Welcome to Special Guest Episode 431 of The Intermittent Fasting Podcast, hosted by Melanie Avalon, biohacker, founder of AvalonX, and author of What When Wine Diet: Lose Weight And Feel Great With Paleo-Style Meals, Intermittent Fasting, And Wine, and Barry Conrad, actor, singer-songwriter, and creator and host of Banter with BC.
Dr. Courtney Peterson is an Associate Professor in Nutrition Sciences at the University of Alabama at Birmingham and an internationally-recognized researcher in the field of intermittentfasting and meal timing. Dr. Peterson conducted some of the first studies of a type of intermittent fasting called time-restricted eating (TRE; daily intermittent fasting) in humans. Her research has shown that iTRE induces weight loss, alters hunger, improves blood sugar, lowers blood pressure, decreases oxidative stress, and activates anti-aging pathways—and that many of these effects are independent of weight loss. Currently, she is the lead or co-lead scientist on some of the largest studies of intermittent fasting in humans, including in patients with type 2 diabetes, prediabetes, and cancer. Her research has been featured in more than 100 media outlets, including NBC Nightly News, The Wall Street Journal, The New York Times, TheWashington Post, Good Morning America, and the BBC.
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TRANSCRIPT
(Note: This is generated by AI with 98% accuracy. However, any errors may cause unintended changes in meaning.)
Melanie Avalon
Welcome to Episode 431 of the Intermittent Fasting Podcast. If you want to burn fat, gain energy, and enhance your health by changing when you eat, not what you eat, with no calorie counting, then this show is for you.
I'm Melanie Avalon, biohacker, founder of AvalonX, and author of What, When, Wine. Lose weight and feel great with paleo-style meals, intermittent fasting, and wine. And I'm joined by my co-hosts, Barry Conrad, actor, singer-songwriter, and creator and host of Banter with BC. For more on us, check out MelanieAvalon.com and BarryConradOfficial.com. You can submit questions for the show by emailing questions at iapodcast.com or by going to iapodcast.com. We would love to hear from you. Please remember, the thoughts and opinions on this show do not constitute medical advice or treatment, so pour yourself a mug of black coffee, a cup of tea, or even a glass of wine. If it's that time, then get ready for the Intermittent Fasting Podcast.
Barry Conrad
Hey, everyone, and welcome back to the Intermittent Fasting Podcast. I'm Barry Conrad, and this is episode number 431. I'm genuinely stoked about today's episode. It's a special one.
A little while ago, a bit of backstory here for you. I was trying to do a deep dive into some intermittent fasting research, and I came across this study. And I could only find the abstract, and so it had an email, and I reached out to this person. And I'm like, hey, do you have the study, the full thing? And she's like, well, actually, it's a series of studies that I've done, but I'd love to actually be on your podcast if you'd have me. And the person I'm talking about is internationally renowned researcher Dr. Courtney Peterson. Welcome to the show, Courtney.
Dr. Courtney Peterson
Thank you, Barry and Melanie, for having me here.
Barry Conrad
It's such a pleasure to have you here. We we always bring a study to start our show off.
And so I was really, really interested in what I found. I mean, you trained in metabolism and nutrition at Pennington Biomedical Research Center, and in chronobiology at Brigham and Women's Hospital. Let's go right to the beginning. What sparked your interest in terminal fasting? And what point did that start? Let's go all the way to the beginning.
Dr. Courtney Peterson
Yeah, so 17 years ago, a long time ago, I was in graduate school for physics. And this was the sort of dawn of podcasts. And I remember one day just being in the kitchen, and I heard a podcast about a new study, where they had asked people to eat in a four hour window, and fast the remaining 20 hours a day. And on the podcast, they said, Oh, the participants, they, the people in the study, they had so many different benefits, it was great for their health. And I thought, Wow, that sounds extreme, but I've never shied away from anything that was extreme.
And I thought, Well, that sounds really interesting. And then over the next maybe two or three years, I got really intrigued by the power of fasting. And this was all through, you know, just reading health forums online. And, and I got to thinking, okay, other types of fasting, I mean, it would be wonderful to do periodic water only fast for a few days at a time, but that's probably too extreme for most people. So if you wanted to get the most anti aging benefits, what should you do? And I sort of came to the conclusion, the answer is probably daily intermittent fasting, because you can do it more often and get a little bit of the benefit every day. And so around I guess this was 2010, I started practicing it myself and was quite impressed. And then in 2011, I switched careers and knew I wanted to study either intermittent fasting or healthy diets. And I reached out to one of the first researchers who had done an intermittent fasting study in humans and joined his lab. And the rest is sort of history. And that launched my career till today where I run I now run one of the largest research labs in the world that studies intermittent fasting in humans.
Barry Conrad
That's incredible. Going back to switching to nutrition, you mentioned previously that you were interested in astrophysics.
What's the connection between astrophysics? How did you get from there to nutrition? It's a bit of fasting. That's a big chasm. What happened there?
Dr. Courtney Peterson
No natural leap there, but I was studying the physics of the early universe less than a second after the Big Bang. Why do we think there are galaxies and clusters of galaxies in the universe today? I just got to the end of my work and I realized most of probably our theories of the early universe are going to be wrong.
At the time, I was influenced by graduation speeches by Steve Jobs where he was saying if he had too many days in a row where if he died the next day, he wouldn't be happy with what he was working on. My version of this was if I fast-forwarded 30 years from now and I look back on my career and I had failed, would I be glad I took the risk? I couldn't say that for astrophysics and I'd always been interested in nutrition. I even really was interested in bodybuilding for a while in my teens, so I just made the switch because I just realized that food has such a powerful ability to serve as medicine. I really wanted to help that field advance and help save more lives.
Barry Conrad
That's incredible. Bodybuilding, even, that's not something that I saw you saying on this podcast. What's the deal there?
