What's the Deal with Intermittent Fasting?

Perry: [00:00:00] Emily, this is our first episode that I think you might be like, viscerally opposed to like, I think this intermittent fasting is something that would anger you at like a deep level, because I don't think I know anyone who eats more frequently than you do. When is the last time you ate? Tell me that.

Emily: [00:00:21] Uh, well, I ate on the way over here. So, breakfast? Um, yeah, ten minutes ago. I object to that. Okay, first of all, I want to say that I was opposed to the sun. I'm not into it. No, I, uh, we've done a lot of episodes full of things. I don't like weird peptides, but it is true that I like to eat very frequently, but. Okay. How long is the longest you've ever gone without eating? Like, not like, okay, not like one time when you had the stomach flu, but like on purpose.

Perry: [00:00:51] No, never on purpose. But because of circumstance. When I was a resident and this was back in the day when we would do these 30 hour shifts, which [00:01:00] is a terrible thing and no one should ever do that. But so I would start at 6 a.m. and I would leave the next day at 1 p.m., and there was definitely a day or two in there where I, like didn't eat for that, maybe that maybe I had lunch or something. But I remember being so like exhausted and hungry on the way home. And I would stop at this place called Bocelli's in Havertown and get a chicken cheesesteak, like a full, like a 14 inch chicken cheesesteak and sit on my couch and eat the whole thing, and then just lie down on the couch and then sleep until like ten at night. That was it's not healthy.

Emily: [00:01:35] But that's not healthy.

Perry: [00:01:36] That was a long time.

Emily: [00:01:37] It's not good for you. It's not good for the people whose kidneys you were working on. It's not good for anyone.

Perry: [00:01:42] It's not. But Emily, you're like, you really believe in fueling your body. You're an exercise person. You. I don't I thought that fasting would be something that is anathema to your sort of worldview.

Speaker 3: [00:01:56] I think that's very interesting. I, uh, I like to. [00:02:00]

Emily: [00:02:00] Eat frequently before exercise, but I will say that I don't eat after like 6:30 p.m., so until the next morning. So I'm not like a late night snacker. I do a thing that some people would view as a form of fasting, where you don't eat while you're asleep. That's my kind of fasting where you don't eat literally during sleep. I have occasionally eaten during sleep, to be clear, but, uh. But I try not to sleep eat.

Perry: [00:02:26] I keep a side of bacon right on my bedside bedside table.

Emily: [00:02:30] I'm surprised it's not like that. The like cheese from the mac and cheese that you have, like a little spoon and like a container of that next to your bed.

Perry: [00:02:38] Yeah, you can stir it in water. Little drink overnight.

Emily: [00:02:40] Great. All right. Let's talk about intermittent fasting, something that I am not a fan of, but we'll find out. Maybe you'll change my mind.

Perry: [00:02:48] We'll see.

Emily: [00:02:49] Probably not, though. I'm Emily Oster, I'm an economist and a data expert.

Perry: [00:02:55] And I'm Perry Wilson. I'm a medical doctor.

Emily: [00:02:58] It's Thursday, October 15th, 2026. [00:03:00] And this is Wellness, Actually.

Perry: [00:03:02] Because you're getting a staggering amount of health and wellness information nowadays from every source imaginable. And some of it is awesome.

Emily: [00:03:10] And some of it is, well, actually bullshit. Fortunately, we're both people who know how to read studies, how to parse the data, and can tell you what's worth thinking about and what you can safely ignore.

Perry: [00:03:24] But before we dig in a note that this podcast is for educational purposes and should not be construed as medical advice. We don't know your unique situation, so talk to your doctor for personal health decisions.

Emily: [00:03:36] This week we're asking what's the deal with intermittent fasting? Perry and I will give the official smash or pass, and then we'll get to your question of the week. But first, let's do the health news roundup after the break. And now for the health news of [00:04:00] the week. Perry Health Secretary RFK Jr. Is establishing a clinic and dedicated billing codes to track serious vaccine side effects. Um. Smash or pass? Yeah. About that.

Perry: [00:04:16] Uh, so okay, it is obviously better data on vaccine side effects is critical. We've talked about this before, but the Vaccine Adverse event Reporting system is potentially the worst, uh, data set on, on, on vaccines that could possibly exist because anyone can submit anything and it's completely unverified. And as we said before, there are reports in there that people got injected and turned into the Hulk and stuff. It is very messy data. So clearly we need better data on this. I think there are some problems with the approach of creating a billing code to report vaccine injuries. That means that a healthcare provider like me could potentially get reimbursed by insurance or Medicare or Medicaid for reporting vaccine [00:05:00] injuries, which does obviously create a bit of a perverse incentive there. And then I think there's the there's this meta issue, which is that because we know who RFK Jr is, the fact that he's couching his language in like, don't we don't we all just want better data? And don't we all just want things to be more safe? It's like a little disingenuous to me. I think the, the idea that is next to this proposal is that there is a, you know, vast undocumented slew of vaccine adverse reactions that we aren't aware of. And the truth is, we are there are other vaccine reporting systems besides the horrible virus. There is lots of post-marketing surveillance going on already. So I think this push, you know, just serves to further erode trust in the vaccine system, which has been one of the greatest benefits to public health in the past century. That's what I think.

Emily: [00:05:59] Yeah, it's [00:06:00] sort of frustrating because, like coming from someone else, this would be, you know, a potentially I can see a frame on this that would that would be something in the direction of, of like fixing the vase and, you know, trying to be better about this. But in the current landscape, it's again, erosion of trust as our core is our core value here.

Perry: [00:06:21] So yeah, since we're talking about erosion, let's talk about erosion of fats. Uh, we got a couple of clinical trials out this week that looked at a new experimental drug called CBL 514. I think that will get changed at some point. And this is a drug that seems to cause fat cells to melt away. I mean, I've heard about 8 million things that cause fat cells to melt away. But I'm, uh, I'm interested. What do we know about CBL514M?

Emily: [00:06:54] Okay, so this is both very interesting and also an example of a of a kind of reporting I [00:07:00] find tremendously frustrating. So this was these clinical trials are reported as in like an abstract at a meeting. And when you have an abstract at a meeting, it's like, it's like a press release, right? It's like a, it's like a, it's a press release. It is, it's a press release.

Perry: [00:07:17] Yeah. It hasn't been peer reviewed.

Emily: [00:07:19] It's like it hasn't been peer reviewed. But more than that, there's no details. Like peer review is not a magic thing, but at least if you could see the whole paper, you could see, you know, what did they do? What happened to these people? Where is there a placebo effect? This is just sort of like, oh, we did this thing and a lot of cool stuff happened. However, having said that, a lot of cool stuff did happen. So this is an experimental injectable molecule drug. They are looking at whether this will like eliminate your fat cells by like causing them to shrivel up and die in cells. Self-destruct, actually. Um, so that's fun. Um, and I think what was interesting here was they have tested this in sort of surface fat. What this [00:08:00] article I read about it describes as, uh, the pinchable, the pinchable fat that sits under the skin. They've already shown you can pinch pinchable fat away. But actually, what's what's more problematic for health wise is visceral fat, which is the fat that gets around your organs. And that's not that's not good. And they show that they could reduce. There was some reductions in visceral fat, um, in this drug actually sort of sizable, about 12%. So again, that's based on this press release. Abstract. Who knows? Um, but it is, it is interesting. We need to know much more about this. To conclude anything. We would need much larger studies. We need much more safety evidence. We need just like literally any additional information about anything would be so deeply helpful, but interesting. Yeah. I like the idea of my fat cells self-destructing.

