Jason Fung: The Complete Guide to Fasting (& how to burn fat)

Content by: Dr Jason Fung

Watch the full interview below or listen to the full episode on your iPhone HERE.

Guy:  This week welcome to the show Jason Fung. He is a Toronto based nephrologist. He completed medical school and internal medicine at the University of Toronto before finishing his nephrology fellowship at the University of California, Los Angeles at the Cedars-Sinai hospital. He joined Scarborough General Hospital in 2001 where he continues to practice.


Audio Version

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Questions we ask in this episode:

  • Fasting can be intimidating and scary. ie: I will starve, waste-away and lose my muscle. Should we be fearful?
  • Is fasting for everyone?
  • The weight loss industry tells us to eat less calories, but snack between meals. Won’t fasting put us into starvation mode?
  • Does fasting give us a license to eat whatever we want when we are not fasting?
  • Can fasting benefit athletes and how would they apply it?

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Full Transcript

Hey everyone, this is Guy Lawrence, co-host of 180 Nutrition, and welcome to another stellar episode of the Health Sessions, where we connect with leading global health and wellness experts to share the best and the latest science and thinking and empowering everyone to turn their health and lives around.

[00:01:00] This week, our awesome guest is Dr. Jason Fung, and we are getting into the topic of fasting. Now, fasting is a topic that we haven’t really covered on the podcast before. I do personally implement little bits of fasting in my life, so it’s great to get a guy that’s been studying it for the last four years and applying it to hundreds and hundreds of patients in his medical practice in the US. We cover things from fasting as an application to obesity, to diabetes, especially Type II, to then obviously just weight loss and the health maintenance and even in athleticism as well, you know, what are the precautions around it, what should be looking for, is fasting hard, can we eat whatever we do outside of fasting and so forth, and why should we do it. Should we be scared of it? Are we going to lose muscle mass? You know, all sorts of stuff. It’s all in there and it was fantastic.

[00:01:30] We had Jason on and basically grilled him for 55 minutes to unleash as much knowledge as we could. No doubt you’re going to enjoy guys, and if you are enjoying the show, please leave us a review on iTunes if you can. Only if you enjoy them of course, but if you subscribe to it, five star it and leave a review for us. It just really helps other people find this podcast as well and get the information, just like yourself right now if you’re a regular listener. That’s one thing I’d ask for guys, and really appreciate it if you do. I read all the reviews and now we’d be happy to read them out on the podcast as well. Anyway, let’s go over to Jason Fung, enjoy.
Hi, this is Guy Lawrence. I’m joined with Stuart Cook. Hi Stu, good morning.

Hello guys.

Our awesome guest today is Mr. Jason Fung. Jason, welcome to the show.

Hey, how are you? Great to be here.

Thank you, mate. Did I pronounce your surname right? I should have asked you before we started


Yeah? Beautiful. Look, the first question I ask everyone on the show is if a complete stranger stopped you on the street and asked you what you did for a living, what would you say?

[00:03:00] I’m a kidney specialist by trade, so I’m a physician. I trained very conventionally, through internal medicine, and then I did a couple of years in Los Angeles for my nephrology. About 10 years ago now, 8 years ago now, I became very interested in the question of nutrition, obesity, because that’s really the core problem of what faces us in the medical world. A lot of the problems that we face are not what we used to face, which is infections and so on. They’re all metabolic problems, that is, Type II diabetes and all the problems that go along with obesity such as sleep apnea, high blood pressure, high cholesterol, and all those sorts of problems. They really take up probably about 40%–50% of the health care budget, so you know, modern Western nations, it’s a huge problem, and worse than that, it’s a growing problem. You’ve all seen the statistics on obesity and Type II diabetes kind of rises right along with that.

[00:04:00] That’s where I really got interested in, trying to see where we kind of went wrong, because obviously what we’re doing was not working. We told everybody, you know, cut calories, eat less, move more. We’ve been saying the same thing for 30 years, we’ve been singing the same song, and nothing has worked. I don’t know why we would keep using it because we knew it didn’t work. That’s really where it came from, that I really started looking into, first, the problems with obesity and the very much related problems of Type II diabetes and how our treatments are really quite incorrect, and really how to properly treat them.

For a bit of a back story as well, Jason, what led you into the world of fasting? Because I know we’re going to be talking about fasting today. Being a doctor, the first thing you started looking at was the obesity problems, and then where did fasting started to play in that journey?

From the obesity side of things, really I recognized that the problem was too much blood sugar. Everybody says I demonize blood sugar; I don’t, it’s a normal hormone, but obviously any hormone, if you get too much of it can be a problem, whether it’s thyroid hormone. Obesity, Type II diabetes are really problems of too much of this hormone. The natural solution then is too look for dietary solutions that reduce it. That was the big problem with Type II diabetes, we had no drugs that would reduce it, so we just kind of kept getting worse and worse.

[00:05:30] Low carbohydrate high fat diets, ketogenic diets, they’re very good at lowering blood sugar. But the problem I had is that my patients didn’t really get any better. It wasn’t because the diet wasn’t good, it’s because it’s complicated for these people. These aren’t people who go on the internet everyday and look for nutrition sort of things. They’re people who are 65, 70 years old, some of them don’t speak English, and they really didn’t know how to follow a proper low carbohydrate diet. It was kind of discouraging, because here I knew that I had kind of zoomed in on the problem, and I knew what needed to be done. Ye, the patients really didn’t know how to do it because this whole low fat kind of craze of the last 40 years, most of them are still in that sort of paradigm of cut your fats, so to go all of a sudden to a low carbohydrate high fat diet, they really couldn’t wrap their heads around it.

