Bonus: 'Fasting' featuring Dr. Jason Fung

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You're listening to Bulletproof Radio with Dave Asprey. Today's episode is going to be a lot of fun because it is with a guy who is a real expert on metabolism, and he's a pioneer at testing intermittent fasting in clinical settings. We have all kinds of information about intermittent fasting that's been out there. It's, you know, a core part of the bulletproof diet. But it's. It's been around in spiritual traditions for a very long time, but the clinical studies of it were lacking. And Jason Fung is the guy who has done a lot of that work, and he's worked on treating obesity and diabetes. He wrote the obesity code, the diabetes code, and today he's talking about one of the four big killers. You know, the things that you have to avoid if you want to live a long time. Cancer is one of the big four things that takes a lot of us out. His book is called the Cancer Code. I'm really excited for this interview. So, Jason, thank you for taking the time.

Oh, glad to be on. Thanks for having me.

I remember back when I was heavy and I was. I tried the Zone diet, I tried the Atkins diet. I had tried all kinds of stuff. And I knew, though, like you said, it was gospel. This is, you know, late 90s, early 2000s, if you don't eat six times a day, I'll go into starvation mode. And someone suggested eating fewer meals. And I was like, oh, God. I still remember it because it was a visceral response. I was like, oh, my God, I'll die. But I wouldn't have died, but I would probably have gotten low blood sugar because I was pre diabetic. And I certainly would have just been unable to think. And so for me, it was really kind of a scary idea that you could even consider fasting. I would have never predicted that years later. Yeah, 24 hour fast. Oops. I guess I did that because I don't have time for lunch. It's okay.

Yeah, yeah.

What do you say to people who have that same visceral response that I did?

I'll tell you. I had the same visceral response. So I remember thinking about fasting for the first time, and I thought, wow, that's such a bad idea. Right? That was my first reaction, too. This was probably 2012, right? I was like, what a bad idea. But then I actually thought, well, what? Wait a second. You know, I see this all the time. I tell people to do this all the time. It's it's what exactly is bad about it. And that's where, you know, I, I was fortunate that I could go into and look at any of the papers that had written the physiology. And it had been worked out, of course, years ago. I mean, all this stuff, fasting, because it's not something that I made up, obviously they talked about it thousands of years ago. But the, there was a lot of myths that had been built up around fasting to really make everybody, you and me included, think it was just so bad for you. So something like your blood sugars will go low, for example. And in fact, if you're on medications, that might be true. But assuming, if you're, if you're not on medications, then your body actually works fine. I mean, that's how we survived as cavemen and cave women who might or might not eat, right? Your body is going to be able to store away sugar. And if it. And so this is called glycogen in the liver, it stores the sugar, and if you run out of that, then your body's gonna start using fat. So that's how it survives and then produces ketones for the brain, so it doesn't need as much glucose and so on. And that's sort of the basis of the ketogenic diet, which is very popular and so on. Other things like, oh, I won't be able to concentrate again, it simply wasn't true. Because when you look at what happens to the body during fasting, in fact, the body doesn't shut down, it actually revs itself up. So it actually increases noradrenaline, it increases growth hormone. So you're increasing your sort of fight or flight response, which is your sympathetic tone. You're actually more focused. You're actually going to be able to concentrate better. So people talk about, you know, some of the, you know, you know, in animals, for example, if you have a big meal, like a lion who just eats, you're not really sharp. If you eat a huge Thanksgiving meal, you're not like, you know, really looking to do some high level, you know, mental stuff. You just want to sit down and watch some football, right? But for animals, for example, you, what you don't want to do is you don't want to face that hungry wolf, because that hungry wolf is not falling down on the job. The hungry wolf is dialed in, zoned in and ready to kill you. So the point is that when your body doesn't have energy, it doesn't eat. It's actually going to shift and start using the fuel that's carried on its own body, but it doesn't decrease it. So you're changing fuel sources, but then you're increasing the amount of fuel that your body is using so that you can go out and hunt. So this is like a survival response. It's actually, you know, you have more energy people sometimes have. You know, I remember one fellow, he came into the office and his wife was like, you know, before he was so slow. Now I can't even keep up with him because he's got so much energy. He's just raring to go. And what you've done, of course, is you've liberated the energy that's carried in that body fat. So as you start to use that body fat, your body's like, Whoa, there's like 500,000 calories of food energy stored in this body fat. Let's go use it. When you eat all the time, of course, you lock all that body fat away because you're not able to access it because you're eating, you're using the food, not your body fat. So that's what I mean by switching fuel sources, your body, when you're not eating, simply switches over to using your body's own stores of calories.

