Latest / Wellness, Actually with Emily Oster & Perry Wilson, MD / What's the deal with intermittent fasting?

Transcript

What's the deal with intermittent fasting? · Wellness, Actually with Emily Oster & Perry Wilson, MD

• 0:01
  Speaker 1: Emily, this is our first episode that I think you
• 0:05
  Speaker 1: might be like viscerally opposed to. Like I think this
• 0:11
  Speaker 1: intermittent fasting is something that would anger you at like
• 0:14
  Speaker 1: a deep level because I don't think I know anyone
• 0:16
  Speaker 1: who eats more frequently than you do. When is the
• 0:19
  Speaker 1: last time you ate? Tell me that.
• 0:21
  Speaker 2: Well, I ate on the way over here. So 10
• 0:23
  Speaker 2: minutes ago. Yeah, 10 minutes ago. I object to that.
• 0:29
  Speaker 2: First of all, I want to say that I was
• 0:31
  Speaker 2: opposed to the sun. I'm not into it. No, we've
• 0:34
  Speaker 2: done a lot of episodes full of things I don't like,
• 0:37
  Speaker 2: weird peptides. But it is true that I like to
• 0:40
  Speaker 2: eat very frequently. But okay, how long is the longest
• 0:45
  Speaker 2: you've ever gone without eating? Not like, okay, not like
• 0:49
  Speaker 2: one time when you had the stomach flu, but like
• 0:50
  Speaker 2: on purpose.
• 0:51
  Speaker 1: No, never on purpose. But because of circumstance when I
• 0:55
  Speaker 1: was a resident and this was back in the day
• 0:58
  Speaker 1: when we would do these 30 hour shifts, which is
• 1:00
  Speaker 1: a terrible thing and no one should ever do that.
• 1:02
  Speaker 1: But so I would start at 6 AM and I
• 1:03
  Speaker 1: would leave the next day at 1 PM. And there
• 1:07
  Speaker 1: was definitely a day or two in there where I
• 1:10
  Speaker 1: like didn't eat for that. Maybe that'll be, maybe I
• 1:15
  Speaker 1: got lunch or something, but I remember being so like
• 1:18
  Speaker 1: exhausted and hungry on the way home. And I would
• 1:20
  Speaker 1: stop at this place called Bochella's in Havertown and and
• 1:23
  Speaker 1: get a chicken cheese steak, like a 14-inch chicken cheese steak,
• 1:27
  Speaker 1: and sit on my couch and eat the whole thing,
• 1:30
  Speaker 1: and then just lie down on the couch and then
• 1:32
  Speaker 1: sleep until like 10 at night. It's not healthy.
• 1:35
  Speaker 2: It's not healthy.
• 1:36
  Speaker 1: That was a long time.
• 1:37
  Speaker 2: It's not good for you. It's not good for the
• 1:39
  Speaker 2: people whose kidneys you were working on. It's not good
• 1:41
  Speaker 2: for anyone.
• 1:42
  Speaker 1: It's not. But Emily, you really believe in fueling your body.
• 1:46
  Speaker 1: You're an exercise person. I thought that fasting would be
• 1:50
  Speaker 1: something that is anathema to- your sort of worldview?
• 1:56
  Speaker 2: I think that's very interesting. I, uh, I like to
• 2:00
  Speaker 2: eat frequently before exercise, but I will say that I
• 2:05
  Speaker 2: don't eat after like 6 30 PM. So until the
• 2:09
  Speaker 2: next morning. So I'm not like a late night snacker.
• 2:12
  Speaker 2: I do a thing that some people would view as
• 2:15
  Speaker 2: a form of fasting where you don't eat while you're asleep.
• 2:18
  Speaker 2: That's my kind of fasting where you don't eat literally
• 2:20
  Speaker 2: during sleep. I have occasionally eaten during sleep to be clear.
• 2:24
  Speaker 2: But I try not to sleep eat.
• 2:26
  Speaker 1: I keep a side of bacon right on my bedside table.
• 2:30
  Speaker 2: I'm surprised it's not like the cheese from the mac
• 2:33
  Speaker 2: and cheese that you have like a little spoon and
• 2:36
  Speaker 2: like a container of that next to your bed.
• 2:38
  Speaker 1: Yeah, you can stir it in water a little. Yeah,
• 2:40
  Speaker 1: it's great.
• 2:41
  Speaker 2: All right. Let's talk about intermittent fasting, something that I
• 2:45
  Speaker 2: am not a fan of, but we'll find out. Maybe
• 2:47
  Speaker 2: it'll change my mind.
• 2:48
  Speaker 1: We'll see.
• 2:49
  Speaker 2: Probably not though. I'm Emily Oster. I'm an economist and
• 2:54
  Speaker 2: a data expert.
• 2:55
  Speaker 1: And I'm Perry Wilson. I'm a medical doctor.
• 2:58
  Speaker 2: It's Thursday, October 15th, 2026, and this is Wellness Actually.
• 3:02
  Speaker 1: Because you're getting a staggering amount of health and wellness
• 3:06
  Speaker 1: information nowadays from every source imaginable. And some of it
• 3:10
  Speaker 1: is awesome.
• 3:11
  Speaker 2: And some of it is, well, actually bullshit. Fortunately, we
• 3:16
  Speaker 2: are both people who know how to read studies, how
• 3:19
  Speaker 2: to parse the data, and can tell you what's worth
• 3:21
  Speaker 2: thinking about and what you can safely ignore.
• 3:24
  Speaker 1: But before we dig in, a note that this podcast
• 3:26
  Speaker 1: is for educational purposes and should not be construed as
• 3:29
  Speaker 1: medical advice. We don't know your unique situation, so talk
• 3:32
  Speaker 1: to your doctor for personal health decisions.
• 3:36
  Speaker 2: This week, we're asking, what's the deal with intermittent fasting?
• 3:40
  Speaker 2: Perry and I will give the official smasher pass, and
• 3:42
  Speaker 2: then we'll get to your question of the week. But first,
• 3:44
  Speaker 2: let's do the health news roundup after the break. And
• 3:58
  Speaker 2: now for the health news of the week. Perry, Health
• 4:02
  Speaker 2: Secretary RFK Jr. is establishing a clinic and dedicated billing
• 4:06
  Speaker 2: codes to track serious vaccine side effects.
• 4:11
  Speaker 3: Um....
• 4:13
  Speaker 2: Smash or pass. Think about that.
• 4:17
  Speaker 1: So, okay. Obviously, better data on vaccine side effects is critical.
• 4:22
  Speaker 1: We've talked about this before, but the vaccine adverse event
• 4:24
  Speaker 1: reporting system is potentially the worst data set on vaccines
• 4:31
  Speaker 1: that could possibly exist because anyone can submit anything and
• 4:35
  Speaker 1: it's completely unverified. And as we said before, there are
• 4:37
  Speaker 1: reports in there that people got injected and turned into
• 4:40
  Speaker 1: the Hulk and stuff. It is very messy data. So
• 4:42
  Speaker 1: clearly we need better data on this. I think there's
• 4:45
  Speaker 1: some problems with the approach of creating a billing code
• 4:49
  Speaker 1: to report vaccine injuries. That means that a healthcare provider
• 4:53
  Speaker 1: like me could potentially get reimbursed by insurance or Medicare
• 4:57
  Speaker 1: or Medicaid for reporting vaccine injuries, which does obviously create
• 5:02
  Speaker 1: a bit of a perverse incentive there. And then I
• 5:05
  Speaker 1: think there's this meta issue, which is that because we
• 5:11
  Speaker 1: know who RFK Jr. is, The fact that he's couching
• 5:16
  Speaker 1: his language and like, don't we all just want better
• 5:18
  Speaker 1: data and don't we all just want things to be
• 5:20
  Speaker 1: more safe? It's like a little disingenuous to me. I
• 5:23
  Speaker 1: think the idea that is next to this proposal is
• 5:29
  Speaker 1: that there is a, you know, vast, undocumented slew of
• 5:36
  Speaker 1: vaccine adverse reactions that we aren't aware of. And the
• 5:40
  Speaker 1: truth is we are. There are other vaccine reporting systems
• 5:43
  Speaker 1: besides the horrible VAERS. There is lots of post-marketing surveillance
• 5:48
  Speaker 1: going on already. So I think this push just serves
• 5:52
  Speaker 1: to further erode trust in the vaccine system, which has
• 5:55
  Speaker 1: been one of the greatest benefits to public health in
• 5:57
  Speaker 1: the past century. That's what I think.
• 5:59
  Speaker 3: Yeah.
• 5:59
  Speaker 2: It's It's sort of frustrating because, like, coming from someone else,
• 6:04
  Speaker 2: this would be, you know, a potentially, I can see
• 6:08
  Speaker 2: a frame on this that would be something in the
• 6:11
  Speaker 2: direction of, like, fixing the VARs and, you know, trying
• 6:15
  Speaker 2: to be better about this. But in the current landscape, it's, again,
• 6:18
  Speaker 2: erosion of trust is our core value here. So, fine.
• 6:22
  Speaker 3: Yeah.
• 6:23
  Speaker 1: Since we're talking about erosion, let's talk about erosion of fat.
• 6:28
  Speaker 1: We got a couple of clinical trials out this week
• 6:32
  Speaker 1: that looked at a new experimental drug called CBL-514. I
• 6:37
  Speaker 1: think that will get changed at some point. And this
• 6:41
  Speaker 1: is a drug that seems to... cause fat cells to
• 6:45
  Speaker 1: melt away? I mean, I've heard about 8 million things
• 6:48
  Speaker 1: that cause fat cells to melt away, but I'm interested.
• 6:51
  Speaker 1: What do we know about CBL-514M?
• 6:54
  Speaker 3: Okay.
• 6:55
  Speaker 2: So this is both very interesting and also an example
• 6:58
  Speaker 2: of a kind of reporting I find tremendously frustrating. So
• 7:01
  Speaker 2: these clinical trials are reported as in like an abstract
• 7:06
  Speaker 2: at a meeting. And when you have an abstract at
• 7:10
  Speaker 2: a meeting, it's like a press release. It's a press release.
• 7:18
  Speaker 1: Yeah, it hasn't been peer-reviewed.
• 7:19
  Speaker 2: It hasn't been peer-reviewed, but more than that, there's no details.
• 7:23
  Speaker 2: Peer-review is not a magic thing, but at least if
• 7:25
  Speaker 2: you could see the whole paper, you could see what
• 7:27
  Speaker 2: did they do, what happened to these people, is there
• 7:29
  Speaker 2: a placebo effect? This is just sort of like, oh,
• 7:32
  Speaker 2: we did this thing and a lot of cool stuff happened. However,
• 7:34
  Speaker 2: having said that, a lot of cool stuff did happen.
• 7:36
  Speaker 2: So this is an experimental injectable molecule drug. They are
• 7:41
  Speaker 2: looking at whether this will work. like eliminate your fat
• 7:46
  Speaker 2: cells by like causing them to shrivel up and die
• 7:49
  Speaker 2: and self-destruct actually. So that's fun. And I think what
• 7:56
  Speaker 2: was interesting here was they have tested this in sort
• 7:58
  Speaker 2: of surface fat, what this article I read about it
• 8:01
  Speaker 2: describes as the pinchable fat that sits under the skin.
• 8:08
  Speaker 2: They've already shown you can pinchable fat away, but actually
• 8:12
  Speaker 2: what's more problematic for health-wise is visceral fat, which is
• 8:15
  Speaker 2: like the fat that gets around your organs and that's
• 8:18
  Speaker 2: not good. And they showed that they could reduce, there
• 8:21
  Speaker 2: was some reductions in visceral fat in this drug, actually
• 8:25
  Speaker 2: sort of sizable, about 12%. So again, that's based on
• 8:28
  Speaker 2: this press release abstract. Who knows? But it is interesting.
• 8:34
  Speaker 2: We need to know much more about this to conclude anything.