[00:06:00] I needed something kind of completely different. One day, I was talking to a friend and she’s talking about a cleanse that she did. It was a seven-day cleanse and you drink the stuff. You don’t eat anything but you drink all this stuff that’s really [inaudible 00:06:14], said “I felt great,” and so on. I thought, “Oh, that’s like fasting.” That’s what I was thinking about. “Oh, that’s a terrible idea. That’s the dumbest thing I ever heard.” Then she’s telling me how good it was, and I’m like, “Huh.”

[00:07:00] My advantage is that I might think it’s stupid, but then I thought for a second, okay what exactly is so stupid about it? Because I knew, kind of peripherally, that people did used to fast routinely. Every Sunday around Easter time, I’d go to church and they’d talk about fasting like for three of four weeks straight. You’d hear all about fasting, fasting, fasting. Nobody actually did it. It was very funny to me now that it’s something that has been part of human history, yet for the last, say 40 years, has been completely forgotten. In fact, the mere mention of it gets the same reactions that I used to give which is just a big rolling of the eyes.

[00:08:00] My advantage again is that I know the physiology, I could go into the medical literature and started looking and say, okay well, I think it’s really stupid but what exactly is so stupid about it? That’s when I recognized that there’s actually nothing stupid about it. In fact, all the changes, which is mostly based on lowering blood sugars, are highly beneficial. In people who are overweight or who have very high blood sugars and Type II diabetes, hey, guess what, if you don’t eat, your blood sugar comes down. If you don’t eat, you lose weight, and there’s nothing wrong with that. This is the way the human body is designed. That’s what fat is, it’s stored food energy, right? That’s what it’s there for, for you to use when you have nothing to eat. It’s not there for looks, right?

[00:08:30] If that’s the case, then why don’t you simply fast in a controlled manner and let your body mobilize this stored food energy. That’s a completely hundred percent natural way to do things. That’s what I did, I just started people on fasting, I monitored … obviously again, my advantage is the I could monitor them closely, watch their blood sugar, adjust their medications … and what I quickly realized was that it was incredibly powerful. That is, we had people who were on 200 units of hormone a day, who three weeks later were on zero. We had people with 30 years of Type II diabetes and within a month and a half, they’re off everything, with normal blood sugars. That’s amazing. In fact, it’s practically … if you were to ask most doctors, impossible. They would have told you it’s impossible. Yet I was here, I was seeing it day after day after day.

[00:09:30] What we did was we started doing it on everybody because we realized that hey, this is very powerful. What we need to do is not belittle people and say, oh you can’t do it because it’s hard. No, it’s hard, but it makes them better so we’re going to give them the support they need to get better. That’s what we did. We started a program, we actually have people all over the world who connect remotely to get coaching and dietary counseling, but really based on helping through the intermittent fasting, what problems can come up, how to deal with them, support, because it does take support, right? That’s the whole idea of what we did.

Fantastic. Quick question, Jason, before … I know you’re going to [inaudible 00:09:45]. How long have you been applying that protocol for?

About four years now.

About four years. You would have seen a lot of people in that time, right.

Yeah, hundreds and hundreds. I don’t think that there’s anybody in the world who has done this in a … use fasting in a therapeutic manner, yes, there are people who say, “Okay, come to my clinic, come for a week and fast,” and then that’s it, but nobody who says “You’re sick,” and this is what I’m going to use to treat you for your disease, for obesity, for Type II diabetes, we’ll monitor you, we’ll check your blood work, we’ll check your blood pressures, and do it as if it’s just part of regular medicine, which it really should be.

[00:10:30] The thing is, it’s so far out of the mainstream that it takes people a little bit of time to kind of understand what’s doing it. The interesting thing is that we’ve had a lot of people be able to maintain their weight loss as well, because I actually think that it’s far easier to maintain your weight loss using some kind of intermittent fasting protocols than standard diets.

When we’re talking about duration here for the fasting, hat does that look like? Because I’ve heard some people say, well, you can do a 12-hour fast if you eat your dinner at 7 P.M. and you eat your breakfast at 7 A.M. and you sleep, you have essentially fasted for 12 hours. Do we need more than that?

[00:12:00] Yeah, I think that the duration is actually flexible. It can be any duration. Fasting is just the flipside of eating, that is, anytime you’re not eating, you’re fasting. The word “breakfast” is very interesting, because what it implies that fasting is actually a part of everyday life. What we should do is keep our feeding and our fasting in balance there. You go back to the 1950s and people are eating three meals a day, and they’re getting about 12 to 13, 14 hours of fasting in every single day. That’s just normal. Finish dinner at 7, eat breakfast at 7, 12 hours fasting, 12 hours feeding, great. Because your body really only exists in one of two states. You’re either storing food energy or your burning food energy. There’s no in between. What happens when you eat, of course, is that blood sugars goes up, it tells your body, store that food energy. So that when you fast, when you’re asleep, blood sugars goes down, your body pulls that energy back up and burns it. That’s why you don’t die in your sleep every single night, right?
[00:13:00] What happens, of course, is that if you now eat like from the minute that you get up to the minute you go to bed, now you’re feeding all the time, you’re giving your body instructions to keep storing food energy. Remember, you can’t store food energy and burn it at the same time. You can’t go both ways; it’s not logical. If you’re always storing food energy, guess what, you’re going to be fat. All you do is you extend that period of fasting and let your body burn some of the stored food energy, and your body knows how to do that. You can do … there are several popular regimens, so there’s 16-hour fast, so you compress your eating window, for example, to 8 hours, like between say 12 and 8 or 11 and 7, something like that. You can go to 24 hours of fasting, which is kind of a one meal a day sort of an idea. If you go 7 P.M. to 7 P.M., that’s dinner to dinner. You can go even longer if you skip a full day, 36 hours. You can go really up to as long as you want. We have people go up to 21, 30 days.
[00:14:00] Mind you, for those longer fast, as with everything, it’s more powerful the longer you go but the more problems you might face down the line so we are careful to monitor them very closely. But again, there’s nothing wrong with you going 30 days even. It’s not easy, but it’s not as hard as most people believe. One of the things with the extended fast which is important is that you do have to be a little bit more careful when you break the fast, you do it gently. You have to make sure if you don’t feel well, of course, not to push yourself, get yourself in trouble.

