The Art of Manliness - #328： The Pros and Cons of Intermittent Fasting

00:00:00.000 Brett McKay here and welcome to another edition of the Art of Manliness podcast.

00:00:18.800 Well, during the past 10 years or so, there's been a lot of chatter about the health benefits

00:00:23.020 of intermittent fasting. That is, going without food for a short window of time on a regular

00:00:27.160 basis. Some of the touted benefits of intermittent fasting include shredding body fat while maintaining

00:00:31.740 muscle and strength, improving blood sugar levels and insulin sensitivity, increasing longevity

00:00:36.360 and improving focus. And yes, some of them even say that it can help fight cancer. But how many

00:00:41.020 of those purported benefits are real and how many of them are just hype? Well, my guest today is a

00:00:44.840 nutrition scientist who has spent the past several years researching and experimenting with intermittent

00:00:48.480 fasting to find out the answers to those questions. His name is John Berardi and he's the co-owner of

00:00:52.780 Precision Nutrition, an online nutrition coaching company. And John has written an ebook that

00:00:56.680 highlights all the latest research on intermittent fasting as well as his personal experiments with

00:01:00.840 several different IF protocols. And he includes all the blood work and everything that went along

00:01:04.940 with that. Today on the show, John cuts through the hype of intermittent fasting and gives us a

00:01:08.840 nuanced look at the benefits and downsides of this diet method. If you've been thinking about trying

00:01:14.020 intermittent fasting, you don't want to miss this show. John breaks down exactly who should use IF,

00:01:19.200 that's intermittent fasting, and who shouldn't, and what kind of results to expect when you fast.

00:01:23.480 After the show's over, check out the show notes at awim.is slash fasting.

00:01:31.320 John Berardi, welcome to the show.

00:01:33.180 Thank you very much. Thanks for having me. It's a huge pleasure and honor that you invited me on.

00:01:37.820 You know, as we were talking about before we started, I have been following the website and the podcast

00:01:43.640 for an embarrassingly long period of time, actually. And yeah, I mean, it was even your site that gave me a

00:01:50.420 lot of motivation and inspiration early on for what we're doing at Precision Nutrition. The idea

00:01:55.140 that you could just love great content and use that as a vehicle to start a business. Like, hey,

00:02:02.680 we're not writing this content for any other reason than to put out fantastic content into the world.

00:02:08.200 And so you were doing this almost before anyone else. And it was like a huge inspiration for us to

00:02:13.740 actually do the same. And so thank you for that. And thanks for all the great stuff over the years.

00:02:18.220 Well, thanks for the kind words. It's very humbly and honored. Thanks so much.

00:02:22.260 So we're talking about intermittent fasting today. Talk about your background first. You're a PhD,

00:02:26.540 but a PhD in what?

00:02:27.700 Yeah. So I have a PhD in exercise and nutritional biochemistry. My route to what I do today is

00:02:35.320 kind of non-conventional. I was, you know, I guess probably the story begins most appropriately when I

00:02:41.120 was a very scrawny high school student or very scrawny growing up in general with asthma and allergies

00:02:47.860 in my puffer everywhere that I went. So I wasn't an athletic kid or anything like that. But, you know,

00:02:53.840 identifying very much with the old Charles Atlas sand kicked in the face by the bully ads. You know,

00:03:00.700 I saved up my dishwashing money when I was 16 and bought a barbell set from Sears. And that sort of,

00:03:07.700 that's where the passion for working out and strength training came from. And I, you know,

00:03:12.380 over the next couple of years, I think two, two and a half years, I put on about 70 pounds of muscle,

00:03:17.840 went on to compete in some bodybuilding and powerlifting competitions. And the discipline

00:03:22.060 that I learned in bodybuilding and powerlifting, you know, the nutrition, the regular workouts and

00:03:28.040 stuff really changed my life. And then I decided to, you know, go to community college eventually

00:03:33.400 and get good enough grades to go to university. So then I did a pre-med undergrad thinking I was

00:03:39.760 going to go to med school. And then I realized that I just don't think I like any of that. You know,

00:03:43.600 I love learning about the body, but I really love exercise and nutrition. So then I did a master's

00:03:49.340 in exercise physiology and then a PhD in exercise and nutritional biochemistry. But, you know, that

00:03:57.700 root kind of grooms you for academics, right? To be a professor or a researcher. And I did that for a

00:04:03.440 few years, but my heart just always kept coming back to coaching. So, you know,

00:04:09.140 throughout those years of academics and research, I was on the side, you know, working with athletes

00:04:16.160 and recreational exercisers who wanted to look and feel better. And at a certain point, I was just

00:04:21.720 like, you know what, let me just do this. Probably very much like what you did with your website.

00:04:26.720 This is the thing that I think about every moment. I'm not thinking about the other things people think

00:04:31.120 I'm supposed to think about. So I'm going to write about it and publish about it. So, you know,

00:04:35.480 over the years, that's how precision nutrition was born with just free articles on the internet.

00:04:40.000 And thankfully to date, it's, it's grown tremendously. And, and, uh, you know, now we

00:04:44.820 have a legit business and, and, you know, since we started over the last 15 years, we've coached,

00:04:50.220 you know, over 50,000 people online and we also have a certification program. So, you know,

00:04:56.040 I often like to say, you know, when I talk about nutrition that, yes, I have sort of an academic

00:05:02.240 pedigree, but it's, it's not the most important part of, of what I do or my experience. I think

00:05:08.340 the most important part is having worked with about 50,000 people and having the experience of

00:05:14.380 taking what you might read about in research studies or on the internet and applying it and

00:05:20.200 actually seeing what works. And then having your whole livelihood based on, uh, paring down

00:05:27.380 all the experiments to the fundamentals that actually do work in the end.

00:05:34.080 So you actually wrote an article for us in 2012. It's like almost five years ago,

00:05:40.320 which I can't believe it's time goes by so fast about intermittent fasting before we get into what

00:05:46.260 intermittent, well, we all know what intermittent fasting is. Fasting is going without food.

00:05:49.880 Intermittent fasting is, you know, doing that on a sort of regular basis,

00:05:53.540 but why have you spent a lot of time researching and experimenting with intermittent fasting?

00:06:00.760 So, you know, I mean, I have this weird thing where my profession is also my hobby

00:06:05.860 and passion and all consuming interest. So, you know, I, I coach a lot of people and I teach

00:06:11.600 other professionals, you know, our system for doing that through certifications and, and, and

00:06:16.360 software and things like that. But, you know, I mean, I'm just forever interested in

00:06:21.540 physique manipulation, health, body composition and performance. You know, I'm in my mid forties.

00:06:27.400 Now I compete in master's level tracks. I'm always experimenting with things on myself and,

00:06:32.880 you know, I have academic training and I have a lot of coaching experience. So I feel like I can do that

00:06:37.520 successfully without too much risk. And, you know, there was, there was a point several years back

00:06:43.740 where I decided that after years and years of weightlifting and, and, you know, sort of bodybuilding

00:06:48.820 and also powerlifting training, I wanted to make a triumphant return to sport, you know,

00:06:55.100 like competitive sports. And I was a runner, a sprinter, a track and field athlete when I was

00:07:00.220 younger. And so I, you know, I was like, ah, I heard about these master's level track meets.

00:07:06.600 Wouldn't it be cool if I could, you know, in my forties run track again? So the problem was I was just

00:07:12.100 too muscular. And I know this is one of these like humble brags, you know, I was just too muscle,

00:07:16.640 you know, muscle bound to run, but I went too much, you know, to be fast. And, and also I hadn't done

00:07:23.620 mobility work that would be corrupt, that would be required or the drills and years. And so I wanted

00:07:29.380 to lose some weight and right around the same time. And this was like, you know, 2010, 2011,

00:07:34.020 there was a lot, a lot, a lot of noise on the internet about intermittent fasting. And nowadays we

00:07:39.720 take for granted this particular truth that we've learned, but back then the whole paradigm around

00:07:46.260 food and nutrition was you have to eat small meals frequently throughout the day for health.

00:07:50.920 And you probably remember this. It was what everyone was talking about. And all of a sudden,

00:07:56.720 this sort of radical band of intermittent fasters were telling people, no, no, no,

00:08:00.720 it won't kill your metabolism. It won't ruin your health. If you went for long stretches without eating

00:08:07.240 in between your meals, whether that's a full day of a fast periodically, whether that's just an

00:08:13.380 extended fast each day. So you eat, maybe skip breakfast. And so you have lunch and dinner.

00:08:19.320 And during those times you make thoughtful choices so that you can get all of your nutritional needs.

00:08:23.740 And at the time it caused a huge rift. It's very much like what's happening now around,

00:08:28.840 should we eat meat or no meat and just plants, you know, with some of the documentaries that have

00:08:33.120 come out recently, it was the same thing. Everyone was just all frothed up about a different issue.

