Fasting with Dr. Jason Fung

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  1. News and updates from Diane [1:49]
  2. Introducing our guest, Dr. Jason Fung [4:38]
  3. The basics on fasting [7:28]
  4. Health benefits to fasting [19:06]
  5. Intermittent fasting and hormone response [31:43]
  6. Benefitting from mini-fasting in combination with keto [46:37]
  7. Who should not be fasting [53:41]
  8. Hypothyroid and fasting [58:22]
  9. How to exercise while fasting [1:03:29]
  10. How to tell if we’re really hungry [1:06:07]

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Diane Sanfilippo & Liz Wolfe | Balanced Bites Podcast | Fasting with Dr. Jason FungDiane Sanfilippo & Liz Wolfe | Balanced Bites Podcast | Fasting with Dr. Jason FungDiane Sanfilippo & Liz Wolfe | Balanced Bites Podcast | Fasting with Dr. Jason Fung

You’re listening to the Balanced Bites podcast episode 298.

Diane Sanfilippo: Welcome to the Balanced Bites podcast. I’m Diane; a certified nutrition consultant, and the New York Times bestselling author of Practical Paleo and The 21-Day Sugar Detox. I live in San Francisco with my husband and fur kids.

I’m the co-creators of the Balanced Bites Master Class, along with my partner in crime, Liz Wolfe. And together we’ve been bringing you this award winning podcast for 5 years and counting. We’re here to share our take on modern paleo living, answer your questions, and chat with leading health and wellness experts. Enjoy this week’s episode, and submit your questions at or on our Instagram page. Remember our disclaimer: The materials and content within this podcast are intended as general information only, and are not to be considered a substitute for professional medical advice, diagnosis, or treatment. Before we get started, let’s hear from one of our sponsors.

Liz Wolfe: The Balanced Bites podcast is sponsored in part by the Nutritional Therapy Association. The NTA trains and certifies nutritional therapy practitioners and consultants (including me; I’m an NTP), emphasizing bio-individuality and the range of dietary strategies that support wellness. The NTA emphasizes local, whole, properly prepared nutrient dense foods as the key to restoring balance and enhancing the body’s ability to heal. Nutritional therapy practitioners and consultants learn a wide range of tools and techniques to assess and correct nutritional imbalances. To learn lots more about the nutritional therapy program, go to There are workshop venues in the US, Canada, and Australia, so chances are you’ll be able to find a venue that works for you.

1. News and updates from Diane [1:49]

Diane Sanfilippo: Hey everyone! It’s me, Diane, here with a very special guest today who I will introduce in just a few moments. A couple of quick updates for you guys. The June 21-Day Sugar Detox kicks off on Monday, June 5th. And I know a lot of you guys have been curious about the program. It’s something that has been running for now more than 7 years. So if you’ve never taken it on, this is a great time to do it. We kick of Monday June 5th. You can go to Jump in, grab the online program and the books that way. Or you can always check out your local bookstore or for the books. But I of course always recommend the online program, because that’s how we get to give you extra goodies, wink, wink. Some fun stuff will be coming up in the next several months or so. So if you jump in and then want to do it again at some point, you can do that. Or join us any time you’re ready.

The 21-Day Sugar Detox coaches program enrollment closes today, as of the day this episode airs, on May 31st. So if you’ve been on the fence, you’ve been thinking about it, curious about it. Even if you’re just interested but don’t think right now is the time; join us over in the Facebook group we have. It’s for the 21-Day Sugar Detox coaches program; it’s called the interest group. You can just search for it on Facebook and you’ll find it. That’s where we’re kind of answering all the questions. I’m doing some live videos covering different topics. Just teaching on different business and connecting that with the 21-Day Sugar Detox coaches program, teaching you guys all this information. So, check it out there. It’s also a great place to be if you’re just curious about maybe doing it next year. This way you’ll be in a spot where I’ll be able to tell you about it when enrollment opens again in 2018.

Finally; I’ve got an event coming up with Cassy Joy Garcia in Vancouver, British Columbia. So if you are anywhere in the area, that’s the only event we have. It’s not another tour, it’s just kind of a one-off. We wanted to do a fun girls weekend, and we decided; “Of course! We should do a book signing, too!” Because that’s really fun for us. So it’s going to be on Saturday, June 10th in Vancouver. You can get to the link from details in the show notes here, and we’ll probably make sure that that’s added to the events page if it’s not already. And RSVP to that. I think you can also get to it from my Instagram link tree thing-a-jiggy. You can RSVP there. So we’ll see you there.