[00:14:30] Jason, the first thing that popped in there, with the different periodizations of fasting that you can do, should we all be considering that or should it be more for people that have chronic illnesses like Type II diabetes, obesity or whatever might be, and then sort of implement that protocol into like a weekly or monthly basis. Then you got the other spectrum where people are health and maybe just looking to optimize health and maintain good health. Where would that fit in with both spectrums, if that makes sense?

[00:15:00] Yeah, absolutely, and that’s just what I tell people all the time, is keep in mind what your goals of treatment are. If your goal of treatment, for example, is just to kind of maintain your weight, you can do it fairly well with a daily 12- or 14-hour fast. That’s just normal. You don’t really gain weight, you don’t lose weight. Again, that’s kind of the 1950s America sort of model. They’re eating white bread, they’re eating cookies, they’re eating ice cream, but there’s very little obesity because they’re not eating all the time. If you look at national surveys of how often they ate, it was three meals a day in 1977 and goes up to six a day by 2005, so they’re constantly. I think that’s played a huge role.

[00:15:30] Now, if you want to … there’s different reasons why people do it. For weight loss, for example, Type II diabetes, it depends on your severity, but typically we will go to a longer fast—not 16 hours for example, which does pretty well for weight loss, but to at least 24-, 36-hour fast for Type II diabetes. For severe diabetes, we often consider doing about a 7- to 14-day fast, and then there’s different reasons again.


[00:17:00] For people who are into athletics, for example, you might do some different fast. There’s something called training in the fasted state, which is becoming very popular, which is again about a 20-, 24-hour fast. Then you exercise, then you eat. That sounds very strange, but physiologically, there’s a huge number of benefits because what happens when you fast is that your noadrenaline goes up and your growth hormone goes up. Those two hormones are considered part of the counter regulatory hormones. Now you exercise, and you can exercise harder than you’ve done before because you’re kind of pumped up from all the adrenaline. Then as you eat, your growth hormone levels are high, so you recover faster. So train harder, recover faster. That’s a huge advantage if you’re talking about any athletics. It’s and advantage you almost cannot afford to skip. That’s merely from adjusting your timing.
[00:17:30] Another advantage of fasting, for example, some people find that they have much higher mental clarity. Again, people think, oh I don’t eat, I’m going to not be able to concentrate. It’s actually the exact opposite. If you think about a time you’re eating a huge meal, like at Thanksgiving or something, you had that huge meal, you’re not really sharp, right? All you can do is kind of sit on the couch and watch football. That’s about it. Whereas on the other hand, when you think about somebody and you say, “Oh that guy’s really hungry,” you know, he’s hungry for success, he’s hungry for power. Does that mean he’s just sitting on the couch watching TV? No, it means he’s energized and out there getting stuff. That’s what it means when you’re hungry. You don’t have all that blood kind of digesting food, so your brain is sharp. Some people really feel that.

[00:18:30] There’s a whole group of people out in Silicon Valley who do this as a sort of a biohack, that is, they’re trying to hack themselves into a higher level of mental performance, not just athletic performance, but mental performance. What they do is they fast and guess what? You’re saving time because you don’t have to eat, you don’t have to shop, you don’t have to clean up, so you get more work done, but the work that you do is on a higher level than you used to do. That’s fantastic because that’s free. It’s like, okay, if you’re in a competition in Silicon Valley, a higher level of mental performance means a lot of money. It’s the difference between success and failure. For these guys, they’re like, okay, they’re going to hack themselves into a higher level of performance, and that’s terrific.

[00:19:00] There’s a story that Phytagoras, the ancient Greek mathematician, required his students to fast before they could come to class. All these ancient Greek thinkers actually did a lot of fasting. Socrates, Plato and all those people. They did it not because they were fat, they did it because they knew that it gave them more mental clarity. We still talk about the classic Greek philosophers, right, the great Greek mathematicians. I’m like, holy, that’s amazing.

[00:19:30] Then you can talk about things like cancer prevention, I know we touched on that briefly, but there’s people who feel, and the research is more shady here, that you can actually prevent cancers from developing because cancers need glucose, and what happens when you fast is that you kind of lock down all that glucose and you kind of starve them out. There are people who suggest that you can actually do this in combination with say ketogenic diets and actually help prevent cancers.

[00:20:00] Do you think as well, Jason, that when it comes to fasting, if you haven’t fasted before and let’s say your diet is fairly processed, do you find there’s an adjustment period to actually getting into fasting?

[00:20:30] Oh absolutely. It’s probably about a two-week period. Generally, what we tell people is that the first couple of times you fast, the first [inaudible 00:20:10], it’s going to suck, because your body’s not used to it and it’s not going to go very well. But you can’t give up because it’s just like exercise. If you start exercising and you go sore muscles, you’re going to go, “Oh man, that guy, he told me to exercise, that’s the worst thing. I’m done!” You don’t do that, right? It’s, “Okay, well I’m not in shape, I’ve got to give myself a couple of weeks, get in shape, then I’ll see how it is.” You can’t say, “Oh my joints hurt after that first run that I did after 30 years.”

[00:21:30] It’s the same thing, the fasting, if you haven’t done it. It’s easier to do from a ketogenic diet or low carb diet for sure, because your body is kind of used to burning fat, so if it’s burning body fat or if it’s burning dietary fat, it makes no difference. It’s much easier, and that’s what we find anecdotally. If you come from a fairly processed, kind of high carb sort of a meal, then yeah, there’s an adjustment. There’s a lot of problems that do come up, things like hunger, things like headaches and so on, and they’re manageable. You have to understand that you can get through it and there’s two ways to do it. One is to jump right in and force your body to adapt, like start with a longer fast, five days, seven days, and just force your body to make that adjustment, or just build it up slowly.

