7 and a half hours. And this has a huge implication, and the—this has become the biggest discovery in the sleep field in the last 20 years, I would say. Um, and we're still trying to figure out uh how this is triggered, whether there are other hormones, other processes that are uh that are involved in this.

But you brought up another important point, that is um there are many hormones that also go up during sleep, and one of them is growth hormone. And you might think that, okay, so adults, we are not growing, why do we care about growth hormone? Actually, we are kind of growing because um your body composition, like for example, all the cells I have today, they will not be with me 10 10 days down the road. Particularly my gut lining will be completely new, just like the snake puts a completely new skin. Each of us is putting a new gut lining in every 10 to 15 days. So that means we are shedding all the old cells and putting new cells. The same thing happens to our skin, to our cornea, the lining of our eye. Um, almost every cell that is exposed to outside or exposed to food and other things inside, they are um damaged and recycled, and the growth hormone plays a very important part in that rejuvenation still, and that happens only when we—and that there is a spike in growth hormone. It just spikes—big spike in the first couple of hours after we go to sleep. So then the point is, well, if you go to—if you delay your sleep time, then what happens? Suppose say I go to bed every day at 10:00, my circadian clock knows, so around 10:30 or 11, it cranks up growth hormone for the next couple of hours, and then it goes down. What happens if I go to bed at 1:00 one day? So two things happen: one is the circadian clock will try to kick in; there's a tiny bleeping of growth hormone maybe when I'm supposed to sleep around 10:30 p.m., and then after I go to bed again, there will be another spike. So that's kind of a uh sleep-driven small spike, but that will not be as big as my first spike. So the bottom line is, yes, you'll get some growth hormone if you delay your sleep, but it is not as good as if you stick to the right schedule every single day. So that's why one point about timing and duration of sleep is maintain relatively similar going-to-bed time. So if you're going to bed at 10:00, yes, go to bed plus or minus 30 minutes or so, and you'll get all the benefits. So the same time and 30 minutes plus or minus, and getting up at the same time? Would you say yeah? Getting up at around the same time will also help because if you're getting up without an alarm clock, that means your circadian clock is actually waking you up. So growth hormone—the rule of thumb is after we go to bed, in the first two hours it peaks. Melatonin, on the other hand, begins to rise 2 to 3 hours before we go to bed, so it begins a slow ramp up, and then it reaches its peak maybe 4 to 5 hours before we wake up. So literally in the middle of our sleep cycle, it peaks, and then it slowly goes down. I'll go to—we'll talk about melatonin when we talk about food.

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And I know from um speaking with some male friends that say that, you know, they're waking up at sort of that between 2:00 and 4:00 a.m., and they're like completely awake. What what's happening there?

Yeah, so there are two things that may be happening: one is um um they're not—the sleep is not deep enough, okay, and uh second is maybe they're going to bed too early, which is not happening, which most likely is not the case, okay, which is not likely the case. So um what we have—so what happens is we know that we go through this REM and non-REM sleep cycle, and then in REM sleep, this is where the rapid eye movement, where eyes are moving, and this is maybe where we're dreaming. And many of us can relate that when we usually wake up from a dream. So that means our dream sleep, this is when our sleep is very shallow, and we are more likely to wake up. And those of us who complain that we cannot—we wake up around 3:00 or 4:00, usually happens around 3:00 or 4:00; it's not within the first 3 or 4 hours of going to bed; it's after four hours of going to bed, because by the time our sleep is getting shallower and shallower, and then something internal or something external can trigger us to wake up. And so it relates to something that we call arousal threshold. What is our threshold that some disturbance will wake us up? So now when we think about arousal threshold, the only thing that we think of is, okay, so there is some noise from outside that will wake us up, but actually there are many things inside our body that will also break this arousal threshold, and we can wake up. Best example is, for example, people who have to go to the—use the bathroom; the pressure in their bladder or the um colon is telling them, "Hey, wake up now, you're going to use the bathroom." Same thing if the if the bed is warm enough, then you'll wake up; you'll feel like, okay, so the bed is too warm. So what happens? We still don't understand why uh our arousal threshold goes down as we—is, for example, a mom and the baby may be sleeping in the same bed; mom might put her hand on the baby; doesn't care; baby kicks the mom, and mom wakes up. So that's the best example of arousal threshold: it's pretty high for the baby, so she or he doesn't wake up, whereas the mom wakes up with his gentle couple of kicks. And then now the grandma will wake up if if the baby just turns on the other side of the bed, because our arousal threshold goes down with age. Um, so now how do we manage that? So what we have seen with food timing: people who avoid food for three to four hours before going to bed, so there is no food, there is no calorie, maybe only water, sparkling water, simple water. You can sell them on water; we haven't done the experiment, but the bottom line is, if there is no—no calorie, then somehow that helps to increase the arousal threshold. What we think might be happening, or reduce the internal problem that happens in our body. So for example, you might not—your body may not wake you up because maybe your bowel movement or your blood pressure will not build up. So we we haven't done why exactly this happens, but what we have seen in many people—not all—avoiding food for 3 to 4 hours before going to bed actually helps them to go through the entire night or get six to seven hours of sleep without waking up after 4 hours and tossing and turning.

