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Katie: Hello and welcome to “The Wellness Mama Podcast.” I’m Katie from wellnessmama.com and wellnesse.com. That’s wellness with an E on the end. And this episode is a long-anticipated one for me personally because I’m here with a researcher whose work I have admired for a very long time. And who I have alerts so when he publishes new data, I go read it immediately. I’m here with Dr. Satchin Panda. You might have heard that name before. He’s a professor at the Salk Institute in California. And his lab studies specifically how circadian rhythm and metabolism is an integral part of metabolic health and longevity.
In his preclinical animal models, he discovered that consuming all calories within a consistent 8-ish to 12-hour window, which is called time-restricted feeding, can sustain daily rhythms and anabolic and catabolic metabolism. And the reason that’s important is that that regulation of metabolism can prevent or even, they’re finding, reverse chronic diseases, and increase lifespan without reduction in actual calories, just a reduction in the eating window.
He’s also the developer of an app called myCircadianClock, which we talk about in this episode, as a tool to figure out your own eating window, and kind of map your own patterns, and it has some logic built in that really helps with that. But he goes through some key takeaways as far as how levers like light, food, and movement can really influence your circadian clock to a pretty extreme degree. In fact, in the mice studies, they found that when mice ate within a shorter window, they had a 28% lower body mass, and a 70% lower fat mass without actually consuming fewer calories. They also had more energy and more coordination.
This is important because this is not the same as fasting. You’re not actually depriving your body of calories, or nutrients, you’re just typically eating in, the sweet spot seems to be, an eight-hour window. So we go deep on that topic. We talk about light signaling and the best way to integrate your light patterns and use light to your advantage. And then when it comes to food, the things that start the circadian clock when it comes to food and stop it, and some solid reasons why you might wanna stop eating a few hours before bedtime, even as much as four or five hours especially if you’re trying to lose weight or reverse factors of metabolic syndrome.
He gives a whole lot of practical tips in this episode. It was such an honor to talk to him. I was already familiar with his work but this episode was a very concise and practical summary of so much of his research with a lot of actionable tools, and he goes into the data of just how impactful they can be. So I know that you will learn a lot from this episode. I certainly did. And without further ado, let’s join Dr. Satchin Panda. Dr. Satchin Panda, welcome to the podcast.
Dr. Panda: I’m glad to be here.
Katie: I’m very excited to get to talk to you. I’ve followed your work for a long time, and I’m so excited to get to go deeper on some of these topics with you today. I know your work touches on many different areas. I think to give context for people listening who may not be familiar with some parts of it, I’d love to start broad. So, can you walk us through kind of the general idea of circadian clocks and why they’re so important?
Dr. Panda: Yeah. So, circadian clock literally means near 24 hours clock. And to make it very simple, these are the programs that are inbuilt in our body to keep us healthy in every hour of the 24 hours day. So, that means these circadian clocks, they anticipate when you’re supposed to wake up. And when you wake up, they prepare your body. They anticipate when you’re supposed to eat breakfast and keep your body prepared to digest and assimilate nutrient. Similarly, they also have optimum timing for your exercise, for sleep, for winding down. Almost every hormone, every brain chemical, every digestive juice, you know, gut, even the gut microbiome, and every single gene is programmed to turn on and off at different time of the day to keep us fit, physically, intellectually, and emotionally, in every hour of the day, because we know that we are not the same person between the middle of the day and middle of the night. We need different emotional state, intellectual state, and physical state at different times. And that’s the job of the circadian clock, to prepare a body, brain, and mind, for different task at different time of the day.
Katie: And another term I would just like to define now that I think might be a new one for some people listening, and I might butcher the pronunciation because I’ve only read it, the suprachiasmatic nucleus. I don’t know if I said that right, but can you explain what that is and how it comes into play?
Dr. Panda: Yeah. So, the way our internal clock is organized is just like there is an atomic clock that keeps track of all the clocks in the world. Similarly, there is a master clock that sits at the base of our brain. And this is a very tiny part of the brain. It’s only the size of a pinhead, you can say. And this sits right above the optic chiasma. So, many of you might know that your right eye sends information to your left brain and the left eye sends information to the right brain. And the way that happens is the wiring from the eyes crisscross at the base of the brain. So, that’s why it’s called…the part of the brain that sits above the optic chiasma is called suprachiasmatic nucleus. And scientists actually came across it kind of accidentally, because in ’70s when they were trying to look at what is this clock, some scientists accidentally damaged this part of the brain in some rats, and they found that when this very tiny part of the brain is damaged, then the rats could not go to sleep and wake up at the predetermined time. They’re night active. They sleep during the daytime.
And when the SCN was damaged they would sleep for one or two hours, wake up and again sleep for one or two hours. So, that’s people figured out that this part of the brain is super important. And later on, what we’re finding is many patients who have dementia, Alzheimer’s disease, and we know that those who are taking care of your aging parents, who have dementia or Alzheimer’s disease, they know that these patients don’t have a regular sleep-wake cycle. And there, in those patients, the suprachiasmatic nucleus is also damaged. So, that’s how we know that this part of the brain is very important for keeping timing, keeping the master timing. But over the last 20 years, we have also learned that every cell in our body has its own clock. Just like I told you there is an atomic clock, but at the same time, we need clocks in our houses. You might need a clock in your kitchen, a clock in your living room, and some people even have clocks in their bathroom and bedroom, everywhere. So, similarly, every cell in our body has its own clock in addition to this master clock.