There’s no right or wrong answers. For example, if you jump in the pool, you can either jump in or you can kind of slowly go in down the stairs one at a time. There’s no right or wrong answer, people do it both ways. But if you find that it’s getting really difficult, we tell people to just actually do the long one and force your body to make that adaptation so that it makes it easier.

Got it.

[inaudible 00:21:55]

Go ahead, Stu.

Just going to think from an athletic perspective as well. There would be concerns about things like muscle wastage. How would we address that?

[00:22:30] There is actually this question that comes up quite a bit. For muscle loss, it happens at around 24 hours, and that’s one of the reasons most people who do it from an athletic standpoint don’t go beyond that. What happens is that your body actually burns … up to 24 hours, it burns the stored glucose, which is glycogen and [inaudible 00:22:34]. But it takes about 36 hours roughly to go into fat burning, so between 24 and 36 hours, that’s actually a period where you’re actually burning some protein, so 24 to 36 hours.

[00:23:00] That’s where people think that you lose a lot of muscle. You do burn protein, but that’s not actually always a bad thing. Let’s leave athletics for a sec and if you just talk about the regular person, people might say well, you’re going to lose a lot of lean muscle if you keep doing 36-hour fast all the time because you’re going to just burn muscle. That’s not actually what happens in real life because you’re forgetting that after that period of fasting, you’re going to rebuild muscle. That’s what the growth hormone is there for. What you do in fact is you actually tear down all this kind of broken down, kind of junky old proteins and then you replace them with new proteins.

[00:24:00] When you look at studies of people who do alternate daily fasting, if you compare it to daily caloric restriction, the lean body mass as a percentage in daily caloric restriction … so if you look at percentage lean mass, in caloric restriction it goes up by about .5%. With the alternate daily fasting, it goes up by about 2.2%. In other words, fasting is about four times better at preserving lean muscle. It’s much better because you can just look at the period where you’re breaking it down, you have to look at the period where you’re building it up.

[00:24:30] Again, the other interesting thing is that for years, we’ve never sent a patient to the surgeon to get flabby skin off. Why? Because all that excess protein, that’s the excess skin, excess connective tissue, blood vessels, all that stuff that feeds that fat, if you don’t break down that protein, it’s going to hang off as loose skin. What we find is that we actually just about never have that problem because the intermittent fasting takes care of that problem for you. Because the body is much smarter than we are. If it sees excess protein that’s hanging around with nothing to be used for, it’s going to break it down.

[00:25:00] Again, thinking about pictures that you’ve seen of, say Holocaust victims. They’re very skinny, they’re very thin because they’ve been starved in a real sense, but there’s no loose skin. The body has used that for fuel. Your body can do the same thing. It’s actually interesting because there’s a process called autophagy where you break down these proteins, and the 2016 Nobel Prize in Medicine was just awarded to one of the early researchers of this process of autophagy. It’s actually considered a very healthy process because you’re taking kind of old protein and replacing it with new protein.

[00:25:30] But if you’re talking athletics now, what you have to do is limit yourself to the shorter periods of fasting—16 hours, 20 hours, 24 hours—because you may or may not want to get into that period of burning. If you are lean compared to if you’re obese, you’re going to burn more protein. Why, because if you have more fat, your body’s going to use more fat. It depends on the context. Yes, if you’re lean to begin with, then you probably don’t want to be going into a lot of these 36-hour fast because you’re going to burn more protein that you don’t actually have that much of or you’re interested in keeping it up. You’re going to skew yourself more towards the shorter end of the spectrum.

[00:26:00] For example, there’s a story of Hugh Jackman, who when he’s training for the role of Wolverine, did a lot of these 16-8, like 16-hour fast and 8-hour eating window sort of thing. He was able to tone himself up incredibly well because he was using this sort of intermittent fasting to his advantage.

[00:26:30] Just to put that into context, and I’m going to use myself as an example. I’m 44 years old, I see myself as relatively healthy, I’ve got good bloods, I’m 70 kgs, almost 6 foot tall, low body fat. How would I use fasting to optimize my health?

[00:27:00] Well again, you probably could go with a short, kind of daily 12, 14 hours and do just fine. People say, do you need to fast? Well, it’s part of everyday life, but you could do kind of three meals, breakfast, lunch, dinner, and be completely fine. Because you don’t need to lose weight, there’s no need for you to expand that. If you want to try and use it to your advantage, then what you could do is go with a 16-8, training in the fasted state … so when you’re doing your workouts, you may be able to do better workouts and build up better by slightly adjusting that. Not huge amount, but you do a 16-8.

[00:28:00] The other thing that some people recommend is kind of a yearly longer fast, like couple of days kind of thing. That’s more for stimulate this … kind of breaking down of cancer or preventing cancer, that kind of thing. If you think about it, that’s not far off of what many religions have always recommended. Don’t eat all the time, but also, around Easter, around Ramadan [inaudible 00:27:53] religions … exactly … well, there’s periods of fasting, some of them fairly long. We’re not saying, oh, go 40 days and 40 nights. We’re just saying hey, maybe a couple of days is okay. Everybody always gets bent out of shape about doing like a five-day fast, for example. I’m not saying it’s great fun. Nobody ever said that it was, but I’m talking healthy here.