Interesting. Is there any correlation with insulin levels in the blood? We haven't done any of that; it will be interesting because I know that there are a lot of people who are not type two diabetic or pre-diabetic; they're completely healthy, but they still wake up. For me, what I have seen is when I'm in a new hotel room with a new bed, uh sometimes certain hotel brands, their beds actually warm up, so I wake up around 4:00 on a warm bed. My rule of thumb is when I'm booking a hotel room, I always ask for two queen beds so that I can just go to sleep. That's a good hack for people who travel a lot. That's a great tip. Thank you for that one. And there's obviously cooling devices, um but you cannot carry all these devices, so roll over or go to the edge exactly. Okay, wonderful. Thank you for clarifying that.

Let's look at nutrition and time-restricted eating, AKA intermittent fasting. Um, this has gotten a lot of publicity; a lot of—a lot of people have tried different versions of it, but before we sort of dig in, can you explain sort of generally what the concept is around time-restricted eating um and why it's so important?

Yeah, so for—as I mentioned, uh we believed for a very long time, we still believe that the light is the biggest uh time giver uh in training stimulus that entrains or synchronizes our internal clock with the outside world, and light goes only through the eyes. So that's why light is so important. But over the last 23 years, starting from 2000, um people did some simple experiments saying, "Well, if light is important, and what is about food?" The reason is um in our liver, gut, and all these digestive and other metabolic tissues, there are many genes, many enzymes that are involved in digesting food, absorbing nutrition, converting that nutrition to energy, or converting that nutrition to various chemicals that are essential for our body. All of these things uh actually turn on and off at different times. So that means there is a circadian rhythm to that. So that means in the morning when you wake up, the clock in our pancreas is cranked up, so that for the first half of the day we can actually eat um carbohydrates without too much spiking our glucose; the glucose, blood glucose, will come down. So all these things happen. So then the curiosity was, "Well, are this all driven by the brain clock that's tied to the light, or there is some connection with the food?" And many labs, including my lab, we figured out that no, actually food—when animals eat, because all these experiments have to be done first in animals, lab rats and lab mice—when mice eat, particularly after several hours of fasting, is a very powerful timing cue to tell all this peri—we call it peripheral organ because they're outside the brain—gut, liver, etc., heart—they actually track when this mice eat, and the clock, the timing, the counting of time, you can say, kind of starts from there. So that means suppose say we feed mice every day at 6:00 p.m., because mice are nocturnal, they're night active, they prefer to eat at night. So every day if we feed mice at 6:00 p.m., then the body's metabolism, circadian clock, everything is tuned so that starting from say 4:00 p.m. onwards, their digestive juice and everything will accumulate, and then the the body is primed to digest that food. So 6:00—6:00 p.m., we give food, bam, there, everything is ready, so they can process that food pretty well. And if we give that food, for example, one day, instead of giving at 6:00 p.m., if we go to say 10:00 p.m. at night, then all these preparations had happened, but then the food didn't show up, and it's almost like inviting somebody for dinner; you have prepared everything, and no show; the guest is 2 hours late. What happens? If food is still and cold, and you're not that excited; you still like to attend your guest, but it's not as good as you expected. The same thing happens when you miss time; you have been—you have been so habituated; your clock is so habituated to digesting, assimilating food so well, and when the food doesn't appear on time, it's delayed, then the digestion, all these processes happen, but not as efficiently as it would have been. The same thing might happen if the food shows up earlier; it may not get digested; it will just sit there for a few hours before it's well digested. So that's the—that's what we found, that the when food appears, and if the food appears at the same time every single day or most of the days, then that triggers all the circadian rhythm, so that the body is prepared to digest that food. So now um, so this is one concept. The second concept is, okay, so the food has to be eaten after breaking a fast; how long that fast should be, right? So this is where all the argument comes, question like, "What is fast? How long is it a fast?" So now we got to go back and think of—not in mice, because mice digest food much faster than we do, but in humans, for example. So if I finish my dinner say at 6:00 p.m., have a good healthy dinner, or whatever I ate at 6:00 p.m., my mouth stopped eating, so from M—for my mouth, the fasting might have started, but then the—actually went to my stomach, true, yeah, and then it will stay in my stomach being digested for the next 5 hours. And so for the next 5 hours, my stomach is not getting rest; it's actually not fasting; it's digesting food. And then after 5 hours, it will leave the stomach