Perry: [00:08:49] Yeah. The cool thing is that like, weight loss reduces fat, usually not. By killing the fat cells. It reduces the amount of oil, the fats in the fat cells. So they shrink instead of go away completely. This [00:09:00] drug seems to make them actually die. And maybe that's better for long term loss of fat. But I don't know, speculative.

Emily: [00:09:06] Also, it just doesn't it sound better? Like, wouldn't you rather have dead fat cells than like just small ones? Me I would.

Perry: [00:09:12] I yeah, I guess so unless, but what if they're releasing all sorts of like evil humours? I don't know, we'll see evil humours.

Emily: [00:09:18] Perry what is it like 1650? Okay, welcome to the past.

Perry: [00:09:22] Gotta get my plague mask out.

Emily: [00:09:24] Uh, the FDA has issued a warning letter to Amazon for selling unapproved over-the-counter herpes treatment.

Perry: [00:09:33] Say more people do not get your herpes treatment from Amazon. That is the incorrect choice. I'm looking at a picture.

Emily: [00:09:44] Now the picture I have to say like you must describe the picture to people. It is insane.

Perry: [00:09:50] Okay. Herp care ointment. Could we not come up with a better name than Herp care guys? Herp care ointment for genital herpes symptoms. It's organic. So here's a picture. [00:10:00] It's got, like, a silhouette of a man and a woman with a red bull's eye target around the genital area. Um, for those of you on video, we'll put this up on video. And, you know, it's got like, and it's like a honeycomb and olive oil and whatever.

Emily: [00:10:15] So if you're, if your vagina is all red and bulls, I'd rub some honey on it. And that's. Yeah. So great.

Perry: [00:10:24] The real, you know, the concern. Okay. There there are no over-the-counter treatments for any sexually transmitted infection. Full stop. That you can. There's nothing you can buy without a prescription that will treat any any sexually transmitted infection. So remember that these things of course, you know, if you read them, they're not saying they cure herpes. That would be very, very illegal. But it would be very easy to think that these products are somehow either making the symptoms better or I think really concerningly decreasing the risk of transmission, which they very much don't. So, you [00:11:00] know, the FDA, I think, is in the right place here to, uh, to send a warning letter saying, you know, don't, don't try to sell things that imply that they're treating a sexually transmitted infection, which is going to increase the risk of transmitting that infection to someone else.

Emily: [00:11:15] Yeah. If you have herpes, there are great treatments for that which you should get. They are medical though.

Perry: [00:11:20] Yeah, yeah. You need a prescription, but you can get them from many doctors, many doctors. That's it for the health news of the week. Okay, now what's the deal with intermittent fasting? So this is a big topic. There's so many people that have asked me about this topic since we started. Um, since we started the podcast. And, you know, I'll admit at first I thought this was just about diet dieting like weight loss and dieting. Oh my gosh, that is the tip of the iceberg. So we've got. We've got a lot to get through here.

Emily: [00:11:58] Okay. I'm going to start by [00:12:00] setting the stage and just explaining what the kinds of not eating are. Because you've probably heard many of them, they have the, uh, uh, they have different acronyms. So okay, let's just run through it. So first there's something called a D, F alternative day fasting. Isn't that also like a German political party?

Perry: [00:12:20] The AfD is the alternative for Deutschland. Yeah.

Emily: [00:12:23] Okay. Never mind. This is a totally different.

Perry: [00:12:26] Uh, party on the rise.

Emily: [00:12:27] Unlike voting for a for a slightly right wing political party. Uh, this is just.

Perry: [00:12:32] Very right.

Emily: [00:12:33] Wing, uh, not eating anything every other day. Very simple. One day you eat, one day you don't eat fine. There's a modified ADF, which is you have on the fasting every other fasting day, you have a small amount of food like 500 calories. There's five two where you eat normally five days a week, very little on two of the days. There's time restricted eating, which I actually think is the sort of most common version of this, which [00:13:00] is like eating within a window like 16 colon eight is one of the things people talk about. It's like you don't eat for 16 hours. You pick eight hours of the day that you eat. You don't eat for the other 16 hours. There's also prolonged fasting, which we'll get to later, which is like multiple days of, uh, of fasting. So when people talk about intermittent fasting, they almost always mean that they are eating in a shortened window in the day. That's like the, when Andrew Huberman talks about that or these guys, this guy, Byron, whatever the like different longevity influencers are doing, they're talking about this like sort of shortened eating window. But fasting in various ways has been experimented. You know, people do all kinds of different kinds of fasting.

Perry: [00:13:45] Sure. Sure. Um, and, and what we're going to circle back to this a number of times, but one of the things that I've been thinking about a lot as I've been researching this is the difference between fasting and calorie restriction, because the truth is that [00:14:00] when you do any type of this fasting, like in general, you're taking in less calories, right? If you don't eat for 16 hours a day and you do eat for eight, it's possible you could get your full load of daily calories in that eight hours. But it's hard. You know, it's a limited amount of time. You get full. Most people are eating less calories no matter what type of fasting they're doing. And eating less calories has a number of benefits that have been shown in multiple studies. And then there's the fasting itself, like the duration without eating. And I think to to understand what might be special about that, we actually have to do a little science and talk about what happens when you don't eat.

Emily: [00:14:36] You get cranky.

Perry: [00:14:37] So can I walk you through the timeline of not eating?

Emily: [00:14:41] All right. Please indicate where the crankiness arrives.

Perry: [00:14:44] Okay. Okay. All right. So from about 0 to 6 hours after you last ate, you're not that cranky. The reason is you've digested a meal. And when you have excess, you know, when you digest all the food and protein, carbohydrates and fat that you eat, a [00:15:00] lot of that through various processes is going to be turned into energy containing molecules, mostly glucose. So you've got a lot of glucose and your body knows that food comes intermittently, and it has methods to store that for later. And the short term storage of glucose is called glycogen, and that lives in the liver. So your body takes that extra glucose from the food you eat. If you're not using it right. Then like Emily, when you're running your marathons and taking your glucose packets, it's probably using that up right away. You've got extra floating around. It'll stick some glycogen in your liver for later. If you continue to have even more glucose, it can put it in long term storage. And that's fat, basically. Right. So so we can store short term and long term. Okay, so 0 to 6 hours, you're fine. You've got glycogen in your liver. That glycogen can very quickly be sucked out of your liver and turned back into glucose. So it's just like, you're doing fine, you're fine. Then things start to tail off a little bit. This is when we start to get hungry. And you know, if you're [00:16:00] pushing a real fast now we're talking, you know, somewhere up around 18 hours. And this is if you're not exercising around 18 hours, the glycogen is basically gone. So the liver is out. If you're exercising, that will happen much quicker. And in fact, you can run out of glycogen stores in your liver, like while you're on a long run, for example. And it you really hit a wall when that happens. But you know, if you're just chilling at your desk like I am, um, got about 18 hours glycogen runs out and then your body's job is that it has to make more glucose. If you're not eating, everything in your body uses glucose for energy.

