The Peter Attia Drive - June 16, 2025


#353 - AMA #72： Fasting： benefits for body composition and disease prevention, potential risks, and Peter's updated practical framework


Episode Stats

Length

19 minutes

Words per Minute

182.4714

Word Count

3,606

Sentence Count

209


Summary

In this episode, we discuss the various types of fasting, which oftentimes can be used interchangeably but actually can mean very different things. We talk about the reasons why people might fast and its potential benefits, focusing on body composition, metabolic health, overall lifespan extension, cardiovascular disease, cancer prevention, Alzheimer s and Parkinson s, along with various autoimmune symptoms including arthritis and more. And finally, we wrap it up with a framework to help you think about this for yourself.


Transcript

00:00:00.000 Hey everyone, welcome to a sneak peek, ask me anything or AMA episode of the drive podcast.
00:00:15.820 I'm your host, Peter Atiyah. At the end of this short episode, I'll explain how you can access
00:00:20.280 the AMA episodes in full, along with a ton of other membership benefits we've created,
00:00:24.900 or you can learn more now by going to peteratiyahmd.com forward slash subscribe.
00:00:30.600 So without further delay, here's today's sneak peek of the ask me anything episode.
00:00:38.800 Welcome to ask me anything AMA episode 72. For today's AMA, we focus on a topic we initially
00:00:46.860 covered all the way back in AMA 11 in January, 2020, which is all things relating to fasting.
00:00:53.780 This is a topic in which my thinking has evolved greatly, as well as one that we get an almost
00:01:00.760 infinite number of questions about from our subscribers. In this episode, we discuss the
00:01:05.740 various types of fasting, which oftentimes can be used interchangeably, but actually can mean
00:01:10.320 very different things. We talk about the reasons why people might fast and its potential benefits,
00:01:15.480 focusing on body composition, metabolic health, overall lifespan extension, cardiovascular disease,
00:01:21.600 cancer prevention, cancer treatment, Alzheimer's and Parkinson's disease, along with various
00:01:26.980 autoimmune symptoms, including arthritis and more. We talk about the potential negative aspects of
00:01:32.200 fasting that everyone should be aware of. And finally, we wrap it up with a framework to help
00:01:36.580 you think about this for yourself. If you're a subscriber and you want to watch the full video
00:01:41.380 of this podcast, you can find it on the show notes page. If you're not a subscriber, you can still
00:01:46.780 watch a sneak peek of this video on our YouTube page. So without further delay, I hope you enjoy
00:01:51.660 AMA number 72.
00:01:58.660 Peter, welcome to another AMA. How are you doing today?
00:02:01.700 Oh, I'm doing well. Thank you.
00:02:03.520 That's good. It's great because today we are going to talk about a topic that I actually looked back
00:02:09.140 and looked. And do you know the first time we covered this topic on an AMA? Any idea when it was?
00:02:14.220 Is the topic F1? No, but it does start with an F.
00:02:18.240 Oh gosh. No, I don't know. So for those listening, it is fasting today. And the first time we talked
00:02:28.180 about it was AMA 11 released January, 2020. All right. Considering this is AMA 72, we've talked a lot
00:02:39.120 about stuff in between then before we've dedicated a full episode to it. Since then, there's been a
00:02:45.720 lot of things that have changed on how you think about this. Your opinions evolved. We've kind of
00:02:50.240 talked about it here and there, but it's also a topic we get asked about so much. And there's so
00:02:54.160 many people who talk about this in different ways. And I think it creates some confusion and
00:02:58.860 you've written about it in the book. You do it with yourself. You have patients who do it.
00:03:03.460 So we kind of gathered all these questions and said, all right, let's dedicate a full episode
00:03:08.580 to this. And in it, we'll first start by just identifying the different terms. I think sometimes
00:03:13.600 what causes confusion is people may say the term fasting or different versions of fasting
00:03:18.260 and mean it in different ways. So once we identify that, we're then going to focus a lot of it on
00:03:23.540 what are the reasons that people may fast? What are the reasons that they see benefits? Anything from
00:03:29.220 body comp to metabolic health to just general lifespan hopes to cardiovascular disease,
00:03:35.700 cancer prevention, treatment, neuro, Alzheimer's, Parkinson's, autoimmune symptoms, arthritis,
00:03:41.940 and more. So a lot of different things that we'll talk about the possible benefits. We'll also look at
00:03:47.400 some possible negative consequences that people should be aware of, and then hopefully wrap it up
00:03:52.020 in kind of a nice framework for people to apply it to themselves and understand how you apply it in