and go to the intestine where the nutrition absorption will happen. So that means from 6:00 p.m. till 11:00 p.m., mhm although I'm not eating, my stomach still has food, and it's still absorbing food; it's not fasting. And then if we think about our gut lining and the stomach lining has to be repaired, so suppose say I went to bed at 10:00 or 11:00, my growth hormone will spike around midnight, and that's when it will tell the repair crew to come and re-relay or repair the gut lining. So that's when all the repair is happening, and that process is not just instantaneous. Those of you who have seen how the um, you know, highways are repaired, it takes time, night. So you can imagine that that's another 6 to 7 hours when this repair happens. So now you can imagine that, okay, so 5 hours, although my mouth started fasting, my gut is not fasting, so there's still 5 hours of digestion, and then you are 6 to 7 hours, at least 7—7 hours when um the repair has to happen. But I'm saying that the stomach stopped its digestion, but the small intestine and large intestine, they still continue absorbing, so there is still work going on. So that's why the actual fasting, or being withdrawn from actively eating food, when it is at least 12 hours, then we know that okay, so the body went through the daily cycle of absorbing nutrition, repairing the gastrointestinal tract, M, and then for the preparation for the next round of food. As I said, the—again, all the digestive juices have to be prepared and kept ready, so that's another few hours. So similar—so if you add this up, for humans, at least 13 to 14 hours of overnight fast is what is needed for this cycle to repeat again in a healthy way, because you can eat; nobody is stopping you from eating, but then two things happen, yeah; you cannot digest, and also you cannot repair. So so this is how the concept of time-restricted eating came, because uh we thought it's—when it comes to nutrition, people always talked with very strong foundation of scientific foundation that the number of calories we eat is—is important; of course that is important, because I just can't go and eat 4,000 kilocalories and then say why I'm getting fat. I know; second, number of calories do matter, and second is the quality of nutrition also matters; I can't just go and eat ice cream only and then say complain why my blood sugar is going up. So those two things matter, but the third thing that we found is timing is very important, because particularly how long we fast and when we started this concept, because it started in my lab 12 years ago, in 2012, and I remember struggling with the title of the manuscript because this experiment was done in mice, and the experiment was very simple: we took two groups of mice, identical, M, same age, same gender, same—born to the same similar parents, in the same room, had the same gut microbiome, at the same food, and the same number of calories every day. The only difference was the first group ate whenever they wanted; there was no barrier, and the second group, they were allowed to eat only for 8 hours in the first experiment, and within 8 hours they ate the same number of calories as the first group. So there's no difference in number of calories, no difference in quality of food; both groups got actually high-fat, high-sucrose, really unhealthy food, and to our surprise, the second group, which time-restricted—because they're eating only for 8 hours, the consistent 8 hours, we didn't move that 8 hours—they're completely prevented from obesity, diabetes, liver disease, um heart disease, and they had way much more endurance. That was the surprising fact, that it's not that they were fasting and they feeling really crappy about life; they were actually more active; they're full of energy; they could stay on the treadmill twice longer than the—at least, mhm. So then we, okay, so what should we—what should the title of the manuscript should be? And then we said time-restricted eating, because we're not changing quality of calories, not changing the quantity of calories, we are just changing the time; we're restricting the time; no calorie restriction. And we did not use the word "fast" because there are a lot of people who actually need to fast, but then they don't want to fast because they hear "starvation," they hear "fast," yeah, a very bad four-letter f-word for them, so they really don't. So that's one aspect, and then the other aspect is, well, we—fasting is very ill-defined, because for example, sometimes people ask me, "Hey, do you fast?" I say, "Yes, I fast between meals," true. Whenever I'm not eating, I'm fasting, yeah, exactly. Yeah, so it's very difficult to define that fast. So that's why we said, okay, so we'll just do this time eating, and I just said—this became—this fell under the umbrella term which is intermittent fasting, because before this experiment, intermittent fasting essentially meant a few things: one, you can fast every other day, which is called every-other-day feeding in scientific literature; it can—it could also mean fasting for two days in a week or one day in a week; it also meant reducing calories only for five or six days in a month or two months. And when this time-restricted eating came, it was kind of a mouthful, so then people said this. So these days, when you say intermittent fasting, most people will think, "Yes, you're doing 8 hours of eating, 