Emily: [00:16:35] Especially, I want to say especially your brain, your brain, like when you're, when you're glucose replete, when you have a lot of glucose and you're continually fueling with your body, with glucose through just eating regular meals, about 20 to 25% of your calories are being used by your brain.

Perry: [00:16:50] Right? So now your body is sensing, I've got no more glycogen. I need to make glucose. What can I make glucose from? And you have two sources left in your body. One is fat and one is [00:17:00] protein, basically muscle. And you can break down fat to make these things called ketoacids. When you hear people talking about the ketogenic diet, this is essentially what they're talking about. In that case, they're just taking in zero carbs. So they're not producing any glucose, which forces the body to make glucose from what it can, or to make energy containing molecules from what it can, uh, fat, but also from muscle breakdown. And you know, what is essentially happening once you're out of glycogen is what, in some cases we would call starving. It is when you are digesting your own body for food and manipulating that is can have both benefits and risks.

Emily: [00:17:46] Yeah that's right. Yes, you can have benefits and risks. I mean you have to you. Yeah. As you said, you sort of have to consume something. And so you might like to consume more of your fat. But, uh, [00:18:00] but you are also consuming your, uh, your muscle. And I think it's worth sort of saying, if you just literally stopped eating for those sort of 2 or 3 days, uh, people used to speculate that like more or less the question is like, what would your brain do? Right? Because your brain is running on glucose, you stop providing glucose, your body can make some glucose. But if you fast for a long period of time, your glucose ends up at about 30, uh, like 30 glucose points or whatever milligrams per deciliter, I think. And you'll just sort of stay at that kind of consistently.

Perry: [00:18:31] That would be pretty low. It's, it's pretty even hard to get to, to a level that.

Emily: [00:18:35] If you fasted for like a, this is like, I'm talking about like a lengthy, like if you fasted.

Perry: [00:18:39] Really starving.

Emily: [00:18:41] You're really starving and your brain starts running on ketones. So your brain will basically can run on, can run on the ketones that are made out of out of fat. So that's kind of an interesting. Your body's interesting.

Perry: [00:18:54] Yeah. There you'll see people online suggesting that ketones are the brain's preferred source of energy. That is [00:19:00] completely untrue. It's like an emergency source because if your brain dies, you die and like it. It will work on this. It's like putting, um, I don't know, like diesel fuel in your gasoline car.

Emily: [00:19:11] Like it's not like that because that would be really your car will stop working.

Perry: [00:19:15] Oh, does it not work? Okay, I don't know, I don't know. Oh, how about putting gasoline or diesel car? I don't know anyway. No, don't do either.

Emily: [00:19:21] It's not like.

Perry: [00:19:21] Not it's preferred.

Emily: [00:19:22] Fuel, but it's not your preferred. Let's just say it. What say the first thing you said was right. I prefer things that don't take gassing up your car. Advice from Perry, who's obviously.

Perry: [00:19:32] Not not not a mechanic, uh, not a mechanic. I'm a doctor, not a mechanic. Okay. One of the interesting things, though, about your body digesting itself that the studies show is that there's this sort of window of time where muscle breakdown is occurring more than fat breakdown. And, and the studies sort of vary here, but it does seem to be in this like 18 to 24 sort of end of day one into day two window, where proteins from muscles, [00:20:00] amino acids from muscles are being broken down for fuel before lipolysis, which is the process by which fat gets broken down, ramps up. So this hasn't been extensively studied, but I actually think there's an interesting argument to be made that a sort of medium duration fast, where we're talking like that, that sort of intermittent fasting 18 to 24 hours or alternate day fasting is potentially the worst for losing muscle, but not losing that much fat.

Emily: [00:20:27] Okay. So speaking of losing muscle and potentially losing fat, I think the first thing we should talk about is once we now understand like kind of what we're. What happens when you fast is whether this is good for weight loss. So this is like if actually, I think you're totally right. This is where I thought people were on this. And I think they have been at various times, but fundamentally, it's not the most interesting stuff in, in literature, right. And the bottom line is it's, it's for the most part, the way people lose weight is by I [00:21:00] mean, the way you lose weight is by consuming fewer calories than you burn. Yeah, that is it. It's more complicated than that to kind of understand, because our basal metabolic rate can change and different things are different about different people over over time. But if you if fewer calories, for the most part, on average, you're going to, you're going to lose weight. This works large like intermittent fasting can produce short term weight loss, like almost every diet that has ever been happening. And it does so because it has. People eat fewer calories and, uh, the sort of randomized trial evidence basically says that what happens is if you are eating fewer calories, in fact, there's like a very sort of a very nice trial where they had people on matched calorie diets. And the question was, are you eating them all? You know, in an intermittent fasting way or whenever you want. And if the calories are matched, the weight loss is also matched. And so that's it. Like. And so [00:22:00] for some people, this is actually an, I think an efficient way to, to diet because it's simple and sort of like, okay, I'm just only going to eat. I'm not going to think that much about it, but I'm only going to eat through these particular hours. Fine. If that's something that works for you, okay. But it's not like better than other ways to get fewer calories.

Perry: [00:22:19] We've said it before successful diets make it harder to eat. So all of the sort of fad diets that that work, you know, from Atkins on down is like, you know, oh, I can't eat these foods that I normally would eat. And it just makes things trickier. I honestly, I have thought like, okay, you could probably make a diet like you're only allowed to eat yellow foods and, but you can eat as many yellow foods as you want. And like, you'd probably lose weight because it's just hard. It makes things harder. But I agree, you know, this is a pretty simple thing to remember. You don't have some long list of foods that are good and bad. It's just like, don't eat between this time. I'll give you a couple numbers. There's a nice meta analysis in the BMJ in 2025 that looked at all the different intermittent fasting ish things like alternate day and 16 to 8 and all the stuff we talked [00:23:00] about combining data from a bunch of different randomized trials. And the best comparison that they had was alternate day fasting versus eating whatever you want. And in that trial or in trials that looked at that, the average weight loss in the alternate day fasting group was about 3.3kg. So that's, you know, 8 or £9 or so. So, so not nothing. But of course, that's first eating anything you want against calorie counting. Not quite as impressive about two kilograms. Um, again, that wasn't matched calories. That was just people doing their best to reduce their caloric intake, which is which as you point out, is, is a tricky thing.

Emily: [00:23:40] Yeah. And I think, you know, this is really reminiscent of basically everything we talk about in the diet literature, which is, you know, many diets of which this is one can produce weight loss over some period. Generally, most of the weight is regained is like a general factor in the literature. [00:24:00] People have a hard time sticking to diets long term. This is part of the reason that GLP ones, I think have been so successful, because changes in your dietary patterns in the absence of medication are difficult to sustain, and that's fine. So if this is an interesting way for you to diet and you would like to try it, great, no problem. But it's not some special magic weight loss trick.