Dr. Courtney Peterson
I did for a short stint in middle school, and this was back in the 80s when my parents didn't know what to do with a teenage girl interested in weightlifting, but I still carry my knowledge of rep ranges and weight ranges and set ranges for different, you know, growth versus strength versus power targets. But just to say, I've always been really impressed and fascinated by how powerful lifestyle approaches are for improving our health and slowing the aging process.
Barry Conrad
Right. And not only are you the principal investigator for several clinical trials on time restricted eating, and as you said, like one of the largest labs, what have been some of the most surprising findings or challenges from leading studies of like the scale, like such a massive scale?
Dr. Courtney Peterson
Yeah, so I'll even just start with a little bit of background on intermittent fasting that's pertinent to aging. Some of the first research done on intermittent fasting actually dates back to the 1940s. It was based on work in the 1930s showing that eating a low-calorie diet, which we now call calorie restriction, which your listeners can just think of as standard calorie counting, so eating fewer calories extends lifespan. It does so quite powerfully. It dramatically slows the aging process. If you do this in mice and rats, they can live up to 40% longer, which is huge. Back in the 1930s and 40s, they were like, well, I don't know if people will do this. I wonder if people would do calorie restriction or calorie counting intermittently and whether it could still extend lifespan. One of the first studies that was actually done on intermittent fasting was done in the late 40s. They found, indeed, that if you fast periodically, so not all the time, that it actually did extend lifespan, and it also reduced the rate at which the rats developed cancer, too.
It had other benefits in proving healthspan. Then research petered along for several decades. Then around the turn of the century, in 2003, there was a very famous scientist who we often think of as the founder, the modern-day father of intermittent fasting research, Mark Mattson. He was having a debate with one of his researchers in the lab. They were debating whether the benefits of calorie restriction were, indeed, due to the animals eating less or if it was because they were eating all their food so quickly, so inadvertently fasting for longer each day. They put this to the test, and they did a study, and they found, actually, that it looks like intermittent fasting has benefits independent of how much you eat, that there's something special about having periodic fasting that can improve brain health and blood sugar control in this particular study. Then fast forward to 2018, and there was a study showing that, actually, in fact, at least 40% of the life-extending benefits of calorie restriction or calorie counting are not due to eating less. They're due to having a longer fasting period. Then, just two years ago, we've actually learned that intermittent fasting is actually more powerful than cutting calories for extending lifespan, at least in animals. We now have four or five different studies showing that intermittent fasting, particularly daily intermittent fasting, extends lifespan in animals. That's where the animal research takes us today, and then I'm happy also to talk about some of the human research, too, but I'll pause there.
Barry Conrad
Right. Well, you know, Mark Metzen, as you mentioned, you know, he had that study, the OMAD study with three meals a day, over 11 days, and you know, with equal calories in both groups, and how they found that the greater weight and they had greater weight in fat loss, but also greater loss in lean mass and bone density.
So from then to now, has the research and the findings changed? Because for someone like myself, I do OMAD, I am big in the gym, I'm all about protein, all about muscle, and I bring that to the podcast as a co-host. Do I have something to be afraid of, Courtney, in terms of losing muscle? Because I don't actually find that I do lose muscle. I find that fasting has been really protective of muscles. So yeah.
Dr. Courtney Peterson
Yeah, the answers depends on how long you fast. So the best research we have suggests that as long as you're fasting for not longer than 36 hours at a time, there's no issue with losing muscle mass.
My lab has shown this. We at one point had the largest data on muscle mass and body fat in individuals, and we found absolutely no negative effects on muscle mass. There was another really great study that looks specifically at muscle protein synthesis, and they found that it does not negatively affect muscle protein synthesis. The one small thing that happens is when you do intermittent fasting, you lose a little bit more, what's called body water, but a little bit more fluid. Now for a lot of people, they're excited about this because it means you're basically retaining less fluid and you're less bloated. And one of the benefits of retaining less food is it actually drops your blood pressure too, which is awesome. So it in particular decreases something called extracellular water. So in some of these studies, the effects they're finding on muscle mass could just be to losing some extra body water because it's such a small effect. For longer periods of fasting, like 36 hours, there is data suggesting that people are losing a little bit more lean mass. So I don't recommend fasting longer than 36 hours.
But one more encouraging piece of data is there now have been probably close to a dozen studies in athletes or resistance trained athletes. And those studies found absolutely no negative effects of intermittent fasting on your ability to have strength gains, or your ability to build muscle, or your ability to perform during any sort of athletic feat.
So no super positive effects either, but at least there are no negative effects there. So you can do intermittent fasting and train as usual.
Barry Conrad
That's really good news for me. You know, a lot of gym bureaus or people that know that I do intermittent fasting, particularly guys in the social media space, fitness influencers or whatnot, they're like, that's misinformation.
You need to eat before you train. How can you fast? So the science is constantly showing that's not the case. You don't need to feel your muscles right before going to the gym or even consume protein right after the gym, right after resistance training. Right.
Dr. Courtney Peterson
Correct. Yeah. The one caveat I will say is we don't know yet, we don't have good data on OMAD. We know for other forms of daily intermittent fasting, like if you're eating in an eight hour window, a 10 hour window and a six hour window, none of those windows seem to have any negative effects on muscle mass. So meaning if you're fasting for up to 18 hours a day, there are no issues.
We just, we only have like a very small number of studies on OMAD, so we don't know for certain. And the reason I bring that up for OMAD is because I guess classically people have thought, okay, you need to space your protein throughout the day. And there's sort of people have often cited a threshold of you can only absorb, you know, up to like 40 grams per meal, but you need to space it out throughout the day. So there may be something there, but we just don't know the answers yet. But most research suggests absolutely no problem.
Barry Conrad
Before we get into aging a bit more, we actually get a lot of questions, Courtney, on the podcast about, you know, should I do longer fasts? For example, 24 to 48 hours, do you think those have unique anti-aging benefits over daily eye protocols such as like an 18.6 or 19.5 or 24, and if, yes, how so?
Dr. Courtney Peterson
Such a great question. A hard question to answer too.