Katie: And so understanding this master circadian clock a little bit better. It seems like there are a lot of things that can influence that clock, and also because of that, we can use a lot of these tools to our advantage. And I know a lot of your work centers around some of these things. But can you walk us through some of the factors that influence that circadian clock the most?
Dr. Panda: Yeah. So, those of you who have lived in northern latitudes, you know that between winter and summer, the daylight changes, and our sleep pattern also slightly changes. And if you’re living in the wild…of course, now, no one is living in the wild, but our ancestors lived. In fact, out of our 200,000 years of history on this planet, only in the last 150 years we have electricity. But before that, our body is designed to track when the day breaks and when the day ends. And the way this master clock is designed to do that is there are special light sensors in our eye. These light sensors are not required to read “The New York Times” headline or read a book, but these light sensors just sense how much blue light is there. And then they send that information to the master clock saying whether it’s day or night. And why blue light? Because sunlight is the richest source of blue light. And that’s why we are designed to track when sun comes up and when the sun goes down.
So, now, the question is, how much of light is good in training or synchronizing our brain clock, our body clock to the outside world? And almost 20 years ago, we and two other labs, we discovered that this blue light sensor is not that sensitive to light. Like, for example, in the middle of the night, if you’re waking up to go to the bathroom, or if you’re spending a night outside camping, there is a lot of lightning or moonlight. It’s not going to screw up the circadian clock because that light is not enough. But if you are sitting next to a bright window, then you get around 1,000 lux of light. And having that light level for half an hour to an hour is good enough to synchronize our brain clock to the outside world. So, how can we use this information? For example, in a cloudy day anywhere in the world, there’s still 5,000 lux of light, whereas if you are sitting in a dark room, or in a room where all the curtains are drawn, even in the middle of the day, you might have only 100 to 200 lux of light, very low. You may be able to read, but that’s not enough to actually turn your clock.
So, that’s why it’s very important to get some daylight or go outside. And that bright light will turn our clock. And we are also learning that the same bright light, the same mechanism, also reduces depression and uplifts our mood. And why this is important is, as many of you know, if you’re a new mom, you’re sleep-deprived at night taking care of the baby. And then during daytime, you may be indoor most of the time trying to catch up with sleep or taking care of the baby. It’s a 24-hour job. And in your subconscious mind, you may be thinking that you are getting enough light, but unless you go outdoor or unless you have a large window and you’re spending a good chunk of your time indoors next to the large window, we actually don’t get enough light.
So that’s why it’s likely that some aspects of postpartum depression that many new moms experience, that may be partly due to lack of bright light during daytime. And that’s why it’s very important to pay attention to how much light you’re getting. And the simple formula would be, as soon as you wake up, it’s much better to go draw up all the…sorry, open your windows or open the curtains and get enough light. And if you can, even if you have a new baby, maybe after a couple of months, it’s also a good idea to go outside with the baby and get some bright light.
So, that’s one aspect of the story. And then the other aspect is in the evening, what happens? Because a lot of us are now changing light bulbs because there is a lot of promotion to get bright blue LED light at home. And we go and see those cells and we bring those 6-pack, 12 packs light bulb and change our light. But if you look carefully, there are at least two different types of light bulbs. One that look really uplifting blue, bright blue, bluish-white LEDs, and they are rich in blue light. And those lights are also super bright, so they can be up to 1,000 lux. If you have two or three of them in your bathroom, that’s almost 1,000 lux. And then there is another variety, which is almost like candlelight orange color, which is a little bit dimmer. And people might think, “Hey, I’m paying so much, why should I get a dim light?” But actually, it’s good to buy that little orange color dim LED light to put in your bedroom or in your living room, because we should avoid blue light in the evening to get a good night sleep.
Another thing is, if you’re going outside to the drugstore or the grocery store, and, you know, you have a whole day of busy life, and in the evening, you may be going out to the drugstore, or if your kid is doing some activity, you may be taking a break to run to the grocery store or drugstore. But most of the drug stores and grocery stores, so even Walmart and many department stores now have this bright blue LED which is almost like you are stepping outdoor in a cloudy day outside. And that’s why I don’t be surprised if you come back from the drugstore or grocery store and if you’re feeling like you’re jazzed up and you can go watch another movie or do some more chores and you’re not sleepy. That’s because of that light. So, that’s why it’s also another good idea to avoid blue, bright light in the evening, for yourself and also for your kids. If you’re taking your kids to the drugstore, then you might be surprised why they are jazzed up after coming back from outside. It’s partly because of that light.
Katie: Yeah. And I think people often underestimate how powerful of a tool light is when it comes to really manipulating sleep patterns. And with kids, this is especially a big deal. And the way I’ve implemented it in my home is we try to all get outside, to your point, and get that early light as soon as possible after we wake up, which really does seem to have an effect on their sleep time later on. And then in our house, the bulbs on the ceiling are those bright blue light bulbs. But at sunset, there’s a timer on lamps that go on, and the big lights go off. And then there’s those lower light orangey bulbs, and that really does start that calming cycle for the kids before bedtime. And it makes sense that that would all be in timing with the sun because that’s, like you said, how our biology has been existing for so long.
