Harvard Intermittent Fasting Researcher Reveals the Clinical Truth Behind Fasting and Real Results

Dr. Courtney Peterson runs one of the world's largest labs studying intermittent fasting in humans  at Harvard,  and her research shows most people are fasting at the wrong time of day. Here's what the clinical data actually says.

Chris Wharton sits down with Dr. Peterson — Harvard researcher and member of the international scientific committee that formally defined intermittent fasting — to break down what rigorous clinical trial data actually says about fasting, meal timing, blood sugar, and weight loss. Not what the headlines say, but what the science says.

In this episode, you'll discover: 

→ Why fasting doesn't work by burning more calories — and what it's actually doing inside your body instead 

→ The single most important variable in your fasting protocol — and why most people are getting it completely wrong 

→ Why the timing of your eating window matters more than the window itself — and how shifting it can dramatically improve blood sugar and blood pressure 

→ What 27 out of 28 clinical diabetes studies showed about intermittent fasting — and why this finding changes everything 

→ The weight loss results you can realistically expect — what the data shows for both short-term and long-term outcomes 

→ How fasting affects hunger hormones — and why people who do it right stop feeling deprived → The specific populations who benefit most from time-restricted eating — and the ones who should not fast at all 

→ How to make fasting sustainable long-term — practical strategies backed by clinical research, not wellness trends

→  Why intermittent fasting may support women’s metabolic health and healthy aging — and why extreme fasting is not one-size-fits-all.

Dr. Peterson has spent years running controlled clinical trials on intermittent fasting. This episode isn't wellness hype, it’s the science.

Courtney Peterson, PhD | Harvard University

Dr. Courtney Peterson is Associate Professor of Nutrition at the Harvard T.H. Chan School of Public Health, with appointments in the Department of Nutrition and the Department of Molecular Metabolism. Her research examines how meal timing, intermittent fasting, and circadian rhythms shape metabolic health, with the goal of developing dietary strategies to prevent and reverse type 2 diabetes and obesity. She led the first human clinical trial of early time-restricted eating, an approach that aligns the daily eating window with the body's internal clock, and her work has helped establish meal timing as a distinct variable in metabolic health, alongside diet composition and total caloric intake. Dr. Peterson holds a PhD in physics from Harvard, where she studied the early universe before turning to nutrition science, along with master's degrees from Tulane in clinical research, Imperial College London in science communication, and the University of Cambridge in applied mathematics and theoretical physics. She previously served on the faculty at the University of Alabama at Birmingham.

Transcript

SPEAKER_01 0:00

The impact of intermittent fasting on aging is hugely exciting. If you look at autophagy as a function of the number of hours someone's been fasting, you tend to see an increase in humans around 11 to 13 hours and it goes up. And they've consistently reported that intermittent fasting seems to lower blood pressure, and the effect's about equivalent to taking a single antihyperintensive medication. We found interestingly that intermittent fasting makes your hunger levels more even keeled throughout the day. In these studies, they'd have people typically eat about 50% of their daily calories for breakfast, and they lost significantly more weight. And not only did they lose more weight, but they were less hungry, which I find amazing, right?

SPEAKER_00 0:37

They were eating more earlier in the day. They lost more weight and they felt less hungry.

SPEAKER_01 0:42

Correct. What do you think is the fastest way towards elevating your blood sugar levels? Big Mac, being sedentary or losing sleep? And the answer is losing sleep.

SPEAKER_00 0:58

Calories, fats, proteins, carbs, and so on. But what if one of the most powerful levers that we have for human health has nothing to do with what you eat at all and everything to do with when you eat it? Because every day our bodies are operating on this internal clock, a circadian rhythm that governs everything from your metabolism to your hormones to how your cells repair themselves. And when what we eat is out of sync with that rhythm, we may be working against our own biology. Today's guest is one of the world's leading scientists studying exactly that. Dr. Courtney Peterson is a leading researcher in nutrition science and circadian metabolism, currently based out of Harvard University. Her lab has conducted some of the first randomized controlled trials in humans on intermittent fasting, helping us to redefine how we think about fasting, not as a tool for restriction, but as a way to realign the body with its natural biological rhythms. What's fascinating about this is that the benefits we see from weight loss to blood sugar control to blood pressure, they don't seem to come from these magic metabolic boosts, but from something much simpler. Changing when we eat changes how our biology responds. This is about separating signal from noise, what data actually shows what we still don't know, and how to apply this in a way that fits real life. Because the most powerful interventions are often, as we know, the ones that are both effective and sustainable. Welcome to the living room. Hi, Courtney.

SPEAKER_01 2:22

Hey Chris, how are you?

SPEAKER_00 2:23

Welcome to my living room.

SPEAKER_01 2:24

Thank you.

SPEAKER_00 2:25

So I thought we would start with um some definitions because I think everyone has heard of this term intermittent fasting through one um resource or another. And I think we often associate that with fat loss mainly, um, or some kind of dietary control. Given your subject matter expertise, why don't we start with your definition of what that means?

SPEAKER_01 2:47

Sure. Um, so intermittent fasting is sort of a broad category of approaches that alternate periods of eating and extended fasting. And I was recently part of like an international consensus committee of scientists and experts around the world. There are about 37 of us, and we convened, and there's a little bit of debate, but what we are now defining intermittent fasting as is fasting for at least up to 48 hours at a time and doing that on a periodic basis. So there are a lot of different types of intermittent fasting, and I like to, because they're so different, I like to group them into three broad categories. So this first sort of category I kind of think of as like periodic water-only fasting, where you pick some number of days per week or per month to have a 24-hour or longer water-only fast. So an example of this is in a lot of religious traditions, they'll often fast one day a week, uh, every week. Another example would be something called alternate day fasting, where every other day you have a complete water-only fast. Uh that's far more extreme. So I don't recommend it for most people, but nonetheless, there are studies on that in humans. Uh, the second type of approaches, and this is where it's a little bit more debated, whether these are genuinely intermittent fasting or not, are what are called um either intermittent energy restriction or modified fasting. And these approaches, you eat a very low calorie diet some number of times per week or per month. So by very low calorie diet, we usually mean about 800 calories a day. I like to translate that into being like one meal a day. So examples of this would be the five two diet, which is very popular in Europe. Well, you pick like two days a week, either consecutive or non-consecutive, to eat about the equivalent of one meal a day.

SPEAKER_00 4:27

And then normal eating for the rest of the correct days.

SPEAKER_01 4:30

Normal eating, yep. Yep. So however much you feel like eating. So, and you may slightly overeat on the other days, but it's not enough to compensate, you still tend to lose weight. Another example of this, Volter Longo has created something called the fasting mimicking diet. And that's where you pick like five days in a row to eat a very low calorie diet. And the the sort of goal with that is to mimic a lot of the benefits of longer-term fasting, but without having to have that 24-hour water-only fast. Exactly. And then your sort of third broad, and there's some debate like whether are you extending your fast, are you not? How much are you really getting those benefits of benefits of water-only fasting? And then your third category of approaches are your daily intermittent fasting approaches, which is what most people think of when you say intermittent fasting. And we have a term for them called time restricted eating, not the best name. Um, but these are approaches where you have a 14-hour or longer daily fast. So, what that means is you're eating within a consistent 10-hour window each day. And by consistent, I mean it's not like, you know, one day you start eating at 8 a.m. and the next day you start eating at noon. You pick like a consistent time. And part of the goal of that is to um kind of get your body to adapt to that time and and kind of um sort of optimize something we'd call like your circadian biology, but we can go into that later. But these are sort of your broad categories of approaches. Among these types of approaches, the most popular is known as the 16-8 diet. And so this is eating in an eight-hour window um and having 16 hours of fasting every day.

SPEAKER_00 6:02

That seems like the least self-punishment.

SPEAKER_01 6:05

It it is. And in fact, I mean, when I first got into the field, so it was 2010. And I remember hearing a podcast where they said, um, they talked about this crazy study, or it was you know, equivalent of a podcast back then, where they had people eat in a four-hour period and fast 20 hours a day, and they said, Oh, this improved their health dramatically, which turned out not to be the case in the study. But I thought that's so interesting. Like, um how do we get some of those benefits, but do something that's a little bit less extreme. And so I think with this daily intermittent fasting, you have the ability to do something that's kind of sustainable, but sort of get those long-term benefits. Whereas some of these other approaches where you have water only fast for some number of days per week, I think they're much more for people who are motivated and want to go to the extreme. But I think for most people, we need something we can do, something like five days a week and still get some of those benefits.

SPEAKER_00 6:58

I guess some people kind of like ripping off the band-aid though, and just get it done in one day, if if there isn't the equivalent upside.

SPEAKER_01 7:06

There, yeah, there is.

SPEAKER_00 7:08

Um not me, by the way.

SPEAKER_01 7:09

No, no. I I think also, I mean, when you do the daily intermittent fasting, we the data generally suggests there's no negative impact on your muscle mass, which is great. But there is some data from the UK that suggests if you fast for more than 36 to 48 hours at a time, you will lose extra muscle mass.

SPEAKER_02 7:29

Yeah.

SPEAKER_01 7:30

So there, I think there's like a sweet spot at dose that's like doable in real life, but not going to have some of the negative effects. Now that might be helpful, you know, these more extreme fasts might be helpful with someone who might have severe obesity or something else, or they have hypertension, they're trying to get to a goal quickly. But I like some of these more sustainable daily things.

SPEAKER_00 7:48

How did you end up studying this? And I think probably more importantly, like what is it that you're actually studying within those broad definitions?

SPEAKER_01 7:57

Yeah, I kind of got interested in the concept of you know, therapeutic fasting or fasting to improve people's health. And in the sort of um my backstory is I used to uh I used to be in physics, so I studied the physics of the early universe. I saw studied something called called cosmology.

SPEAKER_02 8:14

Yeah.

SPEAKER_01 8:15

So I was studying the early universe less than a second after the Big Bang, and we were coming up with all these crazy theories that we're gonna be able to do. Well, there's a name particles period, isn't there? Uh inflation is what I was studying. So um, and we think inflation is important because it gave rise to galaxies and structure throughout the universe. Um, but I realized like 99% of the theories we were working on were gonna be wrong. And I just I, you know, it was the time that Steve Jobs was going around and giving talks, uh, graduation speeches, and he was talking about if he had too many days in a row where he felt um that if he continued, if he died tomorrow and he was doing what he was doing today and he was not happy with that, then he knew he needed to pivot course course. And for me, I was like, I'm not quite as extreme as Steve Jobs. But my version of that is if I fast forward, I'm 65, I'm looking back on my career. If I took a risk and failed, would I be happy taking that risk? And in physics, I would only be happy if I succeeded, but not if I failed. Um, and so then I just thought, I want to be in a space in which if I failed, I was glad I was there and took the risk. And so so part of that's another way of saying like the problem is so important that you know you're working on something of value to humanity that even if you failed, like it was the right problem to work on. And for me, I'd always been interested in health and nutrition. I was sporty as a kid. I mean, I played soccer, I've broken my nose twice playing soccer. So, you know, pretty competitive in in that regard, but also like a science nerd, you know, two two two kind of personality types in the same person. And um, had always been interested in health and realized that a diet, a poor diet is actually the leading cause of death worldwide. So it's roughly about a third of all attributable deaths worldwide are due to poor diet, followed in second place very closely by infectious diseases. And we dramatically underfund nutrition research and there's not enough work. And so I got very passionate about food as medicine and just trying to improve, you know, trying, you know, hoping that that could be my contribution to society. I'm interested in both diet quality and fasting, but I think fasting is something that you know is almost accessible to everyone, regardless of your income level, regardless of what you do. I think there's something in meal timing for everyone. And so I got very passionate about that and and trying to do like more sophisticated research so we can really understand how it affects the human body.

SPEAKER_00 10:39

That's what I love so much about this particular topic is it's very accessible. Yes. Right. And especially given how exciting the data looks, yes, something that we can all engage with in our own way.