It seems like if you're exposed to a lot of chemicals, you're exposed to toxic metals, you're exposed to xenoestrogens, including mold, toxins, all of those are also independent risk factors for obesity and cancer. How do you sort out toxins versus diet if the toxins make you fat?

Yeah, that. There, there is a bit of. It's sometimes hard to tease it out, but, you know, there's, there's statistical ways that you can try to do that. It's not perfect, of course, but if you look at the overall sort of contribution of toxins, they tend to be relatively small because you're not going to get them. So it's hard to get these toxins that are sort of worldwide sort of thing. Right. Whereas obesity, you can track it. It sort of started. It didn't start, but it was the most biggest problem in America and now you see it in Asia and so on. So you can track these things as opposed to certain, say, toxins or aflatoxin, for example, is a. Is something that causes. And wood dust and other things. These all cause cancer, but you're not going to see sort of in all parts of the world as opposed to obesity. So you can try and distinguish between those two. But for sure, those are problems. For sure, we know it. And there's A list of carcinogens that the World Health Organization maintains. But when you look at in a population how much it contributes to cancer overall, it tends to be sort of like 1%, 2%, 3%, which together can be important. But obesity and diet and so on.

Tend to be the biggest part, unquestionably. Do you know why coffee only causes cancer in California?

Coffee is a, is a, is a tough one. I mean the problem of course with these studies is that they typically take coffee drinkers versus non coffee drinkers and then they say okay, well what's the difference between the two? And, and then try and make some conclusion. But this sort of stuff is very hard to. Because there's a difference between coffee drinkers and non coffee drinkers other than the fact that the, the one drinks coffee. Some, you know, might be very, under very high stress, for example, you know, real go getters and other people might be much more laid back. And you know, there's, there's so many differences between the two that it's often hard to distinguish whether it's just the coffee. I mean the same problem exists in all of, all of nutrition. To try and tease out these things is very difficult. So we actually went through a number of these hypotheses for diet. We thought maybe fiber was the problem. That didn't turn out to be the case. We thought it was fat, we thought it was various vitamin deficiencies. So we tried. I'll tell you that they've tried and these are million dollar studies. So they've tried vitamin A, B, C, D, E and they've tried selenium and they've tried omega 3 fatty acids. All, you know, tested the supplements and randomized controlled trials. And of course none of them really had any effect on cancer. Well, some of them did. The vitamin B and C. Vitamin B ones actually tended to increase the rates of cancer. So that wasn't good.

Some of the more advanced biohacking techniques. In fact, the guy who talked about this most was probably James Clements. When he came on the show he wrote a book called the Switch which was brilliant. And he's like, well, go on a protein restricted diet for a month and eat less calories and the next month go on to mtor month. So you're sort of going in this, break things down, clean them up and then build them back. Clean them up, build them back as part of an anti aging regimen. Because if you get sarcopenia, your muscle loss as you age, which just normally happens with every decade, that also tends to, well, you don't get cancer necessarily, but you know, you're walking hunched over and you can see through your skin. And that's not the type of aging that anyone wants either. Do you think that there's validity to that kind of feast famine. Feast famine strategy?