So let me give you examples of certain types of intermittent fasting. So fasting one day a week for 24 hours, we do find that lowers body weight, helps people lose weight. It also helps lower blood sugar levels and it reduces the risk of something we call metabolic syndrome, but you can just think of things like high blood pressure, cholesterol levels, elevated blood sugar levels. That said, that's only, you know, fasting one day a week is actually probably less effective than daily intermittent fasting and improving those same things. And it might just be like the daily dose of extending your fast by say four hours or something like that seems to be a little bit more powerful than a one day a week, 24 hour water only fast for your listeners who are willing to go to a greater extreme than daily intermittent fasting. For instance, there's something called the fasting mimicking diet, where you pick three to five days in a row to eat a very low calorie diet. And the way you can think about it is it's equivalent to eating about one meal a day. And the meal is supposed to be plant based in low in protein. And that type of approach is supposed to give you a lot of the benefits of extended fasting. So for instance, increasing stem cell production around day four and day five, it's also supposed to increase the topology, which is a form of sort of cellular recycling of worn out proteins, and do a bunch of other things. And there was a cool study just out last year showing that that type of approach doing that. So doing this for five days in a row and repeating it once a month for three months reduces someone's biological age, or how young or old their body acts by about two and a half years. So we're starting to see an effect there. They're, they're just not very unfortunately, they're not, there's not a lot of research comparing one type of intermittent fasting to another type of intermittent fasting. So it's hard to say one is better or worse per se. But broad sweeping, there are even more extreme forms of intermittent fasting. Like if you have what we call severe obesity, there's a form of intermittent fasting known as alternate day fasting, where every other day, you have a complete water only fast. So pretty extreme, and you can lose a massive amount of weight from doing it. But most people just can't follow it. And so a lot of the more extreme forms of intermittent fasting, like every other day, you either have a 24 hour water only fast or you one meal a day, studies have just found that people can't sustain that in the long term. And even with the fasting mimicking diet, you know, some patients struggle to maintain that as well. So we're finding the research is showing us that the daily intermittent fasting is most is easiest for most people. And most people are able to stick with it about five to six days a week on average over the long haul.
Barry Conrad
Right speaking of adf there's also the prescription that you can have you know up to five hundred calories on those down days is that still something that you find was it more effective if it's just water on those down days.
Dr. Courtney Peterson
It's probably more effective to have just water on those down days, but the problem is it's just really hard for people to stick with those approaches in the long term.
So I generally would recommend alternate day modified fasting or eating that 500 calories on that down day.
Barry Conrad
Right. And, and so Courtney, for new listeners or for those you've tuned in who don't know, can you dive into what primary versus secondary aging means and where intermittent fasting helps most?
Dr. Courtney Peterson
Yeah, absolutely. So when we think of the aging process, we actually think of it in two ways. The first is called primary aging. And that's classically what most people think about when they think about aging. So it's this concept that over time, your body gets sort of worn out. So these are kind of the classic hallmarks of aging. So it's things like your body becomes a little bit more frail, there's more molecular damage in the body, you know, your blood sugar might be a little bit elevated over time. But this is just sort of the normal, you know, process of your body becoming worn out over time.
And so we call that primary aging. Secondary aging is the idea that as you age, you become more at risk of certain diseases, we call them comorbidities, but you can just think of them as diseases. So aging itself is one of the biggest risk factors for multiple diseases. So that includes things like dementia, cardiovascular disease, stroke, diabetes, hypertension, even something called COPD, which is a lung disease. But there are a bunch of diseases and even other conditions like even hip fractures that we know you're at a much greater risk as you age. And so we often in the field of aging research, we often look at both like, can we help slow down that sort of biological aging or that natural process of wear and tear? And can we also help people live healthier by helping them avoid some of these chronic diseases?
Barry Conrad
Right. We often hear, you know, intermittent fasting can have such powerful effects on aging. And I really do believe that. And I find that in my own life as well. Like I'll have people say, you know, like you look younger now than you did 10 years ago. And you know, that's, that's a flex, but it's true.
And I really can only put that down to fasting. What are the actual biological mechanisms behind that though? So from, for people who don't know from autophagy to hormone regulation to inflammation, can you sort of walk us through how IF could help support healthier aging, like on a cellular level?
Dr. Courtney Peterson
The biggest thing that we've looked at in terms of research is its effects on helping people lose weight. And we have a really good consensus in the field that basically any form of intermittent fasting helps people lose weight. Some of them, the more extreme versions, help people lose weight faster. So for instance, for alternate day fasting, where every other day you have a complete 24 hour water only fast, people can lose 5% of their body weight in just four weeks. So for someone who weighs 200 pounds, you're suddenly down 10 pounds in just four weeks. And so pretty rapid.
And now on the other end of the spectrum is daily intermittent fasting, the one that's most popular. And we call that time restricted eating, or TRE. And it basically involves eating in a 10 hour window or less and fasting for the remaining 14 or more hours of the day. The most popular form of time restricted eating is known as the 16A diet, where you fast for 16 hours a day and eat in an eight hour window. There are now over 125 studies on this, and about 75% to 80% of them all conclude that people lose weight. So if you kind of average the results across all those studies, the effect is sort of moderate weight loss. And to put that in kind of simpler terms, we are finding that it allows people to cut their calories by about 250 calories a day. So that's equivalent to losing about half a pound a week in the average person. We found that in our lab, and we're the first to kind of report that. And then that's been other research labs have found similarly, it helps you lose about a half a pound a week. In the early days, so this is several years ago, we didn't know how intermittent fasting helped people lose weight. We weren't sure if it was because it helped them burn more calories or if it's because it lowers appetite. And what we now know is it absolutely does not help you burn more calories, no magic calorie burning strategy, but it does help people naturally eat less. And we've found in my lab in particular that affects the hormone called ghrelin. So ghrelin is a cute hunger hormone. And it is one of the main signals that your body uses to determine when to eat and how much to eat. And we found that this time restricted eating or daily intermittent fasting lowers ghrelin levels in the morning. And then the really interesting thing is it also seems to increase satiety in the evening, or at least the middle of the evening. So around 8 p.m., we find that people actually are much more satisfied and crave less food. And we also found that it reduces leptin levels, which is a molecule secreted by your body's sort of body fat and helps tell those cells whether they want to, whether you should eat more or less. So we found favorable effects or good effects on leptin too. So it seems like a bunch of these hormones that are all involved in sort of regulating your appetite are positively affected. And then the really super interesting thing is we also ask people like, just tell us how hungry you are, you know, throughout the day, which sometimes is a better measure of whether something's gonna be effective or not.