• 8:38
  Speaker 2: We would need much larger studies. We need much more
• 8:40
  Speaker 2: safety evidence. We need just like literally any additional information
• 8:43
  Speaker 2: about anything would be so deeply helpful, but interesting. I
• 8:47
  Speaker 2: like the idea of my fat self-destructing. Yeah.
• 8:49
  Speaker 1: The cool thing is that like weight loss reduces fat
• 8:53
  Speaker 1: Usually not by killing the fat cells. It, like, reduces
• 8:56
  Speaker 1: the amount of oil, like, the fats in the fat cells.
• 8:58
  Speaker 1: So they shrink instead of go away completely. This drug
• 9:00
  Speaker 1: seems to make them actually die. And maybe that's better
• 9:03
  Speaker 1: for long-term loss of fat. But I don't know. Speculative.
• 9:06
  Speaker 2: Also, doesn't it sound better? Like, wouldn't you rather have
• 9:08
  Speaker 2: dead fat cells than, like, just small ones? Me, I would.
• 9:12
  Speaker 1: Yeah, I guess so. But what if they're releasing all
• 9:15
  Speaker 1: sorts of, like, evil humors?
• 9:16
  Speaker 4: I don't know.
• 9:17
  Speaker 1: We'll see.
• 9:17
  Speaker 2: Evil humors. Perry, what is it? Like, 1650?
• 9:19
  Speaker 1: Okay.
• 9:20
  Speaker 3: Yeah.
• 9:21
  Speaker 2: Welcome to the past.
• 9:22
  Speaker 1: I'm going to get my plague mask out.
• 9:25
  Speaker 2: The FDA has issued a warning letter to Amazon for
• 9:29
  Speaker 2: selling unapproved over-the-counter herpes treatment. Say more.
• 9:36
  Speaker 1: People, do not get your herpes treatment from Amazon. That
• 9:41
  Speaker 1: is the incorrect choice. I'm looking at a picture now.
• 9:45
  Speaker 2: The picture, I have to say, like you must describe
• 9:48
  Speaker 2: the picture to people. It is insane.
• 9:50
  Speaker 3: Okay.
• 9:50
  Speaker 1: Herp Care Ointment. Could we not come up with a
• 9:53
  Speaker 1: better name than Herp Care, guys? Herp Care Ointment for
• 9:57
  Speaker 1: genital herpes symptoms. It's organic. So here's a picture. It's
• 10:00
  Speaker 1: got a silhouette of a man and a woman with
• 10:03
  Speaker 1: a red bullseye target around the genital area. For those
• 10:08
  Speaker 1: of you on video, we'll put this up on video.
• 10:10
  Speaker 1: And it's got a honeycomb and olive oil whatever.
• 10:17
  Speaker 2: If your vagina is all red and bull's-eyed, rub some
• 10:21
  Speaker 2: honey on it and that's so great.
• 10:24
  Speaker 1: The real... You know, the concern, okay, there are no
• 10:30
  Speaker 1: over-the-counter treatments for any sexually transmitted infection. Full stop. There's
• 10:36
  Speaker 1: nothing you can buy without a prescription that will treat
• 10:38
  Speaker 1: any sexually transmitted infection. So remember that. These things, of course,
• 10:43
  Speaker 1: if you read them, they're not saying they cure herpes.
• 10:45
  Speaker 1: That would be very, very illegal. But it would be
• 10:48
  Speaker 1: very easy to think that these products are somehow either
• 10:53
  Speaker 1: making the symptoms better, or I think really concerningly, decreasing
• 10:56
  Speaker 1: the risk of transmission, which they very much don't. So
• 11:00
  Speaker 1: the FDA, I think, is in the right place here
• 11:03
  Speaker 1: to send a warning letter saying, don't try to sell
• 11:07
  Speaker 1: things that imply that they're treating a sexually transmitted infection,
• 11:10
  Speaker 1: which is going to increase the risk of transmitting that
• 11:13
  Speaker 1: infection to someone else.
• 11:15
  Speaker 4: Yeah.
• 11:15
  Speaker 2: If you have herpes, there are great treatments for that,
• 11:17
  Speaker 2: which you should get. They are medical, though.
• 11:20
  Speaker 1: Yeah, yeah. You need a prescription, but you can get
• 11:23
  Speaker 1: them from many doctors.
• 11:24
  Speaker 2: Many doctors.
• 11:26
  Speaker 1: That's it for the health news of the week. Okay. Now,
• 11:29
  Speaker 1: what's the deal with intermittent fasting? So this is a
• 11:35
  Speaker 1: big topic. There's so many people that have asked me
• 11:39
  Speaker 1: about this topic since we started the podcast. And you know,
• 11:44
  Speaker 1: I'll admit, at first, I thought this was just about diet, dieting,
• 11:49
  Speaker 1: like weight loss.
• 11:50
  Speaker 2: It's not just about dieting.
• 11:51
  Speaker 1: Oh my gosh. That is the tip of the iceberg.
• 11:55
  Speaker 1: So we've got a lot to get through here.
• 11:58
  Speaker 2: Okay. I'm going to start by setting the stage and
• 12:01
  Speaker 2: just explaining what the kinds of not eating are. Because
• 12:07
  Speaker 2: you've probably heard many of them. They have the... They
• 12:11
  Speaker 2: have different acronyms. So, okay, let's just run through it.
• 12:14
  Speaker 2: So first there's something called ADF, Alternative Day Fasting. Isn't
• 12:18
  Speaker 2: that also like a German political party?
• 12:20
  Speaker 1: The AFD is the alternative for Deutschland, yeah. Okay, nevermind.
• 12:25
  Speaker 2: This is ADF, totally different.
• 12:27
  Speaker 1: Party on the rise.
• 12:27
  Speaker 2: Unlike voting for a slightly right-wing political party, this is
• 12:32
  Speaker 2: just not eating anything every other day. Very simple. One
• 12:37
  Speaker 2: day you eat, one day you don't eat. Fine. There's
• 12:39
  Speaker 2: a modified ADF, which is you have on the fasting,
• 12:44
  Speaker 2: every other fasting day, you have a small amount of food,
• 12:47
  Speaker 2: like 500 calories. There's 5-2, where you eat normally five
• 12:52
  Speaker 2: days a week, very little on two of the days.
• 12:54
  Speaker 2: There's time-restricted eating, which I actually think is the sort
• 12:58
  Speaker 2: of most common version of this, which is like eating
• 13:00
  Speaker 2: within a window of like 16 colon eight is one
• 13:03
  Speaker 2: of the things people talk about. It's like you don't
• 13:05
  Speaker 2: eat for 16 hours. You pick eight hours of the
• 13:07
  Speaker 2: day that you eat. You don't eat for the other
• 13:09
  Speaker 2: 16 hours. There's also prolonged fasting, which we'll get to later,
• 13:14
  Speaker 2: which is like multiple days of fasting. So when people
• 13:20
  Speaker 2: talk about intermittent fasting, they almost always mean that they
• 13:24
  Speaker 2: are eating in a shortened window in the day. That's
• 13:26
  Speaker 2: like the When Andrew Huberman talks about that or this guy,
• 13:30
  Speaker 2: Byron Johnson, whatever the different longevity influencers are doing, they're
• 13:34
  Speaker 2: talking about this sort of shortened eating window. But fasting
• 13:40
  Speaker 2: in various ways has been experimented. People do all kinds
• 13:44
  Speaker 2: of different kinds of fasting. Sure, sure.
• 13:46
  Speaker 1: And we're going to circle back to this a number
• 13:50
  Speaker 1: of times. But one of the things that I've been
• 13:52
  Speaker 1: thinking about a lot as I've been researching this is
• 13:55
  Speaker 1: the difference between fasting and calorie restriction. Because the truth
• 13:59
  Speaker 1: is that when you do any type of this fasting,
• 14:02
  Speaker 1: like in general, you're taking in less calories, right? If
• 14:05
  Speaker 1: you don't eat for 16 hours a day and you
• 14:06
  Speaker 1: do eat for eight, it's possible you could get your
• 14:08
  Speaker 1: full load of daily calories in that eight hours, but
• 14:11
  Speaker 1: it's hard. You know, it's a limited amount of time
• 14:13
  Speaker 1: you get full. Most people are eating less calories no
• 14:16
  Speaker 1: matter what type of fasting they're doing. And eating less
• 14:19
  Speaker 1: calories has a number of benefits that have been shown
• 14:21
  Speaker 1: in multiple studies. And then there's the fasting itself, like
• 14:26
  Speaker 1: the duration without eating. And I think to understand what
• 14:30
  Speaker 1: might be special about that, we actually have to do
• 14:32
  Speaker 1: a little science and talk about what happens when you
• 14:36
  Speaker 1: don't eat.
• 14:36
  Speaker 2: You get cranky.
• 14:37
  Speaker 1: So can I walk you through the timeline of not eating?
• 14:41
  Speaker 3: Yes, please.
• 14:41
  Speaker 2: Please indicate where the crankiness arrives.
• 14:44
  Speaker 3: Okay.
• 14:44
  Speaker 1: Okay.
• 14:45
  Speaker 3: All right.
• 14:45
  Speaker 4: So.
• 14:47
  Speaker 1: From about zero to six hours after you last ate,
• 14:51
  Speaker 1: you're not that cranky. The reason is you've digested a meal.
• 14:55
  Speaker 1: And when you have excess, you know, when you digest
• 14:57
  Speaker 1: all the food and protein, carbohydrates and fat that you eat.
• 15:00
  Speaker 1: A lot of that through various processes is going to
• 15:02
  Speaker 1: be turned into energy-containing molecules, mostly glucose. So you've got
• 15:07
  Speaker 1: a lot of glucose. And your body knows that food
• 15:11
  Speaker 1: comes intermittently, and it has methods to store that for later.
• 15:14
  Speaker 1: And the short-term storage of glucose is called glycogen, and
• 15:17
  Speaker 1: that lives in the liver. So your body takes that
• 15:20
  Speaker 1: extra glucose from the food you eat. If you're not
• 15:21
  Speaker 1: using it right then, like Emily, when you're running your
• 15:24
  Speaker 1: marathons and taking your glucose packets, it's probably using that
• 15:27
  Speaker 1: up right away. You've got extra floating around. It'll stick
• 15:29
  Speaker 1: some glycogen in your liver for later. If you continue
• 15:34
  Speaker 1: to have even more glucose, it can put it in
• 15:36
  Speaker 1: long-term storage and that's fat basically, right? So we can
• 15:40
  Speaker 1: store short-term and long-term.
• 15:41
  Speaker 2: Okay.
• 15:41
  Speaker 1: So zero to six hours, you're fine. You've got glycogen
• 15:44
  Speaker 1: in your liver. That glycogen can very quickly be sucked
• 15:47
  Speaker 1: out of your liver and turned back into glucose. So
• 15:49
  Speaker 1: it's just like, you're doing fine. You're fine. Then things
• 15:55
  Speaker 1: start to tail off a little bit. This is when
• 15:57
  Speaker 1: we start to get hungry. And if you're pushing a
• 16:00
  Speaker 1: real fast now, we're talking somewhere up around 18 hours.
• 16:05
  Speaker 1: And this is if you're not exercising. Around 18 hours,
• 16:09
  Speaker 1: the glycogen is basically gone. So the liver's out. If
• 16:14
  Speaker 1: you're exercising, that will happen much quicker. And in fact,
• 16:16
  Speaker 1: you can run out of your glycogen stores in your
• 16:18
  Speaker 1: liver while you're on a long run, for example.
• 16:21
  Speaker 2: Sure.
• 16:22
  Speaker 1: You really hit a wall when that happens. But if
• 16:24
  Speaker 1: you're just chilling at your desk like I am, got
• 16:27
  Speaker 1: about 18 hours, glycogen runs out. And then your body's
• 16:30
  Speaker 1: job is that it has to make more glucose. If
• 16:32
  Speaker 1: you're not eating, everything in your body uses glucose for energy.