I think it makes a lot of sense because what you want to do and fasting, of course, does this naturally because when you fast one, you're going to break down stuff because your body doesn't want extra cells, right? So you're going to go into top ofy, you're going to break down cells, you're going to get rid of extra cells, but then growth hormone goes up. So then when you do eat, you rebuild those cells that you need. So that's. That's essentially what you're doing, is you're trying to cycle between sort of breaking down and then rebuilding. Breaking down and then rebuilding, which is the way that you sort of rejuvenate the body, right? That's the whole word itself. You got to get rid of the old stuff, bring in the new stuff. If you keep pushing, you know, it's like if you renovate your bathroom, the first thing you got to do is take out those little tubs and old bath, old toilets, because then you can put in new ones. You can't just put in a tub if you have an old tub there, right? So that's the problem. You really have to cycle between the two. And that's what this sort of natural even on a daily basis, right? You feed and then you fast. You feed and then you fast. That's why you have a term called breakfast. This breaks your fast, right? So that's the point. You're going to store some calories. You're going to build during those eight or 10 hours that you're eating. Then for the 12 or 14 hours that you're not eating, that's when you're going to use those calories and also break down whatever you don't need, right? Your grandmother might have said, you know, that's the time you need to digest your food and so on. But really, I think they're on to something in that this is a natural cycle. We, of course, you know, getting back to this idea of eating 10 times a day completely destroyed that because, you know, instead of respecting the sort of feed and fast cycle which, you know, we've always had, right. Built right into the English language, we said feed all the time, right? And, you know, you heard this, I'm sure, 10 years ago, like, as soon as you get up, eat Breakfast, Breakfast, most important meal of the day. Like, do not even step out your bedroom door before you get a granola bar. And you know, like, why? Like what possible reason would I have to do that and keep eating until you go to bed. It's like, well that's not the way we way I grew up, right? You had dinner and that's it, right? So you have to have that fasting period. So it's the same thing on a mini scale, right? And I think what, what he's talking about is on a monthly scale and I think that makes a lot of sense too.

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Yeah, I mean, it's. So if you're talking about one of the obesity related cancers.

Okay, let's talk about that.

Look at the cause. Yeah. So because if you're lung cancer, of course, then you have to stop smoking. Like, clearly there's nothing else.

Okay, we'll say an obesity related cancer.

Yeah. So like breast cancer, colorectal cancer, liver cancer, pancreatic cancer. Those are obesity related cancer. So the most important thing is to understand that you, you know, there's, there's, if you're overweight, then you need to sort of get back to a normal weight because again, that's a disease of too much insulin. Both are diseases. And then you have to get that down.

Lose weight.

Lose weight is probably the most important thing. Two is probably sugar. Sugar. You know, I don't think there's a lot of people that would disagree. Sugar plays a huge role in all of these diseases. And it doesn't do it in a direct fashion, but it does it sort of in this indirect fashion. It causes a lot of liver fat accumulation and insulin resistance and therefore hyperinsulinemia. So it does this and it's very insidious. And it's also, it's hard for your body to handle that much of the fructose. And that's the problem with the sugar. So cutting sugar is probably one of the, you know, big things. So trying to lose weight, trying to get down, you know, if you have type 2 diabetes, then there are certain drugs that might make things better and certain drugs that might make things worse. So insulin, of course, would not be something that would recommend, but trying to control your sugars through your diet. And there's also certain medications that you can, those would be the, the main things. I mean, they're not, they're, you know, they're common sense, they're logical. I mean, in terms of treatment, you know, you still got to follow whatever the oncologist recommends as the best treatment regimen. Because by the time you get to that stage of cancer, I mean, we spent like millions and millions of dollars trying to figure out the right regimen. And I'm not going to say, you know, they're all wrong. Right. It's, it's it's the regimens that they recommend have been tested. So you do need to take that advice. But there are ways to improve your odds. So getting to a normal weight, cutting down sugar, potentially considering metformin and intermittent fasting has other roles. So one of the roles is in chemotherapy. It actually, they've used it sort of before chemotherapy. It makes it more tolerable and perhaps also makes it more effective. And that's, you know, so they fast 24 hours before. And the idea here is that what you do is by fasting you're putting your cells into this sort of regenerative mode so that when you get the chemotherapy you don't sustain as much of the toxic damage that that accumulates. Whereas the cancer, the cancer can never really go into this regenerative static mode. It's always sort of growing and therefore gets the full brunt of that chemotherapy. So they've used it in small studies where they've used fasting sort of before and after chemotherapy and they found that a lot of people can tolerate it better. So these are sort of, you know, metformin fasting, these are ways to sort of optimize around the treatments that are available.