00:03:57.360 your own life and also how you apply it with patients. So all that said, anything you want to
00:04:03.680 add before we get rolling? No, I don't think so. I mean, obviously I'd love to spend some time
00:04:08.080 talking about Formula One, but I don't think we're going to have time with that aggressive agenda.
00:04:12.320 Do Formula One drivers do long-term fasting? Do you know? I don't know any who do.
00:04:18.000 Well, then that might be the extent of F1 in this podcast. Also, have you been to your
00:04:24.240 kids' school recently? Any elementary kids have strong opinions on fasting that you've heard of
00:04:30.240 recently? No, but I know who to ask, so. There you go. Something tells me that kid's got some
00:04:37.880 opinions on this. I would love to hear what they are. Rolling into it, I always like to kind of do
00:04:42.680 this every now and then because one thing about you is you're not afraid to change your opinion.
00:04:47.520 So when new evidence comes out, you're not afraid to be like, okay, how does that fit in the
00:04:53.020 scaffolding of how I thought about this before? And where does that change? And we usually do it
00:04:57.440 in major episodes, like episode 200, 300 called Strong Convictions Loosely Held on what you've
00:05:03.020 changed your opinion on. And this is a topic where I think your opinion has evolved a little bit as
00:05:08.800 new evidence has come out, as you've seen it in practice. And I think it's always important for
00:05:13.560 people to understand why you feel so strongly about changing your opinion and the ability to change
00:05:19.900 your opinion. Because sometimes in the space, people get really wed to what they think and
00:05:24.460 they'll dig their heels in. And when people change opinions, you'll see comments like, well, how could
00:05:29.980 you say this if you used to say this? And I think it's always helpful for people to hear from you as
00:05:34.740 we set the stage. Why do you think it's so important for scientists, doctors to be able to change their
00:05:41.540 opinion? Well, honestly, I think it's important for everybody to be able to change their mind or change
00:05:47.400 their opinion in light of new information. I also realize that we live in a world today where that's
00:05:52.460 quite difficult. There's a reason I would never be able to be a politician. I think politics is an
00:05:57.340 area where it's very difficult to change your mind and maintain credibility. It seems that the harder
00:06:03.780 you dig in on your position, the more credible you seem. So again, to be clear, I think this should be
00:06:09.100 viewed as a feature, not a bug in life. But it should especially be viewed as a feature in the field of
00:06:16.900 science and medicine, where there's no such thing as absolute certainty. So people have heard me say this
00:06:21.440 before, but everything in science is probabilistic. And there are certain things where the probability is so
00:06:27.460 high that it is effectively a certainty. So if I were to drop a bowling ball while standing on planet Earth, I can
00:06:37.420 say with essentially near certainty that it will accelerate towards the ground at 9.8 meters per second squared.
00:06:44.100 But we shouldn't lose sight of the fact that there's actually a probability function that is telling us
00:06:48.400 that. I've been, as you note, I think, or alluded to, I've had people get angry at me on social media when
00:06:54.220 I've posted, you know, a changing position on something, most notably or most recently, discussions
00:07:00.000 around GLP-1 agonists. And so I think on a recent post, I quoted John Maynard Keyes when he was asked why he
00:07:06.560 changed his mind on something. And he responded, and I love this, when the facts change, I change my mind.
00:07:12.140 What do you do, sir? I love that quote. I think the best way I could say it is the way I try to
00:07:18.080 think on every topic is being in a constant state of evolution. And I'm not wed to being right. I'm
00:07:24.520 wed to knowing what is right. And I think that's probably the single most important piece of my
00:07:32.220 mental scaffolding that if someone asked me, hey, Peter, what's a good way to orient myself to
00:07:39.480 information, I would say that is it. I'm not suggesting that that's unique to me. I think a
00:07:44.100 lot of people do that. But that's what I would recommend to people is orient yourself towards
00:07:49.060 knowing what is right and less around being right. Then you'll constantly find yourself going in the
00:07:55.120 right direction. Thank you for that. Level set. All right, getting started. Fasting. I think it'd be
00:08:01.320 helpful just to define the different terms around fasting. When you've talked about nutrition in the
00:08:06.520 past and you've talked about the need to make sure you watch how many calories you eat, you've talked