Dr. Courtney Peterson
And the fascinating thing is we found with intermittent fasting, hunger levels were more even keeled throughout the day, which is the exact opposite of what I would have expected because I would have expected with intermittent fasting, you might yo-yo between being super hungry and super full. And we found the opposite. People didn't report being, you know, super hungry or super full. They were just kind of more even keeled.
And part of that could be because we've, my lab has found and other labs have found, we were the first to find it, that actually when you do intermittent fasting, it actually lowers your blood sugar levels throughout the day. So you don't get as much of a spike in your blood sugar levels. And we know that spikes in blood sugar levels can trigger hunger hormone. So if you have a big spike and then it comes crashing down, that can kind of trigger your liver to produce a hormone called glucagon, which can suddenly, you know, trigger you to become really hungry again. And so it might be by keeping blood sugar levels more even keeled, that's also causing hunger to be sort of more even keeled throughout the day. And so now we are very confident that intermittent fasting helps you lose weight. It's not a huge effect. So if you want to compare it to a weight loss medication like Osempic, Osempic causes you to lose far more weight, but the good news is it has far fewer side effects than Osempic. So Osempic, there's substantial excess loss of muscle mass. There are also, apparently Osempic was responsible for a large number of emergency room visits last year. It was about 25,000, which was just new research released in the last week, which is a huge number, which is not to say no one should take Osempic, but just to be aware, there are lots of people who don't want to take it and want to go the natural route. And so I think intermittent fasting is a great alternative for that.
On other fronts, on other sort of other ways that we know intermittent fasting works, we think it's not just one thing that it's doing in the body, we think it's doing a bunch of things. So one side, it's definitely improving appetite. The second side is we think it's improving blood sugar control. And we don't fully understand how yet, but what we do understand is that intermittent fasting seems to lower blood sugar levels. And it doesn't seem to be due to just one thing. So it seems like if you have a longer fasting period, that lowers blood sugar. Research from my lab has also showed that if you tend to eat a bunch of smaller meals or a bunch of meals in succession, you can get even a further blood sugar lowering effect. And what I mean by that is if you say you're eating your meals three or four hours apart while you're doing time restricted eating, so say you're eating at an eight hour period and you're still trying to be like, oh yeah, I'm gonna have three meals a day.
Dr. Courtney Peterson
Now you're eating your meals about four hours apart. And what happens, we've found, is that when people are eating their meals three to four hours apart, when they start eating their next meal, their insulin levels or their blood sugar hormone insulin has not yet returned to sort of its normal fasting levels. And so it's still elevated. So if you then eat more food, well, your blood sugar hormone insulin is elevated. Insulin's like, hey guys, I'm here. I can just start moving the sugar out of your bloodstream and into your cells. And so as a result, it sort of prevents that extra spike in your blood sugar levels. And so maybe some benefit too from, you know, still eating, you know, like say three meals a day and not necessarily skipping a meal.
But it also looks like there's some benefits from the time of day that you eat. So most of the research that has reported a benefit for intermittent fasting, it has reported that intermittent fasting improves blood sugar, tends to have people eat earlier in the day. It's not universally true, but it seems that you can get an even bigger effect on improving your blood sugar if you eat earlier. And by earlier, I mean like have dinner by around like six, 6.30 at night. So it looks like there are a bunch of different, you know, I guess separate parts of intermittent fasting that could lower blood sugar. And then of course we know losing weight always lowers blood sugar. And then we also know intermittent fasting does improve blood pressure levels. And we've actually known this for over 50 years that when people fast and even like quite prolonged fasting can dramatically lower blood pressure level. And it seems to work by helping the body release a lot of excess water and salt that it's retaining. So it's again, it's sort of a little bit of a de-puffing, deep loading effect. And we understand some of the reasons why it happens and it's a bunch of different things. So there are hormones involved in blood sugar, sorry, blood pressure regulations such as aldosterone. And as you fast, that hormone goes up and I think it goes down initially. Yeah, it goes down initially and then goes up, but it helps support your body initially just get rid of a lot of water. And then over time, as you're fasting longer, it's like, oh, whoops, I do need to hold on to more water and salt. But the point being that there are a bunch of different things. And then also we know that when you lose weight, which intermittent fasting can do, it lowers those leptin levels from your fat cells and leptin itself can also lower blood pressure. So there are a bunch of different things there. Now, the interesting thing is we don't actually see big effects on cholesterol levels from intermittent fasting. It just doesn't seem to be either a big effect or intermittent fasting doesn't seem to affect it very much.
Dr. Courtney Peterson
That said, if you lose a lot of weight, then intermittent fasting will probably still lower your cholesterol levels. But if you lose a moderate amount of weight, we don't find that intermittent fasting is particularly great at lowering cholesterol levels per se, but it seems to be outstanding for improving blood sugar and blood pressure.
Barry Conrad
So many thoughts, Scotty. This is fascinating. You know, back in the day, I actually used to follow. Have you heard of that book, Body for Life?
Dr. Courtney Peterson
I have. I've never read it, but I'm aware of it. Yes, yes.
Barry Conrad
Yeah, and the whole situation was six meals a day. Six more meals a day because it speeds up your metabolism and you have to keep that fire burning. But what I found with that, like going back from here, is how many just lulls I had in the day. How many, spiking up and down, up and down.
