Season 3

Episode 7 – The Effect of Time Restricted Eating on the Circadian Rhythm – ft. Prof. Satchin Panda

Episode 6 Episodes list Episode 8

In this episode, Bea continues the conversation with Professor Satchin Panda, from the Salk Institute for Biological Studies, this time focusing on the effect that time-restricted eating has on our circadian rhythm.
Satchin gives a detailed introduction to the concept of time-restricted eating (consuming all your daily meals within a specific time window), the numerous positive effects that it has on our health, why it leads to significant improvements in our lifestyle, and how one can go about implementing it into their daily schedule. Satchin also discusses how the concept of intermittent fasting relates to time-restricted eating and compares their benefits and challenges.
To summarise, Satchin introduces his 6-step formula that allows one to stay at their peak optimum performance during the day, as well as to get deep restorative sleep at night.

To better understand your circadian rhythm, check out Prof. Panda’s page or download the app “mycircadianclock” You can purchase Prof. Panda’s books “The Circadian Code” and “The Circadian Diabetes Code”.

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Bea: Hello and welcome back to the Offspring Magazine the Podcast! It’s Bea and I will be hosting today’s podcast. Today will be part two of our conversation with professor Satchin Panda, a professor at the Salk Institute in San Diego, California, who is a leading expert in the field of circadian rhythm research. Satchin Panda is the author of two books “The Circadian Code” and “The Circadian Diabetes Code”. In part one of this podcast last week, we talked about the circadian clock and how we can regulate our circadian rhythm through sunlight and sleep. Today, we will talk specifically about time-restricted eating and how time-restricted eating can affect our circadian rhythm. I hope you will enjoy this podcast!

B: So now, I wanted to talk about time-restricted eating, which is a very hot topic these days. In Europe, I think a bit less so than in America but I think slowly it’s catching on here as well. So what is time-restricted eating and why is it important for our circadian clock?

Satchin Panda: Yeah, so time-restricted eating, the concept started in my lab almost 10 years ago, and it was a very simple concept, because I still work on how light and trends are circadian rhythm. But at the same time, the question that you had posed very early on saying: “how come all the cells in a body, which are hidden and dark, how do they sense light?” And I had the same curiosity almost 12-13 years ago. We did a very simple experiment: we fed mice (mice are night-active so they stay awake in the night and they eat at night, they usually sleep during the day). And we had done all the experiments on how light is sensed by melanopsin and researched the clock, I’ve published quite a few high-profile science papers, but still, I had that curiosity: how come the liver clocks sense light? And if the liver clocks are tied up to the brain clock and to the outside world through light, what happens if we feed mice at the wrong time? So the experiment was simple: we simply fed mice during daytime when they’re not supposed to eat, and then we asked: what happens to the liver clock? And after that time, the conventional wisdom and also there are some scientific publications strongly suggesting that the brain clock sends diffusible or soluble signal through the blood to the rest of the body that entrends all these other clocks. Even experiments done where the liver clock was knocked out and scientists showed that there is still a rhythm in the liver mostly driven by the brain clock. So it was mind-boggling for me to think: “well, if the function of the clock is to optimize our physiology metabolism and behavior – why should the liver clock be tied to the brain clock and not to the food clock when we eat, because the liver should be sensitive to food”. So we did this experiment and to our biggest surprise what we found is: almost everything in the liver, the clock, and the clock regulated genes, everything was tracking food, not the brain clock. And that was kind of an “aha” moment, literally, a light bulb went up because we realized “huh, so then what about other organs?” And in the subsequent years, other scientists also published numerous papers showing that no, food actually is the master regulator of almost all of our peripheral organs and also a majority of our brain tracks food. And you might say, “well, then what was the role of light?” Light is still important because light tells us when to sleep and when to wake up. And we typically eat during our wakeful time, not in our sleep, so indirectly light still controls, through food. So then the question was: “well, if there is the best way to sustain a healthy circadian rhythm, then it would be ideal to eat all our food within a short period of time and then fast for the remaining period”. And that’s how we came up with this idea of time-restricted eating – we did not do caloric restriction, we did not reduce the number of calories, we did not change the quality of food. The simple experiment that we did was: we took a group of mice, those are young, healthy, we divided them into two identical groups – they had the same genotype, same microbiome, the same parents, raised in the same vivarium room, they had the same number of calories, they had the same quality of food, the same high fat diet, western diet, the only difference was: the first group of mice were allowed to eat whenever they wanted, the second group of mice was fed the same number of calories, from the same source, within an eight to nine hours window, consistent window, every night (because mice are nocturnal so we thought, okay, we feed them every night). And just imagine up to that point, nutrition science had taught us that the quality and quantity of food matters. So the amount of the number of calories you consume and the type of food, whether it’s high fat, high sucrose, high protein, all of these things matter. Until that time, 150 years of nutrition research had never established that when to eat will have a huge impact on your health. So we were very sceptical that we’d see some impact but, to our surprise, what we found was: the second group of mice that ate the same number of calories time-restricted, they weighed 20% less, so the body weight was 20% less. And then we’re curious when the body weight is less – are they losing muscle mass or bone mass or water mass – what is happening? And what we found was that 70% less fat mass. The lean muscle, muscle mass was almost identical. And when we opened these mice and examined by a trend pathologist, what we found was: the first group of mice that ate any time whenever they wanted, they had signs of fatty liver disease and also a sign of insulin resistance or diabetes: they had high cholesterol, high blood lipids, all these things that happen in chronic metabolic disease. Whereas the time-restricted-fed mice were completely healthy. Not only that, when we put them on an endurance test, the time-restricted fed mice, even though they were eating only for eight hours, fasting for 16 hours, people thought that since you’re fasting you may be weak, but actually these mice ran on the treadmill twice longer, not five or ten minutes, twice longer than the other fed mice. So that was the first experiment on time-restricted eating in mice and, subsequently, we have done the experiment to see whether eight hours is a magic number – no, no, it’s not. Eight, nine, or ten hours is fine for mice, up to 11 or 12 hours they do see some benefit, but not beyond 12 hours. So that’s the concept of time-restricted eating: that means try to eat all your daily calories, including beverages, not water, within a consistent window of 8 to 10 hours. That’s safe and more practical and pragmatic. And then, for the rest of the time, you can still consume water, plenty of water and, of course, if you have medication and other stuff, then you should follow instructions from your doctors.