14 hours of—16 hours of fast," yeah. Um, so we have done this experiment in many different ways. Coming back to your other question, related question, different forms of intermittent fasting—in mice, we can do—we cannot go below 8 hours because when we go below 8 hours, then mice eat less, and we know that reducing calories or calorie restriction has many benefits, so we cannot figure out whether it's the benefits are due to reducing calories or eating within a set window. So these experiments are not doable in mice. In humans, people have done these experiments; they ask people to eat within 4 hours or 6 hours, and as expected, they also reduce their total caloric intake; they eat less, and of course there is also benefit, but we cannot clearly say whether the benefit is from reducing calorie or eating within a very short period, 4 hours or 6 hours. MH. There are some studies where it's very well controlled; healthy human volunteers are either asked to eat everything within 12 hours, that's the control, or 6 hours; this is a very short window, but you know, this is an experiment; we we are not asking people to do this every single day, mhm, and in those experiments, which came out of um Courtney Peterson's group at University of—who is at University of Alabama Birmingham now—they found that even though the second group that ate within six hours ate the same number of calories, they still benefited in many different ways, including improvement in blood sugar control, blood pressure control, and although these people are not too sick to begin with, so they were little over it, but not incremental benefits, yeah, so the benefits are there. So that's why we said the time-restricted eating is still a valid approach to um to a nutrition. One can combine it with counting calories and paying attention to quality of nutrition, quality, yeah, eating whole foods, and—and because I'm not—I'm not a big calorie-counting fan, but I think it's quality of—like whole foods, and sort of the periphery of the supermarket is generally a good rule of thumb; avoid those little aisles, right? I mean, I guess the biggest challenge in nutrition—there are two big challenges: one is a control for time; like we almost think that our—our body, our human body, is like a machine or a car; people always give that similarity, and you know, machines and cars, they will run whatever time it is, um and you can fill up your gas tank in a car any time of the day; it doesn't matter, but we are not like that, mhm. The difference is you can drive your car whatever time you want or whatever you do to it, but you have to take the car to the repair shop, to the machine, or to the—for regular maintenance; somebody else has to service your car, whereas our human body is designed that if the body can service itself, because that's what happens with circadian rhythm, that period of fasting, that period of sleeping, and aligning fasting with sleeping, that's the best repair mechanism, and nothing can—there is no repair—no, literally no—there is no drug, there is no procedure in hospital that can actually substitute for that repair process; that's so valuable. So that's one aspect: we are not paying attention to timing of nutrition; we feel like we can eat anytime. And then the second thing is beyond C—the problem is we don't know how to prepare a meal; we don't—we don't know how to cook. So then when we don't know how to cook, then the quality of nutrition—we just depend on what is written on the food label, and everything goes south. So with time-restricted eating, what we're finding is very interesting in many studies; what people are finding: if they're only told to eat within say 8 hours or 10 hours—most of our studies we involve 10 hours because what we found is for average people, 10 hours is a good target—of course there are some who really want to optimize, they into biohacking and other stuff, they can do 6 hours, they can do 8 hours—but for most people it's 10 hours, what we find is when people go through 14 to 16 hours of fasting overnight, next day when they're eating, typically breakfast is the healthiest food, a meal of the day, for a lot of us, if we eat breakfast at home, because we have complete control over what we're eating and how much we're eating. So what we find is people eat a healthier breakfast, and since they eat a bigger breakfast—and breakfast doesn't mean morning meal—after the 14 hours of fast or something, yeah—then they don't snack until lunch, so the number of snacking also reduces, and most of our snacks in modern days is really high sugary treats, so that reduces, so it improves food quality, and since the kitchen closes, are they stop eating at 6:00, 7:00, or 8:00—if you think about it, the almost all of our addictions, whether it's alcohol or whether any sweet treat, whatever bad food we are addicted to, that happens typically late at night. So people reduce their alcohol intake, and this is—we're finding in many different studies, and they also reduce their late-night ice cream intake, and in fact, in my house we have seen this; me, I used to—the number of beer bottles, of—the wine bottles we used to go through before and after has dramatically changed now. Amazing. So so in a way, time-restricted eating or intermittent fasting—all the people—people pay attention to timing; it indirectly improves their nutrition quality and also reduces some calories.