• 16:35
  Speaker 2: Especially, I want to say, especially your brain. When your
• 16:39
  Speaker 2: glucose replete, when you have a lot of glucose and
• 16:41
  Speaker 2: you're continually fueling your body with glucose through just eating
• 16:46
  Speaker 2: regular meals, about 20% to 25% of your calories are
• 16:49
  Speaker 2: being used by your brain. Right.
• 16:52
  Speaker 1: So now your body's sensing, I've got no more glycogen.
• 16:54
  Speaker 1: I need to make glucose. What can I make glucose from?
• 16:56
  Speaker 1: And you have two sources left in your body. One
• 16:58
  Speaker 1: is fat and one is protein, basically muscle. And you
• 17:02
  Speaker 1: can break down fat to make these things called keto acids.
• 17:07
  Speaker 1: When you hear people talking about the ketogenic diet, this
• 17:10
  Speaker 1: is essentially what they're talking about. In that case, they're
• 17:13
  Speaker 1: just taking in zero carbs. So they're like, they're not
• 17:15
  Speaker 1: producing any glucose, which forces the body to make glucose
• 17:18
  Speaker 1: from what it can. or to make energy-containing molecules from
• 17:21
  Speaker 1: what it can, fat, but also from muscle breakdown. And
• 17:28
  Speaker 1: what is essentially happening once you're out of glycogen is what,
• 17:31
  Speaker 1: in some cases, we would call starving. It is when
• 17:35
  Speaker 1: you are digesting your own body for food. And manipulating
• 17:42
  Speaker 1: that can have both benefits and risks.
• 17:46
  Speaker 4: Yeah.
• 17:46
  Speaker 3: Yeah.
• 17:47
  Speaker 2: That's right. Yes, it can have benefits and risks. I mean,
• 17:49
  Speaker 2: you have to– yeah, as you said, you sort of
• 17:53
  Speaker 2: have to consume something. And so you might like to
• 17:57
  Speaker 2: consume more of your fat, but you are also consuming
• 18:03
  Speaker 2: your muscle. And I think it's worth sort of saying
• 18:05
  Speaker 2: if you just literally stopped eating for those sort of
• 18:07
  Speaker 2: two or three days, people– used to speculate that more
• 18:12
  Speaker 2: or less, the question is like, what would your brain do?
• 18:15
  Speaker 2: Because your brain is running on glucose. You stop providing glucose.
• 18:18
  Speaker 2: Your body can make some glucose. But if you fast
• 18:20
  Speaker 2: for a long period of time, your glucose ends up
• 18:22
  Speaker 2: at about 30 glucose points, whatever, milligrams per deciliter, I think.
• 18:29
  Speaker 2: And you'll just sort of stay at that kind of consistently.
• 18:31
  Speaker 1: That would be pretty low. It's pretty even hard to
• 18:34
  Speaker 1: get to a level that low.
• 18:35
  Speaker 2: Yeah, if you fasted for like a, this is like
• 18:37
  Speaker 2: I'm talking about like a lengthy, like if you fasted
• 18:39
  Speaker 2: for a week.
• 18:39
  Speaker 1: Really starving.
• 18:41
  Speaker 2: You're really starving and your brain starts running on ketones.
• 18:44
  Speaker 2: So your brain will basically can run on, can run
• 18:48
  Speaker 2: on the ketones that are made out of, out of fat.
• 18:51
  Speaker 2: So your body's kind of an interesting, your body's interesting.
• 18:54
  Speaker 1: Yeah. You'll see people online suggesting that ketones are the
• 18:57
  Speaker 1: brain's preferred source of energy. That is completely untrue. It's
• 19:01
  Speaker 1: like an emergency source. Cause if your brain dies, you
• 19:04
  Speaker 1: die and like it, it will work on this. It's
• 19:06
  Speaker 1: like putting, I don't know, like diesel fuel in your
• 19:10
  Speaker 1: gasoline car.
• 19:11
  Speaker 2: It's not like that because that would be really, your
• 19:14
  Speaker 2: car will stop working.
• 19:15
  Speaker 1: Oh, does it not work?
• 19:16
  Speaker 4: Okay.
• 19:16
  Speaker 1: I don't know.
• 19:16
  Speaker 3: I don't know.
• 19:17
  Speaker 1: Oh, how about putting gasoline in your diesel car? I
• 19:19
  Speaker 1: don't know.
• 19:19
  Speaker 2: Anyway. No, don't do either of those. It's not like
• 19:21
  Speaker 2: either of those things, but it's not your preferred. Let's
• 19:24
  Speaker 2: just say it. Say the first thing you said was right.
• 19:26
  Speaker 2: It's not your preferred thing. It's that don't take gassing
• 19:29
  Speaker 2: up your car advice from Perry, who's obviously- Not a mechanic.
• 19:34
  Speaker 1: Not a mechanic. I'm a doctor, not a mechanic.
• 19:36
  Speaker 4: Okay.
• 19:37
  Speaker 1: One of the interesting things, though, about your body digesting
• 19:39
  Speaker 1: itself that the studies show is that there's this sort
• 19:43
  Speaker 1: of window of time where muscle breakdown is occurring more
• 19:48
  Speaker 1: than fat breakdown. And the studies sort of vary here,
• 19:51
  Speaker 1: but it does seem to be in this like 18
• 19:54
  Speaker 1: to 24 sort of end of day one into day
• 19:56
  Speaker 1: two window where proteins from muscles, amino acids from muscles
• 20:01
  Speaker 1: are being broken down for fuel before fat. lipolysis, which
• 20:05
  Speaker 1: is the process by which fat gets broken down, ramps up.
• 20:07
  Speaker 1: So this hasn't been extensively studied, but I actually think
• 20:10
  Speaker 1: there's an interesting argument to be made that a sort
• 20:13
  Speaker 1: of medium duration fast where we're talking like that sort
• 20:17
  Speaker 1: of intermittent fasting, 18 to 24 hours or alternate day
• 20:20
  Speaker 1: fasting is potentially the worst for losing muscle, but not
• 20:25
  Speaker 1: losing that much fat. Okay.
• 20:28
  Speaker 2: So, uh, speaking of losing muscle and potentially losing fat,
• 20:32
  Speaker 2: I think the first thing we should talk about is, uh,
• 20:35
  Speaker 2: once we now understand like kind of what work, what
• 20:38
  Speaker 2: happens when you fast is whether this is good for
• 20:40
  Speaker 2: weight loss. So this is like, if actually I think
• 20:43
  Speaker 2: you're totally right. This is where I thought people were
• 20:47
  Speaker 2: on this. And I think they have been at various times,
• 20:50
  Speaker 2: but fundamentally it's not the most interesting stuff in, in literature.
• 20:53
  Speaker 4: Right.
• 20:55
  Speaker 3: And the.
• 20:57
  Speaker 2: For the most part, the way people lose weight is by–
• 20:59
  Speaker 2: I mean, the way you lose weight is by consuming
• 21:02
  Speaker 2: fewer calories than you burn.
• 21:04
  Speaker 1: Yeah.
• 21:04
  Speaker 2: That is it. It's more complicated than that to kind
• 21:07
  Speaker 2: of understand because our basal metabolic rate can change and
• 21:10
  Speaker 2: different things are different about different people over time. But
• 21:14
  Speaker 2: if you eat fewer calories, for the most part, on average,
• 21:16
  Speaker 2: you're going to lose weight. This works– intermittent fasting can
• 21:23
  Speaker 2: produce short-term weight loss like almost every diet that has
• 21:26
  Speaker 2: ever been happening. And it does so because it has
• 21:29
  Speaker 2: people eat fewer calories. And the randomized trial evidence basically
• 21:39
  Speaker 2: says that what happens is if you are eating fewer calories,
• 21:44
  Speaker 2: in fact, there's like a very sort of a very
• 21:46
  Speaker 2: nice trial where they had people on matched calorie diets.
• 21:48
  Speaker 2: And the question was, are you eating them all, you know,
• 21:51
  Speaker 2: in an intermittent fasting way or whenever you want? And
• 21:54
  Speaker 2: if the calories are matched, the weight loss is also matched.
• 21:57
  Speaker 2: And so that's it. Like, and so for some people,
• 22:00
  Speaker 2: this is actually, I think, an efficient way to diet
• 22:03
  Speaker 2: because it's simple and sort of like, okay, I'm just
• 22:06
  Speaker 2: only going to eat I'm not going to think that
• 22:07
  Speaker 2: much about it, but I'm only going to eat to
• 22:09
  Speaker 2: these particular hours. Fine. If that's something that works for you, okay.
• 22:14
  Speaker 2: But it's not like better than other ways to get
• 22:18
  Speaker 2: fewer calories.
• 22:19
  Speaker 1: We've said it before. Successful diets make it harder to eat.
• 22:23
  Speaker 1: So all of the sort of fad diets that work,
• 22:26
  Speaker 1: you know, from Atkins on down is like, you know, oh,
• 22:29
  Speaker 1: I can't eat these foods that I normally would eat.
• 22:32
  Speaker 1: And it just makes things trickier. I honestly I have
• 22:34
  Speaker 1: thought like, OK, you could probably make a diet like
• 22:36
  Speaker 1: you're only allowed to eat yellow foods and but you
• 22:38
  Speaker 1: can eat as many yellow foods as you want. And
• 22:40
  Speaker 1: like you'd probably lose weight because it's just hard. It
• 22:42
  Speaker 1: makes things harder. But I agree, this is a pretty
• 22:45
  Speaker 1: simple thing to remember. You don't have some long list
• 22:47
  Speaker 1: of foods that are good and bad. It's just like,
• 22:49
  Speaker 1: don't eat between this time. I'll give you a couple numbers.
• 22:51
  Speaker 1: There's a nice meta-analysis in the BMJ in 2025 that
• 22:54
  Speaker 1: looked at all the different intermittent fasting-ish things, like alternate
• 22:57
  Speaker 1: day and 16 to 8 and all the stuff we
• 22:59
  Speaker 1: talked about, combining data from a bunch of different randomized trials.
• 23:03
  Speaker 1: And the best comparison that they had was alternate day
• 23:08
  Speaker 1: fasting versus eating whatever you want. And- In that trial
• 23:14
  Speaker 1: or in trials that looked at that, the average weight
• 23:16
  Speaker 1: loss in the alternate day fasting group was about 3.3 kilograms.
• 23:20
  Speaker 1: So that's eight or nine pounds or so. So not nothing.
• 23:24
  Speaker 1: But of course, that's first eating anything you want. Against
• 23:27
  Speaker 1: calorie counting, not quite as impressive, about two kilograms. Again,
• 23:32
  Speaker 1: that wasn't matched calories. That was just people doing their
• 23:34
  Speaker 1: best to reduce their caloric intake, which, as you point out,
• 23:38
  Speaker 1: is a tricky thing.
• 23:40
  Speaker 4: Yeah.
• 23:40
  Speaker 2: And I think this is... really reminiscent of basically everything
• 23:46
  Speaker 2: we talk about in the diet literature, which is many
• 23:49
  Speaker 2: diets of which this is one can produce weight loss
• 23:52
  Speaker 2: over some period. Generally, most of the weight is regained.
• 23:57
  Speaker 2: This is like a general factor in the literature. People
• 24:00
  Speaker 2: have a hard time sticking to diets long-term. This is
• 24:02
  Speaker 2: part of the reason that GLP-1s, I think, have been
• 24:04
  Speaker 2: so successful because changes in your dietary patterns in the
• 24:09
  Speaker 2: absence of medication are difficult to sustain.
• 24:11
  Speaker 1: And that's fine.
• 24:13
  Speaker 2: So if this is an interesting way for you to
• 24:16
  Speaker 2: diet and you would like to try it, great.
• 24:18
  Speaker 1: No problem.