B: Wow, I mean that study with the mice that was absolutely fascinating the first time I heard it. That was that’s such a good experiment to do and I can’t believe you had also such good results. And as you mentioned, so they had a 16/8 hour feeding window, and you’ve also touched on that if you do anywhere between 8 and 12 feeding window that should still give you benefits. Have you looked at a shorter feeding window, such as 4 hours or even 2 hours?

SP: Since we do most of our studies in mice, where we control the number of calories, because when you reduce the number of hours you feed mice, you may inadvertently reduce number of calories. So you cannot figure out whether the health benefits or adverse effects that you see is due to calorie reduction or time reduction.

B: Yeah, that makes sense.

SP: So that’s why we cannot do these experiments. And even in humans, all the people have done some experiments with six hours: those are short-term studies and those are not sustainable for a long period of time. And with six hours, four hours, or two hours, we have to also keep in mind that a lot of people who may be susceptible to feeling weak or they may have other conditions that might flare up, if they go through very long period of fasting. So that’s why we are more focused on what is pragmatic for most people, without significant increase in risk from long period of fasting or inadvertent reduction in calories to a point where it’s not sustainable. So that’s why we haven’t gone there, although once in a while, I hear somebody saying they eat two hours, four hours, six hours but we haven’t seen what is the long-term consequences. At the same time, some people say that eat for four hours or two hours, but at the same time, they don’t disclose that they are drinking a lot of coffee and tea, bone broth even, which has a lot of calories. So we’re not going there.

B: Yeah, yeah, okay. And is there a better window that you can choose? Is it better to maybe shift this eight-hour feeding window earlier in the morning or later in the evening?

SP: Yeah, so there’s a lot of discussion about when is the optimum window. And in both my books, “The Circadian Code” and recently I published “The Circadian Diabetes Code”, I discuss how to choose this window of eating. The first thing would be to pay attention to when you eat – because when you say eight hours eating, it has to be a consistent window. So that means I cannot choose to eat from 8 a.m., say, to 4 p.m. today, and then 4 p.m. to midnight tomorrow, and then 10 a.m. to, say, 6 p.m… So when we change that eating window, then it also tries to reset our clock, so our whole body will experience jet lag that you experience when you go from one time zone to another. So the first rule is: try to be consistent, whatever that window is. And the second is, as you mentioned, whether it should be earlier or later. The earlier part relates somewhat to melatonin, what we now know, based on human genetics data, that melatonin is somehow linked to obesity and glucose intolerance or type 2 diabetes. And mouse experiments, and then human experiments, and other mechanistic experiments have revealed something very interesting about melatonin: that melatonin just, like, it might try to put our brain to sleep it also puts up pancreas to sleep. So that means, when there is enough melatonin in our system if we eat a carbohydrate-rich diet, then carbohydrate usually triggers the pancreas to release insulin to maintain blood sugar, but in presence of melatonin, pancreas cannot produce enough insulin, as a result, the blood sugar may remain high for a little longer. So that means: if for most of us melatonin levels come back to baseline after one or two hours after we wake up, that means we should not wake up and immediately start eating, rather it’s ideal to wait for at least an hour or maybe two hours before our first bite. So that means not too early that as soon as you wake up you should eat but at least wait an hour, one or two hours before your first calorie. And then you can count 8, 9, or 10, maximum 12 hours to eat all your calories. Then the next question: what about late time-restricted eating, where you again we can bring up melatonin because, as I mentioned, nearly half of us start to produce detectable amount of melatonin even three to four hours before our bedtime. And since melatonin can interfere with our glucose regulation, then it’s ideal to avoid food for three to four hours before bedtime. So that means if you’re going to bed at 10 o’clock or 11 o’clock, then it’s better to finish your dinner by six or seven, maximum eight o’clock. So that means now if you subtract two hours in the morning after waking up and three hours in the evening before going to bed, then you have a pretty good window, and you cannot move too much within that window. So that’s why the early versus late, here are some constraints. Again, another constraint, practical constraint about eating late is: when we eat late, we are more likely to consume more calories from alcohol and all the other stuff that goes with alcohol – snacks, salty snacks, or cheese, and also dessert. So that’s why people who end their eating window too late into the night, they may actually end up eating some extra calories and maybe some unhealthy calories. So if we combine all of this, then the ideal eating window should start one or two hours after waking up and should end three to four hours before going to bed.