SPEAKER_02 10:50

Yes.

SPEAKER_00 10:51

So so let's talk about the data and and what you found and and you know what your research is suggesting.

SPEAKER_01 10:57

Yeah. So one of the biggest questions I get is it good for losing weight or not? Because I think that's the big motivation. And so back a decade ago, when some of the first studies came out, it's a they suggested that uh these mice or these rodents lost a lot of weight. Um, interestingly, in rodents, it suggested that inner the data suggested that intermittent fasting was helping them lose weight by burning extra calories. And so this is many years ago, but my lab was one of the first to study this daily intermittent fasting in humans. Um, we did one of the first, what are called randomized control trials. So these are just studies that are very, you know, rigorous and are done to the right standard. Um and uh what we and others showed at the time is that this daily intermittent fasting, at least if you're eating in an eight-hour period or less, does help you lose weight. Um, and we also did a bunch of really cool tests where we brought people into the lab and we measured how many calories they burn. Because we were interested in the time, we didn't know, okay, does back then, I mean, there were only maybe like 20 studies on intermittent fasting in humans. We didn't know whether the reason it helps you lose weight is because it suppresses your appetite or it helps you burn more calories. Um, so we brought people into the lab and we had them stay overnight in what looks kind of like a little bit of a fancy ho, well not smell that fancy, but like a fancy dorm room.

SPEAKER_02 12:16

Yeah.

SPEAKER_01 12:17

Um and these devices are called respiratory and metabolic chambers, but we can measure how much oxygen people breathe in and how much carbon dioxide they breathe out. And from this information, we can calculate how many calories they're burning and then how much of that is fat. And the really interesting thing we found is that intermittent fasting does not help you burn more calories. So, you know, myth, myth busting there. Uh, it doesn't look like you magically burn more calories. One of the other things we looked at was people's appetite. And we looked at that both in terms of hormones that control appetite, but also like what do they report? Because sometimes, you know, your hormones may change, you may not be as hungry. So there's not always like a perfect relationship there. Um, but we found interestingly that intermittent fasting makes your hunger levels more even keeled throughout the day, which is the exact opposite of what I of what I thought would have thought. I would have thought that with the intermittent fasting, there are periods where you're like super like I don't want to eat anymore, and then other times where you're just like I'm so hungry.

SPEAKER_00 13:17

I just I've been in one of these chambers at ACU and I don't know if this was psychological. I'm certain it was. I immediately felt hungry.

SPEAKER_01 13:27

I was like, now I need to eat something. Yeah. There's studies suggesting that if you hint to people that they might be hungry, they're gonna be able to do that.

SPEAKER_00 13:32

Yeah, I was very susceptible to that. How long were they in there for? I'm assuming 24 hours.

SPEAKER_01 13:37

Yeah, 24 hours. So they're in there. So um, but we did find a decrease in a hunger hormone called ghrelin in the morning. And then we also measured one of the satiety hormones. Um it's called PYY. And we found that in the middle of the evening, that satiety hormone was actually higher. So at certain kind of points of the day, people's hunger levels seem to be actually lower. Yep. And interestingly, you know, now sort of collecting the data from my lab and other people's lab, what we now know is throughout most of the day, intermittent fasting makes you less hungry. There seems to be for some types of intermittent fasting, there seems to be a window about one to two hours between before bedtime where they're more hungry than if they didn't do intermittent fasting. So if you can kind of make it over that hurdle at the end, um, then I think you're in a good position.

SPEAKER_00 14:25

Wait, let me let me just clarify. Yeah, absolutely. So the people that did uh intermittently fast were less hungry for the last two hours of the day than the people who didn't.

SPEAKER_01 14:36

Uh the opposite. So people so for most of the day, the people too that did intermittent fasting were less hungry. But one to two hours before bedtime, they were more hungry. So they if they can make it over that hurdle before bedtime, we find they're better. Because they get a they get a competitive advantage over most of the day.

SPEAKER_00 14:54

Sure.

SPEAKER_01 14:54

Not just that like little zone before.

SPEAKER_00 14:57

And is uh you know, I think one of the big pushbacks certainly that I've seen is you know, you're you're consuming less calories because you've got a narrower window to window to eat.

SPEAKER_02 15:08

Correct.

SPEAKER_00 15:09

What is there above and beyond the energy deficit that you're creating that indicates that this is a valuable tool?

SPEAKER_01 15:15

Yeah, uh um, sure. I'm gonna finish. And I mean that's valuable in and of itself, of course. Absolutely, absolutely. So now we have a pretty good sense of how much um at least time restricted eating helps you cut calories. These different types of intermittent fasting, they help you cut calories to a different degree. And and some of them are more sustainable in the long term. Like there's some types, and I won't probably don't have time to go through it today that you know just the sustainability isn't there at a year, at a year long. But we do see pretty good sustainability with the time restricted eating. Um, we our best data now suggests that it helps you cut calories by about if you have obesity by about 250 calories a day, um, which is pretty good.

SPEAKER_02 15:54

Yeah.

SPEAKER_01 15:54

That's about an extra two pounds a month, which may not sound like that big given that we're in the era of GLP1s or GLP1 receptor agonists. But to put it in context, we have a lot of debates in nutrition science about low carb versus high carb diets, and the differences are much smaller.

SPEAKER_02 16:11

Sure.

SPEAKER_01 16:11

So if someone's gonna focus, I'd rather have someone focus on when to eat than how much of certain macronutrients to get, at least for losing weight. There are other reasons why I think we do need to think about diet quality. And I actually think diet quality is super important. Um, but it seems to be less important than avoiding processed foods. So Kevin for weight loss of course.

SPEAKER_00 16:30

Correct, correct.

SPEAKER_01 16:30

Yeah. So Kevin Hall did this amazing study at the NIH showing that when you put people on an ultra-processed food diet, they overeat by roughly 500 calories a day. So it's massive. Yeah. So this is a moderate to medium effect, but I, you know, it still gives you a competitive advantage. Now, if you're already lean and healthy, you may not see as big of effects as I'm as I'm stating. But in the long run, we see people typically lose about four to seven percent of their body weight. And for reference, so I'm an obesity researcher, um, our gold standard for weight loss, our goal is at least 5% weight loss for people. So this puts you in that range, right? The GLP ones, you can lose a lot more. So some data suggests in the real world that with the GLP ones, that um in the real world, people lose about a third as much weight as they do in the clinical trials. And then there's also some data suggesting that people tend to regain that weight uh within two years. And when they regain it, they regain more body fat, unfortunately.

SPEAKER_00 17:27

So that that I think is a whole separate episode. But I'm I'm concerned, I'm concerned about the absolutely now.

SPEAKER_01 17:33

We don't now, in fairness, we don't have data on intermittent fasting up to two years. So, you know, I'm I'm insinuating, well, it could be still helpful for folks, but we don't know. These are questions we we need to figure out.

SPEAKER_00 17:44

But it certainly makes sense for long-term sustainable fat loss that you do that less rapidly, right? I think so.

SPEAKER_01 17:51

I think the reason my guess is the reason that we see excess, we see people losing too much muscle mass with the GLP ones is just how rapidly they're losing weight. I don't think there's anything special about GLP ones. My guess is the deficit is just too much.

SPEAKER_02 18:05

Yeah.

SPEAKER_01 18:06

Um, I'll guess. Um, but I'll tell you, I mean, we did a review of all the literature a couple years ago. About 75% of all studies looking at time restricted eating, as long as the eating window was eight hours or less, reported a weight loss benefit. So we have really good data if you look at what are called meta-analyses, that it helps you lose weight. Um, one of the other questions are like, well, is this any better or worse than calorie counting?

SPEAKER_02 18:31

Sure.

SPEAKER_01 18:32

And the data suggests it's about equal, but people tend to like it better. People tend to not like calorie counting, which is hard, you know, because you have to know roughly the calorie content of a lot of food. It takes a lot of work.

SPEAKER_00 18:42

So it certainly feels like less friction to just say just eat within this window. Correct. On that note, does have have we controlled for the type of food that people are eating within that window? And and by that I mean when when calories are controlled. So say that window, the calorie consumption was 2,000. Have we controlled for if it was 2,000 calories from processed food or unprocessed food? I assume the weight loss is still very similar, probably not as good with processed food, and certainly not as good for your health.

SPEAKER_02 19:14

Yeah.

SPEAKER_00 19:14

But but that would explain why it feels a bit more easy to adhere to.

SPEAKER_01 19:20

Yes. No one has. There are a small number of studies testing intermittent fasting in combination with like a Mediterranean diet or a low-carb diet. And some of those studies report extra benefits. Um but we they're not, we don't have many of those studies yet. So I'm not ready to say we have great data for that. Um and then going back to, and then let me also add 10-hour windows, which a lot of people are excited about, we don't have good enough data to suggest um that they help you lose weight. But the effects seems to be less. I don't think that means there's no effect there. I think the effects just a lot weaker with eating in a 10-hour window.

SPEAKER_00 19:57

I think I'm asking for a friend here. What's the what's the maximum amount of time that one can get away with eating for in that in that window? So how can we increase pleasure the most by making the window as big as possible, but still get the benefits?

SPEAKER_01 20:13

Yeah, I I think it it depends. I mean, my my sort of attitude towards these things is pick something you can do five days a week, five out of seven days a week, and stick with it. There is a nice study in rodents, as well as we have work in our lab where we've done analyses saying, okay, what if people only stick with it five days a week? Do they still get benefits? And yes, they absolutely do. Um the benefits are a little bit less, obviously, than seven days a week, but I think we can now say that if you follow it five days a week, it's worth your time. So I would say pick what you can do five days a week most weeks and stick with that. Um, you're gonna get my guess is you're still gonna get benefits with 10-hour window, but I just don't want people to think they're gonna get as big of a benefit as we see with eight-hour windows. And most of our data on humans is on eight-hour windows.

SPEAKER_00 21:02

And do we know if that benefit increases even more if that window is shorter?

SPEAKER_01 21:06

Uh, we don't know yet. People have tested shorter windows. Um, there's like one study I know there are two studies that have tested smaller windows. One found no benefit, the other found a benefit. So I don't know. We don't have quite enough data yet.

SPEAKER_00 21:21

This is really fascinating because I think when we, you know, switch on any kind of media outlet and we see a story about intermittent fasting, we're told so many different things. You know, eat one meal a day, have a 10-hour wind. Like it's and the reality is we don't know for sure. We don't know.

SPEAKER_01 21:36

That's right. And we don't even know how many meal meals you should eat. Yeah. Yeah, we have some data from our lab where we think you might get some extra benefit. And I'm happy this allows me to pivot to another topic, but um, that suggests maybe skipping meals, you may not get as much benefit with intermittent fasting, at least for blood sugar control. So, in one of our studies where we looked at time restricted eating, we put CGMs on participants to CGMs are little blood sugar monitors. You can measure your blood sugar levels across the day. And we had people eat three meals a day within a six-hour window. So it's pretty, you know, it's a little bit more on the extreme end versus eating those same three meals a day over 12-hour windows. And then we looked at their blood sugar levels over the course of the day. And the fascinating thing we found is when people did time restricted eating, we didn't really see a big difference in the blood sugar response at breakfast, but we saw huge effects at lunch and dinner, and especially lunch. And what I mean by that is when participants or when people in the study did TRE, their blood sugar levels at lunch didn't spike very high at all. It was like, it was like they were completely blunted. They just didn't go up very much. And I think what's happening is if you eat a bunch, so you know, rule of thumb, takes about four to six hours to digest a meal. So that's that's how long it typically takes blood sugar levels to go back to normal. So I think what's happening is if you eat a meal at breakfast and your, you know, your blood sugar levels will go up, but your blood sugar hormone insulin will go up too. Yep. And if you eat another meal before your blood sugar levels and your insulin levels have gone back to where they were before the meal, you already have that extra insulin around. And so when you eat your next meal, that other insulin's already there, so it's ready to do its job. So we think actually you will get some perhaps more benefits from not necessarily skipping meals. Now, we don't have clear evidence on this. This is, you know, just speculation based on data we have. Um, but yeah, so but we don't punchline is we don't know for certain. We have no idea how many meals a day. Um outside of weight loss, I think the other interesting areas for me, I think we have really good data now that this daily intermittent fasting lowers blood sugar levels, at least in people who have blood sugar problems. And the other area where I think we have really good data is on blood pressure. Um and so um in people with blood sugar, uh, I just wrote an article where we reviewed all the intermittent fasting studies in patients with type 2 diabetes, type 1 diabetes, gestational diabetes, and pre-diabetes. And the amazing thing, so there were 28 studies we found on intermittent fasting in patients with type 2 diabetes, and 27 out of 28 of them reported a benefit.