Liz Wolfe: Today’s podcast is sponsored by Vital Choice seafood and organics. Purveyor of premium sustainably sourced seafood and a certified B corporation. Vital Choice offers a wide range of fish, shellfish, humanely raised meat, protein rich bone broths, and paleo friendly snacks like organic dark chocolate, super antioxidant trail mix, and bison jerky. As the days get longer and the grilling season heats up, is your source for real food.

2. Introducing our guest, Dr. Jason Fung [4:38]

Diane Sanfilippo: If you’re not already familiar with my guest for today’s episode, let me give you a quick background. Dr. Jason Fung earned his medical degree at the University of Toronto, where he also completed his internal medicine residency before heading to the University of California, Los Angeles, for his fellowship in nephrology. He currently practices as a kidney specialist in Toronto. He is currently the site chief of medicine at Scarborough General Hospital, and the scientific editor of the Journal of Insulin Resistance. During the course of treating thousands of patients, it became clear to Dr. Fung that the epidemic of type 2 diabetes and obesity was getting worse. The prevailing dietary recommendations to reduce dietary fat and calories were clearly ineffective. He founded the intensive dietary management program to provide a unique treatment focus for type 2 diabetes and obesity. Rather than focusing on medications, this clinic focuses on dietary changes that are simple yet effective.

In March 2016, Graystone Books published Dr. Fung’s first book, The Obesity Code, which explores the underlying hormonal imbalance that leads to obesity and recommends effective strategies that address the root causes of weight gain. His second book, The Complete Guide to Fasting, was published in October 2016. This offers a practical guide to all matters related to fasting, including fasting regimens, what to expect, how to deal with problems, and simple remedies. We’re going to be giving away a copy of Dr. Fung’s The Complete Guide to Fasting book, so make sure you check the Balanced Bites podcast Instagram tomorrow for all the details on how to win.

Alright, so today we’re going to talk about fasting. Intermittent, alternate day, extended. All kinds of fasting, and how this can be an extremely therapeutic approach to taking your health to the next level. And we’ve got an amazing guest. We have one of the experts who is out there right now with his book, The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate Day, and Extended Fasting, as I mentioned, Dr. Jason Fung. Thank you for joining me today!

Dr. Jason Fung: Thanks for having me. Great to be here.

Diane Sanfilippo: It’s really exciting. This is a topic we’ve been asked about so many times. We’ve touched on it a bit just from sort of the practical, nutritionist perspective. What we see in our practice when women try and approach this idea of fasting from a perspective of simply an attempt to limit calories, or a way to cut themselves off. And I think what I’m most excited about for our conversation today is getting into a lot of the nitty gritty and some of the therapeutic benefits of fasting. And talking about it more from that perspective. And not thinking about it so much as an approach to diet, as an approach to, a therapeutic intervention.

3. The basics on fasting [7:28]

Diane Sanfilippo: So why don’t you start with the basics. What is fasting? What is intermittent fasting? All different types; how do they differ? Just give us the basics there.

Dr. Jason Fung: Yeah. I think that this is very important, because it really sets the stage. There are lots of different types of fasting. You can go, the classic is really water fasting. So a period of time that you’re not eating. That’s really what fasting is. It’s only the flipside of eating. So any time you’re not eating, technically you’re fasting. And this is something that people have always done. So for example, in the 50s, you would have people that would stop eating after dinner, say around 7 o’clock, and then who had breakfast at 7 a.m., that’s a fast of 12 hours. And that’s where the word breakfast comes from; it’s the meal that breaks your fast. And what it implies is that really it’s just part of everyday life. You cannot break your fast if you haven’t been fasting. So this is something you’re supposed to do every day. And it’s a way to stay in balance. So if you’re feeding for 12 hours, 10 or 12 hours, and you’re fasting for 10 or 12 hours, then you’re in balance.