B: I was just wondering whether it would be important to shift your eating window slightly based on your season? Assuming that you’re not living right on the equator, but, say, in like Northern Europe, in the winter, it sometimes gets dark at 4 p.m. in the afternoon, and I was wondering whether, if darkness causes your melatonin levels to rise, which then get your pancreas to go to sleep, would it be more important then during the winter to have an earlier eating window?

SP: Yeah, so that’s a good point. the thing is if you even if the sun is setting at 4 p.m., a lot of, most of us are still working on a bright light for two or four more hours. We are not sitting in darkness. So I guess, we have to keep in mind when is our habitual bedtime because melatonin release is more tightly connected to our habitual bedtime than to sunset time for most of us in the modern world.

B: Okay, that makes sense. Another question that I often get a lot when I talk to people about time-restricted eating is: they ask me like, “oh, like, do you think it matters if you do it for five days during the week but then you don’t do it on the weekend?” So actually my mom has asked me this question and I didn’t really know what to say, like, I mean I would obviously assume that you have less benefits, but do you still get the benefits out of those five days where you do time-restricted eating, or do the two days where you don’t do it completely, you know, ruin everything that you’ve done during the week?

SP: Yeah, actually we anticipated that your mom might ask you this question so we did the experiment in mice: so we let the mice eat nine hours during the week and then in the weekend we let them free, they could eat whatever and whenever they want to eat. And we had another group that ate nine hours every day including the weekend. And then, of course, we always have a control group that eats whenever they want, ad libitum group. What we found was the weekend party animals they were eating even more per week basis than the ad libitum fed mice. So they really gorge themselves with a lot of food in the weekend. But to our surprise they got almost 80% to 90% of benefits of what the really religious nine hours time-restricted feeding mice did over seven days. So we don’t tell it to our human participants, but we know that if they eat outside the prescribed ten hours window even up to two days, then they do get benefits. And in fact, in our human studies, what we’re finding is if they eat for within 10 hours window for five days and even if they go to 11, 12, or 13 hours, one or two days in a week, they still get a lot of benefits, particularly benefits in blood pressure regulation, and to some extent lipid profile and blood sugar regulation.

B: Okay, well my mom will be very happy about that. So are there particular groups of people that cannot do time-restricted eating and will not benefit from it?

SP: So here’s a thing, like, time-restricted eating does not mean that you have to eat everything within eight hours, time-restricted eating means you have to have a consistent eating window and, as I mentioned it, even after 12 hours people do see benefit. So then the question is: who are the people who cannot, who are so fragile that they cannot eat within 12 hours. And there are very few that come to mind. So for example, maybe you might argue that some type 1 diabetics might become hypoglycemic during the 12 hours fasting period, even if they do 12 hours time-restricted eating. We haven’t seen any evidence that that happens, in fact, this is, I would say, anecdotal because a few types of diabetics I know very well, and when they do stick to a consistent time window, say, 10 to 12 hours, then, surprisingly, what they find is they need less insulin to control their glucose, as if their system anticipation gets used to this program in a way that they can get away with less insulin. But as I mentioned, this is anecdotal, this is not proven in clinic. But, what we have seen, there are some studies that have come out recently from China and also from Europe on type 2 diabetics who are on insulin and for them, time-restricted eating also has similar benefits. So these are randomized controlled trials, although the number of participants who were dependent on insulin were relatively small but still, they reported less insulin use and better glucose control. So that’s one group that we always thought may not be able to practice or may be at a disadvantage but new research is showing: no, they can still do 10 to 12 hours time-restricted eating and can benefit. One thing that we find sometimes is: some people, particularly young women, who are trying to lose too much weight within short period of time, they try to combine many things, they will try six hours time-restricted eating, high-fiber diet, eating only salad with no salad dressing, and running five miles every day (eight to ten kilometres), and, of course, they do feel the burn, they get burnt out literally: they feel very weak, they lose their menstrual cycle, and they report many endocrine disorders. And that’s not directly linked to time-restricted eating, since they reduce calories very abruptly and increase activity. That is known to affect their endocrine system. So that they have to be a little careful when they choose this time-restricted eating, they should not get carried away that they have to lose these three pounds every day.

B: Yeah, yeah, that makes sense. What about children? So let’s yeah, let’s talk really about children, so I guess under the age of 12.

SP: Yeah, so I think, what I feel is, you know, if you look at the sleep recommendation from sleep scientists on children: children under the age of 10 should be in bed for 10 hours or longer. Okay, so that means if they’re sleeping for, if they’re in bed for 10 hours including story time and everything, then they got only 14 hours of eating time. And out of that, it’s not that as soon as they wake up they have to have breakfast, they are still waiting for an hour to do their daily stuff in the morning. And in the evening, again, before going to bed many children they take a shower or they have their bedtime ritual. So as a result, you can see that children, I say that anyone between the age of 10 and 100 should be able to eat within 12 hours.

B: Yeah.

SP: So now, you can see that they should be actually eating for 12 hours and not for 16 hours because they should be sleeping.

B: Yeah, yeah. Yeah, what about pregnant women though? If they do follow time-restricted eating, does that potentially also have an effect on the circadian clock of the newborn by any chance?