• 24:19
  Speaker 2: But it's not some special magic weight loss trick.
• 24:22
  Speaker 1: Yeah. The lesson we've learned here is that whenever we're
• 24:26
  Speaker 1: going to talk about something here, we need to always,
• 24:28
  Speaker 1: when we're talking about intermittent fasting, we always have to
• 24:30
  Speaker 1: stay compared to what? And basically the default comparison really
• 24:34
  Speaker 1: should be calorie restriction. with the understanding that calorie restriction
• 24:38
  Speaker 1: is hard. And if you can get there by intermittent fasting,
• 24:41
  Speaker 1: good for you. That's better. So we're going to take
• 24:44
  Speaker 1: a quick break. And then after the break, we're going
• 24:47
  Speaker 1: to move away from weight loss and into all the myriad.
• 24:51
  Speaker 2: Literally everything else. We're going to move away from weight
• 24:54
  Speaker 2: loss into literally all other aspects of your health next. Okay, Perry,
• 25:04
  Speaker 2: we're back. And we're going to start, we're going to
• 25:07
  Speaker 2: put this in a few clusters. There are a million
• 25:10
  Speaker 2: different things here. I'm going to start with the cluster
• 25:12
  Speaker 2: of metabolism. I'll give you a claim. You tell me. Claim.
• 25:17
  Speaker 2: It resets your metabolism. What would that mean? And is
• 25:21
  Speaker 2: it true?
• 25:22
  Speaker 1: Yeah, I don't think this is true. I don't think
• 25:24
  Speaker 1: this is true. So the claim here is that by...
• 25:30
  Speaker 1: By doing a fast of some form or another, it's
• 25:34
  Speaker 1: like resetting your Wi-Fi router. Things kind of get back
• 25:38
  Speaker 1: to normal and you'll be your old self. The data
• 25:42
  Speaker 1: really doesn't support that at all. So we've got reasonable
• 25:49
  Speaker 1: data that people that do these types of diets have
• 25:53
  Speaker 1: lower insulin levels and better insulin sensitivity. Their LDL, their
• 25:57
  Speaker 1: bad cholesterol goes down. Their HDL goes up. this works
• 26:01
  Speaker 1: a little bit better in trials of alternate day fasting
• 26:04
  Speaker 1: as opposed to the time-restricted eating, like the 16 to 8.
• 26:08
  Speaker 1: And so that's fine, but compared to equivalent amounts of
• 26:12
  Speaker 1: calorie restriction, there is no difference. So in terms of
• 26:16
  Speaker 1: all the insulin, homeostasis, glucose stuff, there's not a lot
• 26:19
  Speaker 1: of evidence that you're doing anything beyond just calorie restriction.
• 26:23
  Speaker 1: But what I'm sort of More interested in is basal
• 26:27
  Speaker 1: metabolic rate, right? So your basal metabolic rate is the
• 26:31
  Speaker 1: amount of calories your body burns just doing its thing, right?
• 26:34
  Speaker 1: You're not exercising. It's just at rest. Your heart's beating.
• 26:37
  Speaker 1: You got to breathe. Your brain is doing stuff. That's
• 26:40
  Speaker 1: your basal metabolic rate. It's going to differ based on
• 26:42
  Speaker 1: your body habitus and a variety of other things. And
• 26:45
  Speaker 1: if anything, I think what we all want is our
• 26:47
  Speaker 1: basal metabolic rate to be a bit higher, right? We'd
• 26:50
  Speaker 1: all love to burn more calories sitting around than we
• 26:54
  Speaker 1: currently do. And the data here is very clear. The
• 26:58
  Speaker 1: more you fast, the lower your basal metabolic rate goes.
• 27:03
  Speaker 1: Because of course it does, right? Evolutionarily- You're telling your body-
• 27:08
  Speaker 1: There's not enough food around. You got to conserve. Exactly.
• 27:12
  Speaker 1: Your body will go through processes that say, oh, okay,
• 27:15
  Speaker 1: we're not in a food-rich environment. Let's turn down our
• 27:19
  Speaker 1: systems and thermogenesis and all these things that contribute to
• 27:22
  Speaker 1: our basal metabolic rate. And so Again, not saying it's
• 27:27
  Speaker 1: not good for you or it's bad for you, but
• 27:30
  Speaker 1: these influencers who are like, oh, once you fast, your
• 27:32
  Speaker 1: body learns to burn fat and all of a sudden
• 27:35
  Speaker 1: it's going to start burning fat forever and not doing
• 27:37
  Speaker 1: anything else. If anything, your body's going to try to
• 27:40
  Speaker 1: conserve calories because for hundreds and thousands of millions of
• 27:45
  Speaker 1: years of our evolutionary history, that is the proper response
• 27:48
  Speaker 1: to a food scarce environment.
• 27:50
  Speaker 3: Yeah.
• 27:51
  Speaker 2: Okay.
• 27:52
  Speaker 1: Rejected.
• 27:54
  Speaker 2: Metabolism rejected.
• 27:55
  Speaker 1: Yeah. Okay.
• 27:56
  Speaker 2: So the second thing in this space that I want
• 27:58
  Speaker 2: to talk about is ketones. People are just like very
• 28:02
  Speaker 2: into ketones. And I would say in this discussion, there's
• 28:06
  Speaker 2: a lot of vague emphasis on when you are fasting,
• 28:11
  Speaker 2: your body is going to produce these ketones and ketones
• 28:16
  Speaker 2: are like a special magic flower that's going to improve
• 28:21
  Speaker 2: everything about you. So Ketones are very, very, very interesting.
• 28:28
  Speaker 2: You know, ketosis is very interesting. Ketones are interesting signaling molecules.
• 28:34
  Speaker 2: I think it is extremely interesting that our brain can
• 28:37
  Speaker 2: run on them. It is very interesting evolutionary adaptation to
• 28:43
  Speaker 2: periods of famine, right? You have like a hungry, hungry
• 28:47
  Speaker 2: brain that needs... fuel. Usually you'd like to fuel it
• 28:51
  Speaker 2: real fast with all the glucose, but you definitely don't
• 28:55
  Speaker 2: want to be in a situation where if you don't
• 28:57
  Speaker 2: have access to glucose, your brain stops working because you're
• 28:59
  Speaker 2: really using that. And so we are kind of evolved.
• 29:03
  Speaker 2: The fact that the brain can use ketones, it has
• 29:06
  Speaker 2: evolved from that potential for famine in the vast history
• 29:12
  Speaker 2: of human existence.
• 29:14
  Speaker 1: So great.
• 29:15
  Speaker 2: But it isn't what our brain would like. It's not
• 29:17
  Speaker 2: our brain's first choice.
• 29:18
  Speaker 1: It definitely isn't. And there are real medical uses for ketosis.
• 29:21
  Speaker 2: Totally. And so the most interesting of which is some
• 29:24
  Speaker 2: evidence that the ketosis is an appropriate way to potentially
• 29:29
  Speaker 2: treat epilepsy, especially in children. And so this actually comes
• 29:31
  Speaker 2: out of the fasting literature. So people had noticed that
• 29:35
  Speaker 2: kids with epilepsy got better when they were fasting, fasted
• 29:40
  Speaker 2: for long periods of time is, of course, not possible.
• 29:44
  Speaker 2: But it seems like that was, in fact, a result
• 29:48
  Speaker 2: of the fact that people do better if their brain
• 29:50
  Speaker 2: is running on ketones, again, if they have epilepsy. And
• 29:53
  Speaker 2: so this has led to one potential treatment for epilepsy,
• 29:57
  Speaker 2: particularly in kids, which is a very, very sharp ketogenic
• 30:01
  Speaker 2: diet with basically no carbohydrates.
• 30:03
  Speaker 1: Yeah. It's a brutally difficult diet to maintain.
• 30:06
  Speaker 2: Very difficult diet to do. So ketones are very interesting,
• 30:10
  Speaker 2: but the idea, there's just nothing in the data that
• 30:13
  Speaker 2: would suggest that somehow having more of them or doing
• 30:16
  Speaker 2: more with them is like somehow preferable or improving anything
• 30:20
  Speaker 2: about your health.
• 30:20
  Speaker 1: Well, yeah. And again, they are signaling molecules. So you
• 30:24
  Speaker 1: do have receptors on cells that detect ketones in the
• 30:27
  Speaker 1: blood and change how the cell is functioning. But on
• 30:31
  Speaker 1: a metabolic level, their primary signaling effect is to decrease
• 30:36
  Speaker 1: the degradation of fat and to suppress muscle building. Because again,
• 30:42
  Speaker 1: you're in a food scarce environment. Now is not the
• 30:45
  Speaker 1: time to be like, putting all your energy into building muscle.
• 30:48
  Speaker 1: It's time to conserve. You want to conserve your fat.
• 30:51
  Speaker 1: And so they do signal, but they don't signal in
• 30:55
  Speaker 1: some magical way that's going to get you shredded. In fact,
• 30:57
  Speaker 1: quite the opposite. They're telling your body, chill out a
• 31:00
  Speaker 1: little bit. We've got to wait until there's food around
• 31:03
  Speaker 1: again before we can really bulk up.
• 31:05
  Speaker 2: I mean, the reality is if you're looking for performance
• 31:08
  Speaker 2: of your brain or your body or anything, you want
• 31:11
  Speaker 2: to be living on carbs. And you see this, of course,
• 31:14
  Speaker 2: in sports. but you also see it in like, you know, chess,
• 31:18
  Speaker 2: like Magnus Carlsen is consumed. He used to consume a
• 31:20
  Speaker 2: lot of, Magnus Carlsen is a very successful chess player
• 31:23
  Speaker 2: and he used to consume a lot of orange juice
• 31:26
  Speaker 2: and like other sugary drinks. And then he, and then
• 31:29
  Speaker 2: at some point he decided that it was like he
• 31:31
  Speaker 2: was having a sugar crash, but, and then he started
• 31:34
  Speaker 2: drinking chocolate milk.
• 31:35
  Speaker 1: Yeah.
• 31:35
  Speaker 2: Um, which, you know, I guess is like also has fat.
• 31:39
  Speaker 2: It's more delicious, I think, and also has fat. But
• 31:42
  Speaker 2: the point is that you need to be consuming something with,
• 31:45
  Speaker 2: with easily available glucose if you want to be performing.
• 31:49
  Speaker 4: Right.
• 31:50
  Speaker 1: Totally. Totally. So we're straying near some, I think what
• 31:54
  Speaker 1: we can put in cluster B of the claims for
• 31:57
  Speaker 1: intermittent fasting, which are like a bunch of cellular buzzwords.
• 32:03
  Speaker 1: So Em, did you come across autophagy in your research?
• 32:07
  Speaker 2: I love autophagy.
• 32:08
  Speaker 1: Yeah.
• 32:08
  Speaker 2: Autophagy is a great, it's a great word. And it
• 32:13
  Speaker 2: comes up a lot in wellness. So it's the process
• 32:17
  Speaker 2: by which cells digest their own like worn out parts.
• 32:23
  Speaker 2: And if we aren't autophagying very effectively, that can increase
• 32:29
  Speaker 2: risks for cancer or neurodegeneration. So you do actually want
• 32:33
  Speaker 2: your cells to be like digesting their worn out parts.
• 32:37
  Speaker 2: So the worn out parts are not just like sticking around.
• 32:42
  Speaker 2: And so when we think about this in the context
• 32:44
  Speaker 2: of fasting, this is the first of many, many findings,
• 32:50
  Speaker 2: which I would describe as mice are not people. So
• 32:54
  Speaker 2: mice fasting is pretty cool. So there's actually like an
• 32:59
  Speaker 2: early study from 2010 in a journal called conveniently autophagy
• 33:05
  Speaker 2: that found that if you leave mice for sort of
• 33:07
  Speaker 2: 16 to 24 hours without any food, there's more autophagy
• 33:11
  Speaker 2: in their brain. So they're like doing more consuming of
• 33:14
  Speaker 2: the worn out parts. And so that could, you know,
• 33:17
  Speaker 2: that's not to say they live longer or anything specific,
• 33:20
  Speaker 2: but it is kind of a particular signal. There are
• 33:23
  Speaker 2: kind of two issues. One is that mice are not people.