Dr. Panda: I mean, you put it perfectly. You know, during daytime, light is the best antidepressant. It’s plentiful and free. You just have to step outside. And similarly at nighttime, dim light or dim orange light can boost your sleep. So, again, by flipping a switch, you can essentially control the hormone in your body, literally, because when you dim down that light, or switch to dim orange light, then you start to produce a little bit more melatonin, which is the nightly hormone. So, you don’t have to actually pop melatonin pill if you can actually dim down your light and produce your own melatonin enough to help you go to sleep.
Katie: And I love that in a world of these, like, trendy bio hacks and expensive supplements, light is a free thing we can get outdoors, even on a cloudy day. And I feel like, from what I read of your work, light is the biggest lever we can move when it comes to this circadian clock. But another one that seems very, very impactful, and I know you’ve written a whole lot about is food and the idea of time-restricted feeding, eating during a certain window, which I think often gets confused with fasting, which, at least from what I understand, is a completely different conversation in some ways. But can you talk about how food influences that circadian lever as well?
Dr. Panda: Yeah. So food… As I told you that almost every organ in our body has its own clock because… For example, your stomach has its own clock so that it times when you’re supposed to eat breakfast, it produces all the digestive hormone and acid, it prepares your stomach to digest food. Similarly, the liver has its own clock to absorb that nutrient, break down your medications that you may be taking, or break down all the toxins. Every organ has its own clock. Then the question is, how are they tied to the outside world?
And I told you, the brain clock, it’s kind of like a master clock. But at the same time, there’s peripheral clocks in all other organs. They also need some cue. So, the biggest cue for them is when you eat. And particularly the two events that are very important, when you eat your first meal, or the first time you eat your calorie, and then when is the last time you eat your calorie. Because, just like our body takes a cue from morning and evening when the sun comes up, and when the lights turn off, similarly, our body takes cue from when you have your first calorie, and then when you have your last calorie. So that’s the equivalent of sunrise and sunset, the breakfast and last bite.
So then what happens is… Now, there are two ways to look at it. When we eat, our organs, our body has to turn on a lot of genes, hundreds of genes, or maybe thousands of genes in different organs, to absorb that nutrient, use that nutrient for your body to nourish itself. And at the same time, just imagine if we take the simple example of blood glucose. Many of you may know that our blood glucose will stay below 100 by 100. That’s 100 milligrams per 100 milliliters. And you might not be too familiar with the metric system, but just remember the number 100. So, an average mom may have 5 liters of blood. So, that means all this sugar that we have may come down to only 5 grams of sugar in our blood, and when that blood sugar becomes 6 grams, then we hit 120 milligrams per deciliter or 100 ml. And that’s at the borderline of, you can say, gestational diabetes or early stage of diabetes. So, our blood glucose has to be very tightly controlled. So, when you have that cup of coffee, you might say, “Oh, I’m just taking half a teaspoon of sugar.” That’s already a 2.5 gram of sugar. So, if your pancreas is not waking up, that can shoot your blood glucose to 130, 140 milligrams per deciliter.
So, that means when we say the first bite of food, the first sip of calorie, we’re really talking about anything that has any amount of sugar or carbohydrate, no matter how little it is. And that’s how the clock takes the cue. And then at the end of the day, just imagine, although your mouth might have finished chewing your dinner at 6 p.m, the food sits in your stomach for at least five hours to get digested. So, that means your mouth might have stopped but the stomach kitchen is still running for the next five hours, and your body is still working on digesting food.
One aspect of the clock is during daytime, it nurtures your body with nutrients, and at nighttime, it needs the downtime to repair, to turn on the genes that repairs our body, detoxifies our body, burn some fat, re-organize glucose, glycogen, all that stuff. So, that means after your last bite for the next five hours at least, the body is not getting that break to turn the clock, to turn on all the detoxification, fat burning, and all this repair process. So that means if you’ve finished your dinner at 6:00 p.m, your repair process doesn’t start until almost midnight. And just like you need at least 8 to 10 hours of window to eat enough nutritious food to nurture your body, your body also needs 8 to 10 hours of complete rest without any digestive process going on to repair our body. So, now if you add up 8 hours of complete rest plus 5 hours of digestion, so that’s almost 13 hours of downtime at least you need every day when there should not be any eating except drinking water should happen.
So, that’s the idea of what we call time-restricted eating. You restrict the timing when you eat. We are not asking you to really reduce your calorie explicitly, although you may reduce some calories indirectly. And it’s very different from fasting, in the sense…when we say fasting, the first thing that comes to our mind is depriving our body of the nutrients that it needs for at least one day in a week. And this is not about depriving your body of nutrient but eating everything within a fixed window, and we’ll get to how long that window is. And if you wanted to make another analogy, so, for example, if somebody gives you a pot of say roses or a rose plant, or a pot of plants, we know that we have to water the plant. If we don’t water the plant, then the plants will die. That doesn’t mean that we have to water the plant every hour in 24 hours. That’s excessive watering and that plant will die. So that’s what we are doing in modern days. We are thinking that as long as our eyes are open, our mouth has to be open. We should be eating into every one or two hours or three hours. And we excessively water that plant, our body, and that leads to its deterioration.