00:08:37.620 And it was, you know, should you eat frequently small meals or this fasting thing? And, you know,

00:08:43.300 when you work in nutrition, there's about, oh, a million messages a day you get about this kind

00:08:48.500 of a thing. And you get these really heated, irrational debates. And, you know, being a trained

00:08:53.900 scientist, it's sort of my mental makeup. And I consider it also my vocation to actually take a

00:09:00.900 non-emotional approach to these things and just test them, whether that's experimentation with small

00:09:06.740 groups of our coaching clients, because we have so many every year that we could do small pilot

00:09:11.480 projects, research projects, comparing two groups on two different types of diets. And we've done that

00:09:17.360 before, or also just on myself and some of the people who work at Precision Nutrition or some of

00:09:22.660 my friends and colleagues. So I was just really fascinated. And the timing came perfect because this

00:09:27.780 big debate was up. I was wondering what all the hype was about. And I also wanted to lose about 20

00:09:33.760 pounds for track and field. So I decided I would try a whole bunch of different intermittent fasting

00:09:38.960 type interventions in my life and document everything to see how it would turn out. So

00:09:44.200 that was kind of the genesis of the experiment. It was part professional curiosity, part personal

00:09:49.240 goal setting, and then also, you know, part just a deep interest in this particular emotional debate of

00:09:56.480 the day. Like what would happen? You know, unlike the debate today around whether you, whether meats

00:10:03.200 are causing cancer and we should all eat plant-based or whatever, which will take 30 years to resolve

00:10:08.580 the intermittent fasting thing you could figure out, at least in terms of body composition and blood

00:10:13.220 markers pretty quickly in like 12 or 16 weeks, you try it, you measure stuff carefully and you see what

00:10:18.760 turns out. So it was the perfect kind of short-term experiment at the time.

00:10:23.320 So yeah, as you said, there's a lot of, there was a lot of hype and there still is a lot of hype and a

00:10:27.560 lot of, you know, talk on the web about intermittent fasting. What are some of the touted benefits that

00:10:33.880 you, that you've seen out there, you know, attributed to intermittent fasting?

00:10:37.140 Yeah. I mean, some of the benefits are, I mean, I like to break things down into different categories.

00:10:42.320 So we could, we could say there are sort of body composition benefits. We could say there are

00:10:48.280 proposed health benefits, and then we can say there are proposed psychological benefits.

00:10:53.040 So if we look at sort of the body composition benefits, well, people say that you can lose

00:10:58.800 a lot of body fat without the traditional pain of dieting. You know, historically when people went

00:11:05.300 on a diet, if they, in particular, if they were active and, and let's say they went to a gym and

00:11:10.080 they hired a personal trainer or diet coach or whatever, they would get that message, small meals,

00:11:14.980 eating frequently throughout the day, maybe cut out carbohydrates. And it's pretty restrictive

00:11:19.160 and it's pretty challenging, difficult mentally, emotionally, even physiologically. Workouts start

00:11:25.920 to suffer and stuff like that. And so, you know, a lot of people are proposing with intermittent

00:11:31.420 fasting, you don't have to deprive yourself so much really. If you're doing, let's say an extended

00:11:37.960 fast, which some people call sort of 16, eight fasting, where you have 16 hours of the day where you

00:11:43.240 don't eat meals and eight during an eight hour window, you do during those eight hours, you can't

00:11:48.960 eat indiscriminately, but there's a lot more latitude in your choices because you've gone through

00:11:54.420 this extended fasting period. So that's one of the proposed benefits. It's an easier way to lose body

00:12:00.040 fat. If you can get past the initial phase of really being hungry in the morning at breakfast,

00:12:04.880 you know, body comp benefits. Then there's proposed health benefits, which are better regulation of blood

00:12:10.580 sugar, lower blood lipids, and a whole host of other things associated with the things we might

00:12:15.940 be able to measure with a blood test. And, you know, things from lowering insulin and lowering

00:12:21.580 inflammation and stuff like that. And some of that does bear out in the literature, just not quite the

00:12:26.520 way that people on the internet are saying. And then the third are the psychological benefits.

00:12:31.180 Now, for a lot of people, hunger is an emergency. It's like when it's time to eat, if you don't eat,

00:12:36.920 you have this sort of preloaded notion that it's an emergency. And if you don't get food,

00:12:42.680 bad things are going to happen. Like you're going to get hypoglycemic, or you're going to get really

00:12:46.960 irritable. Some people call it hangry, like hunger and anger mixed. And I think that's part psychological,

00:12:53.960 but it's also part physiology. It's that you are so trained not to have periods of hunger in your life

00:13:01.800 that you get maladapted type of response when you don't eat. And one of the sort of proposed benefits,

00:13:09.480 and I saw this personally, with doing intermittent fasting, is that you learn that hunger isn't an

00:13:14.540 emergency. You can actually go quite a long period of time without food and be very serene about it

00:13:19.720 if two things happen. One, you know that it's okay, it's not an emergency. And two, you train your

00:13:26.560 body to be what is called metabolically flexible. So for people who are used to eating frequently

00:13:32.280 throughout the day, or even just breakfast, lunch and dinner, what tends to happen is there's a

00:13:38.400 hormone or neurotransmitter slash hormone called ghrelin. And it's an anticipatory hormone. It's a

00:13:44.720 hormone that is released about 30 minutes before your habitual mealtime. So if you always eat lunch at

00:13:50.220 1230, it's going to start coming around 1130 or 12. And it's what makes your stomach start to

00:13:56.660 grumble. It's what starts to make you feel hungry before there's even food around. It's your body

00:14:02.480 saying, Oh, yeah, I know, Brett eats usually around 1230. So let's start getting ready. Now ghrelin's

00:14:09.420 trainable, which means if you change your mealtime after about 14 days, it'll start being released

00:14:14.920 at the 30 minutes prior to the new mealtime. So what tends to happen with intermittent fasting is

00:14:21.620 you start to manipulate ghrelin and make it a bit more flexible. And then you also make your body's

00:14:26.860 use of fuel more flexible. So people who let's say have a hard time losing body fat, in some cases,

00:14:33.660 aren't usually well adapted at using whatever fuels available whenever it's available, including

00:14:40.440 the fuel that's already stored on your body. So you know, unless you're 2% body fat, you have lots

00:14:47.020 of meals stored on you right now. So you don't need breakfast to feed your body the energy that's

00:14:53.420 required. It should just be able to use the meals that are on you all that stored energy that you have

00:14:59.460 through, you know, glycogen through body fat, even through your free amino acid pool, which is the

00:15:06.020 breakdown products of protein. So you should be able to eat the meals that are on you. The problem

00:15:11.660 is if you're not used to going through little periods of a longer fast, your body may have a

00:15:18.300 hard time eating the food that's on you. It may not release the correct balance of hormones and the

00:15:25.460 right amounts so that you can easily use that fuel. And one thing that intermittent fasting does is it

00:15:30.960 trains you to be more metabolically flexible. In other words, if you have to skip lunch and dinner one

00:15:35.940 day, for whatever reason, your body will just easily eat the meals that's on itself without

00:15:41.780 feeling aggravated and angry and hypoglycemic or whatever the feelings that people describe that

00:15:48.500 they may have. So really people break it down in three buckets in terms of potential benefits.

00:15:54.000 One is a body composition one, perhaps lose fat more easily. Two is a health one, perhaps fix a bunch

00:16:01.000 of blood markers for health. And then three is a physiological psychological one, or at least where

00:16:06.400 the two interface, right? Making you more easily able to use the fuel that's on you if you're not

00:16:12.280 eating a meal and also making you, I guess, less of a jerk when you don't need a meal.

00:16:17.060 Let's break this down a little bit. Let's talk about these, the health benefits, these blood marker

00:16:20.060 benefits. I see a lot about this. And you see these studies, they're usually done on animals,

00:16:27.820 mice, and you're like, yeah, intermittent fasting can kill cancer or intermittent fasting can increase

00:16:34.140 longevity and make you live longer. Is there any credence to these research? Will people get those

00:16:38.860 benefits or should they kind of look at it with a bit of healthy skepticism?

00:16:42.660 Yeah. I mean, I think the latter, you know, with nutrition and physiology and biology and health,

00:16:48.480 it is to everyone's advantage to assume that the truth is way more nuanced than anything you read,

00:16:57.100 then even the experts of the day know. If you go into any biological discussion thinking it should be

00:17:06.180 settled or cut and dry, or someone on the earth knows the answer to it, you would be wrong.

00:17:11.160 The truth is, especially when it comes to nutrition, we did an infographic for our website called

00:17:17.880 Why Nutrition Science is So Confusing. And what we did is we compared the nutrition, I guess,

00:17:24.560 the history of nutritional science to the history of chemistry. And really, like, the history of

00:17:29.980 chemistry started being chronicled, like, thousands of years BC, okay? And for the first several hundred

00:17:37.380 years, it was still in the alchemy phase, right? So they were trying to change metals, you know?