[00:29:00] If you think about it again, look at the numbers. If you eat three meals a day, in a year that’s roughly a thousand meals. If you do a five-day fast, you can miss 15, 15 of those thousand meals, and everybody always gets on my case, “Oh my God, you’re going to kill people.” Like, really? Are you serious? If you’re 60 years old, you had 60,000 meals, and I’m telling you to miss 15 of those 60,000 meals. That’s ridiculous that there’s going to be a problem. Our body is obviously going to be able to handle it, and there may be a lot of benefits to it. That’s all we’re saying. You’ve got to understand how to use it, you’ve got to understand what your [inaudible 00:29:01] are. This is where I get a lot of flak from people who are relatively healthy, relatively lean. It’s like, “Oh you shouldn’t do these fasts.” I’m like, yeah, because your goal is completely different than my 350-pound patient with 200 units of hormone. They’re completely different, I’m going to use completely different regimen. You have to understand that. Of course people don’t, they just kind of hear one thing and then say [inaudible 00:29:26]

Another thing I want to raise as well, Jason. If someone’s listening to this and they’re using fasting as a way to maintain their weight, which is fair enough, but doesn’t that give them a license to eat whatever they want outside of that window because then they’re using fasting to bring their weight loss back into that state.

[00:30:00] You can, although obviously it’s not optimal. It’s hard because it’s not exactly the same thing. If you eat a lot of sugar, you’ll be better off fasting than not fasting, that’s for sure, but it’s not like it’s going to make you healthy. You can’t do something bad and then something good and pretend that it’s okay. You still had all that processed sugar and stuff. So it’s not quite that, but it is better than doing nothing at all.

[00:30:30] The whole idea is that for people, it’s actually a lot easier to do it on an intermittent basis, and for people who haven’t done it before, it may be actually much easier for them. Everybody’s tried these caloric restriction diets, right? They don’t work. Period. Everybody’s done it, it never works. We’ve been telling people to do these caloric restriction diets for 50 years, we’ve been singing the same song, and nothing’s been happening.

[00:31:30] The thing is sometimes, it’s just easier to not eat at all. It’s like my son. You can’t get him into the bath, but once he’s in the bath, you can’t get him out of the bath. There’s this whole inertia that goes along with it. Once you start eating, it’s actually a lot harder and takes a lot more willpower to say, “Okay, wow, this is delicious. I’m not nearly full, I’ve only had three bites, but I’m going to force myself to stop even though there’s all this food here and I really could just eat the whole plate.” Why would you do that? Why won’t you just say, “Okay, I’m not going to eat,” don’t even look at it. Go do something else. Watch TV, read a book, do something interesting, and then by that time, everything’s passed, and then you haven’t anything. Guess what, your body will simply eat the equivalent number of calories from your body fat. That’s it.

[00:32:00] Again, people think that it’s really hard. Like I said, it’s not fun. Sometimes it’s just easier than doing the opposite, and you can … because it’s so flexible, you can mix and match. You can [inaudible 00:31:55] lot this week and not at all next week. It’s Christmas, I’m not going to fast, so for a week and a half, I didn’t fast at all. It’s okay, because I’m going to make up for that later on. Or you make up for it before. You can use it to make those adjustments because life is like that. That’s life. Life is not this, life is full of ups and downs, both in stress and personal life, but also in eating.

[00:32:30] That’s the secret. The cycle of life is feast and fast. It’s not constant deprivation. When it’s somebody’s birthday, you feast. When it’s wedding, you’re not eating salad, right? You’re eating cake. It’s not good for you and so on, but it’s a treat. The point is you can’t have treats everyday, and when you have treats, you have to make up for it with periods of fasting. That’s what we’ve always done. Feast and fast. That’s the cycle, and we for some reason think that that’s a really bad cycle, but that’s just life.

Yeah. Jason, you look like a very fit and healthy guy. How often do you fast? How do you bring it into your-

[00:33:30] I do it … the easiest thing for me, I do it probably, 24 hours of fasting is my typical. I rarely eat breakfast because I find it easiest meal for me to skip. Again, that’s probably five or six days out of seven, so Monday to Friday, and when I’m working, I almost … I rarely eat breakfast because I find it easy. Like now, it’s like nothing at all. I get my coffee … instead of waking up, making some eggs, washing up, eating … that’s 45 minutes, right, 30 minutes. It’s like now, I get my coffee, I walk out the door. It’s so much easier, right?

[00:34:00] Then I skip lunch sometimes and then that’s a 24-hour fast. You do that three or four times a week. Truthfully, again, and this is to my point of the multiple benefits, it all depends. When I’m really busy and have a lot of work to do, I fast a lot more. Why? Because I want that extra 30, 45 minutes of time to do work. When I was writing my book, for example, I was fasting all the time. But it wasn’t because I was trying to lose weight, my weight stays relatively stable. It’s because I wanted the 30, 45 minutes everyday, so it’s like four times a week. You know what, that adds up. 45 minutes a day, four days a week, all of a sudden I’ve got an extra three hours. Three hours of extra time every single week.

[00:35:30] People always complain about how busy our lives are, how complex our lives are … well guess what? Fasting is actually a way that simplifies everything. Because it’s not something that cost you money, it saves you money. That’s not something that cost you time, it saves you time. It’s not something that makes your life more complex. Oh, can I eat this grass-fed butter, or is this organic regular butter … Okay, right? It’s not complex. Just don’t eat anything. Have some water, and that’s it. It simplifies your life because it’s almost the exact opposite of every single diet. It’s not something that you do, it’s something that you don’t do. You can add it to whatever diet you feel you want to do. You want to do a vegan diet, you can still fast. You want to do one of these low carb high fat diets, ketogenic with a lot of meat, you can still fast. If you don’t eat nuts or you don’t eat wheat or you want to do a low fat diet, you can still do it. There’s so many different advantages because it’s actually the complete opposite of every other diet that’s out there. It’s like the anti-diet.