So during the time that you eat, your insulin goes up. There are other hormones; other things that happen. But insulin goes up. And that gives your body the instruction to store food energy. And you store it in two different ways; as sugar, which is glycogen in your liver. And when that’s full, then you store body fat. So that’s all that happens. And when you don’t eat; when you fast, then your insulin levels fall, and the falling insulin levels, again gives information to the body that nothing is coming in. We need to start pulling out those calories that we stored away. And that’s why you don’t die in your sleep every single night. Because your body stores it and brings it back. Kind of like your wallet. You put some money in your wallet, you take it out. It goes in, it goes out. And every day, there’s a sort of balance to that.

What gets us into trouble, then, is when you start to let the feeding take over from the minute you get out of bed to the minute you go to the bed. The only time you’re not eating is when you’re actually sleeping in your bed. That idea that you have to eat all the time. Now your feeding and fasting times are out of balance. And that’s what leads to a lot of weight gain. So that’s what fasting is.

Now, there are quite a few variations. Normal, if you go back to the 50s, is a 12 or 14-hour fast. That was considered just normal. Nobody called it anything in particular. If you start to extend it, then you go to, say, a 16-hour fast so that’s what some people call a 16-8 schedule. So, 16 hours of fasting and 8 hours of eating. That’s what makes up your 24 hours in a day. So what it means is that you eat within an 8-hour eating window; say from 12 to 8 or 11 to 7. And that’s a very popular sort of schedule. You might do that 5 or 6 days out of the week. That’s the idea. And you can extend it further. It can be as flexible as you want to be. You can go 24 hours, 36 hours, 42 hours. Then you get into the multiple day fast.

So 24 hours is another popular regimen, where you go from dinner to dinner, or lunch to lunch. So it’s technically perhaps 23 hours, for example. But you might eat dinner, finish at 7 p.m., then you don’t eat again until the next days’ dinner at 7 p.m. So it’s a 24-hour fast. And you might do that slightly less frequently. You might do that, for example, 2 to 3 times a week. If you go for the whole day, and some of these longer fasts we save for; not save. But we use for more sicker patients, such as type 2 diabetic, people who really have a lot of weight to lose. You can go up to 32, 36, 40 hours sort of thing. That means if you eat dinner say on Monday, say you finish dinner at 7 p.m. You would actually go through all of Tuesday and not eat anything, and then go right through to Wednesday morning. So it’s longer than 24 hours. It’s somewhere around 36 hours-ish. If you skip breakfast on that day, it goes into a 40-hour fast.

Then we go into the multiple day fast, and we typically try to avoid the kind of 2-day fasts. There is a very practical reason for that. You can if you want to. But from experience, we know that day 2 tends to be the hardest day of the fast. Some people find it’s day 3. So if you’re going to get to day 2 or day 3, which is the hardest day and then quit, then you’re not getting the maximum benefit, it’s not a very efficient strategy. So once you get past that, every day gets easier. And the reason is that your body has moved into burning fat. So you’ve burned through all the sugar. You’ve gone through the gluconeogenesis stage, and you’re into just burning fat. So your body is really feeding itself from your body fat. In essence, you’re eating breakfast, lunch, and dinner of your own body fat. And that’s perfect. That’s terrific. That’s exactly what we want it to do.

And hunger actually starts to go down. So you can measure the ghrelin, which is a hunger hormone. And you can see that it typically peaks somewhere around day 2. So day 3, day 4, day 5, it actually goes down and down and down. So that’s how people do these extended 7-day, 14-day, 30-day fasts. Because it’s actually a lot easier for them, because the hunger has diminished. So if you’re at day 2, you’re like, “Man, I am never going to be able to go on. That’s the worst day.” If you quit, you don’t get any further benefit. But if you push through that worse day, every day gets easier. And that’s how Jimmy Moore, for example, goes 21, 30 days. And because by day 5, the hunger has gone, you’re feeding yourself through your body fat. You’re feeling good, you’ve got lots of energy. And you’re like; “I can do this forever.” So that’s great. So why would you stop at day 2?

So that’s where we kind of draw the line. We kind of try to nudge people away from doing a lot of 48, 72-hour fasts, to get to the longer stages. Because the average weight loss on a fast is only half a pound of fat per day. It sounds really little. So 6 days of fasting, which seems a lot. And it is. You’re expected to lose only 3 pounds of body fat. That’s it. You are going to lose more than that; you’re going to lose 6 or 7 pounds. But that’s water weight. So you’re going to lose, say, 7 pounds, and 4 of it will immediately come back. And that’s where people say, “Well, that’s all a waste of time.” It’s like, “No. You shouldn’t have expected to lose that much in the first place.” So if you know that ahead of time, if you know it going in, it presents that kind of disappointment because you think that 7 pounds will stay gone but it won’t. 4 of that comes back, it’s only 3 pounds.