SPEAKER_00 24:23

No way.

SPEAKER_01 24:24

So, and we're seeing quite good benefits in patients with type 2 diabetes. So I was actually quite impressed with the level of consensus because I mean, these are this is across the 5-2 diet, you know, fasting mimicking diet. Intermittent fasting that have been tested in patients and people who have type 2 diabetes. So I think, you know, um now in people who are healthy, studies are mixed. Sometimes they suggest a blood sugar benefit, sometimes they don't. But in patients who have who have who have blood sugar problems, there's a benefit. I think what that means is there's probably also a benefit in healthy people, it's just small. It's hard to hard to find out. So I feel quite like the data is really quite good in terms of intermittent fast during lowering blood sugar. And in fact, interestingly, the American Diabetes Association mentions intermittent fasting in its guidelines, but it has not yet reviewed the data on blood sugar. So I'm hoping they they will uh address that. Um, and then for blood pressure, the data's pretty good as well. There, there have been two sort of meta-analysis, or these are studies of studies, and they've consistently reported that intermittent fasting seems to lower blood blood pressure, and the effect's about equivalent to taking a single antihypertensive medication, so it's in about the five to 10-point range. Um, there are many fewer studies in this space, but I think the data, you know, this data is pretty solid and is there. Interestingly, almost all the studies um on time-restricted eating that have reported blood sugar or blood pressure benefits had eating windows that ended by 6 p.m. or occasionally at 7. So maybe earlier in the days better for those benefits.

SPEAKER_00 26:01

Can we can we double click on that? Because I I am really aware and mindful of all of the great data around this topic and have tried myself many times to adhere to all different types of fasting protocols. I I must find I must admit the one, the only one that I've adhered to with any kind of success is 16.8.

SPEAKER_02 26:22

Okay, good.

SPEAKER_00 26:22

Um but and here's the bar I I find it impossible to eat early in the morning and then stop at like 6 p.m. Um, and I have tried for me personally I eat more later in the afternoon and evening than I ever do for breakfast. And it might just be habitual, and it probably I could change that, but I just don't feel hungry when I wake up, and I and I know other people like that as well. But is the data suggesting that we should flip that around the other way and eat earlier in the day?

SPEAKER_01 26:54

So I see that as one of the million-dollar questions in the field. This is like the question we all need to answer so we can provide the general public with the best advice. So, based on the data we have, the good news is it looks like the time of day that you have your eating window doesn't matter very much for weight loss. That's awesome.

SPEAKER_02 27:13

Okay.

SPEAKER_01 27:13

Because we know losing weight is amazing for improving your health. Like you lose your weight, you're gonna improve, you know, all kinds of other aspects of your health, whether that's your cardiovascular health, you know, your blood sugar control in the long run, like weight loss is awesome. There is data suggesting that earlier windows are better for blood pressure, lowering blood pressure, and for lowering blood sugar levels, but it's not at the point where we could, where we are confident enough to know for certain. So, this is one of the things we study in my lab, because I'm very interested in this question. So I am, um, I really focus. So I have one of the largest labs in the world that studies time restricted eating in humans. And one of the big questions I'm interested in is how much of the benefits of intermittent fasting are due to having that longer fasting period versus the time of day that you're eating. My best guess is some things, the daily fasting period matters way more. Like for instance, for weight loss, and other things, the time of day that you eat matters way more. And we just don't know yet.

SPEAKER_00 28:12

Wait, what are the other things?

SPEAKER_01 28:14

Okay, so um, there's something called oxidative stress, which is a form of molecular damage in the body. And for that, it looks like the daily fasting period might matter more. So there are things that seem to, I mean, the data are really preliminary, so I'm not ready to like broadcast to the world, but they're that we're starting to see some clusters, like some things matter more. And it may just depend on how strong our circadian rhythms are. So our circadian rhythms are these 24-hour rhythms in the body. We all have this internal biological clock. This clock makes you better at doing different things at different times of the day. So, for instance, if you're an athlete, the best time of day for competing is the afternoon. And that's because you have the greatest uh muscular strength, the fastest reaction times, the greatest coordination. And so in the middle of the afternoon.

SPEAKER_00 28:58

And we think that's something to do with core body temperature, I think, or that's certainly an element of it.

SPEAKER_01 29:02

Core body temperature is one way we can measure part of the circadian system. But yeah.

SPEAKER_00 29:07

I know most of the world records are set in the athletic world records are set in the early to late afternoon, right?

SPEAKER_01 29:13

Correct. That's exactly the time. Yep, exactly. Um, conversely, in most people, and there are exceptions, um, their best blood sugar controls in the morning. And in fact, we, you know, the fancy terminal uses glucose metabolism, has these really strong circadian rhythms. So we know that that looks like the time of day that you eat. If you eat in alignment with these circadian rhythms that generally make your blood sugar lower in the morning, you're kind of getting a sort of metabolic advantage by eating early in the day. Or in other words, that helps keep your blood sugar levels lower. There's um some really great work out of Israel testing the old adage of eating breakfast like a king, lunch like a prince, and dinner like a pauper, um, without changing what times of day you eat, which is awesome. So this could be another strategy.

SPEAKER_00 29:58

I was just scheduling a bit, not the time of day. Correct. Yeah. So for instance, there's more volume in the earliest meal. Right.

SPEAKER_01 30:06

Yeah. So for instance, in these studies, they'd have people typically do about 50% of their daily calories for breakfast. And then I think it's something like roughly 30% maybe for lunch and 20% for dinner, or they'd have them do the opposite. And they lost significantly more weight. And not only did they lose more weight, but they were less hungry, which I find amazing, right? Because if you're losing more weight, shouldn't you be more hungry? But they were actually less hungry than the control group that was struggling to lose weight. Um, and it also lowers your blood sugar levels.

SPEAKER_00 30:38

Um wait, they were eating more earlier in the day. Yes. They lost more weight and they felt less hungry.

SPEAKER_01 30:44

Correct. Because to me, I mean, like that's I mean, if you think about it from the flip side, that means the group that was eating more for dinner were struggling to lose weight and they were hungrier. So it's like the one-two punch in the opposite direction. Yeah. And so we there's not as much, ironically, there's not as much, maybe it's I don't know if it's ironic, but there's less data on the time of day of food intake. The data we have is very good. It's very consistent. There are not as many studies. We have far more studies on intermittent fasting. So, I mean, I think this is another meal timing strategy. Like if you have people who are like, I can't do intermittent fasting, but I'm willing to change the timing of what I eat in some capacity, or maybe I like I have to have dinner, right? Yeah.

SPEAKER_02 31:24

Yeah.

SPEAKER_01 31:24

And then I would say try to make breakfast andor lunch your largest meals of the day. Make dinner your really healthy meal. Like maybe that's your salads and your fruit and vegetables, or it's like smaller portion sizes. Um, because there is good data suggesting you'll get benefits. So my general approach is I don't think intermittent fasting is for everyone. Um, I think sort of people's lifestyle and behavior matter a lot. And so I think it's really important to take all those factors into account. And so, but I do believe there's something in meal timing for everyone. And it could be as simple as, you know, even like I'm not gonna eat three hours before bedtime. Awesome. You know, because it takes, it takes people on average four to six hours to digest a meal. So if you're going to bed every night while you're still digesting your food, and um, you know, maybe you eat like two hours before bedtime, your blood sugar levels are gonna be elevated for longer. And there's data suggesting that that um makes it harder for your body to break down and burn fat for fuel. Um, so so there's some negative things there.

SPEAKER_00 32:25

I'm doing this completely wrong myself, yeah. Um, even when I am practicing the fasting. And I think that is more just discipline, but I I find it really difficult after like a long day at work to get home. And you know, I'm not when by the time I get home, I haven't got three hours before I go to bed. And I think a lot of people are probably in that scenario, especially certainly with families, and probably find it ri would find it really difficult, regardless of the evidence, to not eat for three hours. Um I also find, and I might be on my own when I say this, that as soon as I start eating in the day, I just feel like the floodgates, right? I'm just I just then I just want to snack all day until I go to bed.

SPEAKER_02 33:08

Yeah.

SPEAKER_00 33:09

And and so I wonder if there is any science to that or that is just me not being disciplined enough. But I feel like when I delay the breaking of the fast in the morning, then that's my only hope of fitting it within a reasonable window.

SPEAKER_02 33:23

Yeah.

SPEAKER_00 33:24

So I guess my my point is, or my question is all things considered, would you say that even with that data, yeah, given how beneficial it appears to restrict the amount of food we eat to with within a certain window, regardless of the the way you choreograph it, there's still probably a big upside, even if it is done later in the day.

SPEAKER_01 33:46

Yeah, absolutely. And what I like to do, it uh none of this stuff is set in stone. Like we may get an amazing clinical trial that answers this definitively. Maybe one of our studies will or someone else's will.

SPEAKER_00 33:56

I really hope so.

SPEAKER_01 33:57

But I like to rank where I think the data is going and then what people pick. Um, so I would say if you have all the motivation in the world, you don't have obligations like kids or things like that, and you want to go the full nine yards. My guess is you'll get the most benefit from doing time-restricted eating early in the day. I'd recommend an eight-hour window or less, sort of as early as you're willing to move breakfast. For folks who are really motivated, they can go to bed on an empty stomach. That was definitely me before having kids. And I did that for years. My sweet spot was like a six to eight hour window. I'd start at 8 a.m. and I finished between two to four, just depending on my meeting schedule. Loved it, felt great, loved my energy levels. Um, I think most people are not willing to do that. Yeah. Um, my second choice would probably, you know, I think this has probably evolved over time. My second choice at the moment would probably be a tie between doing intermittent fasting or the time-restricted eating later in the day, or eating breakfast like a king, lunch like a prince, dinner like a pauper. And I don't know what's best at the moment.

SPEAKER_00 34:58

Yeah. What do you do now?

SPEAKER_01 34:59

Um, I'm sort of like closer to a nine-hour window with kids and just really busy with like moving my lab to Harvard. But um, I'd like to get back to an eight-hour window. I'm gonna play it. So so far it has not really impacted my ability to have dinner. Like I got a two-year-old, like I spend half my meal trying to get her to eat. So it's like not a big deal. Um, but six to eight hours was my sweet spot, you know, that's the thing I really like. So I'm kind of playing it by ear. I definitely like if I, you know, I don't, we'll see what I do long term, but at the moment I'm able to do it without the kids or without it being an issue. But if it is an issue, like, you know, family family comes first, right?

SPEAKER_00 35:40

Of course, yeah.

SPEAKER_01 35:40

I'll I'll still use the broader principles. So for me, I eat about 75 to 80% of my calories before noon. And my body is like really adapted to that. So I get, I mean, talking about you saying some things are easy and hard, I suspect, and we don't have great data on this, that people adapt to what they do in the long term.

SPEAKER_00 35:59

Yeah, yeah, yeah.

SPEAKER_01 36:00

And we have found that when people first change their eating schedules in our studies, they say it's it's actually quite hard. But after a few weeks, they start adapting. And then many people are saying it's a non-issue.