And I'm curious, a few different points I want to touch on: um, what is the minimum time you would recommend? So is it that 14 hours that you were saying in order to have that cycle, those 13, 14 hours overnight? And then differences between men and women, particularly around hormones, for—for women?

Yeah, this is a tricky question because what I believe is anyone from 10 years old to 100 years old can at least fast for 12 hours, yeah, whether we're healthy, unhealthy. And most listeners will think that, "Huh, I—I'm already doing that," but actually that's not true, because when we objectively measured when people are eating—where people have to log every single thing they are putting in their mouth, everything from water to all calorie-dense diets, and of course we figured out which—in—we discounted water and uh some black coffee and other stuff—what we found is when we go from consistency, like within—within 10 days, are you really sticking to that 12 hours or not? We found less than 10% of people consistently eat all their calories within that 12-hour window, less than 10%. We we were surprised, and these are not shift workers; these are just regular people, all staying home, retired, etc. So that means at least once or twice a week we are eating either very late at night or we are waking up very early to go somewhere. For example, when I—when I travel, I get up early, although I'm not eating; when I go to the airport, I see 5:30 or 6:00 in the morning, there's a long line in front of all these food places. So this is another example; you're waking up. So the point is, are you consistent within that? And that's why I believe anyone from 10 years old to 100 years old can and should eat within 12 hours if they're healthy; it's almost like brushing your teeth every day, right? And then the question is, if you want to improve your health, then the question is how far away you are from optimal health. So for example, if all your blood pressure, blood sugar, blood cholesterol are perfectly normal, you don't have any autoimmune disease, you don't have any joint problem, nothing; you're mentally functional; you're sleeping 6, 7 hours, yeah, and you're eating all healthy food, you have no problem, nothing whatsoever, then yeah, you can eat within say 10 hours, or occasionally you can go to 12 hours—it's not a big deal, and you might see—then the question is what improvement I will see. And this is where personally, for example, I—I my target was to hit the age of 50 without being on any medication for cholesterol, sugar, and and blood pressure, and I achieved that, but then you know, once in a while I would get acid reflux, um heartburn. And when I eat within 10 hours or 12 hours within that window, I don't have any heartburn or reflux. So that means I'm fully productive; I'm not worrying about my—my gut health. And when I eat within this 8 to 10 hours, then obviously I'm also finishing my meal 3 to 4 hours before going to bed, MH, so that means I used to wake up at 4:00, just like you mentioned, and when I stop eating 3 to 4 hours before going to bed, I sleep continuously for 6 to 7 hours at least. And uh so this is another example where if you're healthy, you can still do it because it's good for your sleep, and then next day you're feeling more energetic, and your executive function for the first half of the day goes up. Now coming to people who have blood pressure, blood sugar, or blood cholesterol, whether or not they're on medication or not, this is where it becomes a little tricky because you don't want to fast too much. So for example, 8 hours of eating, 16 hours of fast, depending on your blood sugar, how it fluctuates, we cannot say. So this is where you have to consult with your doctor, but if it is blood pressure or blood cholesterol, maybe 8 to 10 hours of eating and the rest fasting might help you. Uh, in fact, almost all time-restricted eating studies have shown improvement in blood pressure, whether the person was taking any blood pressure medication or not. And for cholesterol, it takes a little bit longer, and also diet quality has a huge impact on blood cholesterol, so this is where people have to control. Now when it comes to weight loss, because everybody wants to lose a