00:17:44.520 And nutrition, as a science, really began in the late 1800s. So if we want to liken it to chemistry,

00:17:54.060 chemistry's had thousands and thousands of years to learn stuff, and it still obviously doesn't know

00:17:58.360 everything. Nutrition is still in the alchemy days, right? We are still in the phase where chemistry

00:18:03.160 had tried to start and had not begun with anything relevant or useful yet. And I mean, I'm being a

00:18:10.120 little bit facetious here. But the truth is, nutrition science is so young. So if anyone tells

00:18:16.140 you they know, they probably don't. And it takes a much more nuanced view. So if we look at your

00:18:23.140 question in a very nuanced way, you know, does intermittent fasting have the potential to, like,

00:18:29.780 treat and cure cancer? Well, that seems non-nuanced to me. A nuance there is in rodent models, which we

00:18:39.260 know aren't identical to human models, certain types of intermittent fasting may do a couple of

00:18:45.740 things. With a particular type of tumor, it may actually produce a small regression. Or, and what's

00:18:54.420 been shown way more often, is that when treating cancer, whether it's radiation or chemotherapy,

00:19:01.860 the animals can tolerate a higher dose without side effects, which in many cases is really useful,

00:19:08.560 right? Because the higher dose may be required to shrink the tumor mass. So we see, again, it's

00:19:14.040 subtle things like that. Now, what ends up happening? Well, what ends up happening is people go on the

00:19:17.840 internet and say, hey, look, intermittent fasting cures cancer. And no, but I mean, there's all this

00:19:24.220 intriguing data. Now, the fun thing is when I wrote our original book, you know, experiments with

00:19:29.800 intermittent fasting, which I think is what got us on your radar to do the article on your site.

00:19:36.880 We, you know, I said in the next five to seven years, the researcher really hit its stride and

00:19:42.460 will really figure out what intermittent fasting is doing. Well, as you reminded me in a scary way,

00:19:49.260 like it was five years ago since I wrote that, I wrote the book and we did the article on your site.

00:19:54.220 And, uh, the research hasn't yet hit its stride. We don't know a lot more now than we did then.

00:20:01.400 So, I mean, again, in the book, we sort of review some of the research, but there's, there's a little

00:20:06.220 data to suggest favorable improvements in certain blood markers and, you know, some of these cancer

00:20:12.400 outcomes that we saw. But the notion that intermittent fasting is a sort of this panacea or a cure-all is,

00:20:17.960 it's very false. Um, and you know, as much as it benefited me, you know, and you saw the results

00:20:25.060 of my experiments and stuff, I don't actually do it anymore. There's a whole group of people that we

00:20:30.860 coach that we actively dissuade from trying it until a certain point in their own sort of health

00:20:36.980 and fitness journey. And in women, we're very, very careful because a whole host of things,

00:20:42.020 how intermittent fasting may affect a female body differently than a male body. So I think with

00:20:47.440 everything else, there, there needs to be some nuance and there needs to be some understanding

00:20:52.440 of these sort of conditional if then statements. If you want to try intermittent fasting and you're a

00:20:58.260 woman, then something. If you're, uh, if you want to try intermittent fasting and you're a man,

00:21:04.280 then it may be something different. If you want to try intermittent fasting and you're a man

00:21:08.260 who is young and single with a robust and flexible metabolism, it may be one thing. If you want to

00:21:14.820 try intermittent fasting and you're a man who is middle-aged, who doesn't exercise, who doesn't

00:21:20.540 have a flexible metabolism and has a stressful life, it may be something totally different.

00:21:26.100 And I think, and that's how I think through things. It's, it's really sort of a conditional type

00:21:30.100 of way. If this and this, then what? And the then is different. It's not, if you want to try

00:21:35.740 intermittent fasting, try it because it's good because that is a false statement.

00:21:40.340 Right. So there's a lot to break down there and we will, I want to get to some of those things,

00:21:43.320 especially how intermittent fasting affects men and women differently. But talking about these,

00:21:48.060 going back to these blood markers, uh, you know, one of the benefits is it's supposed to help regulate

00:21:52.200 insulin, uh, regulate blood sugar. I mean, what's the research say about that? What effect does it

00:21:58.240 have on other hormones like testosterone? I think you've written about that. Can you dig a little deeper

00:22:03.940 into that? Yeah, that was part of my, as you recall, my sort of experimentation, you know,

00:22:09.040 it wasn't just how do I feel in, in, in body comp, you know, again, I, I spent a ridiculously long time

00:22:15.320 in university, uh, learning to be a scientist. So, you know, we did photos and we did measures and we

00:22:21.760 did strength measures and all that, but we also did a whole host of, you know, body composition or

00:22:26.220 sorry, blood work analyses. And we even did psychological and psychometric profiles. Cause I want to see,

00:22:31.420 you know, a lot of people talked about intermittent fasting being very good for attention and

00:22:36.760 psychological focus. And, and what I found was it was for a very specific type of task, but for other

00:22:43.480 tasks, it made it worse, right? So again, that's where their subtlety and nuance comes in. Not all

00:22:48.380 attention is the same, but back to your question, you know, the, the notion that something like

00:22:54.640 intermittent fasting could help regulate blood sugar, it has a, has a solid basis. You know,

00:22:59.900 the idea being that if you aren't feeding yourself regularly, you know, external food, breakfast,

00:23:06.700 lunch, dinner, whatever, and you're going periods of time without feeding yourself food, your body has

00:23:12.780 to upregulate receptors, which are these little sort of docking stations on every cell that receive the

00:23:19.680 chemical message of a hormone, for example, to tell the cell what to do. It upregulates some of those,

00:23:26.240 it upregulates the production of certain hormones. So, you know, most people have heard of adrenaline

00:23:32.820 or epinephrine and norepinephrine. Well, when, when we do an extended fast, epinephrine and norepinephrine

00:23:39.740 are upregulated. These are what are often called our fight or flight hormones. But what they also do

00:23:45.460 is help to release body fat stored carbohydrates from their storage depots so that they can actually

00:23:52.660 make, you know, circulating nutrients and also fuel cells. So, one of the ways that intermittent fasting

00:23:59.380 may help with regulation of blood sugar is that you're obviously not taking an external sugar. So,

00:24:06.140 your body finds a way, it trains itself, it becomes metabolically flexible to release only the amount of

00:24:11.460 energy from storage that's required at any point in time and no additional, which means that it finds

00:24:17.920 a way to regulate its own stuff pretty well in most cases. Now, this takes time. And again, it's not a

00:24:23.920 panacea. Generally, when people start intermittent fasting and they're not very metabolically flexible,

00:24:29.800 the first two weeks are a disaster. They're hungry and they're irritable. Their ghrelin hasn't adapted yet.

00:24:35.700 So, like, I can't skip breakfast. I'm just a breakfast person. Well, that's not true. It just

00:24:41.160 takes two weeks for you to realize whether you are or not. And generally, people aren't breakfast or not

00:24:47.240 breakfast people. They can be trained to be either. Likewise, your ability to become more metabolically

00:24:53.100 flexible doesn't change with one or two days. It takes a period of time. So, you know, again,

00:24:59.280 regulating insulin. Yeah, it actually does a pretty good job of that. Although, some of the markers of

00:25:04.960 insulin in my own work, my own experiments didn't markedly change because I was already kind of

00:25:10.520 healthy. So, again, the if-then statements come up, right? If you're already healthy and you switch

00:25:16.120 to intermittent fasting, you may see no changes in blood markers at all. If you are overweight and

00:25:21.440 your blood markers are a mess, any intervention would probably improve that. Intermittent fasting

00:25:26.580 is one of the ones that could. Testosterone and anabolic hormones. Well, they, you know,

00:25:31.960 there's mixed data on those. So, again, it depends on the person and it's another set of if-then

00:25:37.140 statements. But, you know, in some cases, you'll see the anabolic hormones, the muscle building

00:25:42.900 hormones go down. Testosterone, free testosterone, insulin-like growth factor, growth hormone. Some of

00:25:49.980 these things may chronically go down but acutely increase. Like growth hormone, for example, goes up

00:25:55.660 pretty markedly during a fast. But chronically, in other words, measured when those sort of daily

00:26:02.640 increases and decreases are balanced out over time, there may be no effect to total growth hormone

00:26:08.340 load. Although testosterone and IGF-1 might go down. Cortisol, which is a catabolic hormone,

00:26:15.340 tends to go up. So, really, you know, if you're not a physiologist or, you know, have expertise in

00:26:22.060 endocrinology, it's fine. Generally, the hormones can be lumped into catabolic and anabolic hormones.