SPEAKER_00 36:11

Really?

SPEAKER_01 36:11

Yes.

SPEAKER_00 36:11

And I think so much of this is about adherence as well, right? Like if there is a slight edge to be had each day, if you can compound those days over time because it fits into your life in a way that doesn't, you know, suck the joy out of it, then then long term I would I would imagine that that's going to be the most beneficial. I think the nice thing for listeners to know as well is like when you say we don't know for sure about all of these things, we don't know, which is not really what we're led to believe with. You know, we sometimes will see a headline saying, you know, skip breakfast and you'll live longer, for example. And that's not yeah, yeah, and that's not really how the science is.

SPEAKER_01 36:47

This is why I think breakfast skipping has been so controversial. Because um, what's really interesting, there's work out of Japan that shows that about half of people who skip breakfast eat dinner late. And we know eating dinner late isn't is not, you know, not great. Um, but the other half of people who skip breakfast eat dinner at a normal time, so they're doing intermittent fasting. So you're lumping together two very different groups of people. And also in the folks who skip breakfast, regardless of whether they eat eat dinner or late, you're gonna have more people doing shift work. And we know shift work increases your risk of several chronic diseases, cancer, diabetes, hypertension, etc. And a lot of these studies don't take that into account. Like you gotta have these sort of clean data sets to answer answer these questions. Um I've lost my train of thought, but let me go back to one of so I said earlier, like the late time restricted eating and eating early in the day would be my second choices, probably tied based on the quality of evidence. I'd say third would be a simple rule of like don't eat within three to four hours of bedtime or whatever you can make that rule be. Um, just because you're gonna like dinner is the time of day when you have the worst blood sugar control. So the less you can kind of less stress you can put on your system, the better. Stress is not quite the right word, but you know, I think you get my general point. And I would say third, if you're just like, I can't do any of that, make dinner a healthy meal. And the reason why is because if you give someone a healthy meal and junk food meal in the morning, there is a difference in blood sugar, but it's you know, it's on the smaller side. If you give that's that same healthy meal and a junk meal late in the day, there's a much bigger difference in in blood sugar. In other words, that junk food meal later in the day is worse for your body. So if you can still at least make dinner your healthiest meal of the day, you should get some improvement.

SPEAKER_00 38:37

This is going to be my takeaway from today's conversation. Whatever else we talk about. I often will eat myself to sleep. And not just like lots of volume of food. I don't think I overeat, but that's often the last thing I do before I go to bed. So I'm gonna try this this evening.

SPEAKER_01 38:53

There are a small number of studies too that show where they've tested, like regardless of how long what's called the eating window was. So they tested the same eating window early versus late in the day that do find an impairment in fat burning at night. So I think that is not a great deal, not a great thing to have. And they're also some of the genes that are involved in in uh fat burning and and just generally regulating what we call our energy metabolism, or you just think of it as your metabolism. The genes that sort of promote fat storage are sort of, you know, they are increased when you tend to eat later in the day. But again, these are broader principles. I think people should do what they can, and that's what I would hope they take away from.

SPEAKER_00 39:34

And I think the good thing is that especially with something like this, this not doesn't cost anything. Yes, right? It costs time and effort. Exactly. If anything, actually, you probably gain back some time because of you know, less less decision paralysis or decision fatigue throughout the day, which probably actually contributes to the data. Is that like if you're not if it's just a I can't eat outside of this window, there's less likelihood that you're snacking or filling time with you know boredom eating or comfort eating. So I imagine that actually impacts that. Can I ask you a layered question?

SPEAKER_02 40:05

Yes.

SPEAKER_00 40:06

Um, so Will and I, um, who's our chief science officer and who's actually on the podcast, he's here today. Um, we went to a conference not so long ago, and amongst the talks that someone put a graph up about uh emerging therapeutics molecules that are looking to be sort of promising geroprotectors, so things that hopefully in uh at some point will get proven safe and effective for humans, but we're we're some way off that right now, and layered the data we have so far as a as a lifespan intervention, so something that could help increase the number of years we live, um healthy years, one would hope. And then on the next side, layered over intermittent fasting and the impact that has had on lifespan or markers of longevity, and it beat pretty much all of them, right? Or it certainly was competitive of all of those things. Um what would and this is the first part of the question.

SPEAKER_02 41:03

Yeah, that's great.

SPEAKER_00 41:04

Are there markers that we associate with living a longer, healthier life that we see improve when people adhere to this, at least in the studies that you're aware of?

SPEAKER_01 41:13

Yeah, yeah. So I'm gonna answer this question a little longer way because I can provide more important context. So um we have pretty good data now that in most studies in animals, that intermittent fasting extends lifespan. There are some exceptions. For now, there are various types of intermittent fasting that was studied in animals, but time-restricted eating, the data is really quite consistent. The way in which it looks like it extends lifespan is by increasing something called autophagy, which is like kind of cellular recycling of worn out and damaged proteins. And the reason why we think autophagy is involved, and there are not many studies of autophagy yet. So it's like a cellular recycling program. The reason why we think autophagy is evolved, if you do something called knocking out those genes, so if you kind of block them from doing what they should be doing, um, and you prevent that increase in autophagy, you don't get the lifespan extension. There are not many studies on this, but I can think of three studies that have done this and done this well, suggesting that at least this cellular recycling is involved. So one of the ways in which I my guess intermittent fasting is working is by on a very simple weather level, just giving your body more time to rest and recuperate. Like I think we need these contrasts in life, like activity and rest, you know, light and darkness and so forth, um, feeding, fasting. And that's how the body sort of optimally functions. You need the challenge and then you need the recovery, challenge and recovery. Um, and so I think that's a big part of what's going on behind the scenes. So if you look at autophagy as the function of the number of hours someone's been fasting, you see you tend to see an increase in humans around kind of like 11 to 13 hours and it goes up. Um, so I think that's one of the main mechanisms. So for me, the impact of intermittent fasting on aging is hugely exciting. Now I know other people have talked about the profound effects of exercise on lifespan, but a lot of that data is epidemiologic. And my concern is some so you often will hear people say VO2 max is like the best predictor of lifespan. Uh as a scientist, I don't buy it. And here's why. One is epidemiologic data. Two, the way the data is often presented, I think they take the bottom 25% and compare it to like the top X percent of people. Well, if you're picking the bottom 25%, you're gonna have people who are bedridden in there and who are on death's door, right? So, and then in animals where they've tested exercise versus diet for extending lifespan, diet has had the bigger effect on exercise. I could be wrong, but let me just say I just don't I don't accept that as a truism. Um, so I think you know, diet seems to play a big role. Now there are all all kinds of other things that play a big role. So I don't know if diet plays the predominant. Dominant role. But my guess is that we can probably that having a healthy diet or doing intermittent fasting is definitely going to improve health span and lifespan. And we do see that in animal studies. There's some data suggesting that male mice benefit more than female mice in terms of lifespan expansion with intermittent fasting, but there are much bigger differences between male and female mice than there are male men and women or humans. So I take someone with a grain of salt. And the studies that don't find as impressive results for lifespan expansion in females do find impressive results for health span extension in females. So I I think to me, this is, I think, going to be a core component of healthy aging.

SPEAKER_02 44:45

Yeah.

SPEAKER_01 44:45

We talked kind of earlier about, you know, behavioral factors, because I don't study behavioral factors, but I think they're super important. Like what can you sustain in the long term? That's what you should do. Um, but I think there's also going to be some inter-individual, or there's going to be like individual to individual variation, like metabolism and things like that. So in obesity research, we often think that some people have greater what's called metabolic flexibility than other people. So, meaning, in other words, some people get to that fat burning state easier than others. So, one of the things I'm excited about studying in the future is figuring out like what should be someone's personalized eating window. What should it be? Like how many hours should they fast? Why do some people seem to benefit more than others? Is it because some people are sticking with the diet better than others? Or is there something about their metabolism that makes it better or worse? Um yeah, and and there could be timing things. Like we know there's so there's more than one circadian rhythm in the body. Um we know some people tend to be more like morning types and other people tend to be light types. Does this affect, you know, how like the time of day that they should eat, the length of their fasting period? So I think there are all kinds of really important questions that we need to ask. And that's one of the places I'm excited for the field to go in the future. I think it's all figure that out.

SPEAKER_00 46:04

It's extremely exciting, right? Because that get getting that, um, and we call that sort of phenotyping, like testing across these different systems, which is really the true north of what we're doing here is like how do we get more granular data about our biology and our genetics and our preferences, even, and then apply that to this evidence that that we know works. Yes. It's good that there's an unlock there for all of us. It's just figuring out what that is and like and and how to do that with consistency.

SPEAKER_01 46:30

Correct. Yeah, there was um a nice study out of Spain that showed that people who got the same weight loss intervention, those who had stronger circadian rhythms, lost more weight.

SPEAKER_00 46:38

Yeah, I can imagine.

SPEAKER_01 46:39

So now time-restricted eating is a way to maybe improve some of those circadian rhythms or some aspects of the circadian system. So it may be like the combination of a bunch of different strategies. We can, you know, like help people optimize weight loss. But I think there's a lot to be done to figure out like which who benefits most, how do we design these interventions so that they're sustainable? Um, and how much tailoring? Yeah, how does it apply to me as an individual? Exactly.

SPEAKER_00 47:06

And I think that's the challenge for all of us when we're consuming content about health span, lifespan, these these terms that are being thrown around with so many different definitions is what does that mean for me? Right. But what does that mean for me today? Is what we really need to figure out. Hey, I'm gonna move on to the second part of my question. Oh, yes. Um, and I'm gonna push back on the VO2 comment, if you don't mind. The reason being, I think the second part of the question is, you know, with nutrition research in general, which is notoriously difficult to do well, yeah. Right, we have, you know, lots of them are observational studies, also epidemiological studies in large part. There is um huge bias when it comes to self-reporting. Yeah, and we've seen that the the variation in self-reporting is is wildly broad, um, with people you know, um actually telling the truth about what they're eating and the timing, especially. And and so, and then when it comes to animal models, you know, the the metabolism of a mouse is different to a human. Mice typically will just eat over a much broader, larger window if they're given the opportunity to. And so I think and this is why it's so exciting to speak to you because you're studying studying actually what happens in humans under controlled um situations, but even then, yeah, like how does that apply over the long term, right? And I think the trouble with applying any of this data to lifespan is that's also notoriously difficult to measure because we can't wait decades to figure that out. And so I think you know, how do we solve for that with nutritional research, given that as the end consumer, I don't know the difference between some observational study where there's a huge user bias and then a media bias and a study bias and a lot of hype. How do I determine the difference between those? Because I think for exercise, we do have more data on people, or less discord at least.

SPEAKER_01 49:05

Okay, yeah. Um we definitely have more agreement on the exercise side, just the nutrition side.

SPEAKER_00 49:10

I don't think it's a zero-sum game, but I think you have to do it.

SPEAKER_01 49:12

Oh no, I think you need both. And in fact, I would counter argue devil's advocate to myself, which is I think exercise is tremendously important for health too. Yeah, right. Like having a longer life that's not a healthier life, you lose, I think.

SPEAKER_00 49:26

Yeah, and I think the one really good point you make certainly about VO2, like this there seems to be like just three or four tests or metrics that get banded around as like the gold standard for everyone every time. And VO2 is one of those things I think is really important, but yeah, we shouldn't overreach there either.