SP: Yeah, so these are very interesting questions and, unfortunately, in the US, at least there is no active study that I know of going on. But in Europe, there are quite a few studies looking at the impact of 10 hours, or 11, or 12 hours time-restricted eating on women during pregnancy just to manage gestational diabetes. Because you got to have an outcome: what are you trying to control? And the estimate is, in some of the Western Worlds, nearly 60 percent of women experience gestational diabetes. And that diabetes, we know, will have an adverse effect on the child. So if we can manage gestational diabetes better with time-restricted eating, then we’ll actually benefit two lives at the same time. So we are eager to look at the result from those studies going on in Europe. And I, again, this is where our data comes in because, you know, in our research team and also among our collaborators, there are quite a few women who have gone through their pregnancy in the recent, in the last five to ten years. And many of them, I know, they practised some form of time-restricted eating: 10 hours or 12 hours max eating, with everything within 12 hours, and they did not see any adverse side effects. They also did not see any gestational diabetes but, at the same time, this was their first pregnancy or second pregnancy and they were healthy, so we cannot say whether it’s prevented but what we know is it did not have any adverse effect on them or their children. Again, this is anecdotal and we have to wait for randomized control trial.

B: Yeah, yeah, so now we’re talking a lot about time-restricted eating and eating within a time window, but I know there’s also the concept of intermittent fasting, where you fast for maybe, like, full on one day or you calorie restrict on one day, and then you eat whatever you want on the next day. Are there any benefits to doing intermittent fasting versus time-restricted eating?

SP: Well, it’s a, you know, when you go to a restaurant there are menus, so this is different types of fasting menus: you can pick the one that you can that you’re most comfortable with. Now, the point is: well, if you do time-restricted eating – what are the benefits? And if you do intermittent fasting, where you food restrict, restrict calories for one or two days in a week, what are the benefits and potential adverse side effects also? From societal point of view, if you are doing time-restricted eating, you may feel certain kind of restrictions. So, for example, people who commute long distance and they still want to have their breakfast and dinner with their families, then it might become very difficult for them to do time-restricted eating within 10 hours: they would miss out on one meal eating with the family. And for them maybe fasting for a couple of days in a week, in the weekend, or one day in a week is a better alternative. Conversely, some people might think that well, they can actually use it as a lifestyle. So every day it becomes the routine: they don’t have to even think about it it’s automatic and they will try to eat within 10 hours. Or you can also mix and match it’s… what I say is: eating consistently within 12 hours is like brushing your teeth once a day, which will protect you from some dental disease to great extent but, at the same time, if you eat within 10 hours or eight hours, that’s almost like brushing your teeth twice and flushing your teeth, which will still take you a long distance. And then, you know, this intermittent fasting can be going to the doctor once a year, dentist, and getting your cleansing done. So they all come with their own advantages and other stuff. What we see is: time-restricted eating has other benefits that are not, at least, reported. So some benefits are: people tend to sleep well, and this is something that has come out in many studies that the self-assessment of sleep and sleep quality improves under time-restricted eating. Whereas, in intermittent fasting studies, you’ll often see that people report that they’re so hungry that they cannot sleep on the days when they’re fasting. Then the second thing that we see with time-restricted eating: a lot of people, they report less acid reflux or heartburn. And that makes sense because, when we eat late at night, that’s when a stomach is more sensitive to food, it tends to produce more acid, and our mouth, our saliva production goes down to protect us from drowning in our saliva during sleep. And saliva counteracts or neutralizes our stomach acid. So as a result, when you eat late into the night, then you are more likely to be prone to acid reflux. And if you’re time-restricted eating and, particularly, in a way that you are finishing your dinner two to three hours before your bedtime – then you may be less prone to acid reflux and heartburn. So these are some of the benefits that we see in time-restricted that we don’t see, at least reported, in intermittent fasting: one or two days fasting in a week.

B: Yeah, I think time-restricted eating might actually be a tiny bit more sustainable, at least I know, I would find it a lot easier. So yeah, sorry did you still want to?

SP: No, I mean back to your mom’s question: even if you eat outside your 10 hours window, one or two days, if you still see the benefit then it’s more practical for a lot of people.

B: Yeah, yeah, so is there actually a difference in if you do your fasting period while you’re asleep or if you do your fasting period while you’re awake? Like, do you get more benefits by fasting when you’re also being active?

SP: Yeah, so we haven’t looked into that because one thing is – we don’t want people to wake up in their sleep and eat. So we overlap that too much. Another thing is: what’s your goal? Like, for example, some people would like to, say, some rapid weight loss or reduction in fat mass. So in that way, they tend to do more exercise of physical activity in the morning, when they’re still continuing the overnight fast. And we haven’t seen any specific result that is more effective in weight loss or not. It’s just people think that that might happen. So we haven’t seen any definitive result. The bottom line is: whatever suits your lifestyle, you should do the best, you should follow that. And we can come to the exercise point too because the new results from many labs now, from all over the world, are coming to a consensus that afternoon physical activity is much more beneficial than the same physical activity in the morning. With the caveat: we should not forget that any physical activity is good. So if you cannot do in the afternoon, it doesn’t mean that you should stop being physically active, you should do physical activity. But if you want to get the best out of your physical activity, then it’s much better to do in the afternoon. So the reason being: we know that our ancestors, hunter-gatherers and farmers, when they went out to the outside world, away from home, there was a hard stop at sunset time, they have to be home before sunset. Because, I don’t know whether you have ever experienced being out in the wild without any light, it’s very scary very dreadful and with wildlife, of course, in Europe, you don’t have any wildlife…

B: Yeah, exactly.