If you think about it, the math works out quite close to the experimental evidence, which is a pound of fat roughly has 3500 calories. If you’re eating 1800 calories for example, it’s 2 full days of fasting for 1 pound of fat. So if you have 100 pounds to lose, you could really go 200 days to lose all that fat. And that’s a long, long time. Even I don’t recommend people going that long.

So those are the different regimens. And then there’s different types of fasts. What you allow during the fasting period is all different as well. So classic is a water only fast. There’s something called a dry fast, which is used in some religions. Muslims during Ramadan, for example, will neither eat nor drink. So you’re doing 2 things; one is you’re fasting, because you’re not eating. But you’re also getting dehydrated because you’re not drinking. So it tends to make things more difficult than it really should be, because you’re not deriving any medical benefit from getting dehydrated. Because you’re going to drink again after the fast is done, rehydrate.

Some people say, and I don’t have much experience because I never recommend it. But some people say that your body releases the water and you don’t actually get dehydrated. That’s possible. But in either case, our experience from people who do Ramadan is that it’s a lot harder than just simple fasting. So why make it difficult for you; you want to try and make it easy. So we don’t recommend that.

Then you get into variations. So other than water, most people will say teas and green teas and herbal teas are quite fine. Because there’s no calories in it. And also avoid artificial sweeteners and artificial flavors. Crystal Light and that sort of idea. There are some people who do well with it, like diet sodas and so on. But in general, I think it makes it more difficult for people and it also can raise insulin and cause cravings and these sorts of things. So I say no artificial sweeteners, no artificial flavors. Even though there are zero calories. Coffee, for example, black coffee is fine. There are really zero calories in that. We often allow a little bit of cream in it, because it makes it easier, again. But no sugar.

Then you get into other variations, such as fat fasts, where you eat almost pure fat. The idea being that you can take in all these calories, but pure fat has very little insulin effect. And it’s really the dropping of the insulin which causes the weight loss. It triggers your body to release the energy to switch over to burning fat. So you can do these things. So bulletproof coffee, for example, is an example of a fat fast because it’s coffee with all this blended butter, which has very little insulin effect. A lot of calories, but very little insulin effect. So that’s called a fat fast. And some people use something like bacon and avocado during a fast; again, with the idea that this sort of thing.

But now you’re moving further and further away from classic fasting. However, some people do very well on that. So if you’re doing, then it doesn’t matter whether you’re technically breaking the fast or not. And that’s why we allow the coffee with cream. Because if you’re doing well, then who cares? We’re not purists, we’re pragmatists. We just want to get results. So those are the variations. We also allow bone broth on some of the longer fasts. That’s again, there’s calories, there’s protein. It’s not a true fast. But it helps people during their fasting so they can get through.

Diane Sanfilippo: That is a really amazing, well-rounded introduction to fasting. I think a lot of our listeners probably, maybe were shocked to hear that somebody who has got, say, 100 pounds to lose could go 200 days. But when you think about it, that really is kind of the purpose of the storage of all this body fat, is really to help us through those times when we’re not eating. But modern society; there’s an abundance of food all the time everywhere, any kind you want. There’s never an end to it. So I’m really glad to hear the background on all of that. All of the descriptions. I think that will really help people.

4. Health benefits to fasting [19:06]

Diane Sanfilippo: The one thing I want to really hear a little bit more from you on, besides obviously some of the fat burning effects for people. And I think the largest benefit for that sort of, I don’t know, bigger chunks of fat burning as you were talking about. For example, somebody who does have 100 pounds to lose. A lot of our listeners, some of them may be in that camp. A lot of our listeners really are more in the health and longevity. What are some off the benefits to fasting when we perhaps don’t have type 2 diabetes? Or insulin resistance? Or maybe we don’t even have more than 10 extra pounds of body fat kind of sitting on us? I know there are still benefits to fasting, and I think that’s something that our listeners would be really curious to learn a little bit more about.