SPEAKER_01 49:42

Yeah, yeah. Um, all great questions. I don't know how the consumer navigates this. My hope is that the dietary guidelines for Americans take up this topic and it becomes a nutrition guideline. I know they were considering it a couple years ago. Um, my guess is they did not move forward because I didn't hear further. But that may change in the future because it depends on how many clinical trials there were. Like when I got started, there were like a dozen clinical trials on intermittent fasting, and we're now up to over 225. It's a big increase. Um, when I started giving talks, I was like, here are 20 studies, and now I'm like, I can barely, barely discuss them all, which is awesome. Um I I think we, you know, through our conversation, we shared a lot of practical tips. I see these as principles, like what can you do in your daily life, and then you figure out what you can do. Um but yeah, I mean, this is why I think it's important to listen to scientists because things get over overhyped. I mean, one of the reasons I was excited. So I by the way, I've turned down all all other companies that have ever approached me um to be involved in fasting apps. And part of the reasons for for that is I wanted to always have the ability to think independently and change my mind.

SPEAKER_02 50:52

Yeah.

SPEAKER_01 50:53

And what I like that's different about what you're doing at Wonder Health is you're trying to assemble the best scientists in the world and have them tell you what you know is actually true of the literature. So for instance, I'll give this example to people. I'll get asked all the time because I'm a nutrition researcher, what's the latest on protein? I have no idea. And part of that is realizing like you have to know the research out there in such great depth to really know what's going on. So for instance, there was a big headline, I think it's like maybe a year or two ago, that intermittent fasting increases the death rate from cardiovascular disease by like 91 or 90 percent. Yeah. And this was research that had not been published, but was presented at a meeting. And a bunch of us who do intermittent fasting research, um, we reviewed the research and there were all kinds of problems and flaws. So for instance, the the group that was the intermittent fasting group, um, first of all, there are far more smokers in that group. There are far more individuals from minority backgrounds, lower SES, like they were like lower physical activity levels. The groups were just not matched, which since this is an epidemiologic study, you have to have that matching.

SPEAKER_00 52:05

What's the term for that, Courtney? There's a word for that, isn't it?

SPEAKER_01 52:08

It's confounders. Confounders, yeah. Yeah, you so they're all these confounders. So they create, I mean, we would call it like a spurious association, but like a false belief of what's going on. And these were not small differences, these were sort of dramatic differences. Um, second, what the authors didn't advertise is they didn't actually calculate the eating window. They calculated the average of the eating duration, which may sound like a small difference, but it's a big one. And the reason why it's a big one is they counted people as doing eight-hour time restricted eating if they ate over 12 hours one day and three hours the next day, because it averages out less. So we actually looked at their data. Yeah. Sounds like a like like I'm splitting. It sounds like I'm splitting here, just to be honest.

SPEAKER_02 52:49

Yeah.

SPEAKER_01 52:49

But when I looked at their data, 75% of people in their time restricted eating group did time restricted eating on one day, but not the other. And so what they're actually measuring is erratic eating. And so I think the punchline should have been erratic eating increases the risk of death. But interestingly, if you did limit it to people who consistently ate in an eight-hour window on both days, association vanished. Of course. Amazingly. This is why it's so good. This is why you can't know that. Yeah. And and there, they're all there are also sorts of like small details too. Like, as a nutrition researcher, the most common reasons that it looks like someone does intermittent fasting is they didn't fill out the food record.

SPEAKER_00 53:29

Of course.

SPEAKER_01 53:30

And so what that looks like is they've reported two of their three meals a day. Looks like intermittent fasting, but what you're really measuring is people who are on top of their stuff and people who aren't. Yeah. And we generally find in any clinical trial, people who are more on top of their stuff do better. So there's all these other details. And then they found that actually the eight-hour eating window is correlated with a lower risk of hypertension and type 2 diabetes, but they buried that finding because it didn't fit their inflammatory alternatives.

SPEAKER_00 53:53

I think this is why we do need to speak directly to the people that are doing the research, right? Because you will get in the same publication, we'll see, and I mean media publication, we'll see, you know, intermittent fasting adds decades of functional years to your life. And then a year later it'd be like interfist intermittent fasting kills you.

SPEAKER_01 54:09

That's why we look at the consensus. Yeah. This is why we don't, if you're weighing a single study, I mean actually, this is a good rule of thumb. If you're hinging on a single study, then you're probably making a mistake. But if you're looking at the body of research, you're gonna find 75% of studies say one thing, 25% say another thing. The 75%'s probably right.

unknown 54:30

Right.

SPEAKER_00 54:31

Can you explain to the listeners like why like a meta-analysis or randomized control trial would feel more valuable than a than a single study, and and how that they could probably, when observing these headlines or articles, might be able to use that rule of thumb.

SPEAKER_01 54:46

Yeah. So I so in general with epidemiologic studies, so these are studies where you um just ask people, what are you doing? And then you just follow up with what they're doing long term. So we call these like observational studies. So we don't change their behavior, we just see what people are doing and then and follow them long term. Or some many times we just say, How does your health look right now? Is there all kinds of um we call them like reverse associations, but things that would make you come to the wrong conclusion? A very famous example is among like never smokers and never drinkers, sometimes the risk of a disease can be much higher because these are people who, you know, for instance, never drinkers, you have a lot of people who had alcoholism or drank a lot and now are abstaining. And so because they have this history, they'll bring up the death rate in that group.

SPEAKER_00 55:33

I think the same applies to like red meat as well.

SPEAKER_01 55:35

Yeah, but if you have a randomized controlled trial, you bring people in, you have them stop the behavior, you'll see their health improves. So that's why it's so important to do clinical trials. So we always say you can't prove something causes another thing from epidemiologic studies. It does they are useful because they tell us what questions to ask and they can confirm things we see in randomly. And bigger study groups, I assume.

SPEAKER_00 55:56

Yeah.

SPEAKER_01 55:57

But yeah. So the things I tend to trust are large clinical trials and then meta-analyses of clinical trials.

SPEAKER_00 56:04

Could you maybe give a definition of meta-analyses? Like what did because uh there will be people listening that don't really know what that means.

SPEAKER_01 56:11

Absolutely. So meta-analyses are where you go out and look at all the research in an area. So say it's weight loss, you take all the results and you kind of average them together to see what the sort of average effect is weight for weight loss across all the studies. So there's an unbiased look at the research effect. Yeah. So you're averaging over studies where there was no effect, studies that where there was an effect, and you're saying what's the net effect of all this?

SPEAKER_00 56:32

Love it.

SPEAKER_01 56:32

Where does the truth lie?

SPEAKER_00 56:34

Hey, can I can we switch it up a little? Yeah, absolutely. I want to ask you about some specific cases and how they relate to intermittent fasting.

SPEAKER_02 56:42

Yes.

SPEAKER_00 56:42

The first is is there like are we seeing gender differences? Um impact on hormonal or or or menstrual cycle. I I think there's been some compelling data there, but I don't know.

SPEAKER_01 56:54

Yeah, yeah. We actually I I was tapped to give a a talk on women and intermittent fasting in Germany about a year ago. So I've reviewed all that literature. Um, it was really interesting. Prior to that, I had maybe about half a dozen women come up to me and say, say, I stopped intermittent fasting because this influencer told me it was bad and was messing with my hormones. So we actually reviewed all the data, and there's absolutely no negative effects on hormones. There's also a concern. So the one thing that intermittent fasting seems to affect is it seems to slightly reduce testosterone levels in both men and women. We don't see any differences, negative effects on strength. There are a number of studies in people who are either habitual resistance trainers, meaning they've been doing resistance training, or are new to resistance training. And in all those studies, we don't find that intermittent fasting reduces muscle strength, a muscle cross-sectional area, muscle accretion, or anything like that. So it seems to have no effect, which is great. Nothing negative, nothing positive. Um, but there is this reduction in testosterone levels. And there's an increase in something called sex hormone um binding globulin. Thank you. Uh I just want to make sure I didn't say the words in the wrong order. Um and those are the only two hormones we see that are effective. We don't know yet whether there's anything negative with that. We don't see signs that that translates into other negative aspects of health, but it's certainly something that that um happens. Um we don't see any uh negative effects in women. Um, we recently did a s did a study, it was just accepted today where we looked at whether there are differences, thank you, between men and women, and we find no differences between men and women. So, and there was another nice large study published in Nature Medicine, also no difference between men and women for weight loss and other aspects of health, which is different from the animal literature. This is again why I I don't animal literature is super important for me as a scientist, but I don't overweigh it.

SPEAKER_02 58:47

Yeah.

SPEAKER_01 58:48

Um and then the other question I get asked about is menopause. And um all the data, there are probably about half a dozen studies that have looked at postmenopausal women, either in comparison to pre-menopausal women or in general. And if anything, postmenopausal women they benefit just as much from intermittent fasting, if not slightly more, in terms of weight loss. So the good news is it looks like it's great for postmenopausal women too. But I don't see any aside from the small decrease in testosterone, I don't see any negative effects on sex hormones or women. And there was even one study showing that it decreased um PMS symptoms.

SPEAKER_00 59:27

So any anything on fertility?

SPEAKER_01 59:30

No. Um, there's one study looking at eating breakfast like a king, lunch like a prince, and dinner like a pauper, and they found an improvement in fertility in women with PCOS. It doubled the number of women who were able to have um their ovulation cycle restored. Um there was one study in women who were pregnant, and they found no negative effects of a 10-hour window on birth outcomes. So things like how big is your infant, their apgar score, which is like how well they're doing after delivering a bunch of other things. We don't have great data on this yet. In rodents, some of those studies suggest negative effects on fertility. I doubt we'll see that in people because like the amount of the amount of fasting we do in rodents is actually quite extreme to the amount that we actually do in humans.

SPEAKER_00 1:00:21

And I think a 10-hour window, right, is is is so you it's not that you're so manageable. You'd like to think that you're asleep for seven or seven or eight, ideally. Yeah.

SPEAKER_01 1:00:31

Yeah.

SPEAKER_00 1:00:32

Maybe not in practice. What about age-related differences? Do we do we know anything? Like if I'm should this apply in different ways to people at different times of their life?

SPEAKER_01 1:00:41

Yeah, we don't know, but there is um, there are a small number of studies in older adults. One of the most amazing things um is two of those studies have found that time-restricted eating increases uh six minute walk times. Love it. So this is like how far you can walk in six minutes if you're elderly and have mobility issues. And to me, this is actually quite amazing because this is not an exercise approach. This is like diet. Why should diet make you any better at your mobility? There should be absolutely none. Yeah, absolutely none. Um, so I find that amazing. And then about so all of all the studies, so things that intermittent fasting doesn't seem to help with very much cholesterol levels. Um, unless you lose a lot of weight, then it'll lower your cholesterol levels. Um, and then heart rate, at least in the fasting state, but about half of studies that have measured heart rate while exercising find that it lowers heart rate while exercising. So there's some sort of improvement there in cardiorespiratory fitness. And I've been asked, what do you think is going on? I have no idea, uh, which makes it interesting. Like why does it? Yeah, exactly. Exactly.

SPEAKER_00 1:01:43

On that note, are there any observed negatives, any downsides? Uh you know, not just things that don't improve, but things that get worse. Um lean tissue is the one that I I think. Muscle protein synthesis, but I I don't know if that's there's any good data for that.

SPEAKER_01 1:02:05

There's one study, and there's no effect on muscle protein synthesis with time-restricted eating.

SPEAKER_00 1:02:10

Well, calories equated, I calorie macros and calories equated, I would assume.