SP: But once I was in Africa, and I could feel that primordial fear that there might be a lion, there might be something waiting somewhere. So our ancestors had to run back home. And we have seen this in activity that I collected from people who have no access to electrical lighting – the activity just is very high towards end of the day. So as a result we are programmed to go through this high bout of activity late in the late afternoon, early evening. Another thing is: since our pancreas has a circadian clock, that means it’s most sensitive to food or is more able to produce insulin and digestive juice. Pancreas also produces a lot of digestive enzymes in the first half of the day. Towards the end of the day, pancreas slows down, so there is less insulin production. So as a result, you should have a compensatory mechanism to maintain your blood glucose, and exercise is the best compensatory mechanism because when you are physically active, muscles can soak up glucose with very little or no assistance from insulin. And in fact, type 1 diabetics who are engaged in sports, they also experience, when they’re more active in physical sports, they actually need less insulin. So as a result, if you think about how to combine your physical activity, time-restricted eating, and all of these, as a holistic manner to benefit your brain and body, then afternoon physical activity is most beneficial, which may be before or after your dinner. And that way you will get the best out of circadian optimization.

B: Yeah, I mean, what you mentioned about the fact that your muscles can kind of, they have this mechanism to take up some of the glucose, that’s fascinating to me. I think that that’s really really cool. I just wanted to highlight that again so that people don’t miss out on that point.

SP: Yeah, that’s something that’s often people miss out: that we always feel that we absolutely need insulin for our cells to pick up glucose, but muscles constitute the biggest portion of our body and they have an insulin-independent mechanism to soak up glucose. And, of course, if there is insulin, then they’re even more efficient in soaking up glucose with very little insulin.

B: Yeah, yeah, so especially for also type 2 diabetics, I think this could be very beneficial. Yeah, so going back to time-restricted eating and how to actually do it, so there’s two main questions here that I think a lot of people ask: so what about coffee? So black coffee, is that fine in the morning? And then what about some lemon in water? Those are like the two things, I think both don’t have any calories, so are they fine to have in the morning or not?

SP: Yeah, I mean, this is a question we always face. And we say yes, you can have something, it depends on what is the target of your time-restricted eating – why are you doing this? For a lot of us, who are doing it for maintaining blood glucose, body weight, then non-caloric drinks do not matter much. And for those who have certain conditions, they may have to think. So for example, people who have acid reflux, heartburn to a great extent, then maybe drinking too much coffee on an empty stomach might take just a bit your acid reflux, so be mindful about that. If you see your acid reflux is increasing by drinking a lot of black coffee in the morning, then you can adjust. Another thing is a lot of people, they have anxiety and panic attacks, they’re susceptible to anxiety and panic attacks, and caffeine can exacerbate that. So be mindful: if coffee is making you more antsy and making you more panicky, then maybe drinking too much coffee in your empty stomach is not a good idea. Then, of course, the lemon water and then there are many various forms of herbal tea and other stuff: yes, if your target is weight loss, then maybe they’re okay to consume. The reason why, in my first book, and also in my second book, I mentioned: try to have coffee within your eating window and no coffee after lunchtime is, you know, when you drink coffee, an average person will break down half of the coffee caffeine in four to six hours or eight hours, so that means even if you had consumed one double espresso after lunch, you still have one espresso at bedtime so you may not be able to fall asleep that easily. So that’s why from sleep point of view, it’s better to avoid coffee after two o’clock, if you’re trying to go to bed at 10 or 11 something like that. So the answer is: yes, listen to your body, if you’re susceptible to certain conditions then try to minimize caffeine. Otherwise, it may be okay to have coffee. Then, the gray area comes in because people say, “well, you know, I just want a little bit of sugar in that, like, half a teaspoon of sugar, or maybe a little bit of cream just to reduce the bitterness of black coffee”. So now, let’s think about how much of sugar will raise your blood sugar, for an average person like you and I, if you drain all of my blood, you may get five liters of blood, and if the healthy level of blood sugar is 100 milligram per deciliter, that means 1 gram per liter, which translates to: you’ll find only 5 grams of sugar in my blood. That is 1 teaspoon of sugar. Now, if you add just one gram of sugar to this 5 gram, then that becomes 6 gram, that translates to 120 milligram per deciliter: you are at the borderline of pre-diabetes and diabetes. If you add 1 teaspoon of sugar, that’s 10 grams of sugar, that’s 200 milligram per deciliter, you are in the diabetes side. So the bottom line is: we don’t actually, for most of us, we don’t go to that dangerously high level of blood glucose because pancreas kicks into action. So that means, when you add even half a teaspoon of sugar, you are waking up your pancreas your digestive system and everybody, the whole village, to process that extra half a teaspoon of sugar. So when you say “dark coffee”, stick to dark coffee. When you say “black tea”, stick to black tea.

B: Yeah, yeah, so to me it makes perfect sense: what starts, kind of, your clock and, like, when your feeding window starts. But what kind of is a very gray zone for me is: when does the fasting period start? Because we always talk about, maybe, 8 to 16, where you’re fasting for 16 hours. But you’re surely still digesting food in the first couple of hours?