Do you have enough time to talk briefly about metformin? Some new studies that I wanted to chat about? You're good for another couple minutes?

Yeah, yeah, absolutely. So metformin is really interesting because again it plays on a hormone called Ampk, which is again one of these nutrient sensors. And the nutrient sensor, it sort of fools your body into thinking that there's no nutrients available and therefore, you know, cutting growth down. So in diabetics the metformin seems to reduce the risk of certain types of cancer, breast cancer particularly. And therefore some people have started to use it sort of outside of the diabetic realm. And you see that in a lot of longevity people will consider using metformin or some of the related compounds to metformin in an effort. The proof is still to come, I think. I mean I don't think there's any good studies but you know, on the other hand it's a relatively non toxic drug, relatively, because all drugs do have side effects. But we've been using it for 50, 60 years and you know, it's, it's been well tolerated. We know a lot about this drug.

I, I went on metformin when the first anti aging studies came out, early 2000 ish for about three years. But I ended up going off of it because of some early studies about a reduction in mitochondrial function. And just like four days or maybe six days. Before recording this, a new study came out that showed that it was exacerbating age, associated mitochondrial dysfunction and caused a failure of cellular respiration because of what it does to complex one in the mitochondria. And so I've. That plus the vitamin B12, the reduction in sensitivity. I've been reluctant to recommend it as much as I used to for healthy people, but the idea of reducing your type 2 diabetes is so much more overwhelmingly important than that side effect. But if we're looking at a healthy population, that may be one to hold off on for a little while based on that, I think.

Yeah.

Do you agree?

I agree. I've never, I've never recommended it to healthy people, although I know certain other doctors who have done that. So I think that the benefits, again, it's one of these risk benefit things. If you have type 2 diabetes and your option is metformin and insulin, then clearly metformin does better than insulin. But if you're healthy, then what are your benefits? Well, they're fairly murky and so therefore any side effects are going to start to balance because your risk is just so much lower in a healthy population. And the other thing is that these drugs, you know, they might be good for a certain period of time and not be good if you do it continuously. You know, there's, there's lots of drugs that have been like that, right? If you take it, it's good. You take it, it's good. Then you, when you study, oh, you've been taking it for 10 years and it's really bad for you. Right? So some of the osteoporosis drugs were like that. They were good, they're good, they're good. And then, but if you took it for a long time, you got more fractures, actually. So there's sort of a time limit to those because they're interfering with sort of the N things. So if you're, you know, so if you're chronically stimulating or simulating this sort of state of semi starvation, it might be good for a while, but you're not getting the normal growth that you should be getting. Right. So therefore, yeah, maybe in, maybe you do have to cycle these. Maybe you do have to say take it for this and then go off of it and this and that. There's different ways. But, you know, without the studies, it would be hard to know how to recommend it. So I've never really recommended it for healthy people.

I think your, your conservatism was probably warranted there and I've considered, I probably will experiment with taking a metformin on a day when I'm gonna do a 24 hour fast. So I'll turn up the effect of the fast, but the rest of the time I wouldn't take it. Stuff like that, there's all kinds of stuff and we may never do studies on that, but if we know enough about how it works and you see outsized results, you can probably say, okay, this is a healthy practice for me, but it may never be provable. But if you look half the age of your friends, okay, you know, yeah.

And I think these things are relatively low risk too. When you start, when you cycle these things, things of course are going to be a lot less prone to getting into problems. Like if you cycle, say veganism, you're going to be less prone to getting into trouble. Like if you eat eggs every so often or fish every so often, you're going to be a lot less prone to getting into trouble than if you're hardcore. 100%, I eat zero eggs and fish and meat and everything. Right. You could get into a lot of trouble with that. Same for everything. Right. Hardcore keto people worry about that. Hardcore carnivore people worry about that. And some of these diets haven't been around long enough to really know what the long term side effects are. But you know, it seems like you do have, like, there's reasons that you'd have to think twice about doing them hardcore all the time. Whereas if you're just sort of cycling in and out, trying to get the results, targeting them to what you want, like if you have a specific problem, I want to lose weight. Right. Let's target that, let's get to there. Right. And then getting there and then trying your maintenance, those sort of things, it seems like you're going to run into a lot less trouble in the long term.