00:26:27.860 And the catabolic ones are things like epinephrine, norepinephrine, and cortisol. The anabolic ones

00:26:32.260 are like IGF-1 and testosterone. With intermittent fasting, generally, the catabolic hormones or the

00:26:38.220 breakdown hormones go up, which is what you want if you want to lose fat to some extent. And the

00:26:45.300 anabolic ones go down. Now, it's not the same for everyone. And again, there's subtlety and nuance here,

00:26:50.120 but that's what you can expect, both logically and physiologically. In other words, when you look

00:26:54.420 in the research.

00:26:55.600 Okay. Let's go back. So, I have a question. This is a personal one. Maybe it'll help other people

00:27:00.000 figure something out too. Whenever I do intermittent fasting, I always think, well, I haven't had any

00:27:04.580 food. So, like my blood, like carbohydrate especially, my blood sugar should be like below 100,

00:27:12.280 right?

00:27:12.900 Right.

00:27:13.100 But like whenever I fast, like it's always above 100. It'd be like 110, 111.

00:27:18.980 Like what is-

00:27:19.440 And you just use a glucometer regularly to monitor that?

00:27:22.340 Yeah. Yeah. So, I just use the diabetes.

00:27:24.140 Well, it's pretty hardcore, isn't it? Like how'd you get into doing that?

00:27:27.360 Well, it's not a glucometer. It's just like the diabetes test thing, right?

00:27:30.980 Yeah, yeah.

00:27:31.600 I don't know. I was interested in it. And so, I decided to buy one.

00:27:35.440 And because I was, well, there was a time when I was trying to do ketosis and I was doing the keto

00:27:41.660 strips and then I was also just wanting to check my blood sugar on it as well. And yeah, so I started

00:27:47.620 testing, but I've just, I've done that experiment on myself. Whenever I intermittent fast or even go

00:27:51.260 low carb or no carb, my blood sugar spikes, which you think is like so counterintuitive to me. It's

00:27:56.480 like, well, I haven't had carbohydrates, so it shouldn't spike.

00:27:59.680 I know. This is the amazing beauty of the human body and physiology, right? Like we think we're

00:28:07.740 being so clever to outsmart our fat cells and our endocrinology, but there's so many redundant

00:28:13.720 systems to prevent us from doing anything too stupid. You know, for example, blood, regulated

00:28:19.760 balanced blood sugar is absolutely essential to life, regardless of what keto people will tell you

00:28:24.620 or whatever. And they tell you, oh yeah, blood glucose or glucose isn't the best source of

00:28:29.660 fuel. It's ketone bodies and the brain likes those best and blah, blah, blah. But that's very

00:28:36.340 debatable. In other words, just look at what you're talking about there. You don't eat any

00:28:42.380 carbohydrates and your body finds a way to create enough blood glucose to keep glucose stable and

00:28:48.900 keep you alive. Thank you, body. No, we can't outsmart you. So in this case, it's a perfect example

00:28:57.580 of those catabolic hormones in action. What you're talking about here, you know, you are eating low to

00:29:03.120 no carbohydrates or you're fasting. So like literally no food is coming in externally, but

00:29:09.500 somehow your body is producing glucose from your liver. Well, I mean that or other sources that is a

00:29:16.960 product of what we talked about. Epinephrine goes up, norepinephrine goes up, cortisol goes up,

00:29:22.180 the catabolic hormones. Their function is to release stored energy. So your stored energy is

00:29:27.680 being released and bam, goes into your bloodstream and it goes to the cells as required. So it's,

00:29:32.620 it's really, really, you know, a known physiological thing. Again, without like a ton of biology or

00:29:39.760 endocrinology training, it seems super weird. Incidentally, this is also the reason why people

00:29:45.400 often say, let's say with intermittent fasting, well, I feel more energetic. I feel like I have more

00:29:52.000 energy and sometimes focus. Well, the reason is that's what epinephrine does, right? Imagine the

00:30:00.380 fight or flight scenario kicking in. What is supposed to happen if you're being chased by a bear or

00:30:05.860 startled or scared? You're supposed to get super hyper-focused and energetic to get away from the

00:30:12.000 threat. That is why it has nothing to do with carbohydrates and insulin, blah, blah, blah. It has

00:30:17.940 everything to do with the release of epinephrine, the fight or flight hormone that is released when

00:30:23.660 you do an extended fast or when you don't feed your body any carbohydrates and are in an energy

00:30:29.800 deficit. It's the exact thing that's keeping you alive or providing energy or helping you eat the

00:30:36.380 meals that are on you. That's making you feel this particular kind of energy and also increasing your

00:30:42.340 blood sugar. Okay. So let's go back to the body composition. So you were able to lose a lot of body

00:30:47.420 fat using intermittent fasting. What is it about intermittent fasting that allowed you to do that?

00:30:52.920 Is it a combination? Is there something special about intermittent fasting or is it in the end just

00:30:57.860 sort of when you intermittent fast, you end up eating fewer calories than you usually do?

00:31:02.680 Yeah. I mean, that's a great debate that I don't think is resolved, but it may not matter really.

00:31:07.680 The truth is when you do intermittent fasting, you generally will eat fewer calories.

00:31:12.200 The other thing, not just because you are not eating one meal a day or, you know, if you're fasting

00:31:19.340 one day a week, an entire day of no eating, but also because generally people don't make decisions like

00:31:26.620 this in a vacuum. They don't make it a science experiment. They're not like, oh, you know what I'm

00:31:31.280 going to do? I'm going to try intermittent fasting, but I'm going to actually figure out how many calories

00:31:36.160 I was eating on average before intermittent fasting and then exactly match the number of calories

00:31:41.380 while intermittent fasting as I was before intermittent fasting to see if it's the fasting

00:31:46.760 or the caloric load. And I'm going to keep caloric load constant, right? No one's doing that.

00:31:51.600 When you decide to try a health intervention, it makes a whole bunch of other decisions for you too.

00:31:57.760 You start doing intermittent fasting and also you start being more mindful about your food and you

00:32:02.180 start making better food choices. And that generally leads to a lower caloric intake. So it's not only

00:32:07.780 the actual effect of skipping a meal or a whole day of meals, it's the knock-on effect of making a whole

00:32:13.620 bunch of other changes because you're now mindful of this and you've made it a project in your life.

00:32:18.500 So, I mean, that's generally what's happening. People are eating fewer calories than they otherwise

00:32:23.320 would have. Now, is there some other magic physiology at place? Like, is it that growth hormone spike or

00:32:29.620 that epinephrine, norepinephrine? Maybe. That may be part of it. Or it may be 50-50 or maybe 75-25.

00:32:37.200 We don't know. Research, I don't know if it will ever resolve this, like ever, ever. You know,

00:32:42.320 it may take 2,000 years. But again, it probably doesn't matter. My gut feeling, you know, as a

00:32:49.000 scientist and as someone who's practiced this and tried it in a lot of people, is that it's a

00:32:53.580 combination. You know, one, you tend to eat less because you're not eating certain windows. Two,

00:33:00.040 you tend to eat better choices, which means fewer calories because you're choosing better things.

00:33:06.420 Three, there's some hormonal and physiological things happening that are slightly different.

00:33:11.900 So it's probably a combination of the three. But if I were to say the biggest factor,

00:33:17.760 it's probably the energy deficit and the mindfulness to your health and your nutrition

00:33:22.940 that makes the biggest impact. Okay. And another question, when I've done intermittent fasting

00:33:29.600 is I'll see results pretty quickly, but then eventually I don't see them anymore. So are the

00:33:38.020 effects of intermittent fasting acute or chronic? Yeah, I mean, it's really interesting. I think it's

00:33:43.900 highly individual, you know, very much like whether a low carb diet or a moderate carb diet is better

00:33:49.120 also has a lot to do with how you exercise and what your training looks like. You know, it's really

00:33:55.380 interesting because the co-founder of Precision Nutrition, the guy who started the company with me,

00:33:59.680 I had been doing intermittent fasting for a while for this experiment and for my own body change.

00:34:04.200 And it was going really, really well. I mean, I lost about 20 pounds over, you know, 16 weeks.

00:34:10.580 I tried a whole bunch of different protocols. I felt like I plateaued towards the end simply because

00:34:17.760 I got too lean. Like if anyone's interested, you can go look at the pictures. I mean, you know, I did a

00:34:25.960 ultrasound type body fat testing technology. So it may not be perfect, but it's pretty good. And it was

00:34:32.200 reading me at like 4% body fat. So I didn't have a lot more to lose. And generally when you tend to get

00:34:38.820 that lean, a whole bunch of mechanisms kick in to keep you alive. They're like, hey, dummy,

00:34:43.900 we're getting in the danger zone. So appetite gets dramatically upregulated. A whole bunch of

00:34:50.740 neurotransmitters and hormones are released to make you less active. So even though I could show up at

00:34:56.760 the gym the same number of days a week or at the track in between workouts, my body is like, hey,

00:35:03.140 you should stay on this couch a little bit longer, you know? So the activities of daily life go down

00:35:09.780 and we see it over and over and over again in research. When your energy balance gets too negative

00:35:14.280 or you get too lean, your body finds a way to slow you down and conserve energy. And you can be like,

00:35:20.560 no, no, but I'm still working out the same. That's not what I'm talking about here. Your workouts

00:35:25.100 generally only account for about 30% of your metabolic rate each day. The other 70 is your activities of

00:35:30.700 daily life and your body finds a way to slow you down. It finds a way to consume or, sorry,

00:35:36.160 expend less energy. So for me, that's where the plateau happened. It happened at the absolute edge

00:35:42.040 of leanness. My business partner, Phil, though, right around the time I was at my leanest, you know,

00:35:47.360 we were away together. He was getting ready to get married. So we were away in Italy for his bachelor

00:35:52.640 party, his bachelor trip. And he was like, holy crap, dude, I've never seen you in this good of shape.