little bit of weight, which is understandable, because 70 plus percent of people in the western world, and now even in many other countries—that percentage is increasing—have some extra weight, and this is where it becomes a little tricky because do you want to do 6 hours eating or 8 hours eating? And then if you—once you lose the weight that you want, then should you stick to it? And then how much weight do you lose? When I—for example, a couple of weeks ago I was in Chicago, in a completely non-work-related convention, nothing; I—I was not expecting anybody to come up and even recognize me, and then somebody came up to me and recognized me and said, "Oh, I should thank you because I lost 55 pounds"—all that stuff, like 20 plus kilos. And then there was another guy; he came and said, "Oh, I also lost 14 pounds." And then the first guy was telling the last guy, "Look, I lost 55, and yours is nothing." He said, "Well, it depends on where you started." Yeah, it's all relative. Exactly; it's all relative. So and then there was another third person who came and said, "You know, I was doing everything; I'm already healthy, but I tried what you said before on one of your podcasts, and now I'm sleeping better, and that gives me a lot of energy." He's retired; he said, "Now I'm involved in many non-government organization volunteers," so all these bring the joy of life because I'm more energetic. So here is an example of three different people with completely three different kinds of outcomes, yeah: one who says he lost a lot of weight, but he did not have any other problem; although he was obese, he actually had—surprisingly—he had completely normal cholesterol and everything; the second one who lost 14 pounds was on blood sugar medication, blood pressure medication, and also on statin, and now he's completely off of all three; wow; and of course he said that, "Well, it helped me also to—pay attention to my nutrition," because he's now eating better nutrition; and then the third one who is completely healthy is talking about his health. So this is all males. So now coming back to

To getting the cancer itself, even though they were transplanted, even though tumors are placed inside the mammary fat. B. And second, if the tumor is placed and the tumor doesn't grow as aggressively as in the animals that are fed randomly, that it at any time. So, at least for postmenopausal women or premenopausal women at high risk for breast cancer risk, uh, this is important that it reduces the risk for cancer. And we do see, um, you know, cancer survivor safety is a very big thing because in the US alone there are 15 million people who have survived cancer. And those who survived cancer because of the chemo, other treatment, they there is a lot of stress on their system. Many of them they struggle with their heart issues; some of them struggle with their glucose control and mood issues. And this is one thing that we would like to do because we want to see whether cancer survivors can stick to time-restricted eating and can reduce the risk for heart disease and other diseases. Um, the epidemiological studies show that yes, there are benefits, but there has to be intervention studies to put into practice. This is really, really powerful, and I just want to summarize for women because I had been looking at this and I had tried, um, I was like those teenagers or young women you were mentioning; like I've tried a whole skew of different things as well. And depending on which phase of the month it was, I found that it was either energizing me or not, but I was literally reducing it down to sort of eating windows of six hours a day, um, or sometimes even less at times, but sustaining that. But I think one major point you made is to look at two things: one is exercise. So I, I like to be active; I do a lot of exercise and movement during the day. Um, so just to, if there's more exercise to, make sure that the healthy calories being consumed match that. So is that, is that the point? So would you not see any risk in women doing, you know, six-hour eating windows but just ensuring that the caloric load, basically the of healthy calories consumed, is enough to match what is needed for the body to, um, function on a daily basis?