And time-restricted eating is yes, you water your plant, but once or twice a day. So, similarly, in circadian rhythm, using the circadian rhythm finding, what we found is if we feed, even animals, within 8 to 10 hours every day, without even reducing their calories, then the animals remain healthy, they’re protected from a lot of diseases, and now, new studies are showing that they can also live longer. And from that animal studies, now we are using those insights to test whether it also applies to humans. And what we’re finding is, people who consistently eat within a window of 8, 9, or maximum 10 hours, at least for 5 days in a week, they can prevent and, in some cases can reverse obesity, diabetes, cardiovascular disease, and many more.
Katie: Yeah. I think…when I first started reading this, I was astounded at the mice studies. And I’m remembering one I think that showed that mice had from not changing, to your point, how much they ate, but only when they ate. Was it a 28% lower body mass and a 70% reduction in body fat just from timing alone?
Dr. Panda: Yeah. So, in this experiment, we actually fed them the very high-fat, high-carb diet, which is…of course, this was a extreme experiment because we were feeding mice which was equivalent to feeding them only ice cream and nachos every day. But this, we had two groups of mice. They were same age, same genes. They were born to the same parents in the same room. They’d the same microbiome, they’d the same number of calories, they’d the same food. The only difference was the one group of mice were allowed to eat whenever they wanted. So, anytime they were feeling hungry, they could go. And just like in our home, we can go and open our fridge, pick up anything that we want, and eat. So, similarly, these mice were allowed to eat. And then the second group was told that, or they were trained, to eat the same number of calories but within eight hours in the first experiment. And what we found was the eight-hour eaters, we called it time-restricted eating for eight hours because only the timing was restricted, calorie was not restricted. They ate the same number of calories.
So, these eight-hours-time-restricted-eating mice were 28% less and they had 70% less fat mass than the first group. You might think that, okay, so these mice are eating only for 8 hours, fasting for 16 hours. They may be really weak and they do a regular task. So, we actually put these mice on a treadmill. We do have treadmills for mice. And these mice ran on the treadmill. They outpaced even mice that were eating healthy food whenever they wanted. So, we were surprised by that. And then we also put them on balance beams, almost like gymnastics. They have to stay on a rotating drum for a long time, and they even stayed on the rotating drum for a very long time. So, their motor coordination and their muscle performance, as assessed by endurance on a treadmill, they all improved.
They had low fatty liver disease, low cholesterol, normal healthy cholesterol, healthy level of blood glucose. Everything seemed normal at that time. And then we have repeated that experiment with 9 hours eating, 10 hours eating. What we find is in mice, we can go up to 10 or 11 hours. They’re fine. Even mice can eat for 9 to 10 hours for 5 days and 2 days they can party in the weekend. They eat, but still, they were healthy.
We have also taken mice that are fat and they already had disease and put them on eight or nine hours time-restricted eating, and we can reverse many of their diseases, which was very exciting for us because most of us, that is the most relevant experiment for humans. Because often we want to improve our health and we want to do something. So, we tried seeing when do people actually eat? Because, you know, most of us we think that we eat…we have our first breakfast, say, at 7:00 or 8:00, and then we finish our dinner by 6:00. But actually, as I said, even half a teaspoon worth of sugar is enough to break what we call fast because your pancreas has to get up and process that sugar. Just imagine, when is the last time you had that half a cookie or the leftover from your kid’s dinner? What is the first time in the morning when you really want that coffee because you’re sleep-deprived all night and you want to charge up? So you had that coffee with a little bit of cream, or a little bit of sugar, all of those count.
So, what we have done is we made a very simple app called myCircadianClock, and in the first study, we asked people to just take a picture of what they’re eating, whenever they ate anything or drank anything. And we did that for 156 people in the first experiment that was published almost seven years ago. And, to our surprise, what we found was all the people always said that they ate within 10 to 12 hours. That’s what they recall. But over a week or two weeks, what we found is that it’s actually…50% of adults in the U.S. tend to eat with an interval of 14-and-a-half to 15 hours. So, that means if your first calorie in any week…not for any day, in any week, started at 6:00 a.m in the morning when you got up and have that half a cup of tea or coffee with a little bit of sugar. And then nearly 50% of people also had their last sip of milk, or last nachos, or cracker, or whatever it is at 9:00 p.m at night. So, that was the first eye-opening for regard, because less than 10% of people actually eat consistently under 12 hours every day. So, almost 90% of us actually eat outside these 12 hours, at least two or three days in a week.
So, then the question is, can people reduce their eating window and pick a 10 hours window and try to eat within 10 hours? Although, mouse experiments were eight hours. Within that eight hours may be too difficult to stick in the long run, because people do have to share at least one meal with their family. So that’s why we try 10 hours. And what we found is yes, people can actually try 10 hours. And if they do it, they can see a modest reduction in body weight. I don’t say you lose 10 pounds in 10 days. But that weight loss, once it becomes a habit, people actually staved off that extra weight, because many of us, we know that we can try something, lose some weight, and then we get it back within few weeks. So, this doesn’t happen because your body gets used to it. And you also get used to this eating pattern. And they also felt more energetic during the day and slept better at night. The bedtime hunger also went down.