00:35:58.180 Like what's, what's going on. So I told him about it and he's like, cool, I'm going to try that for

00:36:01.680 my wedding. Right. So I remember, uh, you know, his wedding came up very shortly thereafter and he

00:36:08.240 got in great shape doing this. Just like you said, short period of time, he lost like 15 pounds,

00:36:13.100 looked great in his tux, whatever. And then literally like, I didn't see him for a few weeks

00:36:17.860 because he went on the honeymoon and we work in a virtual company. So we only see each other basically

00:36:22.180 from the neck up in virtual meetings. And then the next time I saw him was like a month later and he

00:36:26.360 had totally gained all the weight back. And I was like, Oh, you know, Hey, how's the intermittent

00:36:30.980 fasting going? And he's like, easy come easy go, buddy. Like the minute I stopped intermittent

00:36:36.560 fasting, it was like the weight just came right back on. And so, I mean, it just points out one of

00:36:42.460 the dangers of these sort of kind of what I consider a very quick fixy type of implementations of eating

00:36:49.320 plans, right? Where you're like, yeah, intermittent fasting will shred like 10 pounds really fast.

00:36:54.860 I mean, you just essentially cut out, you know, if you eat three meals a day, you cut out one third

00:37:00.000 of your intake, right? Yeah, of course. But will you sustain that for the rest of your life? If not,

00:37:06.660 by the day you decide to start eating breakfast again, without any sort of commensurate changes,

00:37:11.840 it's going to come right back just as quickly. So it's a really important thing to consider.

00:37:17.360 So let's talk about, you referred to something earlier that intermittent fasting is very

00:37:22.480 individual, right? There's a lot of if-then conditionals going on there. How does,

00:37:28.920 you mentioned men and women, there's a difference there. How do men and women respond

00:37:32.100 differently to intermittent fasting?

00:37:34.820 Yeah, I mean, you know, obviously different individuals are different sort of genetically,

00:37:40.680 lifestyle-wise, et cetera. But generally, when we look at all women's physiological and nutritional

00:37:45.900 exercise research, women are exquisitely sensitive to low carbohydrates and energy imbalances. So in

00:37:54.400 other words, when they get into a negative energy balance, so however it happens, they are burning

00:38:01.260 more calories than they ingest in a day. And whenever they go too low carb for too long, their whole

00:38:09.020 sensing mechanism, hypothalamus, pituitary, these glands that sit at the base of your brain, right,

00:38:15.700 which are sort of the master command centers for all hormones and physiological activity. They sense

00:38:20.220 what's happening, and then they send out messages to the rest of the cells to tell them what to do,

00:38:24.500 and those messages are hormones. They're exquisitely sensitive to energy imbalance and to low

00:38:30.280 carbohydrate intakes. Generally, I mean, you know, the physiological or evolutionary explanation

00:38:36.080 is to preserve body fat and reproductive health, right? Because men are very, they're of very little

00:38:45.360 importance to the reproductive equation. Women are fundamentally important because not only do they

00:38:51.640 have to have a healthy reproductive system to get pregnant, but they also have to have a healthy

00:38:57.040 hormonal system to sustain a pregnancy and deliver a healthy offspring into the world. So this is the

00:39:04.100 evolutionary explanation for why this happens. But it doesn't really matter. It just happens. When

00:39:10.920 women do too much intermittent fasting, they see all kinds of, you know, hypothalamic amenorrhea. So

00:39:18.920 they lose their menstrual cycling. And that's, you know, that's just that's the external symptom. But

00:39:25.300 what's really happening is a massive depression of reproductive hormones, a massive change in neurotransmitter

00:39:33.440 output. And for all kinds of problems down the line, everything from reduced bone mass to thyroid

00:39:39.900 hormone health to the ability to lose body fat or have a healthy balance of muscle to fat, all these

00:39:45.500 things go really haywire in women. And it happens much more easily than men. And it happens much more

00:39:51.900 readily when they do longer term low carb diets, and even intermittent fasting. Now there's loads of

00:39:59.020 women who may be listening to this, they post on our forums, and, and they send us emails all the time

00:40:04.580 or like, you're wrong, Dr. Barati, I've been doing this, and I'm fine. Right. And then, you know,

00:40:10.400 obviously, there's always going to be outliers, we hear from them. But also, we have to look at the

00:40:15.040 time course, I'm not saying it happens in a week, or even three weeks, or even three months. But over time,

00:40:21.740 this, this can happen. I've seen it happen over a year or two years. So people who are saying,

00:40:26.960 no, that's not true. That's not me. And I've done it, like I have personal experience,

00:40:30.720 they may not just be far along yet, or far enough along, to actually see the downstream consequences.

00:40:38.360 So that's the male female difference. You know, generally, I found that really fascinating,

00:40:42.880 fascinating when I was following the intermittent fasting conversation, because most of the very vocal

00:40:49.920 advocates of intermittent fasting on the internet, because you don't find a lot of them in the research

00:40:54.800 world or whatever, because it's not settled yet there. So you find them on the internet,

00:40:58.940 telling stories, writing articles, being on forums and on Facebook. Most of the most vocal advocates

00:41:05.920 are young, single dudes. Totally makes sense, right? They don't have female physiology. And young,

00:41:15.180 single dudes tend not to have partners and kids and demanding careers yet. And so generally,

00:41:23.560 their overall stress load is much lower. And that is a very good set of circumstances for

00:41:30.160 intermittent fasting, overall stress low, because intermittent fasting is itself a stressor. It's

00:41:35.580 probably one of the reasons it's beneficial, because it is a stressor, but thrown onto a very

00:41:40.680 stressful lifestyle. And this is one of the reasons why I stopped doing it. You know, I, my wife and I,

00:41:46.220 we have four children. Now, I have this company precision nutrition with 100 team members.

00:41:51.520 Yeah, intermittent fasting was just another stressor I did not need. And after a while,

00:41:56.720 it became very difficult to sustain. Like I said, it helped with a certain kind of concentration,

00:42:02.240 but made other things much worse, like interacting with my team and interacting with our children.

00:42:07.180 I find that when you're intermittent fasting, your focus on single solo, like writing tasks and things

00:42:13.900 like that is very good, single minded sort of tunnel vision kind of tasks. But if you have to collaborate,

00:42:21.640 solve problems with a team, I don't parent, teach patiently your children, really, really difficult.

00:42:30.060 So, you know, again, there's a couple of the if thens, you know, if you're a woman, you have to be

00:42:34.880 really careful with this, probably don't do it on your own. If you're going to do it, have a coach,

00:42:39.160 coach, and make sure that coach knows what they're doing. And make sure that you guys have an escape

00:42:43.220 plan, like a safe word for when it's time to stop the intermittent fasting because things are going

00:42:48.700 wrong. If you're a man, consider your other lifestyle stressors and what's important in your life.