Perry: [00:24:22] Yeah. The lesson we've learned here is that whenever we're going to talk about something here, we need to always when we're talking about intermittent fasting, we always have to say compared to what? And basically the default comparison really should be calorie restriction with the understanding that calorie restriction is hard. And if you can get there via intermittent fasting, good for you. That's that's better. So we're going to take a quick break. And then after the break, we're going to move away from weight loss and into all the myriad.

Emily: [00:24:51] Literally everything else. We're going to move away from weight loss into literally all other aspects of your health next. Okay, [00:25:00] Perry, we're back and we're going to start, we're going to put this in a few clusters. There are a million different things here. I'm going to start with the cluster of metabolism. I'll give you a claim. You tell me claim it resets your metabolism. What would that mean and is it true?

Perry: [00:25:22] Yeah. I don't think this is true. I don't think this is true. So the the claim here is that by, you know, by doing a fast of some, some form or another, you know, it's like, it's like, uh, resetting your Wi-Fi router, like things kind of get back to normal and you'll be your old self. The data really doesn't support that at all. Um, so we've got reasonable data that people that do these types of diets, uh, have lower insulin levels and better insulin sensitivity. Um, their LDL or bad cholesterol goes down, their HDL goes [00:26:00] up. This works a little bit better with in trials of alternate day fasting, as opposed to the time restricted eating like the 16 to 8. And so that's fine. But compared to equivalent amounts of calorie restriction, there's no difference. So in terms of like all the insulin homeostasis glucose stuff, there's not a lot of evidence that you're doing anything beyond just calorie restriction. But what I'm sort of more interested in is basal metabolic rate, right? So your basal metabolic rate is the amount of calories your body burns just doing its thing, right? You're not exercising. It's just at rest. Your heart's beating. You've got to breathe. Your brain is doing stuff. That's your basal metabolic rate. It's going to differ based on your body, habitus and a variety of other things. And if anything, I think what we all want is our basal metabolic rate to be a bit higher. Right. I would. We'd all love to like burn more calories sitting around than we currently do. And the data here is very clear. The more you fast, the [00:27:00] lower your basal metabolic rate goes. Because of course it does, right? Like evolutionarily.

Emily: [00:27:06] Telling your body.

Perry: [00:27:08] There's not enough food around. Like your body.

Emily: [00:27:10] Conserve.

Perry: [00:27:11] Exactly. Your body will go through processes that say, oh, okay, like we're not in a food rich environment. Let's turn down our systems and thermogenesis and all these things that contribute to our basal metabolic rate. And so again, not saying it's not, you know, it's not good for you. It's good for you or it's bad for you. But these influencers who are like, oh, once you fast, your body learns to like to burn fat and it's going to all of a sudden it's going to start burning fat forever and not doing anything else. Like, if anything, your body's going to try to conserve calories because for, you know, hundreds and thousands and millions of years of our evolutionary history, that is the proper response to a food scarce environment.

Emily: [00:27:50] Yeah. Okay. Rejected. Metabolism. Rejected.

Perry: [00:27:55] Yeah.

Emily: [00:27:55] Okay. So the second thing in this space that I want to talk about is, is ketones. [00:28:00] People are just like very into ketones. And I would say in this discussion, there's a lot of vague emphasis on, you know, when you are fasting, your body is going to produce these ketones. And ketones are like a special magic flower that's going to improve everything about about you. So ketones are very, very, very interesting. You know, ketosis is very interesting. Ketones are ketones are interesting signaling molecules. I think it is extremely interesting that our brain can run on them. It is very interesting evolutionary adaptation to periods of famine. Right? You have like a hungry, hungry brain that needs fuel. Usually you'd like to fuel it real fast with all the glucose, but you definitely don't want to be in a situation where if you don't have access to glucose, your brain stops working because you're really [00:29:00] using that. And so we are kind of evolved the, the fact that the brain can use ketones, it has evolved from that potential for famine in the vast history of human existence. So great, but it isn't what our brain would like. It's not our brains first choice.

Perry: [00:29:18] It definitely isn't. And there are real medical uses for ketosis.

Emily: [00:29:21] Totally. And so the most interesting of which is some evidence that the ketosis is an appropriate way to potentially treat epilepsy, especially in children. And so this actually comes out of the fasting literature. So people had noticed that kids with epilepsy got better when they were fasting. Fasting for long periods of time is of course like not possible, but it seems like the that was in fact a result of the fact that people do better if their brain is running on ketones again, if they have epilepsy. And so this has led to one potential treatment for epilepsy, particularly in kids, which is a very, very sharp [00:30:00] ketogenic diet with basically no carbohydrates.

Perry: [00:30:03] Yeah. It's a brutally difficult diet to very.

Emily: [00:30:06] Difficult diet to do so. But ketones are very ketones are very interesting. But the idea there's just nothing in the data that would suggest that somehow having more of them or doing more with them is somehow preferable, or improving anything about your health.

Perry: [00:30:20] Well, yeah. And again, they are signalling molecules. So. So you do have receptors on cells that detect ketones in the blood and change how the cell is functioning. But on a metabolic level, their primary signalling effect is to decrease the degradation of fat and to suppress muscle building. Because again, you're in a food scarce environment. Now is not the time to be like putting all your energy into building muscle. It's time to conserve. You want to conserve your fat. And so, um, they do signal, but they don't signal in some magical way that's going to get you shredded. In fact, quite the opposite. They're telling your body, chill [00:31:00] out a little bit. Like we've got to wait until there's food around again before we can really bulk up.

Emily: [00:31:05] I mean, the reality is if you're looking for like performance of your brain or your body or anything, you want to be living on carbs. And you see this, of course, in sports, but you also see it in like, you know, chess, like Magnus Carlsen is consumed. He used to consume a lot of. Magnus Carlsen is a very successful chess player, and he used to consume a lot of orange juice and other sugary drinks. And then he. And then at some point, he decided that it was like he was having a sugar crash. But. And then he started drinking chocolate milk.

Perry: [00:31:35] Yeah.

Emily: [00:31:35] Okay. Which, you know, I guess is like, also has fat. It's more delicious, I think, and also has fat. But the point is that you need to be consuming something with, uh, with easily available glucose if you want to be performing.

Perry: [00:31:49] Uh. Right. Totally, totally. So we're straying near some, I think what we can put in cluster B of the claims for, for intermittent fasting, which are like a [00:32:00] bunch of cellular buzzwords. So M did you come across autophagy in your research?

Emily: [00:32:07] Love autophagy. Yeah. Autophagy is a great it's a great word. Um, and I, it comes up a lot in wellness. So it's, it's the process by which cells digest their own like worn out parts and it if we if we are, aren't autophagy ING very effectively, uh, that can increase risks for cancer or neurodegeneration. So you do actually want your cells to be like digesting their worn out parts. So the worn out parts are not just like sticking, sticking around. Um, and so when we think about this in the context of fasting, this is the first of many, many findings which I would describe as mice are not people. So mice fasting is pretty cool. So there's actually like an, an early study [00:33:00] from 2010 in a journal called conveniently autophagy, uh, that found that if you leave mice for 16 to 24 hours without any food, there's more autophagy in their brain. So they're like doing more consuming of the warm up, worn out parts. And so that could, you know, that's not that's not to say they live longer or anything specific, but it is kind of a particular signal. There are kind of two issues. One is that, um, mice are not people. And a particular way in which mice are not people here is that mice have a very high metabolic rate. So having a mouse fast for 24 hours is not a human fast for 24 hours. That's a human fasting for like a week.