SPEAKER_01 1:02:15

I don't remember. I would have to go back and look. But there was no negative effect on muscle protein synthesis. I do still worry about lean mass for people who have done it a long time. Like I think Peter Atia said he lost something like 10 pounds of lean mass, but then when I heard what he was doing, I was like, oh, that's so extreme. I could have told you in advance you would have lost lean mass because you're not just doing TRE, you're having multiple days of fasting multiple times a year. So I definitely don't recommend that unless you have severe obesity and you need something like that. Um, negative effects. I think we do worry about pregnancy. I mean, I don't recommend it in pregnant women. Some intermittent fasting researchers don't feel as strongly as I do, but I wouldn't recommend it in pregnant or breastfeeding women. I would not recommend it in children because one of the ways in which intermittent fasting has positive effects on the bodies, it slows the rate at which your cells grow and divide. Or at least that's the best data we have. And so I don't think it's appropriate for growing individuals. And there's a small fraction of men who are still growing in their early 20s, growing in height. And so I wouldn't recommend it until your mid-20s. Um, but again, I tend to err on the cautious side. And then for shift workers, we don't know what the optimal time of day is for them to eat because they have very different circades. That's a tough gig. That's a tough gig. Yeah. So the best data we have is in people who do what's called simulated shift work, meaning that they're not shift workers themselves, but they adopt these schedules. And for them, it the data suggests it's better for them to eat when the sun is out. So when it's daylight outside, but we don't know for certain because we don't yet have data in people who that those studies are underway, but we don't think we quite have a solid answer yet. So there are not many negative things I know of in human humans. I think the biggest negative things are just the behavioral, which is like how does it impact your family life? Um, but in terms of health, we don't have any strong signals like that.

SPEAKER_00 1:04:03

Let's get into that, like a bit of strategy.

SPEAKER_01 1:04:05

Yes, okay.

SPEAKER_00 1:04:06

Because obviously, as I've explained, is I've I found find it quite difficult to do. And I think people with you know, very busy schedules, certainly with young children.

SPEAKER_02 1:04:15

Yes.

SPEAKER_00 1:04:15

I mean, there's no chance of getting a kid to stick to an intermittent fasting schedule anyway, even if it was beneficial, I think. But um, are there any good sort of practical tips and advice that you can give that can be like good takeaways to help people adhere to it? And the reason I ask that is I think it sounds so compelling. The data is compelling when we compare this to all of these other interventions that we're recommending for improving both quality of life but likely length of life, it seems we don't know for sure, but there's usually a correlation there. Yeah, certainly quality of life, um, but so much of quality of life, I think, for people is joy and you know, community, and and and a lot of that we experience around a dinner table, right? And I think um, so like any good tips or advice that you could give as sort of high-level strategies.

SPEAKER_01 1:05:04

Yeah, I can I can I'll give you several thoughts around this area. I don't have a magic bullet too, um, I'll say. So we have found a small number of strategies strategies really help people kind of stick with this program. One, we find a lot of our participants in our studies like to set alarms to remind themselves when to eat. And I think that becomes a kind of contract with yourself, keeping yourself accountable. And so I think that's great. I don't set them myself, but I think if that works for you, amazing. The second thing that we have found is um for a lot of people, their mood improves. And here's something where we actually have better data for intermittent fasting than calorie restriction. So I'm involved in a clinical trial right now. We're wrapping up data analysis where we compared calorie restriction versus time restricted eating for slowing the aging process. Amazing study. We're measuring things like biological age, stem cell number, telomere length, mitochondrial function, nutrients. Sensing pathways.

SPEAKER_00 1:06:01

Wait, this is ongoing.

SPEAKER_01 1:06:02

Yes. Well, what we finished the study. Well, we finished the study. We're analyzing the data, but I'm I'm still blinded, which means I don't know the results. Oh, okay. I don't know all the results. I know some of them. And we have some signals of some improvements in in biological aging, which is exciting. Um, but from that data, it seems that people's mood improves more with intermittent fasting um relative to calorie restriction. And that's despite the fact that people in our study, people lost more weight with calorie restriction because we did a really intensive version of calorie restriction where they lose like a lot of weight. So I think like big biggest loser style weight loss.

SPEAKER_02 1:06:35

Yeah, yeah.

SPEAKER_01 1:06:35

Uh, but mood was way better. And I'll tell you, in a lot of studies we have done, participants say their mood improves during the colour.

SPEAKER_00 1:06:41

What about energy levels? I think energy is the thing that you know. As soon as I hit my late 30s, 40s, yes, I felt like energy became a thing that I'd never been thinking about before. And now I'm like every day.

SPEAKER_01 1:06:54

It feels is there any any data on that? Yeah, we we have also found that people have reported more energy levels and less fatigue, but we haven't interestingly, we don't see any people don't repute report an improvement in sleep quality. So we're like, where does that come come from? That boost in energy levels. Um, one of our studies, we actually found that people were sleeping less when they did time restricted eating. So at first I was like, I was kind of alarmed by that. I was like, oh no, is it disrupting their sleep? So we looked at whether how hungry they were was, you know, correlating with um the degree to which they're they're they're sleeping and so forth. And when we looked closer at the data, it didn't look like people were staying up later or waking up earlier.

SPEAKER_00 1:07:35

Um interesting you say that because anecdotally, I think when I have been able to stick to it, yes, I think I have slept slightly less, but I feel like that's because I felt like I've needed less sleep.

SPEAKER_01 1:07:45

That's correct. So that's our leading, we don't have proof of this yet. But my guess is it does something called consolidating sleep. So it improves that. So and it and again, this goes back to the idea of like intermittent fasting is kind of this period of rest and repair.

SPEAKER_02 1:07:57

Yeah.

SPEAKER_01 1:07:58

And so if you have that longer period, maybe you don't need as much sleep, or maybe the sleep you're getting is more regenerative. Yeah, more restorative and maybe it alternates your sleeps, you know, it it might improve the amount of deep sleep. Who knows? Um, we will have data to answer this question. We put electrodes on some of our participants, so we'll be able to answer this. Hopefully, for that one. Yeah, awesome.

SPEAKER_00 1:08:17

I guess that makes that makes a lot of sense in that if you're expending less or diverting less energy to digesting food, you can get on with that process of restoration that sleep brings you. Correct. Maybe.

SPEAKER_01 1:08:28

Yeah, correct. Yeah, potentially. Potentially. I don't know. I mean, so again, this is another area like super interesting. I don't know for certain. Um, so other things that I think could help are meal planning. And this is just, I mean, even independent of intermittent fasting, such a great strategy. So we find that people who prep their meals in advance are far more um able to stick with whatever diet they're on. And it can be like, I don't even necessarily mean the the hardcore people who plan seven meals a week and weigh them all out. Like I'm not one of those type of people. I don't have time to be that one of people, but I'll make my food for the day in the morning. Yeah. I just, you know, do that. I have it ready. I'll have leftovers from like the night before. Like that's my lunch, you know. Like, so I think meal prepping matters a lot. And then we've also found that just social support seems to matter.

SPEAKER_02 1:09:14

Sure.

SPEAKER_01 1:09:15

We have people in our studies that range from like their whole family's gonna do it together, which matters a lot, to people who are like, my husband still wants me to cook and then he'll tease me while I'm fasting. And I'm like, well, that's not cool, you know. So even if you, you know, if you if you are even a partner of someone, you know, who that's a great point. If you're still you can at least be neutral, thank you, because you are helping that person.

SPEAKER_00 1:09:38

Because if you're having to prepare food, just being around food makes you feel hungry.

SPEAKER_01 1:09:42

Correct. And we have people who do great with that.

SPEAKER_00 1:09:43

Yeah.

SPEAKER_01 1:09:44

But I'll tell you, it feels a little bit like a punch in the gut if their partner or someone else is teasing them about it and saying, look at this great food I'm eating, right?

SPEAKER_00 1:09:50

So Courtney, I've heard you talk about this uh uh the concept of a metabolic kitchen. Yes. Can you can you explain how that is helping to sort of move the science forward and the implications of that?

SPEAKER_01 1:10:00

Yeah. So one of the things that my lab does that very few labs in the world can do, is we use a metabolic kitchen to do these very precise assessments of people. So most of the studies on intermittent fasting, you go out, you tell people what to do, and they have to change their behaviors. We have this kitchen where we can prepare all meals and we can um, and the beauty of that is then if we have people go do intermittent fasting, um, we can make sure all the groups are eating the same amount of food. So if there's any differences between groups, it's not because one group had cornflakes for breakfast and another group like like skipped breakfast and then had like a turkey sandwich. So we can precisely match and control what people are eating. This also allows us, because we can prepare all meals and we give them to our participants, we can also um prevent them from gaining or losing weight. So a lot of my research has focused on are there benefits of intermittent fasting independent of whether you lose weight? And so in our studies, we were the first to show that intermittent fasting has benefits or at least some types. We don't know how broadly this generalizes, um, can improve some aspects of your health, even if you don't lose weight. So one of in one of our first clinical trials, we had um men with pre-diabetes come in and they followed they ate within a six-hour window or 12-hour window, and they tried both schedules. And on both schedules, we fed them all their meals. And the crazy thing is we actually watched them while they ate all their meals to make sure they're eating at the right time of the day.

SPEAKER_00 1:11:23

So it's a bit like prison.

SPEAKER_01 1:11:24

Yeah, it's a little bit like prison. They're paid. They're paid though. We do pay them well. Um, but this is the second most rigorous type of study you can do, and they're very hard to do. The first most rigorous, which you almost never see done, um, are live-in studies where you don't allow people to leave the lab. You know, it's very hard to find people who are willing to donate two months of their lives for these studies. So we do the next best thing, which they don't live in, but we feed them all their doing it for two months. Uh they can. In our studies, we've yeah, yeah. In our recent study, they did it for two two months. It wasn't a live-in study, but yeah, yeah. They had to eat only the food we served them. They had to video record themselves eating all the meals, and we recorded the timestamps on every single video. So we knew that they were actually following the schedule.

SPEAKER_00 1:12:07

How are you watching them?

SPEAKER_01 1:12:09

Um, they recorded it.

SPEAKER_00 1:12:10

I I envisage it as like an interrogation room with a one-way mirror.

SPEAKER_01 1:12:14

Um, they record themselves on a smartphone and then they upload it to a secure link that no one else can access.

SPEAKER_00 1:12:21

And then how do you know that they weren't sneaking in some more food though? Off camp.

SPEAKER_01 1:12:24

We don't know for certain.

SPEAKER_00 1:12:25

Yeah.

SPEAKER_01 1:12:26

Most of our participants, but it's I'll tell you, it's very hard. It's much harder for them to sneak the extra food because they're so full. Most of our participants say they're really full um because the diets we feed them are generally a little bit higher fiber than they're than they're used to. Plus, they're eating all their food in a short period of time. So we think the amount of cheating is low, but it's far more rigorous. I mean, it's not perfect, but it's far more rigorous than what anyone else is doing.

SPEAKER_00 1:12:51

Well, I would I would imagine that given that they have volunteered to be part of the trial, they're not going to go and then cheat. Or certainly less of them are likely to.

SPEAKER_01 1:12:58

Yeah, yeah, much less likely. Much less likely. And the beauty of this too is when people are cheating, we usually can catch it because normally the way in which we'll see them cheating is they don't record videos of themselves. So we will kick a number of people out of the study if they're not following, not either in the foods or not eating at the right time. So this allows us to catch and weed out the folks who either struggle or or are not usually it's they're not you seriously committed, or they thought it would be an easier study, yeah. Uh, so to speak. So my lab does about half of studies like this that are super rigorous, and then the other half are like sort of classic studies where you go out and tell people to change their behaviors, but they report back to you what they're doing.

SPEAKER_00 1:13:35

Why are more people not doing this?

SPEAKER_01 1:13:37

Expensive.

SPEAKER_00 1:13:38

It's just the cost.

SPEAKER_01 1:13:38

It's yeah, it's it cost and you need more training to do it, um, and you need the facilities to do it. And there are very few um institutions in the world that have these research kitchens. They're not hard to run, but you need a critical mass of scientists to do them, and they're just expensive. So, I mean, before I came to Harvard, I mean, uh, there were probably only like a dozen places in the world that I could go, at least in the US, to do these types of studies. Not because it's hard, but there's not the critical mass of researchers or they don't currently have a kitchen.

SPEAKER_00 1:14:06

This is a whole nother topic for discussion, but it feels like this area of research is so impactful for the nation's health that the funding situation, we should have more than enough coverage. Right.