Katie: And it makes sense that when you are looking at self-reporting versus actually having people track, there would be a difference. I know I’ve seen some of that too of even just the number of times per day people think they eat versus the number of times per day there’s actually a caloric event. It’s a big difference. But I think the really fascinating part about this, and from what you’re saying, we’re seeing this actually play out in humans now as well, not just mice studies, is that it’s not a diet. They’re not restricting any foods. They’re not restricting calories even necessarily. You were actually feeding them high-carb and high-fat, which is the one that tends to put on the most weight in lab studies, and the mice still saw those changes. And so I think learning to understand not just what we eat but when we eat might be a really powerful tool. So it sounds like in humans, have you pinpointed…you said 10 hours is more sustainable, but 8 hours has probably a bigger effect?
Dr. Panda: Yeah. So, we do see that people have now published 4 hours, 6 hours, 10 hours, 8 hours, even 12 hours. Twelve hours didn’t do much good, but maybe if people have lost weight, they consistently stick to 12 hours and eat 2 or 3 meals, maybe they will improve. But the bottom line what we find is 8 hours to 10 hours. If you target for 8 hours, then people still end up at 10 hours eating window.
There are nearly 100 different studies going on around the world on time-restricted eating. And on our platform, myCircadianClock, currently, there are at least a dozen different studies going on. But I can tell you a little bit about what are the studies that have been completed and published. So, there was one study where we took patients who have metabolic syndrome. So, that means they had slightly higher blood glucose, they had excess body fat, or obese, overweight obese, or high cholesterol, high triglyceride, blood pressure. So, any three out of these five criteria they were meeting. And the reason is, if you look around…if your kid is going to high school, I bet that by the time our kids graduate from high school, a lot of us already are meeting one, two, or even three criteria for metabolic syndrome.
So, almost all families who have a kid in high school, I would bet that at least one parent has one metabolic state that’s not ideal, overweight, obese, big belly or abdominal obesity, high cholesterol, high blood pressure, high sugar. One out of these five must be there. So, we brought these people who are also on some kind of medications, because the idea is, well, if you’re taking medication, maybe all these lifestyle interventions may not be that powerful, because medication may be so powerful that nothing else will add up. And this person’s went through 12 weeks of time-restricted eating, self-selected 10 hours. We didn’t ask them that you have to start eating at 8:00 and finish at 6:00, we said depending on your lifestyle, whatever commitments you have, or whether you want to eat breakfast with your family or dinner with your family, accordingly adjust your schedule and pick any 10 hours.
And when they did that, we saw a significant reduction in their body weight. They lost 3 to 4 kilos. They saw a very good drop in blood pressure, which was surprising because usually with such modest weight loss people don’t expect a big drop in blood pressure, but it did happen. And many of them saw reduction in their bad cholesterol or LDL cholesterol, although 12 weeks was not enough to see an increase in good cholesterol, HDL cholesterol. And then those who had pre-diabetes or early stage diabetes, they also saw a reduction in their blood glucose to trending towards healthy. So that was a small study with only 18 or 19 patients. But then these similar studies have been now replicated around the world, and people find similar outcomes.
One thing I must clarify is, in many 10 hours’ time-restrict eating, people might not see a big weight loss, a modest weight loss, at least in the first three months. But if you’re doing eight hours, people may see a good weight loss. And what we’re finding in all this time-restricted eating, although you’re not paying attention to calories, very often people reduce their total calories, because, ultimately, what happens is that extra glass of wine or beer, like, late night and all these other food that goes with it, or women in particular, they don’t want to waste any food. So when the kids leave anything, or they came back from practice, and they say, “Oh, this is a nice cookie, but I don’t like it.” And then moms tend to eat that. So, all of those extra calories are out the door. So, in that way, you don’t have to count calories. By just stopping earlier, you can also reduce calories. And that’s what we find.
Katie: And I’d love to talk a little bit about guidelines for the best timing of this window in…I know that you said that obviously there’s lifestyle factors that come into play. But if someone was just looking at the optimal, it seems like from what you’ve said, stopping that window earlier in the evening might be more beneficial than waiting until the afternoon to start and then eating closer to bedtime, like, where the window goes. As well as I know we’re going to get questions from people who are saying, “Well, if eight hours is great, is three hours better?” Like, what’s the point of diminishing returns? Where should people not reduce fast?
Dr. Panda: Well, I always get that question that if eight hours is better than why not six hours, four hours, etc? So, what we find, particularly for women, is many women, they would…you know, many of us we want to have it all. We want to be in perfect health. We want to try everything. So, some women will try a six hours window, but at the same time, they want to reduce their calories. So they drastically reduce their calorie, eat only salad or something and then start exercising, run 5K every other day. And when all of these things happen at the same time, then you get into what we call a negative energy balance. So, that means your body is spending a lot more energy than what you are taking in. So, that disrupts our hormones, and many women become amenorrheic , and many also might develop weaknesses, cramps, muscle pain, dizziness. And people have shown that these adverse events can happen if people are eating within four, six, three, two, all these hours. So, there is some danger.