Perry: [00:33:42] Yeah, yeah, yeah.

Emily: [00:33:43] They're not like a long time. It's hard to know exactly the the conversion.

Perry: [00:33:46] There has been a human study of looking at autophagy, but it's not terribly compelling. Um, so I did.

Emily: [00:33:54] Find 11 people.

Perry: [00:33:55] Yeah. Um, and, and basically it had, um 11 [00:34:00] adults who had overweight and they had a time restricted eating arm versus sort of a more regular arm. And they showed that a specific autophagy gene increased 22%. Uh, so I don't know that a gene increasing really tells us anything about anything going on in the brain or etc.. But like, again, it makes sense, right? Like as you starve, you start to consume more of your own body. And that's, that's fine. Um, you know, it really remains to be seen whether this makes any difference compared to calorie restriction alone, or whether the cells that are getting eaten are necessarily the cells that are going to give rise to cancer or neurodegeneration, or all the other stuff that gets claimed about this.

Emily: [00:34:40] Or what the size of this effect would be. And I think this is another thing to come back to. Like, let's say this was a true effect on the scale of something, some outcome you would actually care about, like longevity or cancer development. This is going to be like a teeny weeny fraction effect.

Perry: [00:34:56] Right? Right, right. So let's move on to inflammation, [00:35:00] the dreaded inflammation term. No one wants inflammation.

Emily: [00:35:04] No one wants to be inflamed.

Perry: [00:35:06] Um, what do we know about, uh, you know, a lot of people are claiming that immune inflammation, immune reactivity goes down with fasts. Seems to be true from what I can tell.

Emily: [00:35:19] In in, uh, in mice.

Perry: [00:35:21] Yes. In mice. Um, but also there's a 2019 cell study which took 12 healthy volunteers. They fasted for 19 hours and the level of their circulating monocytes, which is an immune like a white cell and immune dropped quite sharply. Similar findings were shown in mouse. They come back after you eat, I guess. I mean.

Speaker 4: [00:35:44] I think there's a really.

Emily: [00:35:45] Important question here, which again, like we're sort of hitting all of these different issues with this literature. But here I think an issue is like, what, what does it mean for this thing to go down? Is that is that good? You know, when you stop [00:36:00] fueling your body, it stops doing stuff, right? It's going to stop doing things that it doesn't really necessarily think are useful right now, because it's sensing like we have to get in the mode of like, there might not be food here. And so the immune system, that's something that's expensive. Like we're we're using it ramping.

Perry: [00:36:19] Up.

Emily: [00:36:19] Energy things. It takes up a lot of a lot of energy. And you might think, okay, right now there's no food. And I'm not really sensing like an immune challenge. And so maybe I'd dial down the immune system because I'm not using it right now. And that's exactly, that's an interpretation of what you see here, but not an interpretation that says like, oh, this is so great. It's an interpretation that's like, well, now when your kid comes home with a cough and they cough on your face, your immune system isn't available because it took a break, uh, because you didn't eat anything and then you might get more sick. So I think it's like a, I don't know, I, I, I find this, I see the results. It only has 12 people in it. Fair [00:37:00] enough. And I question whether it is good.

Perry: [00:37:03] I think that's fair. There's nothing specifically bad about inflammation. In fact that's your immune system doing its job.

Emily: [00:37:10] Yeah. I mean, I like I, I find this discussion I'm not that concerned about inflammation. I realize people don't like to be inflamed. It sounds bad, but I'm not sure it's so terrible. Okay, what about starving a fever? This is my favorite. Um, you know the phrase like, feed a cold, starve a fever. Um, and I think the idea is that if you don't eat when you have a fever, it will get better more quickly, I guess.

Perry: [00:37:37] Yeah. I think that's the idea. And we have the greatest study for this. Yes, it's a mouse study. But I actually I really love it. It's from cell in 26 mice. This is a great study. So researchers took a bunch of mice and they gave them either a bacterial or a viral infection. Okay. So they, you know, had bacterial infection, you know, bad [00:38:00] whatever viral infection, more like a flu type of thing. And then they randomized the mice to anorexia, like they didn't get any food or nutritional supplementation. And what they found was that the starving mice survived longer during the bacterial infection. But they found the opposite for the viral infection, so that the starving mice died more often with the viral infection. They lived longer if they were fed. So bottom line, actually.

Emily: [00:38:27] The advice is opposite.

Perry: [00:38:29] It's completely wrong, right? Like insofar as we're talking about starve, a fever means a viral infection, like the flu or something, which I think most of the time when we have a fever, it probably is a viral infection. This mouse study would suggest no, no, no, you feed that. Now, it is interesting that in the bacterial, you know, much more rare type of bloodstream borne bacterial infections are pretty rare. Fortunately that some starving, you know, might have helped. And there's some logic there. Bacteria much more so than viruses are [00:39:00] using stuff like are using your substrate in your blood to grow and things like that. So, so maybe starving kind of competes with them for growth. There is some data in patients in the intensive care unit with severe bacterial infections that looked at early feeding, like as soon as they get into the ICU and they're super sick and you drop a tube and do tube feeds versus more delayed and, and suggested actually that more delayed feeding led to some beneficial outcomes. This isn't entirely standard of care, but I think it's like it's interesting, but we certainly have nothing on the outpatient side. And I think if you're if you're feverish, if you have a viral infection and you believe in mouse data, then you know, you should probably eat something.

Emily: [00:39:43] Yeah. Or stay hydrated.

Perry: [00:39:45] Hydrate. Oh, yeah. We definitely oh, God, we haven't even talked about dry fasting. I don't even think we have a bullet point. Have you seen this dry? Okay. Side sidebar.

Speaker 4: [00:39:53] I heard of this.

Perry: [00:39:54] As the nephrologist. As the kidney doctor. Don't do this. So dry fasting is fasting. But [00:40:00] you don't even drink. You don't even drink water. It's a absolutely terrible idea. Don't do this. It's bad for your kidneys. It's bad for your brain. It's bad for the rest of your body. Please drink water. Okay. That's it. Moving on. Um, I think our next sort of cluster of claims about intermittent fasting is performance. Like you get these people that are like, okay, I understand it's hard. I know it's tough, you're hungry, you're cranky, but you are going to get this laser laser like focus, you know, in your brain. And maybe it's because the ketones making your brain.

Emily: [00:40:40] Let me ask you a question like, did you eat this morning? Did you eat before this?

Perry: [00:40:44] Okay. Well, all right.

Emily: [00:40:46] For the listener, we had a discussion on Slack about whether Perry was going to eat before the episode. Did you eat before the episode?

Perry: [00:40:52] So I had the brilliant idea that I was not going to eat before the episode because I hadn't eaten since like seven last night. And we're recording. It's like [00:41:00] 11:00, 1130 now. So I was like, okay, I'm coming up on, you know.

Emily: [00:41:03] Getting on your 16 hours.