• 33:29
  Speaker 2: And a particular way in which mice are not people
• 33:31
  Speaker 2: here is that mice have a very high metabolic rate.
• 33:35
  Speaker 2: So having a mouse fast for 24 hours is not
• 33:38
  Speaker 2: a human fast for 24 hours. That's a human fasting
• 33:41
  Speaker 2: for like a week.
• 33:42
  Speaker 1: Yeah, yeah, yeah. They're not happy about that.
• 33:43
  Speaker 2: Like a long time. It's hard to know exactly the conversion.
• 33:47
  Speaker 1: There has been a human study of looking at autophagy,
• 33:50
  Speaker 1: but it's not terribly compelling. It had 11 people in it.
• 33:54
  Speaker 4: Yeah.
• 33:57
  Speaker 1: And basically it had 11 adults who had overweight and
• 34:02
  Speaker 1: they had a time-restricted eating arm versus sort of a
• 34:05
  Speaker 1: more regular arm. And they showed that a specific autophagy
• 34:08
  Speaker 1: gene increased 22%. So I don't know that a gene
• 34:13
  Speaker 1: increasing really tells us anything about anything going on in
• 34:15
  Speaker 1: the brain or et cetera. But again, it makes sense, right?
• 34:19
  Speaker 1: As you starve... you start to consume more of your
• 34:23
  Speaker 1: own body, and that's fine. It really remains to be
• 34:28
  Speaker 1: seen whether this makes any difference compared to calorie restriction
• 34:32
  Speaker 1: alone or whether the cells that are getting eaten are
• 34:35
  Speaker 1: necessarily the cells that are going to give rise to
• 34:36
  Speaker 1: cancer or neurodegeneration or all the other stuff that gets
• 34:39
  Speaker 1: claimed about this.
• 34:40
  Speaker 2: Or what the size of this effect would be. And
• 34:42
  Speaker 2: I think this is another thing to come back to.
• 34:44
  Speaker 2: Let's say this was a true effect. on the scale
• 34:47
  Speaker 2: of something, some outcome you would actually care about, like
• 34:50
  Speaker 2: longevity or cancer development, this is going to be like
• 34:52
  Speaker 2: a teeny weeny fraction effect.
• 34:56
  Speaker 3: Right, right, right.
• 34:58
  Speaker 1: So let's move on to inflammation, the dreaded inflammation term,
• 35:03
  Speaker 1: because no one wants inflammation.
• 35:04
  Speaker 2: No one wants to be inflamed.
• 35:07
  Speaker 1: What do we know about, you know, a lot of
• 35:09
  Speaker 1: people are claiming that immune, you know, inflammation, immune reactivity
• 35:14
  Speaker 1: goes down with fasts. seems to be true from what
• 35:17
  Speaker 1: I can tell.
• 35:20
  Speaker 2: In mice?
• 35:21
  Speaker 1: Yes, in mice. But also there was a 2019 cell
• 35:25
  Speaker 1: study which took 12 healthy volunteers. They fasted for 19 hours.
• 35:30
  Speaker 1: And the level of their circulating monocytes, which is an immune,
• 35:33
  Speaker 1: like a white cell, immune dropped quite sharply. Similar findings
• 35:39
  Speaker 1: were shown in mouse. They come back after you eat,
• 35:42
  Speaker 1: I guess.
• 35:42
  Speaker 2: I mean, I think there's a really important question here,
• 35:46
  Speaker 2: which again, like we're sort of hitting all of these
• 35:49
  Speaker 2: different issues with this literature. But here I think an
• 35:53
  Speaker 2: issue is like, what does it mean for this? thing
• 35:57
  Speaker 2: to go down, is that good? You know, when you
• 35:59
  Speaker 2: stop fueling your body, it stops doing stuff, right? It's
• 36:02
  Speaker 2: going to stop doing things that it doesn't really necessarily
• 36:06
  Speaker 2: think are useful right now because it's sensing, like, we
• 36:10
  Speaker 2: have to get in the mode of, like, there might
• 36:12
  Speaker 2: not be food here. And so the immune system, that's
• 36:15
  Speaker 2: something that's expensive. Like, we're using it. ramping up things
• 36:20
  Speaker 2: is it takes up a lot of, a lot of energy.
• 36:23
  Speaker 2: And you might think, okay, right now there's no food
• 36:25
  Speaker 2: and I'm not really sensing like an immune challenge. And
• 36:28
  Speaker 2: so maybe I'd dial down the immune system because I'm
• 36:31
  Speaker 2: not using it right now. And that's exactly, that's an
• 36:34
  Speaker 2: interpretation of what you see here, but not an interpretation
• 36:37
  Speaker 2: that says like, oh, this is so great. It's an
• 36:40
  Speaker 2: interpretation that's like, well, now when your kid comes home
• 36:42
  Speaker 2: with a cough, and they cough on your face, your
• 36:45
  Speaker 2: immune system isn't available because it took a break because
• 36:49
  Speaker 2: you didn't eat anything, and then you might get more sick.
• 36:52
  Speaker 2: So I think it's like a... I don't know. I
• 36:56
  Speaker 2: find this... I see the results. It only has 12
• 36:59
  Speaker 2: people in it, fair enough. And I question whether it
• 37:02
  Speaker 2: is good.
• 37:03
  Speaker 1: I think that's fair. There's nothing specifically bad about inflammation.
• 37:07
  Speaker 1: In fact, that's your immune system doing its job.
• 37:10
  Speaker 3: Yeah.
• 37:11
  Speaker 2: I mean, I like... I find this discussion, I'm not
• 37:14
  Speaker 2: that concerned about inflammation. I realize people don't like to
• 37:17
  Speaker 2: be inflamed. It sounds bad, but I'm not sure it's
• 37:19
  Speaker 2: so terrible. Okay, what about starving a fever? This is
• 37:23
  Speaker 2: my favorite. You know, the phrase like feed a cold,
• 37:26
  Speaker 2: starve a fever. And I think the idea is that
• 37:31
  Speaker 2: if you don't eat when you have a fever, it
• 37:34
  Speaker 2: will get better more quickly, I guess.
• 37:37
  Speaker 1: Yeah, I think that's the idea. And we have the
• 37:40
  Speaker 1: greatest study for this. Yes, it's a mouse study, but
• 37:42
  Speaker 1: I actually, I really love it. It's from Cell in 2016.
• 37:45
  Speaker 2: Your favorite mice?
• 37:47
  Speaker 1: This is a great study. So researchers took a bunch
• 37:50
  Speaker 1: of mice and they gave them either a bacterial or
• 37:54
  Speaker 1: a viral infection. Okay. So they, you know, had bacterial infection,
• 37:59
  Speaker 1: you know, bad, whatever, viral infection, more like a flu
• 38:02
  Speaker 1: type of thing. And then they randomized the mice to anorexia,
• 38:05
  Speaker 1: like they didn't get any food or nutritional supplementation. And
• 38:10
  Speaker 1: What they found was that the starving mice survived longer
• 38:15
  Speaker 1: during the bacterial infection. But they found the opposite for
• 38:18
  Speaker 1: the viral infection, so that the starving mice died more
• 38:21
  Speaker 1: often with the viral infection. They lived longer if they
• 38:24
  Speaker 1: were fed.
• 38:25
  Speaker 2: So bottom line, actually- This advice is opposite.
• 38:29
  Speaker 1: It's completely wrong, right? Insofar as we're talking about starve
• 38:34
  Speaker 1: a fever means a viral infection, like the flu or something,
• 38:37
  Speaker 1: which I think most of the time when we have
• 38:39
  Speaker 1: a fever, it probably is a viral infection. This mouse
• 38:42
  Speaker 1: study would suggest, no, no, no, you feed that. Now,
• 38:45
  Speaker 1: it is interesting that in the bacterial, you know, much
• 38:47
  Speaker 1: more rare type of, you know, bloodstream-borne bacterial infections are
• 38:50
  Speaker 1: pretty rare, fortunately, that some starving, you know, might have helped.
• 38:55
  Speaker 1: And there's some logic there. You know, bacteria, much more
• 38:58
  Speaker 1: so than viruses, are using stuff, like are using your
• 39:03
  Speaker 1: substrate in your blood to grow and things like that.
• 39:05
  Speaker 1: So maybe starving kind of competes with them for growth.
• 39:10
  Speaker 1: There is some data in patients in the intensive care
• 39:14
  Speaker 1: unit with severe bacterial infections that looked at early feeding,
• 39:19
  Speaker 1: like as soon as they get into the ICU and
• 39:20
  Speaker 1: they're super sick and you drop a tube and do
• 39:22
  Speaker 1: tube feeds versus more delayed and suggested actually that more
• 39:27
  Speaker 1: delayed feeding led to some beneficial outcomes. This isn't entirely
• 39:31
  Speaker 1: standard of care, but I think it's interesting. But we
• 39:34
  Speaker 1: certainly have nothing on the outpatient side. And I think
• 39:36
  Speaker 1: if you're feverish, if you have a viral infection and
• 39:39
  Speaker 1: you believe in mouse data, then you should probably eat something.
• 39:43
  Speaker 2: Yeah. Or stay hydrated.
• 39:46
  Speaker 1: Oh yeah. We definitely went, oh God, we haven't even
• 39:48
  Speaker 1: talked about dry fasting. I don't even think we have
• 39:50
  Speaker 1: a bullet point. Have you seen this dry? Okay. Sidebar.
• 39:53
  Speaker 1: I haven't even heard of this. As the nephrologist, as
• 39:55
  Speaker 1: the kidney doctor, don't do this. So dry fasting is fasting,
• 39:59
  Speaker 1: but you don't even drink. You don't even drink water.
• 40:02
  Speaker 1: It's a absolutely terrible idea. Don't do this. It's bad
• 40:06
  Speaker 1: for your kidneys. It's bad for your brain. It's bad
• 40:09
  Speaker 1: for the rest of your body. Please drink water.
• 40:11
  Speaker 4: Okay.
• 40:12
  Speaker 1: That's it. Moving on. Um, I think our next sort
• 40:17
  Speaker 1: of cluster of claims about intermittent fasting is performance. Like
• 40:23
  Speaker 1: you get these people that are like, okay, I understand
• 40:26
  Speaker 1: it's hard. I know it's tough. You're hungry. You're cranky.
• 40:29
  Speaker 1: But you are going to get this laser-like focus in
• 40:37
  Speaker 1: your brain. And maybe it's because of the ketones making
• 40:39
  Speaker 1: your brain zap.
• 40:40
  Speaker 2: Let me ask you a question. Did you eat this morning?
• 40:43
  Speaker 2: Did you eat before this? Okay.
• 40:45
  Speaker 1: Well, all right.
• 40:46
  Speaker 2: Here's a listener. We had a discussion on Slack about
• 40:48
  Speaker 2: whether Perry was going to eat before the episode. Did
• 40:51
  Speaker 2: you eat before the episode?
• 40:52
  Speaker 1: So I had the brilliant idea that I was not
• 40:54
  Speaker 1: going to eat before the episode because I hadn't eaten
• 40:56
  Speaker 1: since like seven last night and we're recording. It's like 11,
• 41:00
  Speaker 1: 1130 now. So I was like, okay, I'm coming up on,
• 41:03
  Speaker 1: you know.
• 41:03
  Speaker 2: 16 hours or so.
• 41:05
  Speaker 1: I'm going to be quasi-intermittent fasting during this episode. And
• 41:09
  Speaker 1: I said that on Slack and then I'm sitting in
• 41:13
  Speaker 1: my office and like, I was like, oh no, I
• 41:16
  Speaker 1: can't do it. I can't do it. I had to
• 41:17
  Speaker 1: eat something. So I ate.