SPEAKER_01 1:14:18

So actually, there was a heyday for this type of research. It's sometimes called like metabolic ward research. But some of the most profound insights we've got into energy or just metabolism in humans have come from these live-in or inpatient studies. I think it was about, I might be wrong on the timeline, but uh maybe uh two decades ago. The NIH has several different institutes, but they have an institute um um that funded a lot of these programs. They funded what were called GCRCs, but allowed these very precise um studies to be done. And then funding for that got cut and it killed a lot of research in this in this area. So um what it took to for me to get these studies off the ground was actually really hard, not because it the X like it was not rocket science, but the the the will, the funding or whatever to get off the study the ground was hard.

SPEAKER_00 1:15:12

So there's a lot of perseverance.

SPEAKER_01 1:15:13

Yeah, I had to, yeah, a lot of perseverance to achieve the the goal. So but these types of studies when they're done are phenomenal because you get to ask questions like if someone can perfectly stick to a diet, what are the effects on health? So if you, for instance, go out and ask people to follow a Mediterranean diet, you know, they have to understand what that means. They have to have the money to buy the food, you know, and they may not understand what that fully means. But if we can go out and say, eat this food, we've already made it for you, and we'll usually even weigh out this food to the nearest gram. So it's super precise.

SPEAKER_00 1:15:44

Um even when you account for all of those things, yes. Um, if they're not getting the food, then they can just under-report. Like it just happens all the time.

SPEAKER_01 1:15:53

Exactly. So these studies are actually very beautiful when you do them because you can usually see much bigger effects on health. And then you know, okay, this is the true effect on health. Because to me, it answers the question like, is this an approach that's worth us studying? Like, is there value to this? Because if you do a study like this and there's no benefit, well, there's just no benefit. Why are you wasting your time trying to find a way for people to do this?

SPEAKER_00 1:16:14

Can I ask you a personal question then? Given that you have successfully adhered to doing, you know, the earlier version of time restricted eating, yeah. Have you what have been some strategies you've used for yourself with children after that period where you know you have to not eat then until you wake up the next day?

SPEAKER_01 1:16:31

Yeah, biggest secret is to make all my food in advance, like that morning. I just put everything out. So I'm a I'm a four meal a day person. Occasionally I do three, but I like four. There's no there's no scientific reason it works well for me. Um and I think snacking is not great. And our generation, like the younger generation, tends to snack more and eat later at night. Um, so I just weigh them out. I eat at pretty much the same time every day. I get super hungry if I don't because I'm still so hyper adapted to that. So um, I'll usually have my first meals starting between like 7:15 to 7:45. So roughly 7:30. I'll eat my next meal two hours later, my next meal, you know, between 11 and noon, and then I just have one more meal.

SPEAKER_00 1:17:14

What time do you wake up in the morning?

SPEAKER_01 1:17:15

Uh, seven.

SPEAKER_00 1:17:16

Oh, so you're eating fairly quickly after you work out.

SPEAKER_01 1:17:18

Correct. Yeah. One of the other myths is that you can't eat right away when you wake up because a lot of people say you have elevated cortisol levels. That's true. Your cortisol levels are elevated, but there's a little bit of a time delay between when cortisol raises blood sugar levels, like it's not immediate. And moreover, it's it's sort of outweighed by the fact that your body's better at secreting insulin in the morning and your what's called your insulin sensitivity, but the ability of that insulin hormone to do its job is also better in the day. So, yes, cortisol is higher, but it's not the predominant factor that controls your blood sugar level. So if you're eating anytime after about 5 or 6 a.m. in the morning, for most people, there are exceptions. So patients with type 2 diabetes, they're an exception to the rule. People who do shift work, they're exceptional role. But for most people, you're already going to have good blood sugar control. If you can ideally also get outside uh before you eat, um, I, you know, I don't have my glasses here, but I actually have light therapy glasses that I wear in the morning that shine blue, green, wicked. That's great. I use the Pegasi model.

SPEAKER_00 1:18:19

I use them every well, not now, but in the winter I was using them.

SPEAKER_01 1:18:22

Yeah, so most mornings I'll wear though for those for an hour in the morning while I'm getting the kids ready for school.

SPEAKER_00 1:18:26

Do you think they work? I feel like they do.

SPEAKER_01 1:18:28

Well, we're testing them now, one of our clinical trials. Yeah, we're our angle was to see if they improve blood sugar control, fat loss, circadian rhythms, sleep, um, blood pressure, cardiovascular diseases.

SPEAKER_00 1:18:39

I feel like they certainly help me wake up quicker. Yes. And I think if you live in New York, daylight is at a premium when you wake up in an apartment and say, like, yeah.

SPEAKER_01 1:18:48

I'm quite taken with the data on sunlight. Yeah. There's not a lot of a lot of it, but um, or certainly at least the data on circadian rhythms. Um, but the um the bright light will drop both melatonin and cortisol levels, and about it's roughly half of the population, it takes a while for their melatonin levels to drop in the morning, and melatonin will increase your blood sugar levels when it's elevated.

SPEAKER_00 1:19:12

Courtney, this is another question that I'm framing for a friend. They asked me to ask you this. When you say um like breaking the fast, is that nil by mouth? Like nothing other than water, like if if you were to have a black coffee first or electrolytes or some is that allowed or not?

SPEAKER_01 1:19:31

Um, we don't know for certain. Um, most of us researchers, so coffee we don't agree on as researchers, whether it breaks the fast or not. Um, I've done studies both ways, full disclosure, where we've said coffee needs to be in window or you could have it any time of day. A lot of studies will use a cutoff of like five calories. So if something is less than five calories, we count it as fast as you're gonna be like, coffee would probably be fine. Right, exactly. Black coffee would be fine, diet soda would be fine. I don't recommend diet soda, but I've worked in in uh geographic areas where diet soda is much more commonly consumed.

SPEAKER_00 1:20:06

Yeah, than water.

SPEAKER_01 1:20:07

Or in populations because we're often working with people who are sick and want to improve their health or have some sort of condition where they want to improve their health. Um, squeeze of lemon, fine. We say chewing gum's fine. Um the reason why coffee has been controversial is we know it affects some, I'm just gonna say metabolic pathways. And so the question is like, how much does this does this really count? There are some studies, there's some people who say that having a high fat meal shouldn't really count as breaking the fast, but I don't agree with that.

SPEAKER_00 1:20:40

Um wait, who's saying this?

SPEAKER_01 1:20:43

That sounds outrageous to uh I've seen a couple studies in the literature where they try to extend the fast by people giving people a high fat energy bar.

SPEAKER_00 1:20:51

No way. I don't buy it. How does that apply? That that's a made-up rule.

SPEAKER_01 1:20:54

Well, so so a lot of people think that a lot of the mechanisms of intermittent fasting are the same mechanisms for low-carb diets, meaning the ways in which these things work are the same. Yeah, but there are a small number of studies that show yes, there's some overlap, but there are a lot of differences too. Yeah, it's not the same. It's not the same.

SPEAKER_00 1:21:12

It's nuanced.

SPEAKER_01 1:21:13

It's nuanced, yeah.

SPEAKER_00 1:21:14

I think look, the most exciting thing is that as a as a topic as a whole, it this just seems incredibly beneficial for the amount of lift and energy that it takes.

SPEAKER_01 1:21:24

So, yes, there was a nice survey done last year. Um most people don't know this, but intermittent fasting now is about as popular as GLP once, but you see more press on GLP GLP1. So it's the third most commonly practiced diet diet in the US among people who practice or subscribe to a particular dietary uh pattern. So it's kind of exploded in popularity. Um, so it's about 13% of the US population practices.

SPEAKER_00 1:21:49

As it should, you know, I'm I'm I've said this before, I'm worried about the long-term effect on certainly on body composition, like lean tissue mass and bone density for this very rapid weight loss. I think we're starting to see that data on bone now, which we hadn't in the past. And I think that's worrying, especially in an aging population.

SPEAKER_01 1:22:08

Yeah, so um, I'm good friends with the scientists who did the longest study of calorie restriction in humans, and the goal there was to slow the aging process. And the interesting thing they found is around one to one and a half years after cutting their calories by about 25%, body their body weight started plateau. So they started to either, you know, maintain their weight or start to rebound a little bit, but they continued to lose bone afterwards. And that scares me, right? Because technically they're no longer losing weight and they're still losing bone.

SPEAKER_00 1:22:37

Yeah.

SPEAKER_01 1:22:38

So I worry about that. I worry about loss of lean tissue. Um, and that's gonna set you up too to for extra fat to be stored in some of your organs, which we know leads to a lot of these metabolics.

SPEAKER_00 1:22:49

And it just becomes incredibly difficult to get that back, you know, bone almost impossible.

SPEAKER_01 1:22:53

Um yeah, and I'm not opposed to GLP1s. I'm sort of a like, let's do lifestyle first. If all else fails and you have, you know, a severe obesity or some other condition, like these are life-saving drugs. So I don't want to be misinterpreted, but I'm generally a like lifestyle first, fancy stuff second.

SPEAKER_00 1:23:10

Especially if it's for aesthetic or you know, overall um feeling of well-being and not like a dramatic need for weight loss. That is a whole nother episode though, I'm sure. Okay, I'm mindful of your time here, and so I'm gonna move on to some quick fire questions.

SPEAKER_02 1:23:25

Sure. Okay. Okay, great.

SPEAKER_00 1:23:26

And the the only rule here is that you can't spend more than 30 seconds answering.

SPEAKER_02 1:23:31

Okay, fine.

SPEAKER_00 1:23:31

Okay.

SPEAKER_01 1:23:32

Good deal.

SPEAKER_00 1:23:32

What would you say is the most overhyped longevity trend?

SPEAKER_01 1:23:37

Oh my goodness. That is such a hard question.

SPEAKER_00 1:23:41

You can have more than 30 seconds for this then, because it's important.

SPEAKER_01 1:23:44

There's so many. I don't know if there's a standout, but I well then you can't. I think what I would say is a uh a lack of focus on the fundamentals. Which I know you we were talking about earlier, but I generally I'm like a John Wooden kind of people for people who don't know, famous basketball coach and his one of the most women basketball coaches of all times. And he was like, players come in, they want to focus on the layups, but it's all about the free throws that you shoot like a gazillion times a day and like the fundamentals. So I'm a fundamental person. Like, don't look at these trends like right let red light therapy sauna, etc., until you get your own house and gear. So I'll give you an example. So in the last six years, I've given birth to two children. I've lost both my parents. I'm still grieving from the loss of my mom. Um, I've been bedridden from uh uh an epidural gone wrong, um, lost a lot of muscle mass, which I've rebuilt. Um, and I had long COVID or the equivalent, and I haven't slept enough. But I'm getting my life back on gear. So I just started sleeping um the last week. And my process is gonna be so I've always been really good with diet that that comes easily to me. So that's always been in gear, regardless of how cedo life is. But my goals for the, you know, for the first time sleep number one, I'm gonna get back to five sleep cycles a night, which is my target, and then get exercise back in gear. And I'm gonna do all of that and you know create a solid foundation before I think about any fancy tools and other stuff. Yeah.

SPEAKER_00 1:25:10

I think you've effectively answered my next question, which is what is the most underhyped longevity trend? Anything to add to that?

SPEAKER_01 1:25:18

I mean, I think I would say sleep. I think people tend to understand exercise and diet are important, but I would say sleep. Um, and if I were to put a second one, I would put maybe purpose or mental health.

SPEAKER_00 1:25:30

But I love that.

SPEAKER_01 1:25:32

And I think it's not just mental health because you can feel happy, but you can be empty if you don't know like why you're here, what you're doing, or you have like some mission or some purpose greater than yourself. And it can be small, but still meaningful to you. And I think have your life has meaning.

SPEAKER_00 1:25:46

Yeah, and I think it's actually easier to cope with the periods of unhappiness when you have purpose as well.

SPEAKER_01 1:25:52

Yeah.

SPEAKER_00 1:25:52

Okay.