00:08:12.120 about a DRTRCR framework. So do you just want to spend a minute defining these terms as we'll talk
00:08:18.540 about them today? So when we mention different things, people understand what specifically we're
00:08:23.120 talking about. Yeah. So taking a step way back, people criticize me for not being as dogmatic as
00:08:29.900 maybe I once was or as others are when it comes to nutrition. But the truth of the matter is all the
00:08:35.680 available evidence basically says the following. You need to be in energy balance. So too much and
00:08:40.520 too little is bad. You need adequate amounts of protein. That seems to be the one constant.
00:08:46.700 You have to be able to maintain lean mass, but the actual amount of carbohydrates and fats,
00:08:50.600 provided you're in energy balance, doesn't seem to matter that much. You obviously need to have
00:08:54.320 sufficient amount of micronutrients and you need to avoid toxins. And once you sort of get through
00:08:59.520 that, it's an open canvas as to what you want to do. Now, for most of us, I certainly include
00:09:04.480 myself in this position. Maintaining energy balance requires some effort. What that means
00:09:10.300 is I can't just eat whatever I want, whenever I want, in whatever quantity I want. If I did
00:09:17.540 that, I would be out of energy balance. I would be metabolically unhealthy and I would deal with
00:09:23.720 all the sequelae of that. So I can't give you a number as to what people are in my bucket,
00:09:28.760 but experientially through taking care of patients for more than a decade, it appears to be more than
00:09:35.300 80% of people are in my category where they have to pay some attention. And so the framework that I
00:09:41.360 devised around this was this idea of DR, TR, and CR. And you have to be doing generally at least one
00:09:48.920 of those things. So DR means dietary restriction. So you deliberately restrict some element within the
00:09:55.020 diet. The most common applications of this are typically certain macronutrients. So there are
00:09:59.960 people who restrict carbohydrates. There are people who restrict fat. There are people who restrict
00:10:04.460 animal products. There are people who restrict maybe processed foods. There's no right way to do
00:10:09.480 this. There are lots of ways to do it. And any form of DR that is significant enough generally produces
00:10:15.100 the desired effect. The second area is TR or time restriction. This is what people loosely refer to
00:10:20.780 as intermittent fasting or daily time restriction, where you just say, hey, look, I'm not really going
00:10:25.360 to pay attention or dramatically change what I eat or even pay attention to how much I'm eating when I'm
00:10:30.980 eating. But I'm really going to restrict the period of time in which I eat. The narrower I make my eating
00:10:36.260 window, the more I'm going to probably restrict overall calories. Finally, there's CR, which says,
00:10:42.700 actually, what I'm going to do is just focus on minimizing my total caloric intake over the course of the
00:10:48.480 day. And I'm going to do this not necessarily by paying attention to what I'm eating or when I'm
00:10:54.620 eating, but just always focusing on eating less. Obviously, one can choose to mix these. When I was at
00:11:03.160 my absolute lightest and leanest, which was necessary when I was racing a bicycle, I was basically going
00:11:09.540 very hardcore on DR and TR. So I was highly restrictive as to when I ate. I was basically eating one snack and
00:11:17.740 one meal a day. And I was being insanely restrictive on what I was eating. And not surprisingly, I weighed
00:11:25.020 16, 17 pounds less than I do today. So lots of different ways to do this. Now, the problem as it
00:11:31.140 pertains to our discussion today, which is about fasting, is that we don't really have clean definitions
00:11:39.080 of this. The term fasting applies to a diverse set of feeding patterns, but it's a general definition.
00:11:46.500 And it can range from anything like only consuming water for days at a time to what I just described a
00:11:54.560 moment ago, which was time restriction, which is, you know, hey, I'm just going to kind of not eat for
00:11:58.320 16 or 18 hours a day. So I think as we go through this discussion, Nick, we'll certainly shed more
00:12:03.720 light on the different types of protocols and maybe the pros and cons of each.
00:12:07.580 Yeah. And maybe kind of as a follow-up from there, let's just cover what are the most common types of
00:12:12.600 fasting. So when people are talking about fasting, do you just kind of want to list out what those
00:12:17.260 are? And I think we actually have a graph that we look at internally that we can throw up, which
00:12:21.900 would be helpful here.
00:12:24.260 Sure. So as I'm talking, maybe look at what's sitting over my shoulder here. So intermittent