• 41:19
  Speaker 3: Yeah.
• 41:20
  Speaker 1: I'm sorry. I'll have to try that. When we start,
• 41:23
  Speaker 1: when we turn to like the experiential episodes, like when
• 41:26
  Speaker 1: you and I are going to do psychedelic mushrooms together,
• 41:28
  Speaker 1: that's when the intermittent fasting will happen. All right. So
• 41:33
  Speaker 1: I lack the sharp focus that I would have had
• 41:37
  Speaker 1: had I not caved to my hunger a few hours ago.
• 41:41
  Speaker 1: What do you think about this, Em? Like, Magnus Carlsen
• 41:44
  Speaker 1: seems to think, no, like, I need the glucose to
• 41:47
  Speaker 1: play chess well. So is there any, can we support
• 41:50
  Speaker 1: the idea that fasting locks you in in some way?
• 41:54
  Speaker 2: I don't think the data supports this. So there's meta-analysis
• 41:57
  Speaker 2: in 2025 in PsychBulletin that 3,500 people, and it basically
• 42:02
  Speaker 2: finds no effect after a 12-hour fast. You know, there's
• 42:05
  Speaker 2: sort of no difference in attention span. inhibitory control, memory,
• 42:09
  Speaker 2: the kinds of things that we measure to sort of
• 42:10
  Speaker 2: see if people are kind of like able to have
• 42:13
  Speaker 2: an executive function. I find this interesting partly because of
• 42:20
  Speaker 2: its contrast with something like sleep. So, you know, if
• 42:23
  Speaker 2: you deprive your body of sleep for 12 hours, obviously no,
• 42:26
  Speaker 2: but like for, you know, a full 24 hours, 30 hours,
• 42:28
  Speaker 2: it is, substantially, your performance is substantially worse. So you
• 42:33
  Speaker 2: just get like worse and worse and worse as you sleep.
• 42:34
  Speaker 2: As you, as the time gets longer and longer and longer,
• 42:36
  Speaker 2: you just get worse and worse and worse and worse
• 42:38
  Speaker 2: and worse until you just don't. And you don't like,
• 42:41
  Speaker 2: you don't like rebound basically very much. Whereas it's sort
• 42:45
  Speaker 2: of the fasting piece is interesting because I might have
• 42:48
  Speaker 2: expected that people would feel worse that after 12 hour,
• 42:51
  Speaker 2: a 12 hour fast, people would be hungry and distracted
• 42:54
  Speaker 2: by the fact that they are, that they are hungry.
• 42:55
  Speaker 2: And that doesn't seem to show up. It functions pretty similar.
• 43:01
  Speaker 2: It doesn't make people more focused or less focused. It's
• 43:04
  Speaker 2: just like they're kind of the same. I'd be interested
• 43:07
  Speaker 2: to see after 24 hours or 36 hours, are you
• 43:10
  Speaker 2: so hungry that you can't get your act together?
• 43:13
  Speaker 1: I mean, I think, again, it's like your brain is
• 43:15
  Speaker 1: so protected against this. Humans are just so evolved to
• 43:20
  Speaker 1: protect their brain that I might even be surprised even
• 43:24
  Speaker 1: at that extreme if you start getting real brain deficits.
• 43:28
  Speaker 1: There's an exception here, Em. I don't know if you
• 43:30
  Speaker 1: saw in the data where kids and younger people actually
• 43:35
  Speaker 1: did have some decrement.
• 43:36
  Speaker 2: Yeah, kids and younger people do worse when they're fasted.
• 43:40
  Speaker 2: This is, I think, policy-wise a very strong argument for
• 43:44
  Speaker 2: breakfast at school, that if kids are not getting breakfast
• 43:47
  Speaker 2: at home because their families don't have uh, money and
• 43:52
  Speaker 2: don't have food at home, this is like, this is
• 43:54
  Speaker 2: a reason why school breakfast can be potentially very effective
• 43:57
  Speaker 2: at actually raising test scores. Um, because kids might otherwise
• 44:01
  Speaker 2: not get breakfast and then they perform worse at school.
• 44:04
  Speaker 2: And you might imagine, I mean, kids, like they move
• 44:06
  Speaker 2: through their food. You can't eat quite as much. There's some,
• 44:09
  Speaker 2: some are smaller and they like move through their food faster.
• 44:12
  Speaker 3: Yeah.
• 44:12
  Speaker 4: Yeah.
• 44:12
  Speaker 2: Yeah.
• 44:12
  Speaker 1: They have higher, resting metabolic rates per kilogram and they're
• 44:16
  Speaker 1: littler to begin with, their livers are smaller, they have
• 44:18
  Speaker 1: less glycogen. Yeah, I buy that.
• 44:20
  Speaker 2: It's also the case that if you don't drink water
• 44:22
  Speaker 2: per earlier discussion, the dry fast does impact your cognition
• 44:26
  Speaker 2: because you are thirsty.
• 44:29
  Speaker 1: Oh, yeah, yeah, yeah. So yeah, again, don't do dry fasting.
• 44:32
  Speaker 1: That comes from cognition and dry fasting actually comes from
• 44:36
  Speaker 1: Ramadan data. It's really interesting natural experiment of intermittent fasting
• 44:41
  Speaker 1: where people who, you know, Don't have all the other
• 44:45
  Speaker 1: necessarily behaviors that go along with intermittent fasting, like other
• 44:48
  Speaker 1: health-seeking behaviors, because it's a religious fast. It's a different population,
• 44:53
  Speaker 1: so you get kind of a different cross-section of data.
• 44:55
  Speaker 1: But yeah, dry fasting does worsen cognition. But for adults,
• 45:00
  Speaker 1: just not eating, your brain will kind of hang in
• 45:02
  Speaker 1: there such that it is.
• 45:04
  Speaker 2: It'll keep working.
• 45:06
  Speaker 3: Mm-hmm.
• 45:07
  Speaker 2: Okay. So that is your brain performance. I do just
• 45:11
  Speaker 2: want to touch on your athletic performance, which actually the
• 45:16
  Speaker 2: result here is interesting because I would have thought eating is,
• 45:22
  Speaker 2: I mean, I think eating is great. But they have done,
• 45:27
  Speaker 2: so there's a study in men from about a decade
• 45:31
  Speaker 2: ago where they took some fairly well-trained men, and they
• 45:35
  Speaker 2: had a kind of 16-8 fast, but with enough calories.
• 45:38
  Speaker 2: So this is sort of not for weight loss. And
• 45:41
  Speaker 2: they did find a decline in fat mass for the
• 45:44
  Speaker 2: people doing the intermittent fasting. They also had a big
• 45:47
  Speaker 2: decline in their testosterone. So that, you know, like lose fat,
• 45:53
  Speaker 2: but also lose your... lose your vital testosterone.
• 45:57
  Speaker 1: Your precious bodily fluids. Organs or whatever. Well, because testosterone
• 46:00
  Speaker 1: is anabolic, right? Like, again, testosterone builds muscle and things,
• 46:05
  Speaker 1: and that's not what your body wants to do when
• 46:08
  Speaker 1: you're in a food-scarce environment. So all makes sense. Nothing
• 46:11
  Speaker 1: surprising here.
• 46:12
  Speaker 2: We didn't see much. They've tried this in women. They
• 46:14
  Speaker 2: don't see many differences. Probably the most interesting piece here
• 46:17
  Speaker 2: is a meta-analysis of studies of Ramadan, which, again, people
• 46:21
  Speaker 2: are fasting for the whole day. And they, they found that,
• 46:27
  Speaker 2: you know, this study finds a little bit of an
• 46:28
  Speaker 2: impact on sprint performance, again, sort of like a kind
• 46:31
  Speaker 2: of anaerobic, like power, uh, maybe affected by extended fasting, um,
• 46:36
  Speaker 2: but no change in aerobic performance or jump height or fatigue. Uh,
• 46:40
  Speaker 2: there's actually not to get nerd out too much on
• 46:44
  Speaker 2: this space, but this woman named Stefan Hassan, who is
• 46:46
  Speaker 2: one of the best marathoners in the world. And she, uh,
• 46:51
  Speaker 2: I think prior to the Olympics maybe was Ramadan and she's,
• 46:55
  Speaker 2: and she's Muslim. So she was fasting. She was doing
• 46:57
  Speaker 2: all of her marathon training, like completely fasted during Ramadan
• 47:03
  Speaker 2: and she won. So, but I don't think that's because
• 47:06
  Speaker 2: of it.
• 47:07
  Speaker 1: It's just for different reasons. Good for her. I think
• 47:11
  Speaker 1: the big one that everyone kind of has heard about
• 47:14
  Speaker 1: a little bit though, is longevity, right? Like, like we
• 47:19
  Speaker 1: all want to live longer. I mean, I also want
• 47:22
  Speaker 1: to live better. And I think being hungry for 16
• 47:24
  Speaker 1: hours a day is not necessarily living better, but that's
• 47:26
  Speaker 1: just my personal opinion. If you're okay with it and
• 47:28
  Speaker 1: you want to live longer, let's go. We know that
• 47:34
  Speaker 1: in basically every species of animal ranging from like nematodes
• 47:40
  Speaker 1: to all the way up through primates, that severe calorie
• 47:45
  Speaker 1: restriction increases lifespan. That has been well replicated, like fruit flies, mice,
• 47:50
  Speaker 1: all animals, yeast do this. It has not been replicated
• 47:55
  Speaker 1: in humans because humans have a tough time reducing their
• 47:59
  Speaker 1: caloric intake by, you know, they're not trapped in cages
• 48:02
  Speaker 1: and whatnot. And also we don't have enough time to
• 48:05
  Speaker 1: run studies for the hundred years that would be necessary
• 48:08
  Speaker 1: to tell if humans are really living longer from calorie restriction.
• 48:12
  Speaker 1: There's a study in 2023 in Nature Aging that took
• 48:16
  Speaker 1: 220 humans and assigned them to 25% calorie restriction. So
• 48:22
  Speaker 1: they were like, OK, for the next two years, you're
• 48:24
  Speaker 1: going to eat 25% fewer calories per day. By the way,
• 48:28
  Speaker 1: they only achieved a 12% calorie restriction.
• 48:30
  Speaker 2: 25% calorie restriction for two years? That's a very long time.
• 48:33
  Speaker 1: It's very hard. And they couldn't do it because it's
• 48:35
  Speaker 1: really hard. And they're not locked in cages getting food
• 48:38
  Speaker 1: like mice. But the outcome here was an epigenetic clock,
• 48:42
  Speaker 1: which is like this, you like measure DNA markers and
• 48:45
  Speaker 1: you sort of do some statistics and you're like, okay,
• 48:47
  Speaker 1: like this DNA looks, in this study, one of the
• 48:50
  Speaker 1: epigenetic clocks they used said they were two years, they
• 48:54
  Speaker 1: had two years fewer, they're essentially, they're clocked in age
• 48:58
  Speaker 1: over two years. So they were two years younger by
• 48:59
  Speaker 1: the end. But the other two epigenetic clocks they use,
• 49:02
  Speaker 1: because there's a bunch of different ones you can use,
• 49:04
  Speaker 1: showed no difference. Um, I'm skeptical of epigenetic clocks to
• 49:08
  Speaker 1: begin with. I think they're not very useful on the
• 49:12
  Speaker 1: individual level at all. That said, that's the best we
• 49:16
  Speaker 1: have in humans.
• 49:17
  Speaker 2: But it's also not about fasting. This is about calorie restriction.
• 49:21
  Speaker 2: It's not about fasting.
• 49:22
  Speaker 3: Right.