And then there is no long-term studies to show whether this is sustainable and whether it doesn’t have any impact on your health, because, you know, when we’re fasting, our body actually tends to produce the same digestive juice, the bile acids, and everything for our digestion. And if we don’t use it, it just stays there. And that’s also not good. So, that’s why some people think that if you shrink the eating window too short, then you may be at risk, although we haven’t seen clearly any proof that eating within three, four, five hours may increase your risk for gallbladder disease or other things where there is excess bile acids just sitting there without being used.
But coming to morning or evening, this is where the science of circadian rhythm actually comes into play. So, let’s start from the evening. So, for example, as I mentioned, a body starts to produce melatonin to put us to sleep. And melatonin production typically begins two to three hours before our habitual bedtime. So, for example, if you tend to go to bed at 10:00, that means by 7:00 or 8:00 your body has begun to produce melatonin. And it’s going to rise slowly until you go to bed, or maybe up to an hour or two even after going to bed it still continues to rise.
So, now what is the relation between melatonin and metabolism or digestion? Melatonin, just like it puts your brain to sleep, it also puts your pancreas to sleep. So that means it also slows down your pancreas. So that means if you’re eating too close to your bedtime, within two to three hours of bedtime, then you may be eating that meal but your body is not ready to process that carbohydrate, because almost all meals have some carbohydrate. Even if it is 5 to 10 grams of carbohydrate, that needs to be assimilated. So, the body is not ready to process that carbohydrate well, so your blood glucose is likely to stay a little higher for a longer time. And also when this tiny bit of insulin continues to come to your bloodstream, it’s also likely to make your body make more fat and store it. So, that’s why eating too close to your bedtime, or eating within two to three hours before going to bed is not a good idea, it doesn’t help you with your blood glucose, and it may actually help your body to store more fat. So, that’s one thing we can take away from the science of circadian rhythm.
And in the morning, the same thing happens. Although you set the alarm, you wake up because you have to prepare your kid to go to school, all these other morning chores you may have to do, but the inside of your brain didn’t hear that alarm clock, because the alarm doesn’t stop melatonin production. Melatonin production still continues. So, that’s why when you wake up after an alarm and you’re still feeling sleepy because your sleep hormone is still high, and it will take at least an hour, or in many cases two hours, for that melatonin levels to come down.
So, that means right after waking up, if you’re eating or drinking something that has sugar or carbohydrate, then, again, the presence of melatonin may not help you digest that food properly or control your blood glucose.
One more thing is as soon as we wake up, our cortisol, our stress hormone level also begins to rise. And that’s why we need that to keep our body going. And the stress hormone levels peaks around an hour after waking up. So, I call it the changing of the guard. The night hormones are going down and day hormones are going up. And both these hormones are not good for better glucose control. So, that’s why we should avoid eating or drinking anything that has calories, coffee, tea, etc., with calories, at least for an hour, or ideally two hours after waking up.
So, now, if we put this together and we know that an average adult should try to be in bed for eight hours so that you can get seven to seven-and-a-half hours of restorative sleep. So, if you’re in bed for 8 hours, and if you try to avoid food for 2 hours before going to bed and try to avoid food for 2 hours after waking up, then you already take out 12 hours when you should not be eating. And that helps you to figure out from the remaining 12 hours when you can set up your 8 hours or 10 hours eating window.
Katie: And I know one question I’m sure you get a lot but I know we’ll get on this is, it makes sense when you explain about carbohydrates or fat or anything that starts that digestion cycle. What about non-caloric drinks? I know people are gonna be like, “What about herbal tea? What about black coffee?”
Dr. Panda: You know, in the beginning, I was saying well, coffee, tea, all these things matter because, you know, if you stand in front of a Starbucks coffee or Dunkin’ Donut, you’ll see that almost 9 out of 10 people would like to have the tea or coffee with something on them. So, that’s why… And people always think, “No, it’s just a tiny bit of cream,” or, “It’s just half a teaspoon of sugar. How can it do any damage or something?” So that’s why initially, I used to say, “No, all of these matter.” But if you’re really strict and if you can drink tea or coffee or, you know, your lemon water and herbal tea, all of these things without any sugar or fat or cream, then maybe they don’t count towards your calorie intake or the eating window. And again, if you’re on medication, like, you know, a lot of people who may be on thyroid medication that you have to take in the morning with empty stomach. Some medications, for example, blood pressure medications people may be taking before bedtime, those medications don’t count towards your eating window. So, you should also not count them.
Katie: That was gonna be my next question. You anticipated it before I could even ask it.
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What about…I know obviously there aren’t studies specific to children, and restricting food in children is not a thing we would or could study. And I can only speak from the firsthand experience on the family side of this. But I’ve noticed as a mom, if you can kind of work this eating window into just your family culture, and maybe have an earlier dinner at night and not have snack foods out at night, I do seem to notice a difference in my kids. I know there’s no specific data on this, but would the same guidelines likely apply, as long as kids are, of course, getting enough nutrients, enough calories during their eating window? I would assume there’s no disadvantage that we know of to kids stopping eating a few hours before bed.