What I love about fasting is that it just removes all that. And yeah, it definitely stabilizes you throughout the day. There's less decision fatigue around meals and what to eat. And I definitely find the benefits of that. And what you also said that stuck out to me was 10 hours. 10 hours, as little as 10 hours fasting. You're gonna see benefits there. You mentioned.
Dr. Courtney Peterson
10-hour eating window.
Barry Conrad
eating window. You also mentioned the, the when I was going to ask. So is it, is it more about the fasting length, Courtney, or is it when the fast happens early versus late? Because I eat, I'm kind of all over the place. I just sort of time it around my lifestyle.
It's not necessarily just the morning, just the evening, but it's usually around 4 PM ish, but that can often be later. So what are your thoughts on that? Is it about keeping it more uniform to see more benefits or is intermittent fasting just protective regardless of the time of day?
Dr. Courtney Peterson
Yeah, all great questions. The answer is I think it's all of the above.
And let me also go back to your question. Let me also clever I'm not saying I think people should eat six meals a day. I certainly don't.
Barry Conrad
No, I don't know. No, no, I was more saying like what I noticed when I did eat that way compared to now, like it's a huge difference.
Like you don't have to eat all day to keep your metabolism spiked.
Dr. Courtney Peterson
Correct. And we now know that's not true, that you don't have to like eat lots of meals throughout the day. And by and large, for the most part, it really doesn't I mean, certainly for weight loss, it doesn't look like the number of meals you eat per day makes a big difference. So you know, current current thinking is, you know, do what works for you.
Okay, so back to your great question. So I think the answer is, all three matter. And what I mean is the fasting duration matters. So longer fast, the better, in general, you know, up to a point up to the point of maybe 36 hours. Number two, time of day probably matters, but only for certain parts of your health. And I'll cover and I'll mention, I'll go into detail on what that means. And then third, the regularity seems to matter too. But we don't have a great understanding of it yet. But I'll tackle each of these. So the great news is for weight loss, it does not look like it matters very much what time of day you do intermittent fasting. So that's fantastic news. So there may be a small benefit from eating early in the day. But by and large, it looks like no matter what time of day, you practice time restricted eating or intermittent fasting, you're going to get a weight loss benefit, which is awesome.
The one caveat I will say is we're starting to see the amount of weight loss for a 10 hour eating window is not as good as for an eight hour window. If you're able to do eight hours, I would recommend that our data, the research at least is so much more compelling for eight hours, we see clearly better benefits for eight hours as opposed to 10 hours. So if you can do that, great. If not do 10 and just rock 10. I usually recommend that people start at 10 and then work their way down if they can. On the question of blood sugar, it looks like the time of day that you practice time restricted eating matters. And when we look at all the research that's been done, it looks like eating windows that end by 6pm tend to improve blood sugar levels. And then eating windows that end after 6pm don't. This is largely true, but there's always like there's always a caveat, right? So if you lose a lot of weight, no matter what time of day you do intermittent fasting, you're going to get a blood sugar benefit because weight loss, you know, is always going to help you help improve your blood sugar. But if you don't lose a lot of weight, and you're just doing this to roughly maintain your weight, you're going to get a much bigger blood sugar benefit from eating early in the day.
That said, that's not practical for everyone. But if you can do it, that's great. And the reason why we think this is the case is your body has an internal biological clock known as the circadian system. And the circadian system helps your body be better at doing different things at different times of the day. So for instance, your best sports performance and your greatest muscular strength and your fastest reaction times are in the middle of the afternoon. So like this is where you're going to get your sort of best if you are, you know, an Olympic athlete, that's when you're going to get your best performance.
Dr. Courtney Peterson
Conversely, at nighttime, your body starts to produce the sleep hormone melatonin. So that's the best time at night to sleep.
And in the morning, that's when you have your greatest testosterone production and also when most people have their best blood sugar control. And we also know that when you eat in the morning, you burn very slightly more calories when you eat in the morning than when you eat in the evening. Now, it's not a huge effect. It's, you know, about equivalent to eating a few extra bites of apple. But the point being, we have a bunch of evidence suggesting that your metabolism is kind of like optimally suited to eat food earlier in the day. And by early in the day, I would say, you know, the best time of day is probably about mid morning, mid to late morning. So about like the 10 11am windows, that's when we find the body is most sensitive to the blood sugar hormone insulin. So that's when your muscle cells and your fat cells are both are most like, Oh, yeah, if you give me sugar, I can take it up quickly and keep your blood sugar in a good range. What's really interesting is we discovered in the late 1960s, early 1970s, that if you give someone a blood sugar test, or a meal, say at in you know, in the morning at 9am in the afternoon at 3pm and in the evening at 8pm. their blood sugar levels will spike significantly higher in the afternoon, in the evening, even though they're eating the same meal. In fact, the effect is so large, people, for instance, who have prediabetes as measured by a blood sugar test in the morning, they're metabolically equivalent to being diabetic when they eat dinner at night. It's like your body's almost in a different state of metabolism across the day. If you can eat more of your food early in the day, and by early in the day, we can take this in a couple of different directions. One is you can just do intermittent fasting and say like, hey, I'm going to make breakfast and lunch my largest meals of the day. Or you can even say, hey, I'm going to follow the old adage of eating breakfast like a king, lunch like a prince, and dinner like a pauper. Some people might say, hey, look, I can't move dinner earlier, or I'm not willing to eat breakfast later, I got kids, or I've got my job or something like that. For those folks, I would say, don't worry about it. Just try to make breakfast and or lunch your largest meals of the day. Make dinner like your salad meal or your super healthy meal. For folks who can do intermittent fasting, I would say, if you can eat early in the day, great, do it. If you can't skip breakfast, still do the intermittent fasting, and just try to avoid eating right before bedtime. And you're still going to get a lot of those benefits.
And blood pressure is also similar in that in a bunch of studies, we're seeing that intermittent fasting or eating early in the day seems to be better at lowering blood pressure than eating late in the day.