00:42:54.100 Young single dude, yeah, give it a try. You're probably going to be fine. Middle aged dude with a

00:42:58.940 lot of work and family responsibilities. This may not be so good for you, you know, because the reasons I

00:43:06.580 said. So those are some of the conditionals. Gotcha. Well, let's go. Let's add another

00:43:10.460 conditional. All right. So if you're young, single, go to go. If you're middle aged, got family kids,

00:43:16.420 stressful job, maybe not. But what about the type of training you do? Does intermittent fasting work

00:43:23.060 better for different types of training? So like, let's I know intermittent fasting is really popular

00:43:26.740 amongst long distance runners, particularly the low carb stuff. They're all about, okay, you're aerobic,

00:43:32.580 you want to burn fat instead of carbs and intermittent fasting as a tool for that. Is there any credence

00:43:38.040 to that idea? You know, I think this is one of the most heated debates because the entire history

00:43:43.340 of sport nutrition is really founded on endurance exercise. You know, I mean, the field, I often joke,

00:43:49.360 the field of sports science was founded when there was like a little extra space in a real physiology lab

00:43:56.160 and someone stuck a treadmill in it. And they're like, we can do muscle biopsies and measure glycogen

00:44:00.900 and people can run on that thing until they get exhausted. That's actually, and that was like the

00:44:05.820 first 20 years of sports science and sports nutrition in particular, measure the amount of

00:44:11.680 glycogen in a muscle by chopping a chunk of muscle out, do it in runners who can run on that treadmill

00:44:17.380 because treadmill doesn't take up a lot of space in the lab. And so, but the history of sports

00:44:23.140 nutrition and actually bears out that, well, I don't know, this whole modern idea of athletes doing

00:44:29.780 best on low carb diets. Well, you're just hearing the outliers. You know, now I'm not saying it's

00:44:35.740 false. What I'm saying is there's nuance here too. For example, if you are the type of person who

00:44:41.080 could train on a lower carb diet to get a whole host of physiological adaptations that are beneficial,

00:44:49.240 but then leading up to an event can load your glycogen high. You're probably in the minority,

00:44:55.700 but it's a cool minority to be in because you might see some interesting benefits, but not everyone's

00:45:00.820 in that group. So yeah, I think we have to be really careful. There's a lot of loud voices on

00:45:05.540 the internet that take up too much of the mindshare around this. Most of the elite endurance athletes

00:45:11.280 do not follow low carbohydrate diets. But with that said, we'll get to the broader point you're

00:45:16.800 trying to make, which is exercise. Does exercise influence this? And the answer is yes. I mean,

00:45:21.220 there's obviously people who don't exercise at all. And the question is, is intermittent fasting for

00:45:25.240 them? I think the answer is whether they exercise, if they don't exercise, there's another criterion

00:45:32.840 that's more important, which is how much nutritional experience do they have? You know, when we coach

00:45:39.000 people, and again, there's a lot of them in every year and we see all different levels, you know,

00:45:42.400 we work with 20 different professional sports teams right now, all the way down to non-exercisers who

00:45:48.620 are interested in just losing weight, you know, maybe three, 400 pounds. And so for people without

00:45:53.740 much nutritional experience, we never, never start them at intermittent fasting. It's probably a recipe

00:45:59.660 for a whole host of weird food beliefs, and possibly even disordered eating. Sometimes you just need

00:46:07.620 reps or practice and making healthy eating choices at breakfast, lunch and dinner. So that's where we begin.

00:46:14.240 So if someone is not really mindful about what they eat, the first thing is get mindful about what you

00:46:19.800 eat, and practice just like if you're learning to play the guitar or language, you got to put in reps

00:46:24.280 every day, or else you never get good at it. So it's breakfast, lunch and dinner, let's get the reps

00:46:30.500 rather than let's just chop out a whole meal and teach you a whole different skill set that probably

00:46:35.440 isn't that beneficial to you in the long term. So if someone does an exercise, we rarely ever start them

00:46:40.480 at intermittent fasting, unless they have a lot of nutrition experience, and they make good food

00:46:46.300 choices already, then it's an option. But there's probably 10 others we could go with. If someone

00:46:51.900 does exercise, it depends on the volume and intensity. Elite athletes probably shouldn't do

00:46:58.000 intermittent fasting as a regular practice throughout the entire training year, they could do it during

00:47:04.400 low volume periods of training, when body composition is really important, like they have to lose body fat.

00:47:10.480 But as a way to enhance performance, I would say like 9.5 times out of 10, no, it won't enhance

00:47:16.800 performance. The only reason I would ever give it to an elite athlete is if they have body composition

00:47:22.460 management to do. And I would never do it during their heavy training periods of the year, because

00:47:28.180 just more stress on top of more stress plus heavy training periods are for physiological adaptation to

00:47:34.380 make you either stronger, faster or have a better aerobic system. And this isn't going to support that.

00:47:39.420 So that's, that's kind of how I break it down. So now we've done the two ends of the spectrum, we've done

00:47:44.500 dozen exercise, and elite athlete. Now let's go into the middle, someone who goes to gym three, four times a

00:47:50.140 week does strength training, you know, like you and I were talking, if you get really into barbell training

00:47:54.620 or something like that, the way that I think there's a particular type of intermittent fasting that may be

00:48:00.160 effective for that if you want to try it. And that's the 16 eight style, where on your non training days,

00:48:06.540 when you do actually eat, you just eat, you know, protein, vegetables, you know, very moderate or even low

00:48:13.740 carbohydrate. And then on your training days, after you train, very high carbohydrate, that I found to be very, very

00:48:21.140 effective if someone is going to do this, again, recreational exerciser, on training days, a lot of calories

00:48:28.280 during your eating window, and a lot of carbs, and on your non training days, keep the carbs really low

00:48:33.880 and moderate your calories. That I think could be very effective, because generally recreational

00:48:38.660 exercisers want to see some performance benefits. But generally, it's about this fine balance between,

00:48:46.400 you know, doing well in the gym and getting a little bit better and also looking good naked,

00:48:50.840 right. And that's what intermittent fasting can actually help with quite a bit looking good naked.

00:48:55.780 Again, though, there's a whole bunch of other ways to look good naked, you know, through more mindful

00:49:01.300 choices through very specific manipulations and macronutrients and calories. So it's one choice.

00:49:07.820 So, you know, start to see I'm very sort of system based thinker. So a flow chart kind of comes out of

00:49:15.120 this, you're like, if doesn't exercise, no nutrition experience, probably not intermittent fasting,

00:49:20.960 if doesn't exercise some nutrition experience, maybe intermittent fasting, if elite athlete,

00:49:27.200 no, under all conditions, except has to lose body fat, and in a low volume training period,

00:49:33.460 if recreational exerciser wants to look good naked and, and have small increases in strength over time.

00:49:40.860 Yes, it's one of a few options for doing that.

00:49:43.420 Right. I love that. Yeah, I used to intermittent fast regularly, a few years ago. And this was I was I

00:49:52.560 had an eating window from 12pm until 7pm. But then I, I stopped because I got really into barbell

00:49:59.920 training. And I just noticed that my progress, I just I plateaued. And I tried changing the

00:50:07.880 programming that didn't do anything. So I was like, Okay, it's the diet. And I was also doing low carb,

00:50:13.060 at the time, which I found come to find out that's not good if you want to get stronger. Because

00:50:20.020 strength and it's like a very intense is very anaerobic. So you need carbohydrates. And I also

00:50:24.560 I did, I got my, my genetic, did my genetic testing. And what I found out was, I actually do better on a

00:50:32.900 lower fat, higher carbohydrate diet.

00:50:37.740 That's right.

00:50:38.340 That's another kind of conditional put in there. Like, everyone, these, these guys that, you know,

00:50:43.620 you know, that really promote high fat, low carb, you know, intermittent fasting, like,

00:50:49.480 it probably works for them, because their body is geared towards that. And so they, they sort of

00:50:56.620 universalize that and generalize and say, This is for everybody. That might not be the case.

00:51:00.240 Yeah, it's, it's true. And you know, there's also this other factor, we often say it's, it's what

00:51:06.560 works for you, for now, under the conditions that your life is in now, right? Because the notion that

00:51:14.260 somehow, as a young person, like we talked about, let's say young dude with few stressors and

00:51:20.740 responsibilities, that a particular diet that works for you now will be the same diet that works for you

00:51:25.640 in 30 years. If you get married, have children have a aggressive career, we have to take into

00:51:32.260 account that that may be false. So there's, there is the genetics, there's the lifestyle piece, and it

00:51:37.640 all plays together. And usually the most vocal proponents are people pretty new in their journey,

00:51:42.460 right? I mean, this isn't just with nutrition, it's with every other evangelism there is, right?

00:51:47.540 You're like, I found this thing. It's amazing. I'm feeling good on it, whatever it is, belief in a

00:51:53.440 particular theory, religion or a nutrition system. And it's people very early in their journey,

00:51:59.780 who are the loudest about it. And they seem so convincing, right? But you know, the that ignores

00:52:06.000 the for now, it worked for you. For now, it may not work for you for later. We did a great piece on a

00:52:14.500 physician, who's a good friend of mine, who was a big low carb advocate for years. And we called it

00:52:21.520 carb confessions, you know, it's the story of a low carb convert. So for years, he's a big proponent

00:52:27.040 of low carb eating. And then someone convinced him to do a little experiment. Very much like you is

00:52:33.020 very into strength training. And he just added some carbs and like, all these things improved his

00:52:39.020 blood work is strength, all this. And he was just like, it was a very difficult realization for him.

00:52:45.020 Because he was like, wow, like, how could I have been so locked into this one way of thinking for

00:52:51.260 so long? And it's very easy to explain. But it's very difficult when you're living it, right? So

00:52:57.120 so so that's really it. You know, our whole philosophy at precision nutrition is being

00:53:02.180 nutritionally agnostic. In other words, being open to every and all nutritional possibilities

00:53:08.800 that could help a person at a different stage in their lives. So there's, there's a particular kind

00:53:14.980 of person who over the course of their life might need to do a paleo style diet for a while and a low

00:53:20.160 carb for a while and an intermittent fasting for a while and then a high carb for a while and then

00:53:23.900 maybe a vegan diet for a while. And all those possibilities are okay. You know, it's our belief

00:53:29.840 that there are principles that live like at a higher level than the macronutrient split of a diet.