[00:36:30] That’s the advantage. I used it a lot more for time saving and especially like … I went on a cruise in the summer, and I seriously gained a lot of weight. It was like, okay, time for a little fasting. That was about the only time I really said, “Okay, this is bad, [inaudible 00:35:55]” That was that, but I had a great time. I didn’t really watch what I did, and guess what, in a couple of weeks, I was back [inaudible 00:36:05], it’s like, “Okay, that’s good.” The key is that I was able to enjoy myself on that because I was around other people who weren’t really very strict, and you go out and you don’t want to be that guy who doesn’t eat this and doesn’t eat that and a big party pooper. You do it, and then it’s like, but I’m okay because I know I have a tool that I can use to bring myself right back down and then I’ll have forgotten about it two weeks later. But I’ll remember that I had a great time. That’s the whole idea, it’s flexible and powerful.

I like it, I like it. It’s perfect advice. You mentioned a book as well, you’re writing a book. I just wanted to touch on that as well. Was the book with Jimmy Moore? We’ve had Jimmy on the show before. I wanted to find out a little bit more about-

[00:37:30] Yeah, so the first book I wrote was called The Obesity Code, and that’s really a book about what causes weight gain. Everybody thinks it’s about calories, but it has nothing to do with calories. It goes over why the whole idea of calories is so incorrect. The reason that it’s incorrect is because our body really just doesn’t have any way to measure calories. If you eat say a hundred calories of cookies, or a hundred calories of broccoli, people pretend they’re the same thing because it’s all about the calories. Well, the body responds entirely differently the minute that food goes in your month. The cookies, the blood sugar goes up, your body starts to store fat. The broccoli, it doesn’t, and it has a lot of nutrients and all this other stuff. But, the point is, that the body just doesn’t care about calories because it has no way to measure it.

[00:38:30] The reason that we’ve fallen so far off the track is because we completely misunderstood the cause of weight gain. If you think that too many calories causes weight gain, then you’re going to say, okay, then I’m going to lower my calories. We all did that, it didn’t work. Because you have the entire wrong idea. What actually causes weight gain is really hormones that tells our body to store fat. When you’re storing fat, you’re going to gain weight. The whole idea is if your blood sugar is high, how are you going to lower your blood sugar? That’s the whole key to weight loss. That’s really what it goes over in detail. It’s not a real diet book, it’s kind of a science book.
Then I touch on low carbohydrate diets, ketogenic diets and intermittent fasting, but intermittent fasting was like one chapter of that book. Then all of these people had a lot of question about regimens and practicalities and how to do it, what are the problems that come up, and that’s what we cover.

[00:39:30] I met Jimmy in Cape Town, and we’re talking about fasting, and he’s like, “Okay, well, what’s a good resource for this? What’s a good book I can just go out and buy? There is nothing. There is nothing. He’s like, “What about websites? Is there anybody that talks about it?” I’m like, “I talk about it. That’s about it.” Nobody really talks about fasting at all. It’s a really undercovered area. Then he’s like, “Okay, well if there’s no book, let’s write a book.” I’m like, “Hey, that sounds like a great idea.” That’s how that book came about, which is The Complete Guide to Fasting.

Yeah, and Jimmy’s got some great results, from what I hear as well, since he’s been bringing in fasting.

[00:40:00] He’s done some longer fast and he’s really showing how it’s doable for people. He did a 30-day fast, a 21-day fast, and he … You know how he is, he’s out there showing people. He did a daily kind of update on his fast. You can watch him and he’s like, “Yeah, I feel great.” Everybody thinks you’re going to be curled up on the couch in the fetal position for 21 days. It’s not. He’s out there, he’s doing everything he normally does, and why not? Your powering your body on the food that you stored away, that you’ve carried on your body. What’s the difference between powering yourself on food you’re eating now and powering yourself on food you ate from a month ago that’s carried around on your body as body fat.

[00:41:00] It takes a lot more fasting than you would actually … most people believe. If you look at how much fasting causes weight loss, a pound of fat is roughly 3500 calories and most people eat somewhere around 1800, 2000 calories a day. It takes almost two full days of fasting to lose one pound of fat. That’s incredible, so a 20-day fast which everybody thinks wow, that’s really long, and it is, is you might only expect to lose 10 pounds of fat. You’ll probably lose a bit more than that. You’ll probably lose 20 pounds, but a lot of that will be water weight which will come back. That’s why people say, “Oh, it’s failed, because you lost 20 and gained 10 back.” No, because you should have only expected 10 to begin with. That’s the key to that. If you understand that, then you know.

[00:41:30] So if somebody is doing a 20-day fast or 21-day fast, would you alter the way you go about your daily life during that time? Would you still be exercising regular like you normally would? Would you lose muscle mass a bit on 21 days? I know we spoke about short windows. How would you approach it?
[00:42:00] Yeah, you should do everything you normally do on fasting days that you do on a regular day because really, the way you have to think about it is that you’re feeding your body with body fat. You’re eating breakfast, lunch, and dinner of body fat. That’s the way you have to think about it. In terms of muscle loss, there is a study, muscle turnover, on that, and again, there is some protein loss as you go through. Not all of it is muscle, but you can also expect to regain some of that once you start re-feeding.
[00:42:30] Again, there’s a difference between obese patients and lean patients. People who are lean are going to burn … if you’re obese, for example, when you measure how much of your calories comes from fat during a fast, it’s like 90 plus percent. If you take a look at that same fasting period and put a lean person in, it’s like 70% body fat. There’s a hell of a lot more protein loss because there’s not as much body fat. Again, you have to really look at what you’re trying to do here because if you’re obese, then these long ones are not really that big of a deal.

[00:43:00] That makes sense, that makes sense. Last question, Jason, I’m just trying to clarify things as well. For people that are then doing the intermittent fast and might be 12, 18, 24 hours and might be a few times a week, in that other window period of eating, what you’re saying is just eat when you’re hungry and stop when you’re full, pretty much, and not be so concerned about how much food that you eat. You can eat in abundance if you want, but …

[00:43:30] Yeah. The key is to eat real foods because the thing about satiety is that if you look at processed foods, they don’t activate satiety mechanisms. You can say eat to satiety but you have to eat careful because the qualities [inaudible 00:43:38]. For example, if you eat steak, you eat and then at some point, you really just can’t eat anymore. These are like those eating competitions. Like you look at them and they’re green. You can eat any more, even though it looks delicious to the person who hasn’t eaten.