It's really hard to make that call because I know being an experimentor, we really don't know what will happen because there is immediate, what's the window? Yeah, no, we always think about the immediate impact; we don't think about the long-term impact, because particularly this is, this is a problem that's very close to my heart because we are doing now studies on what is called relative energy deficit in sports because nearly 42% of athletes, both male and female, they are in an energy deficit. That means they're eating less than how much their body is spending, and in these cases, we, um, this is so widespread, but still there is no animal model because you cannot sample their blood, their organs, etc. So what we're doing that, and we are finding that there is so much impact of this, there's so much adverse impact of relative energy deficit because it compromises your bone health, and you may not see how it is compromised right now because you may be very strong, you may be, you may not be hitting a wall or falling, but you know, 5 years or 10 years down the road, if you have really low bone mineral density, that can hit you there, or if you have microfractures. So that's one thing, and another thing we are also finding in animal models: these threads affect different organs. You, in females, it affects the uterus; in males, it affects a lot the kidney, and um, the impact is all over the place, like in the brain it affects the depression and anxiety center of the brain. So that's why I'm really hesitant to say whether somebody should go eat within 6 hours. The problem is if you're eating within 6 hours, there is a good chance that one or two days in a week you may not have the time or you may not have access to good nutrition to eat enough, and that's when you might lose your performance one or two days, then you'll blame, and you know you are on the knife's edge at that point. Okay, you make a little bit of a mistake, so that's why I'm very hesitant to say one should do six hours. Yeah, I mean, that's why 8 to 10 hours is a good rule of thumb. Yeah, okay. No, but I, I think that's good because I'd love to ask you like, uh, before we, we finish up, for optimizing longevity and from the research you've done and what you've seen as well, what would be, and I know people are different, etc., but sort of for a general healthy person, not taking medication or either, or what would be your, um, protocol that you would say from eating and and sleep.

Yeah, there are six um points we have to keep in mind. Uh, number one: try to maintain a regular time to go to bed and be in bed for 8 hours so that you can get 6 to 7 or 7 and a half hours of sleep. MH. Um, because when we sleep well, then the brain and body actually repairs itself much better, reset, rejuvenates for the next day way much better. So that's number one. Number two: after waking up, try to wait for at least an hour or ideally two hours before your first meal of the day, first calorie of the day, because that's when your sleep hormone melatonin is slowly coming down and your stress hormone spikes reaches its highest level within an hour of waking up. M, and you don't want to eat when your stress hormones are pretty high and your sleep hormone is still mildly elevated because your body cannot process nutrition pretty well. So that's number two. MH. Number three is try to have breaking the fast or breakfast at a consistent time. MH. So it's breakfast is not the first meal that you eat right after waking up; it's actually the meal that you are eating after at least 12 to 14 hours of fasting. So try to eat the first meal at a consistent time and then eat all of your rest of the calories within the next 8, 9, 10, maximum 12 hours, never beyond 12 hours, and then the last meal should be. So that's the number three. So let's stop. Fourth one is try to step outside during the day, ideally the first half if you can, to get at least 30 minutes of daylight or sunlight. Mhm. If you cannot, it's okay; you can get any time 30 minutes of daylight; it's good enough for the average person. And then the fifth one will be exercise. Those, um, any exercise is better than no exercise, no doubt about that, but if you want to get the best out of your exercise and reduce the risk for injury, then afternoon exercise is much better than exercise late at night. Early morning afternoon exercise has been shown to significantly reduce blood pressure, reduce blood sugar, um, then the same exercise in the morning. And since the body is warmer and the joints are more flexible, there is reduced risk for injury. That's why afternoon exercises. I thought first thing in the morning is beneficial in terms of blood flow to the brain for BDNF benefits. Well, the thing is, uh, we, if you look at the activity of ancestral populations, their morning activity. MH. They have a spike in afternoon activity; there is no doubt about that, but the morning activity is much higher than the average person's activity spike in the modern world. So, so what I say is in the morning, if you really want to be, if when people have plenty of time, at least go outside, go for a walk for 10 or 15 minutes, and this is very important, particularly for college students and high school students because you know, a lot of them they don't, they haven't had enough sleep. So for them, really going out in the morning and getting that morning light, and you know, they're healthy, they can run, and they can do some activity that's way much better. I'm talking about for the regular folks who are, you know, beyond 50, and then they, they have a little bit of time, they cannot go every day. Okay. Yeah. So then number six. Yeah, what number six? MH. Number six is your last meal should be at least 3 hours, ideally 4 hours before going to bed, and um, in this last three hours before going to bed, you should also dim down your light, so no bright light and no food three hours, and ideally meditate or do something, read a book, right? Yeah, calm the nervous system. So these are the, these are the six uh simple foundations for circadian rhythm, and I guess almost everybody will benefit one way or the other by following this. Yeah, and for people listening, I'll, I'll put a summary together with this podcast episode of Dr. Sachin Su's ultimate longevity circadian rhythm optimization. Um, before we finish up, I, I'd like to ask a question: if you could live to 150 years old with excellent health, how would you spend it? 150? Yeah. So, uh, the idea is very simple: in every 10 years you have to reinvent yourself, do something new, like Madonna. Yeah, I mean, she's actually, she's, she's an amazing person; people love her or hate her, but that's what the sign of successful people are. Yeah, yeah, very polarizing. Um, no, that's, that's true in everybody's life, like, um, we have to reinvent ourselves; we have to do something new. And when I look at my own personal professional career, the first 10 years was light, the second 10 years was time-restricting, um, and then now I'm really interested in this exercise and the balance between exercise and nutrition, how the optimal balance can drive a lot of performance, and then the suboptimal balance can feel good now but can have adverse effects. So, similarly, every 10 years come up with a new idea. I mean, the world is so big; there are so many interests. Just live full of life. Yeah, stay curious. I love it. Where can people learn more about what you're up to, um, and what would you like to share with people, any website, um, donations, um, for your lab, um, social media, etc.?