Dr. Jason Fung: Yeah. There’s actually a huge number of benefits. They’re different. So there’s the metabolic benefits. And this is where it’s kind of important to address some of the myths about fasting. So one of the big myths is you should never, ever skip a meal because your metabolism will go into starvation mode. So the idea is that you’re going to shut down your metabolism. So if count calories, for example, and suppose that you normally take 2000 calories per day, your burning 2000 calories per day, because you’re not gaining or losing weight. However, you’re at a weight that’s higher than you would like. So you want to lose 10 or 15 pounds, for example. So you say, “What I’m going to do is go down to 1500 calories, and I’m going to increase my exercise. Therefore, if I’m burning 2000 and taking in 1500, therefore there’s a net deficit of 500, I’ll lose a pound per week. In 15 weeks, I’ll lose those 15 pounds. Yah, hooray, we’re all done.”

That never happens. Ever. And we’ve known this for 100 years. The experimental evidence is very clear that when you do that, you will initially lose weight, then you’re going to plateau. Even at that 1500 calories a day that you are taking in. You’re weight then starts to go back up. Eventually you feel cold, you feel tired, you feel hungry, and your weight goes back to what it was. 10 or 15 pounds back up. That’s what always happens. And that’s been everybody’s experience. And the reason that that happens is because your body is simply not stupid.

If you are burning 2000 calories, and taking in 1500, your body knows that if you keep that up, you will die. So it quickly ramps down its metabolism to match it at 1500. In fact, it goes below, because it needs a little bit of a margin of safety. So it will go down to say, 1400. So you’re taking in 1500, and now your burning 1400. You’re not losing weight. It’s starting to come back up, despite the fact that you stayed on that diet. But because you’re burning 1400, this is the basal metabolism. That’s what goes to generate body heat, it keeps your heart pumping, it keeps your extremities warm, it keeps your liver working, your heart working, and all that. You’re using less energy, your body is shutting down, basically. So, you’re cold. You’re tired, you’re hungry, you feel like crap. And your weight is coming back up. And that’s what always happens. Because your body has that ability to ramp it down. Just like if you normally earn $100,000 a year, you spend $100,000. Now your salary goes to $50,000. You don’t keep spending $100,000, because you will go to jail. That’s simple. So you’re not stupid, your body is not stupid. That’s what it does. It goes down, and that’s it. You’re toast.

And this is really one of the most unfair things we do, as medical professionals, to people. Is say that, “Oh, this is what you need to do. You just need to cut your calories. Count your calories, cut your calories, and that’s it, you’re done.” We know that has about a 99% failure rate. And when people fail, we then point the finger at them and say, “You don’t have enough willpower. You didn’t follow the diet. You didn’t do what I told you to do. Because the advice is good. You’re just defective somehow. You’re a glutton, you’re a sloth.” And that’s really the most unfair thing we do. Because we know that 99% of people fail. So how do you blame them for failing when you know that they will fail right from the get-go. And it’s proven. What happens to our body; we have studies going back close to 100 years that show this.

So where fasting is a benefit from a metabolism standpoint is that your basal metabolic rate doesn’t go down. Which seems counterintuitive. Because if you go from 2000 calories in, 2000 calories out, and you go to zero. What happens is that your basal metabolic rate stays close to 2000 calories. And you say why? How is that so? And the reason is that your body is actually switching fuel sources. So because your insulin is dropping precipitously low, your body now switches from burning food to burning stored food. Which is body fat. I mean, that’s what it’s there for. It’s not there for looks. It’s there for you to use as energy when you have nothing else. So you start burning body fat. And your body is like; “Whoa, there’s tons of this stuff. Let’s just burn it. I have 200 days that I can burn it for straight.” So go ahead.

At the same time, if you look at what happens to your hormones, there is something called counterregulatory hormones, and they run counter to insulin. That is, insulin tends to drive blood glucose down, and store food energy. These counter regulatory hormones tend to pull energy back out of your body and make it go up. And what are these hormones? They’re the sympathetic nervous system, noradrenaline, and growth hormone. So in fact, your body is not shutting down. Your body is being activated. So the sympathetic nervous system is the so-called fight or flight response. It’s a mild activation of your body; noradrenaline pumps your body up. Growth hormone gets your body ready to build new protein when you start eating again. So in fact, what you’re doing is you’re pumping out all these hormones to keep your basal metabolic rate high. And that’s why your basal metabolism doesn’t drop on fasting the same way.