Perry: [00:41:05] Or so. I'm going to be quasi intermittent fasting during this episode. And I said that on Slack, and then I'm sitting in my office and like, I was like, oh, no, I can't do it. I can't do it. I had to eat something. So I ate, I ate. Yeah, yeah. I'm sorry. I'll have to try that when we start, when we turn to like the experiential episodes, like when you and I are going to do psychedelic mushrooms together, that's that's when the intermittent fasting will happen. All right. So so I lack the sharp focus, um, that I would have had had I not caved to my hunger a few hours ago. What do you think about this? M like Magnus Carlsen seems to think no, like I, I need the glucose to play chess. Well, so is there any can we support the idea that fasting locks you in in some in some way?

Emily: [00:41:54] I don't think the data supports this. So there's meta analysis in 2025 and Psych bulletin that [00:42:00] 3500 people and basically finds no effect after a 12 hour fast. You know, there's sort of no difference in attention Inhibitory control memory, the kinds of things that we measure to sort of see if people are kind of like able to have an executive function. I find this interesting, um, partly because of its contrast with something like sleep. So, you know, if you deprive your body of sleep for 12 hours, obviously, no, but like for, you know, a full 24 hours.

Perry: [00:42:28] 30 hours.

Emily: [00:42:29] It is substantially your performance is substantially worse. So you just get worse and worse and worse as you sleep, as you as the time gets longer and longer and longer, you just get worse and worse and worse and worse and worse until you just don't. And you don't like you don't like rebound basically very much. Whereas it's sort of the fasting piece is interesting because I might have expected that people would feel worse, that after 12 hours, a 12 hour fast, people would be hungry and distracted by the fact that they are that they are hungry. And that doesn't seem to show up. It sort of seems like on that scale functions [00:43:00] pretty similar. It doesn't make people more focused or less. It's just like they're just kind of the they're kind of the same. I'd be interested to see after 24 hours or 36 hours. Are you so hungry that you can't get your act together?

Perry: [00:43:13] I mean, I think again, it's like your brain is so protected against this, like your humans are just so evolved to protect their brain that I, I, I might even be surprised even at that, at that extreme, if you start getting real brain deficits. Um, there's, there's an exception here. M I don't know if you saw in the data, um, where kids and younger people actually did have some, uh.

Emily: [00:43:36] Yeah. Kids and younger people do worse, uh, when they're fasted. And we actually sort of this is, I think policy wise, a very strong argument for, for breakfast at school that if kids are not getting breakfast at home because their families don't have, uh, money and don't have food at home, this is like, this is a reason why school breakfast can be potentially very effective at actually raising test scores. Um, because [00:44:00] kids might otherwise not get breakfast and then they perform worse at school. And you might imagine many kids like they move through their food. You can't eat quite as much. There's some stomachs are smaller and they move through their food faster.

Perry: [00:44:12] Yeah, yeah, yeah. They have higher resting metabolic rates per kilogram and they're littler to begin with. Their livers are smaller. They have less glycogen. Yeah, I buy that.

Emily: [00:44:20] It's also the case that if you don't drink water, per earlier discussion, the dry fast does impact your cognition because you are thirsty.

Perry: [00:44:29] Oh yeah. Yeah yeah. So yeah, again, don't do dry fasting. Um, that comes from cognition. And dry fasting actually comes from, uh, Ramadan data. It's really interesting, uh, natural experiment of, of intermittent fasting where people who, you know, don't have all the other necessarily behaviors that go along with intermittent fasting, like other health seeking behaviors because it's a religious fast or somewhat it's a different population. So you get kind of a different cross-section of data. But, um, but yeah, dry fasting does worsen cognition. But for adults, just [00:45:00] not eating your brain will kind of hang in there such that it is.

Emily: [00:45:04] It'll keep working.

Perry: [00:45:06] Mhm.

Emily: [00:45:07] Okay, so that is your brain performance. Um, I will do just want to touch on your athletic performance, which actually the result here is, is interesting. Um, because I would have thought eating is, I mean, I think eating is great. Um, but they, they have done. So there's a study in men from about a decade ago where they took some, you know, fairly well trained men and they had a kind of 16, eight fast, but with, with like enough calories. So this is sort of not for weight loss. And they did find a decline in fat mass for the people doing the intermittent fasting. They also had a big decline in their testosterone. So that, you know, like lose fat, but also lose your, lose your, your vital, your vital.

Perry: [00:45:57] Your precious bodily fluids.

Emily: [00:45:58] Or.

Perry: [00:45:58] Whatever. Well, because testosterone [00:46:00] is anabolic, right? Like, again, a testosterone builds muscle and things. And that's not what your body wants to do when you're in a food scarce environment. So all make sense. Nothing surprising.

Emily: [00:46:12] Didn't see much. They've tried this in women. They don't see many differences. Probably the most interesting piece here is, uh, is some meta analysis of studies of Ramadan, which again, people are fasting for, for like the whole day. And they, they found this study finds a little bit of an impact on sprint performance again, sort of like kind of anaerobic like power, uh, may be affected by extended fasting. Um, but no change in aerobic performance or jump height or fatigue. Uh, there's actually not to nerd out too much on this space, but this woman named Sifan Hassan, who is one of the best marathoners in the world. And she, uh, I think prior to the Olympics, maybe was Ramadan, and she's and she's Muslim. So she was fasting. She was doing all of her marathon training, like completely [00:47:00] fasted during Ramadan and she won, so wow. But I don't think that's because of it. It's just for different reasons. Good for her.

Perry: [00:47:10] I think the big one that everyone kind of has heard about a little bit though, is longevity, right? Like, like we all, we want to live longer. I mean, I also want to live better. And I think being hungry for 16 hours a day is not necessarily living better. But that's just my personal opinion. If you're okay with it and you want to live longer, let's go. We know that in basically every species of animal, ranging from like nematodes all the way up through primates, that severe calorie restriction increases lifespan that has been well replicated like fruit flies, mice, all animals, yeast do this. It has not been replicated in humans because humans have a tough time reducing their caloric intake [00:48:00] by, you know, they're not trapped in cages and whatnot. And also, we don't have enough time to run studies for the 100 years that would be necessary to tell if humans are really living longer from calorie restriction. There's a study in 2023 in Nature Aging that that took 220 humans and assigned them to 25% calorie restriction. So they were like, okay, for the next two years, you're going to eat 25% fewer calories per day. By the way, they only achieved a 12% calorie restriction, so.

Emily: [00:48:30] 25% calorie restriction for two years. That's a very long time.

Perry: [00:48:33] It's very hard. And they couldn't do it because it's really hard and they're not locked in cages getting food like mice. Um, but the outcome here was an epigenetic clock, which is like this. You like measure DNA markers and you sort of do some statistics and you're like, okay, like this DNA looks in this study, one of the epigenetic clocks they use said they were two years. They had two years fewer. They're essentially they're clocked in age over two years. So they were two years younger by [00:49:00] the end. But the other two epigenetic clocks they use, because there's a bunch of different ones you can use showed no difference. I'm skeptical of epigenetic clocks to begin with. I think they're not very useful on the individual level at all. That said, that's the best we have in humans.

Emily: [00:49:17] But it's also not about fasting. Like this is about calories.