Dr. Courtney Peterson
So there are at least some aspects of health that seem to be influenced more by the time of day that we eat rather than the fasting duration, or just that you can get a bigger benefit from eating earlier in the day than you can by having a longer fast. But we're still trying to figure out all of this and make sense of it.
So my lab has a study right now, a really big study where we're comparing doing intermittent fasting early versus late in the day. And we're not allowing people to lose weight. And we want to kind of know the question, are there sort of intrinsic benefits? But there are studies, really interesting studies showing that if you skip breakfast, even if you do intermittent fasting, this seems to potentially not really improve your blood sugar levels, even though you you would hope it would are in some of these studies, it's actually meaning making blood sugar worse. Now my sort of counter argument is most of these studies are only like a day long or six days long. And so we are in our current study, we're testing this for a much longer period of time, because we suspect the body adapts over time and gets better, you know, at certain things at different times of the day. So for instance, when people do Ramadan intermittent fasting by only eating at night, we find after about a month, their hunger hormones change what time of day they're secreted. So the body adapts over time. So I'm hoping about a year from now, if you call me up, we'll have an even clearer answer of the effects on blood sugar. But this is the best, what we know based on the best research that we have.
Barry Conrad
amazing information. We actually talked about Ramadan fasting a couple of weeks ago. It's really fascinating because it is different how they don't, they only have nothing, they don't even have water.
So the results in terms of muscle losses, that's actually different. So can you talk about the difference between Ramadan, EG having nothing compared to having black coffee throughout the day compared to having 500 calories on a down day of ADF? How is muscle affected compared to regular intermittent fasting and Ramadan fasting?
Dr. Courtney Peterson
Yeah, Ramadan fasting is such a hard topic. I often shy away from it because it's hard.
But just for your listeners, Ramadan intermittent fasting is typically fasting during daylight hours. And it's what you might call complete fasting or another term would be dry fasting, which means you eat no food and no water while the sun is out. And then you'll start eating, you know, after dusk. But you can also eat before dawn. And what's super interesting is the way people practice Ramadan fasting, intermittent fasting is so different. And what I mean by that is some people eat before the sun rises. And again, after immediately after the sun sets, and they still eating pretty healthily. Other people might eat nothing in the morning, stay up late at night and then eat around 12. So if you look at all the research that's been done on Ramadan intermittent fasting, some studies find people get unhealthier during the month of Ramadan. And other studies report that people get healthier or it has no effect on health, it really just depends on what people do.
And often during that month, people often change what they eat. So it becomes really hard to kind of see the forest through the trees, so to speak. So it's hard for me to have a good answer on that. I do I am aware of some studies that show that Ramadan intermittent fasting negatively influences muscle mass. I'm also aware of some studies suggesting that Ramadan intermittent fasting do done during a certain trimester, a pregnancy is linked to lower IQ scores. And I apologize, I just can't remember which trimester it is. I think there are some cautions. But again, it I think it's it's all in the devil's and the details. I think it's how you do it. I think if you do it, well, you're in a good position. But if you use it as an excuse, or if it, you know, I don't even mean to cast it that negative. But if if you do it and inadvertently end up, you know, effectively binging and eating unhealthily, because you've been fasting all day, including dry fasting, then it's probably not great.
And then the other issue is the sleep disruption. So it can disrupt sleep. And it's definitely not eating in alignment with the circadian rhythm. So for non religious reasons, I would not recommend it, you know, and then obviously, for religious reasons, I think, you know, it's important to to just say, you know, do whatever works for you there.
Barry Conrad
I'm from South Africa, Courtney, and my mom, one of her best friends was Muslim. She was married to a Muslim man, and we always would go over to their place during Ramadan because when the sun went down, we had this massive feast and we'd just eat with them.
But it was definitely, you know, it's not a sort of a quote unquote diet that you prescribe on the daily. It's sort of like, as you said, some people could maybe get unhealthy.
Dr. Courtney Peterson
Correct. And people often do it for spiritual purposes. And for that, I understand it can be absolutely transformative. I'm just talking more about the health aspects.
Barry Conrad
Speaking of the devil being in the details, Courtney, can you break down for our listeners in simple terms how intermittent fasting actually influences biological age? Or the key markers of health span? And if so, how strong is the evidence? What is your latest take on that for our listeners?
Dr. Courtney Peterson
Great. So let's switch to primary aging, which is super fun. So one of the really interesting things we've learned from animal studies is we now kind of understand why intermittent fasting extends lifespan. So in science, we can sometimes do what are called knockout studies, which means we can block a certain gene from doing its job. And so people have experimented with, if I block this gene, can intermittent fasting still extend lifespan? And what we found is that it looks like intermittent fasting extends lifespan by increasing autophagy. So autophagy, it's sort of a, well, I guess the root origin of the word is self-eating. But it's this concept that cells are constantly sort of rejuvenating themselves. And one of the way they do this is they take out worn out and damaged proteins. And they sort of break them down and then recycle those components. And so when autophagy is higher, what that means is more of those damaged proteins are being recycled, and then new proteins are taking their place. And what we found is that intermittent fasting dramatically increases autophagy. But if you kind of knock out that gene or you prevent those autophagy genes from doing their job, intermittent fasting can't extend lifespan. So this tells us very clearly that it's autophagy that allows intermittent fasting to increase lifespan.
And my lab a few years ago, we were looking at certain aging-related pathways. And we definitely found that intermittent fasting, this time-restricted eating in particular, did increase one of the key autophagy genes. And so we see clear evidence that it's increasing autophagy the same way in people. And we also, in our study, we were measuring how many calories people were burning in the middle of the night. We did find that there seemed to be a little bit more protein turnover, which may sound like a bad thing, but it's not a bad thing. Because if you're sort of recycling more proteins, that's a good thing. Other things that we see, so when we think of aging, let me take one step backwards. We now have this sort of framework for viewing aging, and we have what we call, I think we're up to 12 or 13 different hallmarks of aging. And you can just think of these as components of aging. So sort of key drivers of aging are things like, we think your body produces less stem cells as you age, it creates more, there's more damage in your mitochondria as you age. So mitochondria, the little factories within cells that generate energy, we find that the bacteria in your gut sort of decline with age, or there are some problems with them with age. Your body's immune system is not as good as fighting disease with age. There's more molecular damage, such as oxidative stress with age, but there are a bunch of these things that happen with age. We have also found in my lab, one very cool thing, which is intermittent fasting helps reduce.