Dr. Panda: I mean, if you’re talking about, say, toddlers, up to toddlers, right? So, of course, we have to be very careful because the newborn they repair every two hours, three hours depending on their growth, etc. But now, suppose I think about kids between the ages of say two and seven or eight. This case, according to sleep scientists, there should be sleeping for 9 to 10 hours at night. And hopefully, you’re not waking up your kids in the middle of the night to feed them between 3:00 and 8:00 or 9:00 because they should be sleeping 9 to 10 hours. And as soon as they wake up, you don’t have to feed them within 15 minutes of waking up. They can wait for half an hour or an hour in the morning or half an hour or hour even before bedtime because many moms tend to feed their kids, toddlers, and then give them a bath or something and then there is some storytime. So, if you think about it, you’re actually giving… It’s a healthy habit to have one to two hours of no snacking before going to sleep. So, the bottom line is, anyone from, I would say, a 3 or 5-year-old to a 100-year-old can actually eat everything within 12 hours.
And, as I mentioned, less than 10% of people actually eat consistently within 12 hours. So, you can have a routine that, okay, so kids can eat 12 hours. And then the adults, if you set a goal of 10 hours, then that’s a good goal. And then it becomes the question. So, if adults are eating for 10 hours and toddlers can eat up to 12 hours, then there must be some meals where the toddlers will eat and adults will watch. Yes, that’s okay, because, you know, for example, you can give your kids the morning breakfast and, you know, kids don’t like half of the breakfast. They will leave that breakfast and you can have that afterwards, or something like that. So, you’ve got to figure out a way where there is at least one meal the toddlers will eat and you don’t have to give them company.
Katie: And you mentioned the app that you’ve made, the myCircadianClock app. Is that one that people can download and use if they want to actually track their eating window?
Dr. Panda: Yeah. So people can…anyone anywhere in the world can download. It’s only in English unfortunately right now. And for the first two weeks, we just asked people to log their data too, and that also helps you understand your food. So, for example, even myself. When I started logging my own food, I realized how many times I was snacking throughout the day because I come to office and somebody brings cookies, somebody brings home-baked cake, and somebody offers a fruit and I cannot say no. So I realized that I was eating 8 to 10 times although I was thinking that I eat only breakfast, lunch, and dinner. So, that even counts. And after two weeks, it will also give you a lot of health nudges and tips, very simple one sentence that comes through the app to tell you about sleep, food, exercise, etc. And there is a 12-weeks program that people can follow and say try to stick within 8 to 10 hours. It doesn’t actually tell you whether you have to do 8 hours or 10 hours or 6 hours because it’s up to you to see how you want to do it.
One more thing is since this is an academic app, we do not sell any of the data. You’ll not get any extra emails, because I know sometimes I sign up for some apps and then every three hours I get an email or push notification. We don’t do that. The reason why we have it is we want to understand, what are the barriers to a healthy lifestyle? What keeps people…because we all want to be healthy. But there are personal barriers, family barriers, structural barriers, or workplace barriers. So, for example, those of you who are doing shift work, or gig work, or doing independent work from home, sometimes it’s very hard. Because, particularly women with children, all women with children do a full-time job. Raising a family, taking care of the family is one full-time job. And if you’re doing a job outside your home or in addition to raising a kid, that’s a second full-time job. And that itself is a barrier to following a healthy lifestyle. And we want to understand that.
And what we also see is nearly one in five adults in the U.S. does shift work. That means they’re doing night shift, morning shift, evening shift. And even if you are not doing shift work, but your significant other is doing shift work, very often women are the caregivers in the house. In addition to giving care to the sick one, they also give…they are very kind and mindful of their significant other, so they tend to stay off late to give company to their significant other who may be coming back from shift work or going to shift to eat with them, to sip a tea or coffee with them. So, I call they’re secondhand shift workers. And just like smoking, secondhand affects our health. The secondhand shift work, trying to give company to your loved one who may be working late at night or early in the morning, or even giving company to your high school kids who are doing some extracurricular activity very early in the morning or very late at night, that put a lot of pressure. That is a significant barrier to healthy lifestyle. We also wanted to understand what fraction of the population actually does this secondhand shift work, and how it affects us? So that’s why we’re collecting this data. We try to refine how we can implement this. And it can also lead to public policies.
So, for example, in collaboration with my collaborator, Horacio de la Iglesia in Seattle, a few years ago, we wanted to see what happens if school start time is delayed by an hour? Because teenagers have a slightly different circadian system. They are more sensitive to light, so they tend to go to bed late at night. And those of you who might have noticed the trend recently, when you went to school, maybe your assignments were due during the school time. But now with the digital world, the assignments are due at midnight in high schools and colleges. So, your teenage kids are more likely to stay up late to finish that assignment and submit it just before midnight, and then they’re less likely to wake up early in the morning to go to school, so their grades might suffer.
So, this is one example where Horacio tried to test the impact of delayed school start time and found that when school began after 8:15 in the morning instead of 7:15 in the morning, kids got 34 minutes extra sleep, their grade improved by 4.5%, there was less tardiness because they were always on time in school, and it improved the health of kids. Just imagine if you give a sleeping pill to your kid, then that will extend sleep by 15 to 30 minutes. So, that means, by delaying school start time in Seattle, essentially it was equivalent to putting 54,000 kids on sleeping pill every single day. So, these are some of the outcomes of doing this epidemiology or large-scale studies that will find the trend. What might have bigger impact on public health, whether changing, for example, shiftwork or even if you go and canvass your school board? “Hey, kids should have a homework assignment deadline of 10:00 p.m, not midnight.” That will have a huge impact on everybody’s health in your house. So those are these kinds of stuff we want to understand, what are the simple stuff that can be implemented at public health level, in school, at workplace, that will have a bigger impact beyond the workplace, beyond school?