Perry: [00:49:20] This is just about.

Emily: [00:49:21] Calories, not about fasting.

Perry: [00:49:22] That's right. Yeah. And we have a mouse study though that that does what you would want, I think, which is that they randomized mice to different levels of calorie restriction. And whether they got that through just like less food over the whole day or, or fasting. And the fewer calories the mice had, the longer they lived. And layering intermittent fasting or any kind of fasting on top of those reduced calories had no difference on mouse outcomes. So I think the best data we have now for longevity is calories matter, and fasting does not.

Emily: [00:49:53] Yes. And yeah, calorie restriction is for another. Let's leave calorie restriction for another day.

Perry: [00:49:59] Okay?

Emily: [00:49:59] Talk about [00:50:00] weather. Weather that is really. But bottom line, fasting. Fasting. No. Okay, so the last piece, I think sort of all of this up till now, I would summarize as it doesn't really look like intermittent fasting or time restricted eating or whatever you want to tell actually does anything that's especially meaningful. Um, it is worth talking a little bit about more serious longer term fasting, right? So to distinguish between the kind of I'm not, you know, I'm, I start my last meal at 3:00 in the afternoon or I never eat before lunch or whatever is the, the thing from kind of significant, like I'm going to fast for many days. And you might imagine both. You might imagine this would be different in either direction. You might imagine that actually there is some benefit to fasting, but you need to fast for a very long time to get into it. Or you might imagine that fasting for a very long time is is bad.

Perry: [00:50:59] Yeah. [00:51:00] And, and here's where you see the claims that on online that really kind of start to flirt with some real danger. So I think we do have to address them. I'm going to start with the growth hormone thing. So growth hormone had actually a moment in the wellness in like the 70s. It was one of the first real like I remember one of my mentors in med school had a book on his shelf that was that was called like grow Young with growth hormone. And people were injecting themselves with it. It was kind of newly discovered and it was like, oh, it's this this magical thing. It is true that prolonged fasts increase growth hormone and they increase it significantly. So Journal of Clinical Investigation, 1988, six healthy men, a five day complete fast. They drank water but five days zero food. Their growth hormone growth hormone level went up by threefold. And you'll hear the influencers talk not about the specific study, but they're like fasting makes your growth hormone triple or quintuple and like growth hormone so good because it makes you grow and be strong and stuff like [00:52:00] that. That is not what this study showed. Actually, some of you may know that growth hormone works via a bunch of sub hormones that do different things, and the one that causes muscles to be built is called IGF one. So in the normal state, growth hormone signals, IGF one, IGF one signals muscles to grow.

Perry: [00:52:20] And the influencers will tell you that, well, therefore if growth hormone is high, then fasting makes it high. You're going to get stronger. In this study, the IGF one level fell. So growth hormone has many effects besides increasing IGF one. One of them is to break down fat for fuel. And that's what growth hormone was doing. And because your body knows when it's starving, it is not going to upregulate IGF one to help you build muscle in the middle of a famine. It does not happen. It doesn't work that way. It would be terrible if it worked that way. So a five day fast is called Starvation. It does do things. It does biologically active things, but in [00:53:00] general, not the things that at least the influencers are telling you are going to change your life and make you super strong. Yes, you'll lose fat because obviously you're going to digest fat, you're going to digest muscle as well. And by the way, most of these studies will show of the total body mass lost, you get about two thirds lean mass loss and one third fat mass, which is just about the opposite of the ratio we see from other methods of weight loss where you lose, you know, sort of half to two thirds fat mass and then one third lean mass.

Emily: [00:53:29] Not great. I mean, I think what's what's sort of tempting and sucks and sucks one in about this, this whole intermittent fasting space is that you do, you know, potentially see some loss in, in fat mass, which people think of as as good. And then there are many other things that change. And so it's an example of something where like, if you don't let somebody eat for five days, a lot of stuff's different. Like your body is not. That's not its intended goal. And so many things will change. And depending on how you interpret those [00:54:00] things, they could be good. They could be, they could feel good, they could not feel good. But like, of course, like it's a famine. A lot of blood markers are going to be different in a famine. And so it feels one can argue that things are happening. You know, this is a this is a biologically active process, which is true, but that is different from saying it's it's good. Okay. So it is it is possible to live a very long time without eating at all. Uh, world record is held by a guy named Angus Barbieri who, uh, this wasn't recent. This is like in the 1960s, 50s or 60s.

Emily: [00:54:37] He lived for 382 days without eating. He started at £450. He had water, tea and coffee, vitamins, also some potassium, sodium. So you actually you do need some electrolytes and vitamins if you're not going to eat. Um, and you didn't eat anything for 382 days, he lost quite a lot of weight. He was down to £180. He actually kept [00:55:00] it off for a pretty long, uh, for a pretty long time. My favorite fact about this is he only pooped every 37 to 48 days. So. Go back to our episode on poop. That's not the recommended, not the recommended frequency. You know, this actually was like it was called therapeutic starvation. And it was something that was for some period of time, kind of briefly in, in vogue. And, and, you know, the, the idea is, of course you're eating, you're eating, you're literally eating your body. And if there's a lot of, as my grandmother would refer to it, living off your hump. Um, and that is a way to lose a lot of weight. Uh, but also, um, sometimes people died. So this isn't, this is not a recommended approach to weight loss.

Perry: [00:55:46] Yeah, yeah. It's been, it's been given up because he's. Angus Barbieri is sort of the survivor of this protocol. There are a number of people who died. They tend to die of heart failure, arrhythmias, lactic acidosis, and so on and so forth. So but yeah, he would lose weight [00:56:00] in 382 days is a long time. Um, okay. We have to address this because the most dangerous thing you're going to see online, um, surrounds cancer. And I'm going to play an Instagram reel that makes me very uncomfortable.

Speaker 5: [00:56:14] If you had cancer, what would you do? Let's say it's stage four cancer. If I had that right now, I would stop eating and I probably wouldn't eat for 20 days and try to go for 30 days. Why? Because you are literally going to starve all the resources from cancer. It can't survive, but your body can survive. Cancer actually is very sick inside a tumor. It's very necrotic. There's dead dying tissue. It's hypoxic. What's the best sledgehammer? Is it chemo that kills also your cells? Or maybe would it be starvation? We call it fasting. If you did a long fast like that, that would put you in a better place. And then you can go to one meal a day.

Emily: [00:56:51] Okay. That's a very disturbing reel, Perry.

Perry: [00:56:54] I know, I know. I debated showing it to you. Um, let me just say, there's a lot [00:57:00] wrong with this. First of all, there's a complete absence of data like this is based on absolutely nothing. Um, there's no human data that suggests that prolonged fasting changes cancer outcomes we're going to touch. Well, you know, we did our due diligence. We'll look at some of this data in a second. Um, but it also, of course, has the, the typical sort of wellness grifter thing of like, why would you use chemotherapy? Like that kills all the cells, right? Which is super dangerous. There have been plenty of people who have fallen for this kind of thing and forgone chemotherapy and died of their cancer. Um, and I also just want to say that the number one predictor of survival and cancer, if you account for the type of cancer in the stage, is frailty or the opposite of frailty, performance status. So the weaker you are during cancer treatment, the more likely you are to die of cancer. Um, and encouraging people to do a 20 or 30 day fast with stage [00:58:00] four metastatic cancer is, um, it's just like the height of irresponsibility. And I hope people understand after having listened to this episode, that this is not how this works. Like the there are changes that happen during fasting. Those changes have nothing to do with whether cancer is spreading through your system or not.