Dr. Courtney Peterson
a type of molecular damage called oxidative stress, which is effectively from electrons bumping around and just creating damage in the body. And we were able to show that intermittent fasting reduces this oxidative stress, even if you don't lose weight, which means if you are just into healthy aging, you don't even want to lose weight, you can get some of these anti-aging effects.
And I now know of at least two studies that have found that intermittent fasting for, gosh, let's see, one study they tested the effects after eight weeks and the other was about 12 weeks or three months. And both studies found that just doing intermittent fasting for that shorter time period reversed biological age by about two and a half years. So that's super cool. And now we're getting better and better technologies for estimating someone's true biologic age. So definitely watch this space. Other things that I think are really exciting coming down the pipeline, I'm involved in a study right now where we're looking at whether intermittent fasting can increase stem cell production by the body, which would be amazing. And one of our thoughts is maybe it can because we know calorie restriction can increase stem cells in the body. And so we'll be looking at that.
There is some evidence that intermittent fasting can improve the immune system, but it's not through sort of classic immune molecules that are released. It seems to empower certain types of immune cells more to target disease. So for instance, it helps with some of the T cells that are really good at killing cancer cells. It helps increase T cells that are better at killing cancer cells.
And then it also lowers a hormone called insulin-like growth factor one. And this particular hormone can stimulate the growth of cancers. So in general, we want lower levels. And the great thing we know about intermittent fasting is it does lower insulin or this IGF-1 level in the body. So we think there are just like a bunch of ways or different aspects of aging that intermittent fasting is really targeting.
Barry Conrad
It's amazing. You know, Courtney, you touched on autophagy, and it's one of the most it's one of the most talked about benefits of fasting, but it can seem ambiguous or mysterious to people.
So from what we know, when does autophagy actually start to ramp up in a fast and how long do you need to go without food to really see a kick in?
Dr. Courtney Peterson
Yeah, so typically about 11 to 13 hours of fasting in humans is around the time we'll start to see more dramatic increases in autophagy. And it's really important to for people to know that autophagy is really increased while you sleep. And that's really the best time of day. So I'm going to also get on my general health horse here and recommend that people get good overnight sleep. And honestly, that would be my top recommendation followed by intermittent fasting second.
But my number one recommendation for autophagy would be good sleep while it's dark outside. One other study I do want to mention is last year there was a great study looking also at brain aging. And they similarly found that about eight weeks of intermittent fasting reduced brain aging by the equivalent of a little over two years. And they also found that an improved executive function and learning and memory. And then we also have data from our lab showing that intermittent fasting increases something called brain derived neurotropic factor, which is just a fancy name for a little hormone that helps stimulate neurons in the brain to sort of regenerate and to survive.
Barry Conrad
Amazing. Courtney, question for you. Is a calorie a calorie a calorie? So how important are food choices?
Because a lot of people when they do come to me asking, heard about this intermittent fasting thing, you can eat whatever you want, right? Is that quote unquote true? How important are dietary choices?
Dr. Courtney Peterson
Yeah, so I'm going to answer that in a couple of different ways. So one, you can still get the benefits of intermittent fasting, even if you don't improve your diet. I do still think, based on the best research, it's probably more important to eat a healthy diet than to do intermittent fasting or engage in meal timing, but I think they're both really important for health. And that's what we're learning.
Like both, you can dramatically improve your health by eating the right things and eating at the right time of day. So you can definitely get the benefits of intermittent fasting without eating a healthy diet. I still recommend eating a healthy diet. And my biggest recommendation there is just to eat whole foods. Kevin Hall, who was at BNIH until recently, big research on ultra processed foods kind of showed the worst thing that you can do is to eat ultra processed food. When people eat ultra processed foods, they often overeat by 500 calories at a time. So if your listeners can do one thing, I would say stick to whole foods as much as possible. Ignore about like, you know, all carbs are bad and stuff like that. I do recommend avoiding high glycemic index for carbs, but I think whole fruit is great. Whole grains, as long as it's not overly processed, is also great. But there are some whole grains that are a little too processed that I think get sort of lumped in with, you know, healthier whole grains.
Barry Conrad
Yeah, Courtney, what protocol do you follow? Can I ask, what do you, 18.6, 16.8, OMAD?
Dr. Courtney Peterson
Yeah, absolutely. So prior to having kids, I typically ate within a six to eight hour window. I like four meals a day, but I'm also fine doing three. I usually do four, just because I really like that.
And right now, so I just weaned my second kid from breastfeeding a few months ago, I'm eating in within more like I would say an eight to 10 hour window, depending on the day, but I plan to eventually move back to eight hours or less. And when I go out to eat, I just do what everyone else is doing. I just don't sweat it.
Barry Conrad
Yeah, me too. I'm the same way. It's not the end of the world. It's what you do most of the time. That's sort of my train of thought.
We get this question a lot on the podcast. How long should you eat? What does OMAD mean? This is maybe controversial to ask, but Courtney, what is one meal a day? Is it one plate? Is it in four hours? What does OMAD actually mean, in your opinion?
Dr. Courtney Peterson
I've seen, among scientists, I've seen sort of two definitions. One is one meal a day, and the other one is eating within a four-hour period or less. I don't think we have a good consensus on it, but I think either of those are reasonable ways to look at it.