SPEAKER_01 1:25:53

But sleep. I think too many people cut their sleep short. And my guess is you know, actually, one of the things I used to like to say to some of my students in the lab is what do you think is the fastest way towards elevating your blood sugar levels? Big Mac being sedentary or uh losing sleep? And the answer is losing sleep. With sleep restriction, four to six hours, you can worsen insulin sensitivity by about 33% overnight.

SPEAKER_00 1:26:16

How much are you averaging a night right now?

SPEAKER_01 1:26:19

Um, last night I got about seven and a half hours of sleep. But I've been more I've been closer to seven, but my sweet spot is seven and a half to eight.

SPEAKER_00 1:26:26

So that's my first goal for Do you track your do you wear a wearable?

SPEAKER_01 1:26:30

I do, but I'm not a huge tracker.

SPEAKER_00 1:26:31

No, me neither.

SPEAKER_01 1:26:32

Because I'm more of a like, let's focus on the fundamentals. So I actually am using the tracker right now to measure my sleep time. Um and I'll measure my steps. But that's it. I don't tend to do fancy stuff. Occasionally I'll measure my heart rate if I want to be in a certain zone.

SPEAKER_00 1:26:46

I think capturing that data is incredibly valuable. More data is better. Yes. But I don't think you need to do it continuously, especially when you start to get some intuition about what is right for you and the longer you you do it for. So I like to do it like every quarter. I'll do a couple of weeks of tracking everything.

SPEAKER_01 1:27:00

Yeah.

SPEAKER_00 1:27:01

And then I can observe that.

SPEAKER_01 1:27:02

I think intensive tracking for short periods of times is fantastic. I actually do. So let me make an exception to the rule I said. So I think intensive tracking for a short period of time is really helpful. We see it a lot actually for nutrition studies, because sometimes people are like, oh, I think I know how much I'm eating. And they're like, doll up a peanut butter here, but it's like double. It's two tablespoons, not one, or something like that. So I think intense periods of tracking to see where you are are great, but long term I'm a more of a minimalist.

SPEAKER_00 1:27:28

What does a what does a normal day of eating look like for you? Not the timing, but the types of food.

SPEAKER_01 1:27:35

Um, so this is where I have kind of like a rough formula per se. And I think it keeps it easy, but it still gives me flexibility. So uh morning is a smoothie. It's a giant fruit smoothie with flax seeds, bananas and orange, berries, a little bit of almond milk, and a little bit of protein powder.

SPEAKER_00 1:27:52

But you put the orange in with almond milk.

SPEAKER_01 1:27:54

I do.

SPEAKER_00 1:27:55

It's criminal.

SPEAKER_01 1:27:57

A little bit of dates, yeah.

SPEAKER_00 1:27:58

Okay.

SPEAKER_01 1:27:59

Uh so this is my sweet. Spot. It works well for me. I just rotate the berries every day. So keep it interesting. Second meal of the day is a lot of fruit, dried fruit, fresh fruit, nuts. I'll do a handful of nuts. I'm really quite convinced by the data on nuts.

SPEAKER_02 1:28:15

Agreed.

SPEAKER_01 1:28:16

Which is kind of ironic because I was recently part of nutrition class and a lot of people still fear fat. And I believe they're good carbs and bad carbs and good fats and bad fats.

SPEAKER_00 1:28:25

So um we had Darius Mozarium from Fruitish Medicine and last week.

SPEAKER_01 1:28:30

Um lunch for me is always a meal of beans, mostly beans and vegetables. And then I'll do a third of a pound of steam greens, and then my last meal of the day is a fruit smoothie with um two-thirds of a pound of greens.

SPEAKER_00 1:28:41

What's your guilty pleasure?

SPEAKER_01 1:28:43

Chocolate, dark chocolate. I'll often have a square or two a day. So that's my treat. You know.

SPEAKER_00 1:28:47

Do you ever drink alcohol?

SPEAKER_01 1:28:49

I don't. Uh very rarely. Um, largely it's for reasons of taste. But yeah.

SPEAKER_00 1:28:55

It's going out of fashion anyway.

SPEAKER_01 1:28:56

I know it is, surprisingly. Yeah. But yeah.

SPEAKER_00 1:28:59

What do you think is one trend we'll look back on in 10 years' time and say, I can't believe we used to believe that's true, or I can't believe we used to do that.

SPEAKER_01 1:29:08

Gosh, I feel like we go through all these trends in nutrition about, you know, fat is bad, fat is good, protein is bad, protein is good. And I think we'll just go more towards focus. My hope is whole foods and processed foods. Um, there are other things, but in that direction as well.

SPEAKER_00 1:29:26

I think this is we're making progress.

SPEAKER_01 1:29:27

Yeah, I think so too. Um, and then I think we focus a lot on aesthetics and trying to slow the aging process from aesthetics. So I wonder if certain aesthetic approaches will be like, why did we ever do that?

SPEAKER_00 1:29:40

Why do we care about that? Right, yeah.

SPEAKER_01 1:29:42

Yeah.

SPEAKER_00 1:29:43

What is one thing?

SPEAKER_01 1:29:44

Not that I don't think people will care about aesthetics, but they'll probably tend to use more natural approaches. So I'll give you an example. I've not had any treatments done myself, but like uh we inject our face or society, a lot of people inject their faces with these artificial fillers. And I think in the long term, people will go with more natural approaches like fat fat grafting, or I forget the term for it, but you know, implanting fat rather than these artificial fillers.

SPEAKER_00 1:30:08

Yeah, things like that. There is a time for that, and I don't know.

SPEAKER_01 1:30:10

I know, and I should know it, but I don't I don't remember it.

SPEAKER_00 1:30:12

Yeah, okay. I'm gonna find that out on this.

SPEAKER_01 1:30:14

Yeah, but I think we'll be going for more natural approaches like maybe microneedling with PRP or some things like that, or using light and less of these um more artificial.

SPEAKER_00 1:30:23

What is one thing that you wish you'd known 20 years ago that you would tell yourself back then?

SPEAKER_01 1:30:32

Oh my goodness, in regards to health or broadly speaking, life.

SPEAKER_00 1:30:38

Well either.

SPEAKER_01 1:30:41

Oh gosh, I don't know. That is a tough thing.

SPEAKER_00 1:30:44

These are not really quickfire, are they? Like my question.

SPEAKER_01 1:30:48

That's okay. You can just philosophical. I don't know. I think my weakness from a health perspective is stress. Some of that's time management. I feel like I have great skills, but I need even even better skills than I have with everything on my plate. So I think maybe this is not quite a perfect answer, but I think figuring out how to deal with stress, what that looks like, work-life balance. I work intensely hard, carving out time for myself is hard. Yeah. I don't have an answer, but that's a weakness. No, that is a fair one.

SPEAKER_00 1:31:19

Yeah.

SPEAKER_01 1:31:19

Yeah.

SPEAKER_00 1:31:20

Okay. If money were no object, you have all the resources in the world, yes, all the funding, all the backing in the world.

SPEAKER_02 1:31:27

Yeah.

SPEAKER_00 1:31:27

What unanswered question within your domain would you like to answer? Like if we could get any amount of funding to answer a question or move the science forward, what would that be?

SPEAKER_01 1:31:37

Yeah, two. And I know exactly what they are, and I've been thinking about them for years. Okay. Um, the first one's in the realm of intermittent fasting, the second's in the realm of diet quality. For intermittent fasting, I want to bring people in the lab, test uh intermittent fasting by eating early in the day, or time restricted eating by eating early in the day, late in the day, and do really deep, we've been calling it phenotyping. But I want to know, um, I want to also use something called stable isotope tracers, which is a fancy way of like tagging molecules so we can follow them in the body. So I want to do is line up what's going on with metabolism, like where people are in their sort of fat burning versus glycogen store burning process as a function of the number of hours they've been fasting, and then also overlay that with measuring the hallmarks of aging or major biomarkers of aging and measuring them at least once an hour over the course of the day. So we can kind of see not only how the degree of fast, that both the time of day you're eating and the amount of fasting you do, you do affects these biomarkers, but also understand like how much of this varies individual by individual. Like, you know, if you have excess fat to lose, maybe you need to fit fast longer to get to these sort of like therapeutic, rejuvenative, rejuvenative range. So these are very hard and very expensive studies to do. So for instance, I had, you know, a two and a half million dollar grant from the NIH, and we did a similar study to this called our meal timing study, where we brought people and we couldn't measure all these things because it was so expensive. But just to bring people in and to measure primarily just a small number of things like glucose, insulin, and blood pressure. I mean, we could only we ran less than a hundred people and we couldn't even do any of these assessments. I mean, so they're so expensive. So that would be the first dream study. And then we can also look at all these inter-individual differences, but I think a study like that could blow open multiple fields. So I've been thinking about how to get that funded for years because I can't fund that under a traditional NIH mechanism. And the second study in diet quality is I'm really interested in focus medicine. Like, can you take someone with a chronic disease? You know, about 30 years ago, we used to think type 2 diabetes was not reversible. Um, we now have data from something called the direct trial, where putting people on a very low calorie diet, so less than 800 calories for about 12 to 20 weeks, um, puts people in remission from type 2 diabetes. About 46% of patients go into remission. I'd love to push that higher and test different diets for diabetes remission and see if we can get it just by improving diet quality, not by cutting calories that dramatically. Um, so I'd love to do a study to see if we can reverse type 2 diabetes testing different diets for that, which would also be an expensive study. But those are my two dream studies. Those are my two dream studies. Okay. If I could if I could only do two other studies for the most of my life, those would probably be it. And I would measure in the first study, I'd measure biological age. Maybe there's one other study I have that would compete with that, but that gives you a sense.

unknown 1:34:31

Yeah.

SPEAKER_00 1:34:32

I think that's where there are companies that can sort of step in and that before. Yeah, some parts of it. In some part. Yeah. Yeah. Okay. Two more questions. Yes. And then I and then you're free.

SPEAKER_02 1:34:43

Okay.

SPEAKER_00 1:34:44

First one is uh what makes you most optimistic about this field at the moment? You know, what what in the space? And it can be in a different domain of science. So, like, where are you where are you feeling positive?

SPEAKER_01 1:34:56

Um, I think the number of people who are interested in intermittent fasting and nutrition has dramatically increased. And I think now the current administration is trying to get nutrition taught more in medical schools. So I think where I think the interest is there. We just need the funding to make things happen.

SPEAKER_02 1:35:15

Yeah.

SPEAKER_01 1:35:16

So um, for instance, less than 5% of the NIH budget funds nutrition, even though it's the leading cause of death and disease. And so I I I think I think the will to do the work is there now. And interestingly, I think all of the popularity in social media has been good for scientists in a sense. I think people tend to think of it as all negative. And yeah, there are now negative elements, but I think there are a lot of positive elements. I think we just need the pathways to get there. I don't want to say quite that we need a moonshot in nutrition because it's not one single effort, but I think we need the government, private individuals to help us get there because the will is there. It's just that the pathways or the funding is not quite there.

SPEAKER_00 1:35:58

Okay, last one.

SPEAKER_01 1:35:59

Yes. This is time. Okay.

SPEAKER_00 1:36:02

If the listeners of this podcast are only tuned in right now, okay.

unknown 1:36:07

Yeah.

SPEAKER_00 1:36:08

What would be the one takeaway that you would give them?

SPEAKER_01 1:36:12

I would say that our best evidence in people suggests that eating um having a longer daily fasting duration, ideally, if you can do 16 hours a day, if not 14, and or eating early in the day looks like it improves their health. And if they can come up with some sort of daily schedule that can follow five days a week that incorporates this principle, they'll probably see some health improvements.

SPEAKER_00 1:36:37

Courtney, thank you so much. That is a privilege and a pleasure.

SPEAKER_01 1:36:41

You're welcome. Thanks for having me.

SPEAKER_00 1:36:43

I'll see you for episode two.

SPEAKER_01 1:36:44

Okay, great.