00:12:29.300 fasting, I kind of referred to that a moment ago. That's the intermittent abstinence of food from
00:12:36.100 anywhere, depending on who you read. I typically refer to it as sort of 12 to 24 hours. Some of
00:12:42.220 the literature says actually it could be 12 to 36 hours. And I think it depends on whether you're
00:12:48.800 referring to time-restricted eating or TRE, during which period of time food intake is limited to short
00:12:55.100 periods of time within a day, or something called ADF, which is alternative day fasting, where you
00:13:02.760 alternate a day of regular feeding and a day of not feeding. So again, if you look at this graph
00:13:08.500 or this figure, you can see what an ADF protocol might look like. And again, the pink squares on
00:13:16.160 this over the course of a seven-day week show you days of either complete or significant caloric
00:13:21.820 restriction. So you could see in the ADF, you've got a blue day on day one, three, five, and seven. So
00:13:27.800 just normal ad libitum feeding. And then day two, four, six, you've got anywhere from zero to 25%
00:13:33.960 caloric intake, depending on how aggressive you want to be. Contrast that with periodic fasting,
00:13:38.620 where you have just a period of normal ad libitum days, followed by a couple of successive days,
00:13:44.520 could be more than one, of course, of complete caloric restriction. Time-restricted eating,
00:13:48.500 on the other hand, each day has a period of caloric restriction. In my view, it's very hard to call
00:13:53.800 it TRE if it's less than 16 hours. Although I guess technically people might consider it TRE if
00:13:59.480 it's less than 12, but I would say sort of 16 to 18 is what most people are doing there.
00:14:03.900 And then finally, long-term fasting, where you just have a number of days stacked up. So again,
00:14:08.880 that's probably a helpful way to orient people to fasting. Just one interesting historical piece
00:14:15.500 of context. My book, I think it has two chapters on nutrition. There was originally a section in there
00:14:20.920 that I thought was still in there. And when we were preparing for this podcast, I went back to
00:14:25.140 look at it and I'm like, where is it? Where is it? Where is it? And I realized we cut the entire
00:14:29.080 thing out. In the part of the book that I wrote about fasting, there was an entire section I had
00:14:33.420 written about the world's longest recorded fast, which was by this guy named Angus Barbieri, who was
00:14:40.280 a Scottish fellow in the late 60s, dramatically overweight, probably in the ballpark of about 450 pounds,
00:14:47.420 but did a medically supervised fast for, get this, 382 days. So 382 days, he was hospitalized,
00:14:57.260 consuming nothing but tea, coffee, sparkling water, vitamins, and yeast extract. Over that period of
00:15:03.740 time, over a year, he lost 276 pounds, taking him down to a body weight at discharge from the hospital.
00:15:12.120 If my memory serves me correctly, of about 170, 175 pounds. And what was really interesting is there
00:15:18.440 was an article written about in a medical journal, it might've even been the New England Journal of
00:15:21.600 Medicine, roughly six or seven years post-discharge from the hospital, and he still maintained a normal
00:15:26.560 weight. He might've been about 10 pounds heavier than he was at the time of his discharge, which was
00:15:30.680 a completely normal weight for him. So again, it was just a very interesting story. And of course,
00:15:35.840 speaks to the body's remarkable resilience, provided there's enough fat to metabolize.
00:15:42.120 I do love the idea of if we asked you how many chapters were in your book and you had a list
00:15:47.740 out, you would probably list out 30. Cause you'd be like, oh, we talked about this, talked about
00:15:51.860 this, talked about this. So it does speak to the good job that the editor did in editing that guy
00:15:58.280 down. But I do love the concept of you telling a patient, Hey, go look at this chapter in Outlive
00:16:03.720 and them just scrolling through.
00:16:05.280 Right. They're like, ah, there's no such thing.
00:16:06.760 Yeah.
00:16:06.920 Yeah. And you'd be like, no way. I definitely wrote about that.
00:16:10.700 What's really sad by the way, and I don't know how this happened, but I can't even find the Google
00:16:15.320 docs of the 80 to a hundred thousand words that were discarded. I'm sure they exist somewhere.
00:16:22.320 I went to look for them to see if I could pull up the story on Angus and I couldn't find him.
00:16:25.880 I do. I am sure there is a graveyard of Google docs around that book that are somewhere in the
00:16:32.840 ether. You've done a lot of these yourself. So just out of curiosity, how many of those
00:16:37.960 different types of fasting protocols that we talked about have you personally done at one point?
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