00:53:37.200 You know, because you and I both know vegans who are very healthy, lift weights, strong,

00:53:43.560 have a great blood profile, and also people who eat lots of meat and very little vegetables

00:53:47.880 in the same exact situation, healthy, strong, lean, whatever. So neither of those camps can be

00:53:56.700 totally right. If vegans are like how the meat eaters are unhealthy and what fat whatever,

00:54:02.060 and the paleo people say the same about vegans, the evidence of just experience has to tell you

00:54:09.020 that's not true. There are people who are healthy in both camps. So it must not be the macronutrient

00:54:16.820 breakdown or the absence or presence of meat that is the differentiator. Both camps must share something

00:54:22.660 in common that transcends what they're fighting over, that helps them both be healthy, lean,

00:54:28.600 and strong. And that's what we set out to find and help people achieve in whatever way fits into

00:54:33.940 their lives. And I think that's really a key take-home message for the nutrition dialogue

00:54:38.960 nowadays. I love that. Yeah. People can get very ideological when it comes to food. My wife and I

00:54:43.940 joke like food's the new religion. Totally. Like people are less religious, but like we are religious

00:54:48.600 about our food or our workouts. And that analogy extends. Like you could come up with 50 different

00:54:55.220 examples of that. I believe it. It's true. It is treated very much that way. And people organize

00:55:01.320 into tribes and they fight over belief systems. And, you know, the prevailing pressure is to come up

00:55:08.580 with one true, you know, nutrition belief, one true God, whatever it is. Right. So, yeah, I very much

00:55:17.680 agree. It's become that way, at least in the subcultures that think a lot about this.

00:55:21.820 Yeah. So, we've been talking a lot about the nuanced benefits of fasting and the downsides of

00:55:29.340 fasting, because there are some. We haven't talked about like just fasting protocols. You mentioned

00:55:33.280 one, which was, I think it was 16-8 is what you said. So, it's 16 hours of fasting, eight hours

00:55:39.940 feeding window. So, what would that look like for somebody like in a typical day?

00:55:44.220 Yeah. I mean, the ones that I tried in my experimentation that we logged and recorded,

00:55:49.140 one was just a once a week fast where every Sunday, I just wouldn't eat any food. So,

00:55:55.440 I'd eat my last meal Saturday evening around 10 p.m. And then I would either fast until Monday

00:56:01.640 morning. So, it was kind of like a day and a half, or I would have a meal at 10 p.m. on Sunday. So,

00:56:06.900 it's just 24 hours without eating. I know some listeners are probably shuddering to think about

00:56:11.420 that. Like, oh my God, won't you die? And the answer is no. You know, the first few times,

00:56:17.120 it is very challenging though. You know, I'll give you that because of a whole host of

00:56:21.040 expectations our body has about feeding. But that's what I started with. And for people who

00:56:26.860 are interested in, let's say, the health benefits of fasting, it's the one I actually recommend they

00:56:31.940 start with because it's very controlled. Like, if you do the 16-8 thing, which we'll talk about in a

00:56:37.240 second, you have to commit to kind of doing it often, right? This, you only have to commit to it,

00:56:42.480 let's say, once a month or once every three months. Or, you know, I eventually got to once

00:56:46.520 a week. But that was one of the protocols. The most researched protocol, and I think this is the

00:56:53.280 worst idea for active people, is called every other day fasting. So, literally, you will only eat every

00:56:59.600 other day. This is the one that's been shown to have the most, let's say, longevity benefits,

00:57:05.340 possible health benefits. But I think this, that's a function of very much like calorie restriction,

00:57:13.420 just radically reducing your calorie intake. And that's okay if you're inactive. I'm not sure it's

00:57:18.940 the best way to get healthy. But if you're active, it's a nightmare. It's terrible for performance in

00:57:23.760 the long run. I also think there's a social downside too, right? Because like, most of our

00:57:29.660 socializing revolves around food. Absolutely, right? I mean, there was a point, you know,

00:57:34.440 when I did my experiments, we had only two of our four children, where like, I was literally not

00:57:42.160 eating meals with my family. You know what I mean? It's, well, daddy's going a different plan,

00:57:47.400 you know? And I mean, that was just with my family. And then, like, when you talk about outside the

00:57:52.860 house social experiences, yeah, I mean, I might as well wore a t-shirt that said, like, I have weird

00:57:59.900 nutrition beliefs, you know what I mean? And yeah, so there is a social downside. You know,

00:58:05.860 the 16-8 protocol, you know, is generally, it can be constructed in a host of different ways.

00:58:13.180 But the way most people talk about it is, like you did, from about noon till 7 or 8 p.m. is your

00:58:18.500 eating window. And then the rest of the time, you just don't eat. And functionally, what that looks

00:58:23.360 like is you have lunch and dinner. And now for really performance or, let's say, strength training

00:58:28.780 oriented people, what they would try to do is have a strength training session at the end of their

00:58:35.280 fast, right? So do that at like 11 or 11.30 or 12. So if, like, let's say I work from home,

00:58:42.120 so I have the luxury of working out when I want. But if you don't, you might work out over your lunch

00:58:46.540 break. And then you have a big lunch, and then you have a dinner, and then you just don't eat again

00:58:53.500 until the next day after your workout. And so it's pretty straightforward. And, you know,

00:58:58.580 the idea is to be still mindful about your choices, eat lots of veggies, eat, you know,

00:59:04.100 a required amount of protein. You know, again, if like, I don't believe that the average strength

00:59:11.200 trainer who isn't over fat should be on a low carb diet all the time. So you get loads of carbs in

00:59:18.080 after strength training on those days. And then maybe, like I said, on the non strength training

00:59:22.820 days, you cut the carbs back a little not to zero, but a little bit, you know, that that pretty

00:59:28.480 effectively is the protocol. So it's a little bit of intermittent fasting and a little bit of

00:59:32.520 carbohydrate cycling and a little bit of meal timing. So this one is sort of has a little bit

00:59:37.700 more complexity to it. And it's the one I saw the best results with, personally. But again, I mean,

00:59:44.460 I'm not doing it anymore. So there's, there's a certain testimony to that there. You know,

00:59:49.920 I often say when people ask me for nutritional supplement advice, which supplements should I take?

00:59:55.480 One of the first things you want to know is, you know, what does the person that you're asking

00:59:59.500 take? Your goals may be different, your physiology may be different. But you want to know at least that

01:00:06.000 the person that you're asking for advice eats their own dog food to begin with, you know. And so I

01:00:11.160 thought intermittent fasting was cool. It was a cool thing to experiment with, but I didn't want

01:00:15.040 to do it in the long run. Because there were other options for eating well and being healthy and being

01:00:19.860 fit that didn't involve, you know, skipping meals every day, having this long period of time without

01:00:26.120 meals. And also the side effects of that, which for me was I would become sort of pretty irritable

01:00:32.420 towards the end of the fast. I wasn't able to share meals with my family regularly. So some of the

01:00:37.660 costs were too great. But generally those are the three big ones, you know, the maybe once a week

01:00:42.820 or once a month do a fast. And that one is very easy to discount. Like, oh yeah, you just skip meals

01:00:49.560 on a Sunday once a month. What could that possibly do? But there's some data suggesting that it could

01:00:54.380 actually help improve metabolic flexibility pretty effectively. Just that one fast, you know,

01:00:59.860 training your body one time a month to eat its own meals may actually last for the whole month until

01:01:06.860 the next one. So I wouldn't discount that one. Then there's doing that a bit more regularly.