Well, I love your reasoned, rational thought process about cancer, about fasting. You know, you don't jump on the bandwagon too soon, but you're way ahead of the curve. And you're so willing to say we don't know. But you're also the rare doctor who's willing to say we don't know. But the most rational thing that makes sense given what we do know is probably this and we'll see more studies. That's a very rare thing for anyone with a license. So thank you.

Thank you. And thanks for the, you know about the cancer code because, because that really was I was trying to do is write a book for Somebody who sort of all of a sudden finds out, oh, I have cancer, like, what am I going to read? Like, how do I know more about this? Like, what's happening in my body? Because sometimes you get out there and you read and it's like, there's nothing nobody's talking about. Like, what is it as a disease? Like, that's. That was such an interesting question to me is what this disease actually is and how our thinking about it has completely changed in the last 10 years. And then people will say, hey, this is an interesting sort of thing. It doesn't change, perhaps, what the treatment is, because you're still going to do mostly what the doctor tells you to do, but at least you have an inkling of what's going on in your body so that you're not just sort of out, you know, dealing with the complete unknown. So, yeah, thank. Thanks for that. I really, really appreciate that.

You're. You're welcome. You've. You've done an active service. And I. I like to tell listeners this. No one who knows what they're doing writes books for money. Like, it takes so many thousands of hours. And, like, you pour your soul into a book and yes, you do get paid for the book. You do not get paid as much as you do practicing medicine or being an entrepreneur. Like, I write, my book says Acts of Service and Acts of Love Learning. And I could tell from reading your book that you were putting the pieces in order for yourself as you were doing it so that you could be better at teaching it. So it is a book that, I mean, that is on my shelf. And it's like, you need to read that. If cancer is your four killers, you know, there's four. Diabetes is the first one because it makes the other three more likely. But cancer is the biggest one right up there with cardiovascular disease. They kind of race depending on.

Absolutely. Number one and two.

Yeah, yeah. So you wrote the book.

Let's say.

Here's what you do.

Yeah, I hear you about the writing. Because it's like, you write not because you want to, you write because you have to, because it just ain't worth it otherwise. Right. Because sometimes you get these people who say, oh, you wrote it for the money. I'm like, if I was doing it for the money, I'm telling you, I could have done a lot of other things that would have done a lot better than that. You write it, people, because. And I, you know, I totally hear you on that, because it's like, I remember I finished the book. I finished the diabetes code. And then I started reading up on cancer because I found it, like, honestly, I thought the whole scientific journey was just a fascinating story. And it's like, oh, I have to write this. You have it on your chest, you have to get it off your chest. And then it's like, ah, okay, I've said what I have to say, right? You don't write it because. Because, oh, I need to write a book. I need to make money. You do something else for that, right?

Yeah, absolutely. You do something else for that. But it's well done. And for people listening, if you decide you're going to read the cancer code, if you have cancer in your genes and in your family, and your mother and father got it, and your siblings did, you might want to read this book. And if you have cancer or you've had cancer, which means you have a greater chance of it coming back, you might want to read this book. And one thing you absolutely have to do, and this is funny, but it's actually proven to reduce cancer. And it's leave a positive review when you read a book that's worthy of a positive review. And the reason that reduces cancer, and I'm not joking about that, is that gratitude in multiple studies reduces inflammation in the body. And it's the least you can do if you tip your barista. You also should leave a review for your authors. It doesn't take very long. Thanks, Jason, for being a continued voice of curiosity and reason in the bizarre world of health and medicine. You're doing a fantastic job.

Thanks so much. Thanks for having me on. This is great.

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