• 49:23
  Speaker 1: And we have a mouse study, though, that does what
• 49:25
  Speaker 1: you would want, I think, which is that they randomized
• 49:28
  Speaker 1: mice to different levels of calorie restriction and whether they
• 49:31
  Speaker 1: got that through just less food over the whole day
• 49:35
  Speaker 1: or fasting. And the Fewer calories the mice had, the
• 49:40
  Speaker 1: longer they lived. And layering intermittent fasting or any kind
• 49:43
  Speaker 1: of fasting on top of those reduced calories had no
• 49:46
  Speaker 1: difference on mouse outcomes. So I think the best data
• 49:48
  Speaker 1: we have now for longevity is calories matter and fasting
• 49:52
  Speaker 1: does not.
• 49:54
  Speaker 3: Yes.
• 49:54
  Speaker 2: And yeah, calorie restriction is for another. Let's leave calorie
• 49:58
  Speaker 2: restriction for another day.
• 49:59
  Speaker 1: Okay.
• 50:00
  Speaker 2: Whether that is really, but bottom line fasting, fasting, no. Okay.
• 50:06
  Speaker 2: So the last piece, I think sort of all of
• 50:08
  Speaker 2: this up till now, I would summarize as it doesn't
• 50:13
  Speaker 2: really look like intermittent fasting or time-restricted eating or whatever
• 50:17
  Speaker 2: you want to tell it actually does anything that's especially meaningful.
• 50:24
  Speaker 2: It is worth talking a little bit about more serious
• 50:28
  Speaker 2: longer-term fasting, right? So to distinguish between the kind of
• 50:32
  Speaker 2: I'm not, you know, I'm, I still have my last
• 50:34
  Speaker 2: meal at three o'clock in the afternoon, or I never
• 50:36
  Speaker 2: eat before lunch or whatever is the, the thing from
• 50:40
  Speaker 2: kind of significant, like I'm going to fast for many days.
• 50:43
  Speaker 2: And you might imagine both, you might imagine this would
• 50:47
  Speaker 2: be different in either direction. You might imagine that actually
• 50:50
  Speaker 2: there is some benefit to fasting, but you need to
• 50:52
  Speaker 2: fast for a very long time to get into it.
• 50:55
  Speaker 2: Or you might imagine that fasting for a very long
• 50:57
  Speaker 2: time is, is bad. Yeah.
• 51:00
  Speaker 1: And, Here's where you see the claims online that really
• 51:04
  Speaker 1: start to flirt with some real danger. I think we
• 51:07
  Speaker 1: do have to address them. I'm going to start with
• 51:09
  Speaker 1: the growth hormone thing. Growth hormone had actually a moment
• 51:15
  Speaker 1: in the wellness in the 70s. It was one of
• 51:17
  Speaker 1: the first real I remember one of my mentors in
• 51:20
  Speaker 1: med school had a book on his shelf that was
• 51:23
  Speaker 1: called like grow young with growth hormone. And people were
• 51:26
  Speaker 1: injecting themselves with, it was kind of newly discovered. And
• 51:29
  Speaker 1: it was like, oh, it's this magical thing. It is
• 51:33
  Speaker 1: true that prolonged fasts increase growth hormone and they increase
• 51:37
  Speaker 1: it significantly. So Journal of Clinical Investigation, 1988, six healthy men,
• 51:42
  Speaker 1: a five-day complete fast. They drank water, but five days,
• 51:46
  Speaker 1: zero food. Their growth hormone level went up by threefold.
• 51:51
  Speaker 1: And you'll hear the influencers talk, not about this specific study,
• 51:54
  Speaker 1: but they're like, fasting makes your growth hormone triple or
• 51:56
  Speaker 1: quintuple and like growth hormone so good because it makes
• 51:58
  Speaker 1: you grow and be strong and stuff like that. That
• 52:01
  Speaker 1: is not what this study showed, actually. Some of you
• 52:05
  Speaker 1: may know that growth hormone works via a bunch of
• 52:09
  Speaker 1: sub hormones that do different things. And the one that
• 52:12
  Speaker 1: causes muscles to be built is called IGF-1. So in
• 52:15
  Speaker 1: the normal state, growth hormone signals IGF-1, IGF-1 signals muscles
• 52:20
  Speaker 1: to grow. And the influencers will tell you that, well, therefore,
• 52:22
  Speaker 1: if growth hormone is high, then fasting makes it high.
• 52:25
  Speaker 1: You're going to get stronger. In this study, the IGF-1
• 52:28
  Speaker 1: level fell. So growth hormone has many effects besides increasing IGF-1.
• 52:34
  Speaker 1: One of them is to break down fat for fuel.
• 52:37
  Speaker 1: And that's what growth hormone was doing. And because your
• 52:40
  Speaker 1: body knows when it's starving, it is not going to
• 52:42
  Speaker 1: upregulate IGF-1 to help you build muscle in the middle
• 52:45
  Speaker 1: of a famine. It does not happen. It doesn't work
• 52:48
  Speaker 1: that way. It would be terrible if it worked that way. So-
• 52:51
  Speaker 1: A five-day fast is called starvation. It does do things.
• 52:57
  Speaker 1: It does biologically active things, but in general, not the
• 53:01
  Speaker 1: things that at least the influencers are telling you are
• 53:04
  Speaker 1: going to change your life and make you super strong. Yes,
• 53:06
  Speaker 1: you'll lose fat because obviously you're going to digest fat.
• 53:09
  Speaker 1: You're going to digest muscle as well. And by the way,
• 53:11
  Speaker 1: most of these studies will show of the total body
• 53:15
  Speaker 1: mass lost, you get about two-thirds lean mass loss and
• 53:18
  Speaker 1: one-third fat mass loss. which is just about the opposite
• 53:21
  Speaker 1: of the ratio we see from other methods of weight
• 53:24
  Speaker 1: loss where you lose sort of half to two-thirds fat
• 53:27
  Speaker 1: mass and then one-third lean mass.
• 53:30
  Speaker 2: Not great. I mean, I think what's sort of tempting
• 53:33
  Speaker 2: and sucks one in about this whole intermittent fasting space
• 53:38
  Speaker 2: is that you do potentially see some loss in fat mass,
• 53:41
  Speaker 2: which people think of as good. And then there are
• 53:45
  Speaker 2: many other things that change. And so it's an example
• 53:48
  Speaker 2: of something where like if you don't let somebody eat
• 53:49
  Speaker 2: for five days, a lot of stuff's different. Like your
• 53:52
  Speaker 2: body is not– that's not its intended goal. And so
• 53:57
  Speaker 2: many things will change. And depending on how you interpret
• 53:59
  Speaker 2: those things, they could be good. They could feel good.
• 54:02
  Speaker 2: They could not feel good. But like of course they're–
• 54:04
  Speaker 2: like it's a famine. A lot of blood markers are
• 54:06
  Speaker 2: going to be different in a famine. And so it feels–
• 54:10
  Speaker 2: one can argue that things are happening. You know, this
• 54:14
  Speaker 2: is a biologically active process, which is true, but that
• 54:18
  Speaker 2: is different from saying it's good.
• 54:20
  Speaker 1: Okay.
• 54:21
  Speaker 2: So it is possible to live a very long time
• 54:24
  Speaker 2: without eating at all. World record is held by a
• 54:29
  Speaker 2: guy named Angus Barbieri. who, this wasn't recent, this is
• 54:35
  Speaker 2: like in the 1960s, 50s, 60s. He lived for 382
• 54:39
  Speaker 2: days without eating. He started at 450 pounds. He had water, tea,
• 54:45
  Speaker 2: and coffee vitamins, also some potassium, sodium. So you actually,
• 54:49
  Speaker 2: you do need some electrolytes and vitamins if you're not
• 54:51
  Speaker 2: going to eat. And he didn't eat anything for 382 days.
• 54:56
  Speaker 2: He lost quite a lot of weight. He was down
• 54:58
  Speaker 2: to 180 pounds. He actually kept it off for a
• 55:00
  Speaker 2: pretty long time. for a pretty long time. My favorite
• 55:04
  Speaker 2: fact about this is he only pooped every 37 to
• 55:08
  Speaker 2: 48 days. So go back to our episode on poop.
• 55:14
  Speaker 2: That's not the recommended, not the recommended frequency. This actually
• 55:19
  Speaker 2: was like, it was called therapeutic starvation. And it was
• 55:22
  Speaker 2: something that was for some period of time, kind of
• 55:24
  Speaker 2: briefly in, in vogue. And, and, you know, the, the
• 55:27
  Speaker 2: idea is of course, you're eating, you're eating, you're literally
• 55:29
  Speaker 2: eating your body. And if there's a lot of, as
• 55:31
  Speaker 2: my grandmother would refer to it, living off your hump.
• 55:35
  Speaker 2: And that is a way to lose a lot of weight,
• 55:39
  Speaker 2: but also sometimes people die. So this is not a
• 55:45
  Speaker 2: recommended approach to weight loss.
• 55:47
  Speaker 1: Yeah. Yeah. It's been given up because Angus Barbieri is
• 55:50
  Speaker 1: sort of the survivor of this protocol. There are a
• 55:53
  Speaker 1: number of people who died. They tend to die of
• 55:54
  Speaker 1: heart failure, arrhythmias, lactic acidosis, and so on and so forth.
• 55:58
  Speaker 1: So But yeah, he would lose weight in 382 days
• 56:01
  Speaker 1: is a long time. Okay, we have to address this
• 56:04
  Speaker 1: because the most dangerous thing you're going to see online
• 56:08
  Speaker 1: surrounds cancer. And I'm going to play an Instagram reel
• 56:13
  Speaker 1: that makes me very uncomfortable.
• 56:14
  Speaker 2: If you had cancer, what would you do?
• 56:17
  Speaker 4: Let's say it's stage four cancer. If I had that
• 56:19
  Speaker 4: right now, I would stop eating. I probably wouldn't eat
• 56:22
  Speaker 4: for 20 days and try to go for 30 days.
• 56:24
  Speaker 3: Why?
• 56:25
  Speaker 4: Because you are literally going to starve all the resources
• 56:28
  Speaker 4: from cancer. It can't survive, but your body can survive.
• 56:31
  Speaker 4: Cancer actually is very sick.
• 56:33
  Speaker 1: Inside a tumor, it's very necrotic.
• 56:36
  Speaker 4: There's dead, dying tissue.
• 56:38
  Speaker 1: It's hypoxic.
• 56:39
  Speaker 4: What's the best sledgehammer? Is it chemo that kills also
• 56:42
  Speaker 4: your cells? Or maybe would it be starvation, what we
• 56:44
  Speaker 4: call fasting? If you did a long fast like that,
• 56:47
  Speaker 4: that would put you in a better place, and then
• 56:49
  Speaker 4: you can go to one meal a day.
• 56:52
  Speaker 2: Okay, that's a very disturbing reel, Perry.
• 56:53
  Speaker 1: I know, I know. I debated showing it to you.
• 56:57
  Speaker 1: Let me just say, there's a lot wrong with this.
• 57:01
  Speaker 1: First of all, there's a complete absence of data. Like
• 57:04
  Speaker 1: this is based on absolutely nothing. There's no human data
• 57:08
  Speaker 1: that suggests that prolonged fasting changes cancer outcomes. We're going
• 57:11
  Speaker 1: to touch it. You know, we did our due diligence.
• 57:14
  Speaker 1: We'll look at some of this data in a second.
• 57:17
  Speaker 1: But it also, of course, has the typical sort of
• 57:19
  Speaker 1: wellness grifter thing of like, why would you use chemotherapy?
• 57:22
  Speaker 1: Like that kills all the cells, right? Which is super dangerous.