Because remember; your body has two fuel sources. Food and stored food. You’re switching them when you fast. When you simply reduce the food; you simply reduce what’s going in. But because you’re still eating all the time, you’re not able to access those stores. Because you’ve stored it away. Your body has no instruction to switch over and use it, so it’s still locked away. All the fat is kind of locked away where you can’t access it. Your only access is to the food that you eat, and you’re not getting as much, so you ramp it down. So that’s the difference. There’s a huge metabolic barrier to weight loss, and that’s one of the huge advantages to fasting in terms of weight loss.

So that’s one of the metabolic benefits; keeping your energy high. And that’s why people feel so good when they’re fasting. We get people; and keeping in mind, again, that if you do it for the first time, you may not feel so good. It does take a little bit of time for your body to get used to it, just like ketogenic diets. There’s the so-called keto flu, which is a fairly well-known phenomenon, which when you start with the ketogenic diet, you feel a little crappy for a few weeks, until you can get your body sort of used to it. So you get the same thing with fasting. The first couple of times will suck; that’s what we say. They will suck, and there’s nothing I can do. But you do it, you get through, you let your body get used to the fasting, and pretty soon your body is able to switch fuel sources much easier. So that’s the one thing. They feel good when they come back. They say, “Wow, I have so much energy!” Why? Because you’re finally letting your body burn the fat. And that’s what we all want it to do. We want to burn fat. And how are you going to burn fat if you’re still eating all the time? You’re not letting your body digest the food. Because that’s the problem. Fasting is not about calories. If you take any period of time, you can eat the same number of calories. But it’s about lowering the insulin. So it’s about time, letting your body have a period of time where your insulin levels fall. To let your body digest the food and start to use it. So that’s the real metabolic advantage.

And then you talk about other advantages. There are all kinds of other health benefits to fasting that are really just being recognized. These are a lot more experimental. There’s not as much data behind them. But at the same time, they’re very intriguing. One of the things you get during fasting is something called autophagy. So autophagy is a very hot topic in science circles, because 2016 Nobel prize in medicine went to one of the pioneers of this research. And it was really studied in yeast and other small organisms, so it’s a pathway that has gone a long time.

So what autophagy is is the breakdown of sort of subcellular proteins that are sort of old and junky. So if your body senses that you’re not eating, what it does. There’s a period of time it burns through the sugar, but there’s a period of time; somewhere, 16, to 24, to 36 hours. Somewhere in that time where it actually starts to break down some protein to produce glucose. And everybody thinks that’s a really bad thing, breaking down protein. “Oh, that’s bad. Oh, that’s bad.” But it’s actually not bad. Because when you break down the protein, you’re taking old, sort of defective, junky old proteins, you’re breaking it down for energy, but at the same time the growth hormone levels go up so that when you feed again, you’re going to rebuild that protein. So in fact, rejuvenating yourself. You’re actually reversing a lot of these sort of processes that can lead to disease. That is, certain diseases are caused by sort of buildup of all this excess junk in your body.

So Alzheimer’s disease, for example, is a buildup of all this excess protein in the brain that clogs everything up. And perhaps, and it’s very interesting but not proven. Perhaps that will let people prevent Alzheimer’s disease. Same with cancer. Maybe your body will be able to prevent the development of cancerous growths because they’ll just get fed into the fire to get burned. And then when you rebuild them, you’ll just rebuild normal cells. Again, very, very interesting.

And when you go back in history, you see that people have always had this idea that they should do, once in a while. Once a year or whatever, some sort of longer fast in order to kind of clean house. So you have the Christian period; the catholic period of Lent, which just passed. Jewish will have fasting during Yom Kippur, and Muslims will have fasting during Ramadan, which is their holy month. So all these religions kind of independently came up with this idea that there’s something really intrinsically healthy about, once in a while, just not eating and letting your body clean itself out. And that’s what they’re called; cleanses, detoxes. All this sort of idea. And it sort of pervades throughout history that yes, this is something that’s very good for people to do. There are people who talk about it as an anti-inflammatory; maybe it decreases the inflammation so that disease such as lupus, rheumatoid arthritis perhaps are better, as well as all kinds of other things. If you lose weight then your back pain, hip pain, joint pain. Obviously if you’re not carrying those extra 20-30 pounds, that’s going to be a benefit to you. So that’s the kind of…

Diane Sanfilippo: {laughs} Just a few benefits.