SP: Not first couple of hours actually, the stomach emptying takes five hours on average. So that means if your last bite happened at 6 p.m., your stomach empties at 11 p.m. And then your small intestine still, large and small intestine are still doing their duty for next couple of hours at least. So when you are fasting or when you are depriving your body of eating food, then you have to subtract at least five hours from that fasting window to say how many hours your system is actually getting rest. Because, imagine, when you are… just, if we think about the digestive system itself, just the stomach lining itself, stomach is a very interesting organ because, if you think about it, all types of food that we eat it’s all digested to a great extent in the stomach. There is a lot of acid, there is a lot of digestive enzymes, they break them down. Just imagine, you are eating meat! And that’s being digested in your stomach and your stomach is essentially meat! So there’s a lot of damage that happens to your stomach lining during the day when you’re eating. And that lining has to be repaired at some time. And that repair can happen in your sleep, when your brain produces growth hormone. And that growth hormone acts on stomach lining, the cells in the stomach lining, to divide and fill in the gap of the holes that are left by this digestive process, the bystander damage that happens. And just like you cannot repair a road when the traffic is still going, you cannot repair easily the stomach lining when there is food in the system. And so that’s why, even if you are not eating for 12 hours, if you subtract the five hours, then your stomach may be getting some rest for seven hours. And during that seven hours, it has to repair and get prepared for your next meal. So the bottom line is: subtract at least five hours from your fasting window and that may be the time your stomach is seeing no food. And then if you go to intestine, then it’s another two to three hours.

B: But then, surely then, based on that, the bigger meal you eat, so if you have a massive meal in the evening, you should probably be extending your feeding window. And if you have a very small dinner, you could probably still get the benefits by having a shorter feeding window.

SP: Yeah, so it’s always, if we combine all of these, then now, it makes sense that in the morning your stomach is repaired, your pancreas is most productive in producing digestive juice, and your insulin production is also much better in the morning. So if you eat a bigger meal in the morning, then it’s always better for your body. And it’s a big meal in the morning, some physical activity in the late afternoon, and small meal before bedtime. And that way you can combine all of this into an optimum circadian lifestyle.

B: But if you only start really fasting, let’s say, after five hours of your last meal, would it be okay to still have a snack after, like, in one hour, since you still have food that you’re digesting?

SP: Well, so this is an interesting question that we hope that the gastroenterologist will answer. So the point is, when we eat, our stomach ph drops because we need that acid production to digest our food. And the question is: after the digestive process has started, when we eat a snack, is the stomach sensitive enough to produce an extra acid and digestive juice to digest that? Or is it not diluting the digestive process to this extent that it will actually slow down the digestion and will extend it more? So that’s a question that we haven’t seen anybody answering. But there is new technology, nowadays, there are probes that people can swallow just like a pill that will monitor the digestion process in the stomach and transmit that information to outside the body, we can collect that: the temperature, pH, and the stomach motility, all of that. So I guess these are some of the questions that we’ll soon see answers to. And then we’ll figure out whether frequent snacking is better in terms of digestion and stomach health than big meals.

B: Yeah, well, that’s fascinating that you can just take the pill and it gives you so much information. Yeah, I did not know that. Yeah, and so another question that I had was: does time-restricted eating have an effect on like leptin and ghrelin, so these hunger hormones?

SP: Yeah, so there are some new studies showing leptin, ghrelin are modulated by time-restricted eating. Those are some of the animal studies and also some new human studies coming up. The bottom line is: whether the changes are sufficient to change hunger and satiety, and what we have seen so far is people who do time-restricted eating, they report less hunger at bedtime. And that means that maybe their neuroendocrine system is changing in a way that they’re actually seeing the benefit of those changes by less hunger and more satiety.

B: But yeah, so I guess we’ve covered hunger hormones now.

SP: Yeah.

B: And then, the other really fascinating thing that I read in your book was the fact that time-restricted eating has an effect on the gut microbiome. And I’m really interested in the gut microbiome, just because I think a lot of people don’t really talk about it. So can you tell us a bit more about how time-restricted eating affects the gut microbiome?

SP: Yeah, so if we think about the gut and the microbiome, when we eat and when we fast changes a lot in our biome, just like we discussed: the pH drops as soon as we eat, similarly, the food itself and what is in the food changes the microbial environment. And we know that different microbes like different environments: some grow very well in low ph, some like a high pH, some might need a lot of food around, some might need less food. So as a result, as you can imagine, during the process of time-restricted eating, the gut environment changes dramatically. So since the microbes have a very short lifespan – few minutes to an hour or so – they can flourish when there is favorable condition for them. So as a result, what we find is: both these feeding microbes and the fasting microbes, they all proliferate and, as a result, we have more microbial diversity under time-restricted eating. So we have many different types of microbes, doing different tasks, so that increases. Now the second is: are there specific microbes that benefit us? And again, this experiment was done in mice, but what we found was: under time-restricted eating, certain microbes that break down complex carbohydrates, the composition changed in a way that they broke down complex carbohydrates in the lower gut, where the complex carbs are broken down to simple sugars, but the lower gut in mice does not absorb that simple sugar. So as a result, although they were eating the same number of calories, they actually excreted that extra sugar. Same thing happens with bile acid: so microbes create our bile acids, bile acids are products of cholesterol in our liver, what we had seen, in time-restricted eating, a liver breaks down cholesterol to bile acid. And those bile acids are excreted to the digestive system. And in the digestive system, the gut microbiome can process those bile cells in different ways: in a way that they cannot be re-observed by the body again but they’re excreted out in the poop. So as a result, what we found was: time-restricted-fed mice were excreting more bile acids, literally, excreting breakdown product of cholesterol – which might help explain why time-restricted eating mice had low plasma cholesterol. And they’re also excreting some of the glucose that was the digestive product of fibers and complex carbs. So these are some of the benefits we have seen so far in mouse model. We haven’t seen much data from human studies on gut microbiome or fecal content or fecal microbiome yet.