01:01:11.660 I also tried fasting like two times a week versus every other day or just once. And that really put

01:01:17.100 a dent in my performance. Then again, there's a 16-8 and some people even take it further. There's a,

01:01:22.640 there's a protocol. Some people have called the warrior diet, which is a bit more nuanced,

01:01:26.520 but generally it's one meal a day. So you just have one big meal to account for all of your calorie

01:01:31.680 needs. And then the rest of your day is a fast. Some people swear by it. I think it's probably

01:01:37.780 too difficult to get enough nutrition in that one meal if you're highly active. But again, these are,

01:01:43.600 these are the protocols that at least have a lot of attention right now. And there's probably not

01:01:48.420 too much else. I mean, we're, we're just talking about a particular theme here. Do you eat one meal

01:01:53.820 a day, two meals a day, or three meals a day? The longer you extend the fast, the more of the fasting

01:01:59.880 benefits you might get. Although there eventually comes a bit of a trade-off with being able to get

01:02:06.020 enough energy and actually feeling good about your life and your day. Yeah. I mean, is there a timeframe

01:02:10.340 like you have to hit this timeframe if you want to get the benefits of a fast, like, could you fast for

01:02:14.440 eight hours and get benefits or do you have to like, you know, it's like, is there a minimum effective

01:02:18.560 dose is what I'm asking. Yeah. No, no one really knows. I mean, one, some people use the growth hormone

01:02:24.480 response as a marker, right? So growth hormone is a whole, is a hormone that's released in times of

01:02:31.460 a bit of a negative energy balance or even stress. So we'll sort of use this growth hormone sort of

01:02:36.300 cortisol kind of release as a marker. So they say, well, after eight hours, growth hormone and cortisol

01:02:41.820 are still kind of normal, you know, or at least within a physiologically normally expected range

01:02:47.060 at 12 hours, they start to jump at 16 hours. They're pretty high at 24 to 36 hours. They're like, it's like

01:02:56.720 you're actually doing performance enhancing drugs. So if you look at those markers, generally 12 to 16 hours

01:03:03.860 shows a good spike. So, I mean, you could use that as a surrogate. It's very crude, but yeah, I mean, you know,

01:03:11.900 for, if you want to get the benefits of fasting somewhere in the 12 to 16 hours, Mark is probably

01:03:18.260 good. I had a friend who did a kind of a different protocol. He would have only breakfast and dinners.

01:03:23.380 So every day he would get about two 12 hour fast, right? So he would get his overnight fast from 8pm

01:03:29.320 dinner to eight in the morning breakfast, and then the 12 hours from breakfast to dinner. And he seemed to

01:03:34.360 enjoy that and feel good. And it fit his lifestyle well, because he worked in a high stress workplace and

01:03:41.200 didn't like to stop for lunch. So he had a big breakfast and a big dinner and that was okay for

01:03:45.920 him. So I think it's really tempting to look for the magic formula, right? You're like, it has to be

01:03:52.080 a certain number of hours. It has to be this way. I mean, I get emails from people all the time. They're

01:03:56.440 like, I'm doing the fast and I have coffee in the morning. Does that break the fast? Well, no, there's no

01:04:01.940 calories in it. What if I put one teaspoon of almond milk in? Does that break the fast? You know,

01:04:09.040 they start to get at these weird kind of clarifications that probably are losing sight of

01:04:15.440 the forest for the trees. You know, it, no, you're not fasting if you have some calories during that

01:04:20.940 time, but have the benefits gone from high to zero? Absolutely not. Gotcha. Yeah. I mean, in my

01:04:27.480 experience, so I used to do the sort of the 8-16 thing. I no longer do that. I only fast,

01:04:33.660 I fast on Sundays. So I'll, you know, most Sundays I'll do a fast from Saturday night,

01:04:40.140 my dinner to 12 o'clock on Sunday. And then once a month I'll do like a full 24 hour fast.

01:04:46.120 And that's kind of my thing now. That's what I do. And during the rest of the week I eat,

01:04:49.780 you know, from breakfast until dinner. Yeah. And I still do that. The same that you're talking

01:04:54.220 about periodically. I do it randomly, but periodically. And for me, the one thing I found that's

01:04:59.380 interesting, and if you're interested in body comp and health and you'll be like, whatever,

01:05:02.720 or what is this guy talking about now? But the one thing that I found that's interesting about it is

01:05:07.800 while there may be a small physiological benefit in terms of retaining metabolic flexibility from

01:05:14.220 doing that every once in a while, I find some other things happen in my mind and personally for me.

01:05:21.560 One is it's kind of cool to not eat all day on that day. Like to not even think about my meals,

01:05:28.080 to have to cook meals for myself or clean up after myself. I still have to do it for my family. I'm not

01:05:32.140 fasting my three-year-old, you know, but that's kind of cool. Two is it's a little bit of a test

01:05:39.640 of my, I don't know, discipline and strength because at points during that day, as I suspect

01:05:44.520 you feel as well, you get hungry and it's very comfortable to just go have a snack, but to actually

01:05:50.980 sustain yourself during that uncomfortable feeling and not give into it feels like a test of my

01:05:58.720 discipline and strength. And I like to do that periodically. And then the third thing is it is a

01:06:03.860 very strong reminder for me, and this may not be important to other people, about what a privilege

01:06:09.040 food and eating is for me. You know, there are lots of people who are food insecure in our own countries,

01:06:18.720 you know, US and Canada and elsewhere around the world who don't have the choice whether they eat or

01:06:24.140 not, they don't get to make this decision. And so it kind of reminds me of that. And I, and I find

01:06:29.460 that helpful just as, as a human being. Yeah. I mean, those, that's why it's not so much for the

01:06:34.400 health, but if it's more of just an exercise and discipline and willpower. Yeah. I mean, it kind of

01:06:39.500 reminds me of the cold shower thing. I don't know. Have you ever gotten into doing that? No. Yeah. I do

01:06:43.860 cold showers regularly. Absolutely. It's that for me. And, and, and one of the guys who works at

01:06:49.380 Precision Nutrition is a good friend of mine, who's a former special operator in the Navy,

01:06:53.700 he and I've talked about this a lot. And where we've both concluded is, are there physiological

01:06:58.160 benefits? Maybe. Are they overstated? Absolutely. What's the biggest benefit I get out of doing it

01:07:05.680 once in a while? It's a practice of being comfortable with discomfort. People give business

01:07:14.400 advice all the time. You have to lean into your discomfort. If you're uncomfortable, you got to do it.

01:07:18.760 But how often, but that's just like people wagging their finger and proselytizing over how you should

01:07:24.060 live your life. Right. When do you get practice doing uncomfortable things? Well, there's, there's

01:07:30.080 psychologically uncomfortable things. There's, you know, work things related to that, but cold showers

01:07:36.020 are the most concrete example of that. Like it sucks to stand in freezing cold water. It's never stopped

01:07:43.060 sucking, you know, but if you can find a way to step into freezing cold water, not tense your body up to

01:07:52.400 breathe through it, to actually have an inner dialogue that says something like, this is what

01:07:57.680 cold water feels like. Not, I have to get out of this. This is an emergency. And it's one, and I bring

01:08:04.300 this up because it relates to one of the interesting things with intermittent fasting, obviously.

01:08:08.560 It's that hunger. And we started the call with this hunger is not an emergency generally,

01:08:14.960 right? It's just the thing you've trained yourself to think is an emergency. Very much like when you

01:08:20.700 jump into cold water, all of your instincts tell you jump out. This is horrible, but you can actually

01:08:26.960 change a narrative and say, this is, this isn't horrible. It's what cold water feels like. Oh, okay.

01:08:34.060 Well, if I can sustain this, I can probably do other challenging things in my life. So

01:08:38.640 I think both of these things actually speak to that in some way. And, and I think a lot of people try

01:08:44.260 and glorify the physiological benefits when a lot of the benefits actually come from this.

01:08:49.700 That's awesome. Yeah. Well, John, this has been a great conversation. Where can people go to learn

01:08:53.400 more about your work?

01:08:54.780 Yeah. I mean, just if they pop over to precisionnutrition.com, that's where, that's where we do

01:09:00.280 all of our stuff. And like I said, very much like your site, you know, which was a early model

01:09:05.140 for hours, you know, we've just been publishing free, very well-researched, comprehensive nutrition,

01:09:12.640 fitness, health articles for a very long time. I think we have over a thousand free articles on

01:09:17.460 the site. You don't have to give your name and email address or anything. Just, they're just there

01:09:21.020 for people to learn more from. So, you know, for everyone listening in, I thank you for spending all

01:09:25.740 this time with us today. Hopefully you learned something. And if you're interested or passionate

01:09:30.800 about health and fitness, come check us out at precisionnutrition.com.

01:09:35.080 Awesome. John Berardi, thank you so much for your time. It's been a pleasure.

01:09:37.480 Thanks, Brett.

01:09:38.380 My guest is John Berardi. He is the co-owner of Precision Nutrition. It's an online nutrition

01:09:42.220 coaching company. You can find out more information about his work at precisionnutrition.com. And if

01:09:46.520 you're looking specifically for that ebook on intermittent fasting, go to precisionnutrition.com

01:09:51.120 slash intermittent-fasting. You can download it. It is free. Also check out our show notes at

01:09:55.720 aom.is slash fasting, where you can find links to resources, where you can delve deeper into this

01:10:00.280 topic. Well, that wraps up another edition of the Art of Manliness podcast. For more manly tips

01:10:15.860 and advice, make sure to check out the Art of Manliness website at artofmanliness.com. If you

01:10:19.540 enjoy this show, have gotten something out of it, I'd appreciate it if you take just a minute to give

01:10:23.020 us a review on iTunes or Stitcher. That helps us out a lot. As always, thank you for your continued

01:10:26.700 support. And until next time, this is Brett McKay telling you to stay manly.

The Art of Manliness - July 31, 2025

#328： The Pros and Cons of Intermittent Fasting

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