[00:44:30] But, and we’ve all had this phenomenon, is that if you have a huge meal and then somebody says, “Oh, you want another pork chop?” You’re like, “Whoa, no way.” But then somebody says, “Oh, how about a slice of apple pie?” You go, “Yeah, sure.” It’s like okay, what’s the difference? Again, here’s the thing. The calories, they might give the same number of calories, a small pork chop and a slice of apple pie, because that apple pie has a lot of calories. But the thing is that the apple pie is highly processed, it’s highly refined, and it doesn’t activate the satiety mechanism. What activates satiety mechanism? Protein does, fat does, but when you have just almost pure carbohydrate, it doesn’t. Same as fructose.

[00:45:00] I used to think this. Even when I was a child, I used to think, this is very interesting that you can eat a meal with water and be full, or you can eat a meal with Coke. You’d be equally full, but you took an extra thousand calories with that Coke. I was like, “Why is that?” It’s a lot of calories, but no satiety at all. That’s the sugar. The sugar really just doesn’t fill you up, which is why you say, well, if you want to have some snack or something, the worst thing to have is some sugary snack, which is what we all give the kids. It just doesn’t fill you up at all. But if you have fat, if you have protein, well there are natural mechanisms. Even carbohydrates, but not processed ones, like beans and so on. Well if you eat a lot of beans you’re just not going to feel it.
[00:46:00] Same even with something like potatoes, for instance. It’s a natural food, you got to remember. But it’s actually fairly filling … if not potato chips, but natural potatoes, like deep-fried [inaudible 00:45:40] might be different, but if you’re full and somebody says, “Here, you want a baked potato?” You’d be like, “Whoa, no way.” [inaudible 00:45:48]. Again, there’s natural satiety mechanisms that are there that are going to make you stop. As long as you stick to real foods and avoid the processed flour and sugars and so on, yeah, eat until you’re full because your body will tell you to stop.
[00:46:30] This is the whole thing with the sort of … there’s this whole notion out there that we’re programmed to eat, like eating robots. You put it in front of us and we’re going to eat until we get fat. There’s no truth to that whatsoever. In fact, there’s multiple mechanisms that stop us from eating. In the stomach, there are stretch receptors, if you eat too much, your stomach will stretch, it’ll tell your brain to stop eating. There’s [inaudible 00:46:37] which is activated by fat. Once you eat [inaudible 00:46:40] enough, it’ll tell you to stop eating. There’s protein YY, again, protein activates it, if you get enough, it’s a satiety mechanism. There’s multiple overlapping mechanisms to stop us from eating. When it’s highly processed, we bypass all those.
[00:47:30] This idea that we’re just programmed to eat and it’s like … okay, that’s just so untrue. There’s no truth to it but it sounds great on TV. It’s like oh, because we have food all the time, that’s why we’re all fat because we have food all the time. It’s like, well they had food all the time in 1950 as well. There was no starvation, but people were okay, they didn’t eat all the time. It’s a very interesting, the entire field of … I find it actually very fascinating, the entire field of obesity and so on, because there’s so many misconceptions out there about what we should do and what we should not do, but really, getting back to the real basics of eat real food, fast, you’d probably go a long way with those two simple principles.

[00:48:00] I know, it’s incredible, isn’t it? That’s beautiful, it’s a great answer. Thank you, Jason. Just looking at the time as well, we have a couple of questions we ask everyone on the show, Jason. The first one is, what are your non-negotiables to be the best version of yourself?

[00:48:30] That’s a hard one. I think that maintaining a healthy living, it doesn’t necessarily mean a specific weight, but obviously the most important thing to all of us is our health. Because you could be a billionaire but if you have all kinds of illnesses and cancer, well, it just ain’t worth it. I’d rather be kind of middle class, you know, have a house and a mortgage and a car that’s not too fancy, than a quadrillionaire with terminal cancer. To us, that’s really the most important thing, is maintaining good health.

[00:49:30] That doesn’t necessarily mean that you have a six-pack and you can bench 300 pounds. You can do fine just maintaining yourself in a normal way, and that’s where fasting is very good because … and it’s not the weight that’s the most important, it’s the waist size that’s most important. A very simple rule of thumb is keep your waist size, measured around, to half of your height. If you keep that, you can see from studies … so for example, I’m 65 inches, five food six, so 33 inches is the maximum I would want to be. The waist, which is the fat that accumulates around your waist, is actually far more dangerous to you than all the other fat.
[00:50:00] If you look at the metabolic syndrome, it doesn’t have a weight category. It measures the weight size, and that’s because that’s the most important. Once you get above a waist to height ratio of .5, then you see the complications really go high. It’s a way to stay healthy and it’s a lot easier to maintain that. I like to look at that as a good proxy of good health. It’s a simple way to measure. Because obviously some people don’t exercise much and do fine, and some people exercise a lot and do fine as well.

Fair enough. I’ve got a last question, Jason. What’s the best piece of advice you’ve ever been given?