B: Yet. I’m awaiting those studies. And so now, I just wanted to move a bit away from how to implement time-restricted eating and just talk a bit about diabetes, just because I think in your book, you mentioned that time-restricted eating has the potential to even reverse type 2 diabetes. So can you talk a little bit more about that?

SP: Yes, so diabetes, as we know, at least falls into three or four different categories. One type of diabetes, we talked about, is gestational diabetes that happens only during pregnancy. And then there is early-stage diabetes that we call pre-diabetes, when the blood sugar level is between 100 to 120 125, depending on the country milligram per deciliter. And then our list is type 2 diabetes can be people who are diagnosed with type 2 diabetes, and only last three to four years, they are taking only one medication maybe metformin not on multiple medications. And then, later-stage type 2 diabetes can be more serious: people may be taking three to four medications and maybe even taking insulin. And then type 1 diabetes. What we have seen so far in animal models and in human studies is time-restricted eating 9 to 10 hours of eating or 11 hours of eating in humans can reverse pre-diabetes – a lot of them can become normal, can get their normal glucose back. Those with type 2 diabetes are listed who are not on medication yet, they may also be able to better control their diabetes. And they may come back to either pre-diabetes level or even normal level. Of course, it needs some more discipline because they have to combine that with maybe more fiber and less simple sugar. When it comes to type 2 diabetes, we’re on medication or one or more medications, what we have seen from clinical studies in humans, time-restricted eating can reduce the number of medications are taking or, in some cases, reduce the doses of medication they’re taking. So these are some of the benefits that have already been published. We should also not forget that diabetes doesn’t come alone. In my recent book, “Circadian Diabetes Code”, I mentioned that diabetes comes with its sinister friends who are: hypertension, high plasma lipids, obesity, all these other things. And what is more important is: time-restricted eating, in almost all studies, have shown to improve blood pressure control. So that means, if your hypertension is much better control, then that’s good news because many diabetic patients actually ultimately move towards heart disease because of their high blood sugar, high cholesterol, high lipids, and also high blood pressure. So time-restricted eating helps to reduce the severity of diabetes by reducing risk for cardiovascular disease. We also see time-restricted eating reduces plasma lipids, particularly triglycerides and LDL cholesterol. In short-term studies, up to three months of time-restricted eating, we haven’t seen increase in good cholesterol or HDL cholesterol but we know that HDL cholesterol can take a little longer, so we have to wait to see whether long-term six months of time-restricted eating may improve HDL or may improve the capacity of the HDL cholesterol to extract cholesterol away from atherosclerotic plaque (because that’s a functional readout). So in a nutshell, yes, time-restricted eating is highly beneficial for people with pre-diabetes or listed as type 2 diabetes, and those who are on medication may consult with a physician, because there are certain diabetes medications, which are more aggressive in reducing blood glucose. When combined with time-restricted eating, those medications might have an adverse effect in pushing a patient towards hypoglycemia.

B: I’m still, I’m really fascinated by this concept that by following time-restricted eating that may allow you to either reduce the dosage of medication or it could maybe even enhance the effect of medication. That concept really fascinates me and I think you, also in your book, kind of mentioned that with cancer and time-restricted eating, and the links of that. So maybe we can talk a little bit about cancer and time-restricted eating?

SP: Yeah, so we have to, kind of, start with the flip side of that: whether circadian disruption increases the risk for cancer. And in fact, the world health organization has classified shift work, particularly shift work of nurses, firefighters, painters, and bakers who work around the clock – those professions have been categorized as potential carcinogens. So that means they go through so much disruption that they are more prone to certain types of cancer, mostly colon cancer, breast cancer, and some other cancers. So now there are now epidemiological studies coming out of Spain and many other countries showing that people who eat their dinner before 9 p.m. (because in Spain people many people eat dinner very late at night), those who eat dinner before 9 p.m. have reduced risk for breast cancer and certain kind of other cancers, prostate cancers, and colon cancer. Then, people who have survived breast cancer, if they have 13 hours of overnight fasting and 11 hours of eating, they’re at a lower risk for cancer recurrence. So we know that many breast cancer patients see lots of the cancer and it reduces this relapse risk. So there is enough epidemiological human studies suggesting that eating within a sort of time or finishing your dinner earlier might actually help you reduce the risk of cancer. And in mouse studies, which can be done more controlled way, now there are publications showing time-restricted eating can reduce the risk of breast cancer model or, if the mice already have experimental breast cancer, then the tumors don’t grow as aggressively as those with ad libitum. So there is now enough growing evidence, fortunately, from both human epidemiological studies and from pre-clinical animal studies, suggesting time-restricted eating can help people to reduce the risk of cancer. Why this is important is, in western world, as we live longer and longer, there is 42 percent chance, that means 4 out of 10 people, are likely to get diagnosed with cancer in their lifetime. And that’s why, if we can reduce cancer risk, even in one or two percent of the population, I’m hopeful. Even more, then we are looking at a lot of added years healthy years to our lives.