Generally when I've seen OMAD in the literature, the shortest eating period I've seen people quote is an hour and a half, I think, an hour to an hour and a half, and the longest I've seen is a four-hour period, if that's helpful. So I generally think of less than four hours if it's a single eating instance as OMAD.
Barry Conrad
Yeah. And speaking of just different opinions and views out there with so many voices on social media now and science constantly evolving, there seems there's a new health claim every day. So some are more evidence-based than others.
What are some of the biggest myths or misconceptions about intermittent fasting that you'd like to set the record straight about?
Dr. Courtney Peterson
Ah, that's a good question. I see, it's very interesting because I see extremes on either end of the spectrum. And what I mean by that is I see both people in the general public and other scientists say intermittent fasting is the greatest thing ever and improves everything about your health and you're going to magically transform. That's not true.
The effects are moderate, but I think they build so nicely over time. And we can still get quite dramatic improvements in blood sugar and blood pressure levels in people as long as they stick with it over time. Weight loss effect is moderate. Like I said, I mean, you're going to get bigger effects with ozmpic, but I mean, what a great tool to maintain your weight or even lose a moderate amount of weight. And then to slow the aging process. I suspect if you accumulate this over decades, you're going to be in a great position. But I also see people on the other end of the spectrum, including many dietitians completely poo-pooing it or other scientists saying there's nothing to look at here. It's just a fancy way to cut calories and research in my lab and other labs have shown like even if you don't cut calories, you can still get some benefits.
And some of the benefits and improving oxidative stress were also independent of what time of day you eat. So we, I think, you know, for those of us who actually really know the science out there, I think they're clear benefits. I think they're moderate benefits. I'm still really excited about it.
I think we're going to help a lot of people. Estimates are now roughly 10% of the population or of US adults are following intermittent fasting, which is roughly the same number who are ozmpic. So I think the science is there. And I'm hopeful that in the next, hopefully the next five to seven years, we'll have dietary guidelines saying that intermittent fasting is effective. And if you can do any sort of strategic meal timing, you should do it.
Barry Conrad
Amazing. And Courtney, for people who might be new to IF, what's one practical takeaway that an audience can implement starting today? They're new, brand new to it. What's one thing?
Dr. Courtney Peterson
Oh, great question. The first, I mean, my usual advice for newcomers is the following. Start with a 10-hour window, adjust to that, and then see if you can push it lower and experiment and find a sweet spot. If it just doesn't work for you, two things are really important to know. So one, we have found that generally it takes people a while to adapt to it. So some people say, oh, I'm never hungry at this time of day or I can't do this. We find that it actually, when people first switch to an intermittent fasting diet, it temporarily feels hard. And then after a month, many people start feeling like, okay, I'm getting the hang of this and I'm adapting. So if it feels hard in the beginning, hang in there, give it a little longer try, because your body's just adapting to eating at a different time at day. So it takes a while for those hunger hormones to transition to make you hungry on your new schedule and to sort of overcome that inertia. Yeah, and just be patient.
And it's not an all or nothing. So a lot of people will say to me like, oh, I thought I had to do it every day of the week and I was like, no, five or six days a week, you're gonna get most of the benefits. So don't sweat it. This is not black or white by any means.
Barry Conrad
Amazing advice. I think I'm going to steal that, start with the 10 hours and see how you go. What excites you most, Courtney, about future fasting research? What's next on the horizon for you?
Dr. Courtney Peterson
Yeah. So we are currently, I say we, but I'm part of a larger team. We're hoping to do a five-year study, which would be amazing, of intermittent fasting and comparing it to calorie counting for slowing the aging process. So that's huge. This would be a giant study funded by the largest federal agency or the federal government in the U.S. So we're crossing our fingers that that gets funded, but we would be looking at whether we can slow the aging process over five years, which has never been done before. So super excited about that.
And then we have two studies in my lab right now where we're trying to see if we can improve people's blood sugar control, people who have type 2 diabetes, and see if we can potentially even reduce their need for medication, which is exciting. And then we have one other study that we're still working on where we're taking cancer patients and seeing if intermittent fasting can help shrink their tumors and also reduce the sort of nasty side effects of chemotherapy and radiation. Because there's a bunch of studies in animals showing that if you combine intermittent fasting with chemotherapy and radiation, those animals survive so much better. And what's interesting is there's a sweet spot. If you start the intermittent fasting prior to chemotherapy and radiation, you get these huge improvements in shrinking their tumors. But if you do the intermittent fasting after they do the chemotherapy and radiation, you don't get the same huge benefit. And it seems that the intermittent fasting kind of helps chemotherapy and radiation better kill the tumors while protecting healthy cells. So we're kind of testing that now in people to see if it can help.
Barry Conrad
that's absolutely amazing and to wrap things up corny if you had to choose a final meal what would it be.
Dr. Courtney Peterson
Oh, a final meal on Earth?
Barry Conrad
Yeah.
Dr. Courtney Peterson
Oh, gosh. Okay. So I would probably do a combination of healthy and unhealthy foods. Something with chocolate and then something with fruits. Like I love watermelon in berries, raspberries and strawberries.
Oh, and I love stone fruit. So probably cherries and white nectarines are amazing. And then I would probably do something like some dark chocolate or like dark chocolate covered like mint ice cream or something like that. It would be both those things.
Barry Conrad
Sounds tasty. Well, Courtney, where can people find you before we go? Find you online.
Dr. Courtney Peterson
Yeah, so I currently do not have a big social media presence, but I have a web page at the University of Alabama at Birmingham. So if they just search my name, Courtney Peterson, and UAB, then they can find me there.
Barry Conrad
Amazing. Courtney Peterson, it's been an absolute pleasure having you on the show. Thank you so much for making the time.
Dr. Courtney Peterson
You're welcome. Thanks for having me.
Barry Conrad
And thank you all for tuning in, we'll catch you next week. Bye.
Dr. Courtney Peterson
Thank you so much for listening to the Intermittent Fasting Podcast. Please remember, everything we discussed on this show does not constitute medical advice, and no patient-doctor relationship is formed.
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