Emily: [00:58:21] Yeah. And again, as you as you say, I think when people have advanced cancer, it can also be can often be quite difficult to eat. It can be quite difficult to get a sustained amount of calories, and people lose weight and lose weight and lose weight. And that is a consistent predictor of mortality. So encouraging people to eat less feels just unbelievably irresponsible.

Perry: [00:58:41] Yeah. Now, there has been some research into fasting as a treatment for the toxicity of chemotherapy. So, you know, chemotherapy typically nausea is a major issue. And there was some reasonable mouse data that suggested that short term fasting again, talking about like, you know, less [00:59:00] than a day type of fasting prior to chemotherapy treatment, reduced symptoms that didn't replicate very well in humans. Unfortunately, I did find one trial, um, called, uh, the direct two trial, which was in Nature Communications in 2020. This took 131 patients with stage 2 to 3 breast cancer, not metastatic stage 2 to 3 breast cancer. And they did sort of a modified fast, like reduced, but dramatically reduced calorie intake for the four days prior to chemo. They were their primary outcome was to show whether Chemotoxicity would differ. And it didn't. So they didn't show like more or less hair loss or more or less nausea, unfortunately. But in a post hoc analysis, they thought that the people who fasted might have had a higher rate of radiologically complete or partial response. So that's a when you look at the mammogram again, do things look smaller? This is a very small study. It's the only one I was able to find. And I will say that the American [01:00:00] Society for Clinical Oncology says there's insufficient evidence, evidence for or against fasting prior to chemo. And again, they're talking about limited periods of fasting. So it's like, you know, if you if you're worried about chemo, nausea, and you want to not eat for 16 hours prior to chemo, that seems fine. But please don't believe that this is a substitute for actual cancer therapy. It's not.

Emily: [01:00:23] Yeah, it's worth noting that even that trial excluded people with a BMI outside of the normal range. The BMI of that, that was too low.

Perry: [01:00:30] Yeah. It would be very unethical to have people who are underweight not eating.

Emily: [01:00:35] Okay. This, I think, leads to the other sort of serious moment here, which is just to say there are a variety of people who should not do this kind of fasting. Obviously, people with eating disorders. This kind of fasting is part of a disordered eating pattern, or certainly can be people who are taking medications for their diabetes also should not fast in this way because of hypoglycemia concerns. Older adults who [01:01:00] are already losing lean mass. Please don't stop eating. People with gout. Gout isn't very common, but if you have gout, ketones are not good for you because they cause problems with your. They compete with the uric acid to get out. And. I would say kids and teens should not do this just given their, uh, cognitive reaction. And also the eating disorder piece from before.

Perry: [01:01:24] Totally agree. I think the biggest and most important question, though, of this entire episode is, is, is this one, which is. But can I drink coffee? That would be the thing that stops me.

Emily: [01:01:35] That would stop me for sure. But many of these many protocols do allow you to have black coffee. All right. Um, and our friend, uh, Angus for his 382 day cast. He did drink coffee.

Perry: [01:01:50] Okay. Well, it worked. It worked for good old Angus. So, yes, you can drink black coffee. Go for it. Oh, boy. All right, m here we are. Intermittent [01:02:00] fasting. Smash or pass.

Emily: [01:02:03] I'm a pass on this. Uh, I don't think the evidence suggests this is an effective way to improve people's health. Um, yeah. It's okay. I'm a little hedgy here because I do think for some people, as a weight loss strategy, the simplicity of this is very appealing. Not that fasting for five days, but the kind of only eating in a window. So I can sort of see the see the value for some people, but I'm a smash or sorry, I'm a pass, largely because I think it's so oversold that as to be disturbing.

Perry: [01:02:35] I will smash it because taking in less calories is generally a good thing. And it's an easy way, I think, to take in less calories. But please don't take that as an endorsement of the 50 million ridiculous claims that are made about intermittent fasting online.

Emily: [01:02:51] It's like one of our few disagreements.

Perry: [01:02:54] I was looking back. We've had we've had a couple. It's all right.

Emily: [01:02:59] Okay, guys.

Perry: [01:03:00] That's [01:03:00] it for intermittent fasting. Your question of the week after the break. And we are back with your question of the week. If you have a question of the week, come visit us at wellness.fm. Leave a question and a voice note and we may play your question on the air. Here's our question this week.

Mailbag: [01:03:22] Hey, Emily and Perry. My name is Caroline and I am from West Boylston, Massachusetts. I have not been eating a lot of lunch meat for the past five years. Um, mostly because I've been pregnant three times, but also because I've heard a lot about how bad processed meat or lunch meat is for you that it might be a carcinogen. Um, but now my three young children are very interested in him and cheese sandwiches. And, you know, it's very easy to pack for a child. It's a ham and cheese sandwich. Um, should I be worried? Should I try to steer them towards something else? Um, what are our thoughts on [01:04:00] deli meat? Good. Bad and indifferent. What do you think?

Perry: [01:04:04] Emily, I won't surprise you to hear that I am a lover of deli meats and bacon as well. Uh, what do you think?

Emily: [01:04:14] There is a lot of observational data suggesting that consumption, high consumption of processed meats, uh, is linked to higher rates of cancer. However, I am very skeptical of all of that data. I think that it is a all the times when we're looking at diet and health outcomes, the data is tremendously confounded by other differences across individuals. Um, so I think this is fine, honestly.

Perry: [01:04:44] Okay. I'll say, you know, everything in moderation. These are very salty. So if you are on a salt restricted diet because of high blood pressure or heart failure, you definitely want to avoid this stuff. But if you're otherwise healthy and you want to do smoked meats, yes, I agree, there is some data out there that's concerning. I don't think this is something [01:05:00] I would want to eat every single day. Um, but I think, you know, bacon on Sundays is just fine.

Emily: [01:05:08] You think it's a sometimes food.

Perry: [01:05:10] It's a sometimes food.

Emily: [01:05:14] All right. That's it for today. Uh, join us next week when we will ask, what is the deal with eating organic? Well, this actually is produced in association with iHeart media. Our senior producer is Tamar Avishai, our executive producer at iHeart is Jennifer Bassett. Our theme music is by Eric Deutsch, and our content is for educational purposes only.

Perry: [01:05:38] If you like the show, help other people find us. Leave a rating and review on Apple Podcasts or your podcatcher of choice and help us spread the word about the show. You can follow us on Instagram at Wellness Pod. And don't forget, we want to hear from you. Head over to wellness.fm and leave us a question for our mailbag or suggest a topic for a future show.

Emily: [01:06:00] We'll [01:06:00] let the influencers have the last word.

Influencer: [01:06:02] All right, I started intermittent fasting again, so I'm not eating before 12 p.m. and after 6 p.m.. So the meals are just oh, they're incredible. Oh my God. It makes food more enjoyable.