B: Wow, that’s really fascinating! So it really seems like, if you have a regulated circadian clock, and you do this via sleep, sunlight, time-restricted eating, you can really enhance basically the quality of your life because you can, it seems like, you can really prevent certain diseases. So I think that nicely highlights how important this is.

SP: Yeah, I mean we evolved on this planet for 200 000 years, and we have been selected because we were under a lot of environmental stress, pathologic stress, and other stuff. But one common theme throughout our 200 000 years history on this planet was: we, humans, didn’t have much opportunity to eat after sunset. And we didn’t have much to do after sunset, except trying to sleep for 7-8 hours. And we’re exposed to a lot of light during the day. So now, if we combine all these into one simple formula, then, I would say, there are six steps to the formula. One is: try to go to bed at a consistent time every night and be in bed for eight hours. So that at least you can get seven hours of sleep. Because most sleep scientists agree that adults should get seven hours of restorative sleep, and having that sleep will improve brain function and will reduce the risk for Alzheimer’s and dementia, many affective disorders, and will also allow our body to repair reset and rejuvenate by itself. So number two is: after waking up wait for at least one or two hours before your first meal because that’s the time when the night hormones are going down, day hormones are waking up, rising up. Your organs are not fully prepared to digest food efficiently so waiting for one or two hours is the best way to start your day. And the number three is to eat your breakfast at a consistent time, and then count 8, 9, 10, or maximum 12 hours to eat all your calories. Because time-restricted eating actually synchronizes your metabolism, optimizes it, and also entrends most of your circadian clock outside the hypothalamus. And then, number four is to get some daylight because daylight is the best antidepressant. It’s plentiful and free, you just have to step outside for 30 minutes to an hour. And then the next one, is fifth, is try to get some exercise, even 30 minutes of brisk walking, if you can combine it with afternoon outdoor brisk walking, then that’s most effective. Because late in the afternoon is the time when our muscles are most prepared to exercise and our body is at a lower risk for injury. And then, number six, the last rule, is: try to avoid food and avoid bright light for two to three hours before your bedtime. Because that’s the best way to wind down your brain and body to get into a deep restorative sleep that everybody deserves. And we hope that this kind of lifestyle will form the foundation for everybody, irrespective of age, gender, ethnicity, income level, or health condition, to enhance and sustain optimum physical, intellectual, and emotional performance. That’s a universal human aspiration and also a human right. So I hope that at least few hundred thousand people can try to practice this and see their health improve. Thank you.

B: Very nice summary! I think that, you know, I can basically say, if you don’t want to listen to everything, you just want a quick summary, just go to the last 30 seconds. Because you summarized it very nicely. So I also think that it’s a good, it’s a good time to end the podcast I think we’ve talked a lot and there’s a lot of information. And I would say that if people want to know more, then your books are the perfect way to just learn more about this topic. So maybe you can mention again the title of your two books so people can…?

SP: Yeah, so the first book is “The Circadian Code”, which has now been translated to quite a few languages, including German, Italian, actually I have the German and Italian versions right here. And then Polish, Russian, Chinese, Korean, quite a few languages. And then the second one that just came out is “The Circadian Diabetes Code”, which is primarily focused on diabetes. Because what we are seeing is nearly half of the adult population in the western world and also in southeast Asia are at high risk for pre-diabetes, they already have pre-diabetes or type 2 diabetes, are almost progressing towards that. And that’s more than a billion people. And if we can prevent, reverse diabetes, even in a few million, that would be a huge achievement for this field.

B: Yeah, definitely. And I’ve read both the books, I really enjoyed them. Do you have a plan for a third book?

SP: Not yet.

B: Not yet. I mean, I guess your second one just came out. So I’ll I’ll be waiting for that. So yeah thank you again so so so much for giving us the opportunity to talk to you. I’m I’m hopeful that other people will enjoy this conversation as well.

SP: Yeah, have a perfect circadian day!

B: Thank you. Well, for me it’s basically the end of my day now. So I’m getting ready to shut down the lights and prepare for sleep.

SP: Thank you!

B: Okay, that’s part two, thank you all so much for listening! If you would like to learn more about Satchin Panda, you can follow him on Twitter or check out his website. And another great way to learn more about Satchin Panda’s research is to read his books: “The Circadian Code” and “The Circadian Diabetes Code”, which have now been translated into several languages and can be purchased online. And if you like our podcasts make sure to follow us on Twitter, LinkedIn, and Instagram. Thank you all for listening! Bye!

Offspring Magazine the Podcast is brought to you by the Max Planck PhDnet Science Communication Group, known as the Offspring magazine. The intro-, outro- music is composed by Srinath Rankumar. And the pre-intro jingle is composed by Gustavo Carrizo. Give any feedback, comments, or suggestions, please feel free to write us at Until next week! Stay safe, stay healthy, bye!
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