Katie: I love that you’re doing that kind of work and research. And I think shiftwork could be its own whole, well, series of podcasts, but at least one. I’d love to do a follow-up one day, especially…I love the idea of secondhand shift workers, and moms certainly would fall into that category very often. I think, obviously, that gets very nuanced in food timing and light timing and everything when you’re talking about shift work, but I’d love to briefly also touch on movement and exercise, because this is another lever that can influence circadian clock. So, what does the research say on that?
Dr. Panda: So, as I mentioned, that only in the last 150 years, we have been living or spending most of our time indoors. But before that, we humans used to be hunter-gatherers or farmers, and we didn’t have electricity. So that means, just before sunset, everybody had to finish their outdoor work and then huddle indoor. And as a result, actually we humans are designed to have more physical activity late in the afternoon or early evening. So, that means our body temperature is warm around that time, our heart is pumping well, our lungs are very active and we have digested our breakfast and lunch, so we are full of energy. And what the circadian researchers are finding is that’s the best time for our muscles to do exercise. And also, since our body is ready, there’s also less chance of injury from exercise if we do exercise in the late afternoon or early evening.
Then, another aspect of circadian rhythm is… As you know our pancreas is most active in the first half of the day, and then as the day progresses towards evening, it’s very tired. So, that means its insulin production is slowing down. But at the same time, just like insulin helps our body to absorb glucose and maintain blood glucose at a healthy range, if you just do exercise, the muscles can also soak up a lot of glucose without help from insulin. So, that means, just before your big meal or just after your last dinner, physical activity, or some even modest amount of exercise will help you absorb that glucose.
And the way that people have done the experiments now, they have taken people with Type 2 diabetes and given them the same exercise in the morning or in the afternoon. And what is surprising is those who did evening exercise or late afternoon exercise, they could reduce their blood glucose significantly, whereas the morning exercise group did not see a big dent, did not see a change in their blood glucose level. And that was really surprising because we always thought that exercise is good, of course, and any exercise anytime of the day should reduce your blood glucose. But it was surprising to see that, among Type 2 diabetes, evening exercise was much more effective in reducing blood glucose. So, the bottom line is, whether you are fit, or whether you have pre-diabetes or diabetes, afternoon exercise is always much better than exercise in the morning. But at the same time, we should not forget that exercise at any time is much better than no exercise at all.
Katie: So, as we get to the end of our time, just to kind of sum up some key takeaways and make sure I’m remembering all the steps in order. An ideal kind of circadian-optimized day might look like waking up around when the sun rises and getting that natural light in the morning, but delaying, at least calories, for 1 to 2 hours after waking up, and then starting that 8 to 10-hour window from that first calorie and actually tracking it, timing a workout to be in that afternoon or early evening, but not late evening window, and then giving the body at least those few hours before bed without calories again, and adjusting light patterns in the home, and kind of target all those levers to optimize the circadian clock?
Dr. Panda: Yeah. Even if you can do two or three things out of these, then that itself is a good lifestyle modification. And, you know, one thing is, mothers set the trend, set the lifestyle of the next generation, because whatever you do, your kids will learn and they will pass it on to their kids. So, whenever moms adopt a lifestyle, it influences the lifestyle of their significant others, and also the kids. So I’d strongly encourage all of you to pay attention to circadian rhythm. Try to optimize, try to find what are the barriers in your own home, address them, and you will lift up. When you change your lifestyle, you change the lifestyle of four or five other people around you. So really powerful in changing the health of the society’s and health of the family.
Katie: And, as a bonus, your kids sleep better, which means everyone gets to sleep better. I love, like I said, how your work focuses on these things that are largely either inexpensive or free. The food we’re already eating, just timing it differently. The light that we can already get anytime by going outside, and that you really make tangible how big of a difference some of these things can make. And like I said, I think shift work deserves its own whole podcast that I’d love to do as a follow-up one day. But for people who aren’t already familiar with you and following you, where can they follow your work and keep learning more? I know you mentioned the app. Are there other places they can go to keep learning from you?
Dr. Panda: I would say the myCircadianClock website itself has a lot of blogs and articles. And people can also follow my Twitter, @SatchinPanda. And there’ll be a lot of information in these two channels.
Katie: Awesome. Well, I’m incredibly grateful for your time today. As I said, I’ve followed your work for a long time and I’m a very big fan of yours. So grateful for you sharing your wisdom with us today.
Dr. Panda: Thank you, and have a perfect circadian day.
Katie: Thank you. Thank you as always to all of you for listening, sharing your most valuable resources, your time, your energy, and your attention with us today. We’re both so grateful that you did and I hope that you will join me again on the next episode of the “Wellness Mama” podcast.
If you’re enjoying these interviews, would you please take two minutes to leave a rating or review on iTunes for me? Doing this helps more people to find the podcast, which means even more moms and families could benefit from the information. I really appreciate your time, and thanks as always for listening.