Yeah, so many of my research that, um, actually made headlines, for example, the discovery of blue light-sensing protein and then time-restricting, many of these were not funded by federal grants that typically funds research, but those are mostly funded by philanthropy foundations, etc. So that's why when individuals, whether it's, um, small donations or big donations, doesn't matter, when they, uh, donate to my lab, uh, they can donate by panda.so.edu/giving, and I guess, uh, or donate, I guess you can put it on the show notes, um, then that helps us to go try risky, high-risk, high-impact kind of, uh, experiments. And so that helps, even small donations help in the sense we have a lot of young trainees, uh, who could have gotten a much better job, you know, selling products, um, writing codes for big tech companies, but they decided to do science, and these donations help them to go to conferences, meetings, present their work, and sometimes they have young children; they can find daycare for their children when they're going and doing, going to conferences. I remember there was a nice call for funding by Jonas Salk because I, you know, I work in the Salk Institute. Jonas Salk, who made the polio vaccine, and she had this call, she said, well, you, this was in the '70s, right? So things are very cheap, said your $1 donation will buy a lab coat for the researcher, and your $1000 donation will give the researcher all the reagents they need for one [Laughter] week. Well, prices have gone up a little bit since then as well. We, so that's, and then second is I, I'm, um, I try to be active on Twitter, so my Twitter handle is @SainPanda, and then also I try to be active on Instagram @SainPanda. So those are the two, and then we do have two different entities: one is MyCircadian.org, that's a research app people can download and sign up and share their own, um, habits with us, so that, that's completely researched, so we don't sell any information; every all the data is anonymized. And then I also have a commercial app called Get On Time Health, and this is for people to pay a little subscription and then track how they are following their circadian rhythm. So those are some of the resources people can have access to. Perfect. And we'll link everything in the show notes. Sain, do you have any final ask, recommendation, or any parting thoughts or message for my audience today? I think people always think of longevity as, as you said, living up to 150 years or something like that, but in my mind, longevity starts every single day. Every single day we should feel like we're at our peak performance; we beat our yesterday's performance, something like that. To be healthy in single every single day is what matters. And those of you who are not thinking that, why should you live up to 150 years or 100 years, or why, why should you not enjoy your life now by engaging in unhealthy habits? You know, being unhealthy is very expensive; it's not easy; you might think it's easy, but it's very expensive for you, as your medical bill; it's also socially, emotionally very expensive and taxing for all the loved ones around you because when we fall sick, we become a burden on our loved ones. And the best thing we can give to our loved ones, whether it's our children or spouse, is to give them a worry-free day, so that they are not worrying about my health, my disease, my doctor's appointment, etc. So that's the, that should be the drive to live healthy. Yeah, and arguably if you're living healthy today, you have more energy, you feel more vibrant, and you're actually living better and having more fun too. So, yeah, on that note, thank you so much. I, I know we've gone on for quite a while; I just saw the time. Thank you so much for your time today; it's been such a pleasure to have you on and, and sharing your wonderful work. Thank you so much. Thank you, and have a perfect circadian day.