• 57:27
  Speaker 1: There have been Plenty of people who have fallen for
• 57:29
  Speaker 1: this kind of thing and forgone chemotherapy and died of
• 57:32
  Speaker 1: their cancer. And I also just want to say that
• 57:37
  Speaker 1: the number one predictor of survival in cancer, if you
• 57:41
  Speaker 1: account for the type of cancer in the stage, is frailty,
• 57:45
  Speaker 1: or the opposite of frailty, performance status. So the weaker
• 57:50
  Speaker 1: you are during cancer treatment, the more likely you are
• 57:54
  Speaker 1: to die of cancer. And encouraging people to do a
• 57:58
  Speaker 1: 20 or 30-day fast with stage four metastatic cancer, it's
• 58:04
  Speaker 1: just like the height of irresponsibility. And I hope people
• 58:08
  Speaker 1: understand after having listened to this episode that this is
• 58:11
  Speaker 1: not how this works. There are changes that happen during fasting.
• 58:17
  Speaker 1: Those changes have nothing to do with whether cancer is
• 58:20
  Speaker 1: spreading through your system or not.
• 58:21
  Speaker 3: Yeah.
• 58:21
  Speaker 2: And again, as you say, I think when people have
• 58:24
  Speaker 2: advanced cancer, it can often be quite difficult to eat.
• 58:27
  Speaker 2: It can be quite difficult to get a sustained amount
• 58:30
  Speaker 2: of calories and people lose weight and lose weight and
• 58:33
  Speaker 2: lose weight. And that is a consistent predictor of mortality.
• 58:36
  Speaker 2: So encouraging people to eat less feels just unbelievably irresponsible.
• 58:41
  Speaker 3: Yeah.
• 58:41
  Speaker 1: Now, there has been some research into fasting as a
• 58:45
  Speaker 1: treatment for the toxicity of chemotherapy. So, you know, chemotherapy,
• 58:49
  Speaker 1: typically nausea is a major issue. And there was some
• 58:54
  Speaker 1: reasonable mouse data that suggested that short-term fasting, again, talking
• 58:58
  Speaker 1: about like, you know, less than a day type of
• 59:01
  Speaker 1: fasting prior to chemotherapy treatment reduced symptoms that didn't replicate
• 59:04
  Speaker 1: very well in humans, unfortunately. I did find one trial called.
• 59:10
  Speaker 1: The DIRECT-2 trial, which was in Nature Communications in 2020.
• 59:15
  Speaker 1: This took 131 patients with stage two to three breast cancer,
• 59:19
  Speaker 1: not metastatic, stage two to three breast cancer. And they
• 59:22
  Speaker 1: did sort of a modified fast, like reduced, but dramatically
• 59:26
  Speaker 1: reduced calorie intake for the four days prior to chemo.
• 59:30
  Speaker 1: Their primary outcome was to show whether chemotoxicity would differ,
• 59:34
  Speaker 1: and it didn't. So they didn't show more or less
• 59:36
  Speaker 1: hair loss or more or less nausea, unfortunately. But in
• 59:40
  Speaker 1: a post hoc analysis, they thought that the people who
• 59:44
  Speaker 1: fasted might have had a higher rate of radiologically complete
• 59:48
  Speaker 1: or partial response. So when you look at the mammogram again,
• 59:53
  Speaker 1: do things look smaller? This is a very small study.
• 59:56
  Speaker 1: It's the only one I was able to find. And
• 59:59
  Speaker 1: I will say that the American Society for Clinical Oncology
• 1:00:01
  Speaker 1: says there's insufficient evidence for or against fasting prior to chemo.
• 1:00:06
  Speaker 1: And again, they're talking about limited periods of fasting. So
• 1:00:09
  Speaker 1: it's like if you're worried about chemo nausea and you
• 1:00:12
  Speaker 1: want to not eat for 16 hours prior to chemo,
• 1:00:15
  Speaker 1: that seems fine. But please don't believe that this is
• 1:00:19
  Speaker 1: a substitute for actual cancer therapy. It's not.
• 1:00:23
  Speaker 3: Yeah.
• 1:00:24
  Speaker 2: It's worth noting that even that trial excluded people with
• 1:00:26
  Speaker 2: a BMI outside of the normal range with a BMI
• 1:00:29
  Speaker 2: that was too low.
• 1:00:30
  Speaker 3: Yeah.
• 1:00:30
  Speaker 1: It would be very unethical to have people who are
• 1:00:33
  Speaker 1: underweight not eating.
• 1:00:35
  Speaker 3: Okay.
• 1:00:36
  Speaker 2: This I think leads to the other sort of serious
• 1:00:40
  Speaker 2: moment here, which is just to say there are a
• 1:00:41
  Speaker 2: variety of people who should not do this kind of fasting. Obviously,
• 1:00:45
  Speaker 2: people with eating disorders, this kind of fasting is part
• 1:00:48
  Speaker 2: of a disordered eating pattern or certainly can be People
• 1:00:52
  Speaker 2: who are taking medications for their diabetes also should not
• 1:00:55
  Speaker 2: fast in this way because of hypoglycemia concerns. Older adults
• 1:01:00
  Speaker 2: who are already losing lean mass, please don't stop eating.
• 1:01:04
  Speaker 2: People with gout, gout isn't very common, but if you
• 1:01:06
  Speaker 2: have gout, ketones are not good for you because they
• 1:01:11
  Speaker 2: cause problems with your, they compete with the uric acid
• 1:01:14
  Speaker 2: to get out. And I would say kids and teens
• 1:01:17
  Speaker 2: should not do this just given their cognitive reaction and
• 1:01:21
  Speaker 2: also the eating disorder piece from before.
• 1:01:24
  Speaker 1: Totally agree. I think the biggest and most important question, though,
• 1:01:27
  Speaker 1: of this entire episode is this one, which is, but
• 1:01:31
  Speaker 1: can I drink coffee? That would be the thing that
• 1:01:34
  Speaker 1: stops me.
• 1:01:35
  Speaker 2: That would stop me. But many of these many protocols
• 1:01:39
  Speaker 2: do allow you to have black coffee.
• 1:01:42
  Speaker 3: All right.
• 1:01:44
  Speaker 2: And our friend, uh, Angus for his 382 day cast,
• 1:01:48
  Speaker 2: he did drink coffee. Okay.
• 1:01:50
  Speaker 1: Well, it worked. It worked for good old Angus. So yes,
• 1:01:53
  Speaker 1: you can drink black coffee, go for it. Oh boy.
• 1:01:57
  Speaker 1: All right. Um, here we are intermittent fasting smash or pass.
• 1:02:03
  Speaker 2: I'm a pass on this. Uh, I, I don't think
• 1:02:06
  Speaker 2: the evidence suggests this is an effective way to improve
• 1:02:09
  Speaker 2: people's health.
• 1:02:11
  Speaker 1: Um, Yeah.
• 1:02:13
  Speaker 2: Okay. I'm a little hedgy here because I do think
• 1:02:16
  Speaker 2: for some people as a weight loss strategy, the simplicity
• 1:02:19
  Speaker 2: of this is very appealing. Not that fasting for five days,
• 1:02:22
  Speaker 2: but the kind of only eating in a window. So
• 1:02:24
  Speaker 2: I can sort of see the value for some people,
• 1:02:28
  Speaker 2: but I'm a smash or sorry, I'm a pass largely
• 1:02:30
  Speaker 2: because I think it's so oversold that as to be disturbing.
• 1:02:35
  Speaker 1: I will smash it because taking in less calories is
• 1:02:38
  Speaker 1: generally a good thing. And it's an easy way, I think,
• 1:02:42
  Speaker 1: to take in less calories. But please don't take that
• 1:02:44
  Speaker 1: as an endorsement of the 50 million ridiculous claims that
• 1:02:48
  Speaker 1: are made about intermittent fasting online.
• 1:02:50
  Speaker 2: That's like one of our few disagreements.
• 1:02:55
  Speaker 1: I was looking back. We've had a couple. It's all right.
• 1:02:58
  Speaker 2: Okay, guys.
• 1:03:01
  Speaker 1: That's it for intermittent fasting. Your question of the week.
• 1:03:05
  Speaker 1: after the break. And we are back with your question
• 1:03:12
  Speaker 1: of the week. If you have a question of the week,
• 1:03:14
  Speaker 1: come visit us at wellnessactually.fm. Leave a question and a
• 1:03:18
  Speaker 1: voice note, and we may play your question on the air.
• 1:03:21
  Speaker 1: Here's our question this week.
• 1:03:23
  Speaker 3: Hey, Emily and Perry. My name is Caroline, and I
• 1:03:25
  Speaker 3: am from West Boylston, Massachusetts. I have not been eating
• 1:03:29
  Speaker 3: a lot of lunch meat for the past five years,
• 1:03:32
  Speaker 3: mostly because I've been pregnant three times, but also because
• 1:03:35
  Speaker 3: I've heard a lot about how bad processed meat or
• 1:03:39
  Speaker 3: lunch meat is for you, that it might be a carcinogen.
• 1:03:45
  Speaker 3: But now my three young children are very interested in
• 1:03:48
  Speaker 3: ham and cheese sandwiches. And you know what's very easy
• 1:03:50
  Speaker 3: to pack for a child? It's a ham and cheese sandwich.
• 1:03:54
  Speaker 1: Should I be worried?
• 1:03:55
  Speaker 2: Should I try to steer them towards something else?
• 1:03:59
  Speaker 3: What are our thoughts on deli meat? Good, bad, indifferent?
• 1:04:02
  Speaker 3: What do you think?
• 1:04:04
  Speaker 1: Emily, it won't surprise you to hear that I am
• 1:04:07
  Speaker 1: a lover of deli meats and bacon as well. What
• 1:04:13
  Speaker 1: do you think?
• 1:04:14
  Speaker 2: There is a lot of observational data suggesting that high
• 1:04:19
  Speaker 2: consumption of processed meats is linked to higher rates of cancer. However,
• 1:04:25
  Speaker 2: I am very skeptical of all of that data. I
• 1:04:28
  Speaker 2: think that it is all the times when we're looking
• 1:04:31
  Speaker 2: at diet and health outcomes, the data is tremendously confounded
• 1:04:35
  Speaker 2: by other differences across individuals. So I think this is fine, honestly.
• 1:04:43
  Speaker 1: Okay. I'll say everything in moderation. These are very salty.
• 1:04:47
  Speaker 1: So if you are on a salt-restricted diet because of
• 1:04:49
  Speaker 1: high blood pressure or heart failure, you definitely want to
• 1:04:51
  Speaker 1: avoid this stuff. But if you're otherwise healthy and you
• 1:04:54
  Speaker 1: want to do smoked meats... Yes, I agree. There is
• 1:04:57
  Speaker 1: some data out there that's concerning. I don't think this
• 1:04:59
  Speaker 1: is something I would want to eat every single day,
• 1:05:04
  Speaker 1: but I think bacon on Sundays is just fine.
• 1:05:08
  Speaker 2: You think it's a sometimes food?
• 1:05:10
  Speaker 1: It's a sometimes food.
• 1:05:14
  Speaker 2: All right. That's it for today. Join us next week
• 1:05:18
  Speaker 2: when we will ask, what is the deal with eating organics?
• 1:05:24
  Speaker 2: Wellness Actually is produced in association with iHeart Media. Our
• 1:05:28
  Speaker 2: senior producer is Tamar Avishai. Our executive producer at iHeart
• 1:05:32
  Speaker 2: is Jennifer Bassett. Our theme music is by Eric Deutsch.
• 1:05:35
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• 1:05:38
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• 1:05:41
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• 1:05:44
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• 1:05:46
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• 1:05:51
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• 1:05:53
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• 1:05:56
  Speaker 1: mailbag or suggest a topic for a future show.
• 1:06:00
  Speaker 2: We'll let the influencers have the last word.
• 1:06:01
  Speaker 3: All right, I started intermittent fasting again, so I'm not
• 1:06:04
  Speaker 3: eating regularly.
• 1:06:05
  Speaker 1: Before 12 p.m.
• 1:06:06
  Speaker 3: And after 6 p.m. So the meals are just, they're incredible.
• 1:06:18
  Speaker 3: It makes food more enjoyable.