The best piece of advice I think would really just to think for yourself. There’s a lot of people out there that give a lot of advice, and not all of it is wrong, but you have to see what works for you. Some people, they’ll do long fast and love it, and some people will do long fast and they hate it. Well guess what, you shouldn’t do long fast. Just because somebody else does it doesn’t mean you should do it. We all like different things. Some people like Led Zeppelin and some people like Britney Spears. It doesn’t mean somebody’s wrong and somebody’s right. It just means we are different.
[00:51:30] What you have to do is take the advice and say well, is it really working? If you say okay, I’m going to follow this reduce my calories, low fat advice. Is it working? If it’s not working, then it doesn’t matter that every dietician and every doctor and every association says that you should do it, you’re not doing well. Then you’ve got to change it and find something for you

[00:52:00] That’s probably the most important thing, and it’s important for me because I really had to kind of unlearn a lot of what I was taught in order to understand this whole process. I think that to me, it’s important to maintain a little bit of independence of thought, and it’s always good to listen to people, but you always got to use common sense. This is where we kind of get into this trap of listening to the experts and then throwing out our own common sense. That if somebody tells you, “Oh, you should eat all the time and you’re going to lose weight.” I’m like, okay, that really sounds dumb. It sounds stupid. But, “Try it,” and guess what, people do, and they gain a lot of weight because they’re eating all the time. It’s like, okay well, that was really bad advice. It sounded like bad advice, and it was really bad advice.
[00:52:30] Then it’s like, okay, common sense will tell you that you shouldn’t do it. What happens is that we get into this brainwashed state where we think, oh every expert, every doctor tells me to eat six times a day. I’m doing terribly eating six times a day but I’m going to keep doing it, and I’m going to make fun of those people who try to eat once or twice a day.
[00:53:30] You shouldn’t do that. Think for yourself, use your common sense, and you got to follow your own path. Because there are people who do terribly on low carb diets and then they say, “Oh I followed a high carb diet and did really well.” I’m like, great. I don’t care what you eat. If you’re feeling well and doing well, then you can go on doing whatever it is you do. But if you do poorly and then you come to me, I’ll say, “Let me give you some advice. You can try and change it this way or this way or this way and see if you do better, but don’t be so dogmatic that you have to … “Oh I have to do this,” “I have to do this.” No. Your body will tell you. You always got to come back and [inaudible 00:53:28] our bodies are wonderful machines because they know a lot more than we do and they can take a lot more, and they’ll always help us. But you got to listen to it. You can’t just say, “Oh, I’m just going to eat even if I’m not hungry.”
[00:54:00] You hear this all the time. If you’re not hungry at breakfast, it doesn’t matter, you still go to stuff your face with a couple of slices of toast. [inaudible 00:53:51] That’s not a winning strategy for weight loss. If you’re not hungry at breakfast, don’t eat that two slices of toast. Then people do better and they’re like, “Okay, I guess you’re right.” It’s like, well, it was common sense.

Stu It makes sense.

[00:54:30] That’s … yeah, it makes sense. I think that’s just a think for yourself kind of … and recognize that everybody is different, so you can’t say that just because you guys say it worked, just because that Fung guy says that fasting is good, it doesn’t mean that it will be good for everybody. It doesn’t it’ll work for everybody. You’ve got to tweak it and find a way to make it work for you. But it’s a tool in our tool belt. Probably the most powerful tool that we have. To throw that out and not use it at all, to me is completely nonsensical.


That’s good advice.

Yeah. Jason, if anyone wants to get any more of you, where’s the best place to send them website-wise?

I’m on my website as www.intensivedietarymanagement.com. That’s focused mostly on science, and then also on dietdoctor.com which is Andreas Eenfeldt’s website, I’m on there as well. There’s a lot of great stuff on intermittent fasting, lot of great stuff on low carbs and recipes, very easy to use. Both of those websites are excellent.

Beautiful, and of course there’s the book The Complete Guide to Fasting with you and Jimmy Moore, which was released last October, November if I’m not mistaken?

Yeah, late October.

Excellent. Well we’ll link it all to the show notes. This will go out to everyone across our audiences and I’ve no doubt they’re going to get a great deal from today’s topic. Thanks so much for coming on, Jason, and sharing your wisdom. It’s the first time we’ve-

Oh, thank you.

First time we’ve covered fasting on the show and yeah, it’s fascinating stuff. Awesome.

Yeah, absolutely. Thank you.

Thank you so much, Jason.

Thank you, gentlemen. Bye-bye.

Okay, bye-bye.

All right.

Dr Jason Fung

This podcast features Dr. Fung who is a Toronto based Nephrologist (kidney specialist). Dr Fung graduated from the University of Toronto and finished his medical specialty at the University of California, Los Angeles in 2001. He is the author of the bestsellers ‘The Obesity Code’ and ‘The Complete Guide to... Read More

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7 Replies to “Jason Fung: The Complete Guide to Fasting (& how to burn fat)”
Adrien says:

Its works really well from my own experience. I suffer t from Diabetes II treated by Metformin.
Now I don’t suffer anymore and I’m doing on daily base Intermittent Fasting. Thanks so much to Dr.Jason Fung its change completely my life. I’m his ambassadress today to every body that gives me compliments I’m told my story how dr Jason Fung his book came in to my life.

Guy Lawrence says:

That’s fantastic to hear Adrian! So glad to hear it’s working out for you 🙂

karen says:

Thank you the podcast with Jason Fung. I need to lose weight and his fasting theory makes sense.
Keep up the good work.

Guy Lawrence says:

You’re welcome Karen!

sam says:

If I go for a long fast, so I dont send any food into my stomach. Doesn’t it irritate me with gas, problems or those gastric juices eat my stomach inner layer and cause ulcers? What do you suggest me to do? Thank you for the reply. …Sam

Guy Lawrence says:

Hi Sam… I would email Jason’s team as they have vast experience on this:
Hope that helps.

Nicola Slade says:

Oh, thank you JF – I now feel free not to eat bloody breakfast. The nutritional people always banged on about how important it is, etc, etc. So I can eat over an eight hour period and fast for sixteen hours. I’m very slightly overweight so that’ll do me.
Years ago I did a carbohydrate lovers diet – where I only ate carbs for one hour a day (as much as I wanted) – and I lost a terrific amount of weight.
Thanks and regards Nicola

Comments are closed.