Dr. Jason Fung: {laughs}

5. Intermittent fasting and hormone response [31:43]

Diane Sanfilippo: Just a short list. You know, something that you said kind of struck me when you were talking about the math approach to fat loss. I mean, some people call it weight loss just in general, but we are talking about fat loss. When we talk about the reduced calorie approach versus perhaps a reduced feeding window, but isocaloric. So talking about; what if somebody were to eat the sane number of calories, but shrink their feeding window to something like you recommended, or you mentioned, I should say, 16 hours of fasting, 8 hours is your timeframe of perhaps eating. I’m curious; have you seen that as a more effective approach for slow but perhaps sustained to whatever level is necessary fat loss, perhaps, eating the same number of calories so that we’re not slowing the metabolism. But having those breaks where, for a generally healthy person we’re talking about at this point.

Dr. Jason Fung: Yeah.

Diane Sanfilippo: Maybe; we call it the vanity 5 or 10 pounds around here, because when someone says they want to lose 5 pounds, I’m like, “You don’t probably need to lose 5 pounds.” You know? That’s not a health issue, it’s just a vanity issue. But that’s kind of the question of; will we get those health benefits, but also not suppress our metabolism, and perhaps see our body able to burn fat more efficiently?

Dr. Jason Fung: Yeah. So if you’re talking about; there are two separate questions. Let me just get to the vanity 5 pounds. There is nothing wrong with using a bit of extra fasting around the time that you want to look good. Like high school reunion; hey, you want to drop 5 or 10 pounds? So you do a kind of alternate day fasting for a couple of weeks, that will give you what it takes to lose 5 or 10 pounds. Guess what? It’s entirely natural. Your body knows how to handle that. And in fact, if you think about some of the benefits we talked about, you may actually feel and look better. So the classic example I always use is that Beyoncé used to use this Master Cleanse, which is this weird concoction of, I think it’s lemonade, maple syrup, and cayenne pepper. It’s not truly a fast, but it’s close enough. The number of calories are not that high. That’s all you’re drinking for like a week. So it’s close to a fast; not a true fast. But did you see how she looked? She looked amazing. It was tremendous. And the secret is that it’s entirely natural and healthy because you’re actually kind of getting rid of all this excess junk in your system.

It’s interesting because I think that if you go to Hollywood, and the red carpet, and so on; my guess is that of the women, for example, I’d guess that 80% of them do this anyway. And they look good. And they don’t ever talk about it, because they think it’s really unhealthy. It’s kind of taboo, and there’s this whole mix up with anorexia nervosa so they never talk about it. But I think they all do it. Because why? Because it works. And you look good doing it. But the point is, you don’t need to eat all the time. So if you have a goal of losing a few pounds because you want to look good; hey. That’s ok. You can not eat for a period of time. Does your body know that you’re not eating because it’s Lent, or because you want to lose 5 pounds for your high school reunion? I don’t think so. It’s the same with whatever you do. So why is one ok, and the other not. It’s like, “Oh, I’m fasting for Ramadan,” well that’s good. But, “Oh I’m fasting because I want to drop 5 pounds and fit into my dress.” Oh, that’s no ok. Are you crazy?

As doctors we know this. Because we tell people to fast all the time. You go for a colonoscopy, you need to fast. You go for an ultrasound you need to fast. You go for surgery you have to fast. You go for fasting blood work, you have to fast. So we tell people to fast all the time. And guess what? Nothing bad happens. So if you’re talking about vanity, it’s not that bad a thing. Everybody wants to look good, and if you look good, you feel good. You have better self esteem, and your cortisol level goes down. It’s not a bad thing. So I tell people, don’t worry about it. If that’s your goal, that’s what you want to do, it’s ok to do that.

The other; what was the other question that we were talking about at the beginning?

Diane Sanfilippo: How that kind of plays against the idea of reducing calories. Because you were talking before about the whole starvation mode thing, and that doesn’t actually happen when we fast. But it can happen either the “starvation mode” or suppressed or lower metabolism if we simply eat fewer calories. Which, I think this is just a big point that a lot of our listeners are going to be so curious about how that works differently mechanistically. Because for so long, you know it’s been ingrained into people’s heads that, eat less to lose weight, but eating too little is so bad. It’s like, why does our body know the difference between no food, and that’s a positive thing for a certain amount of time. And we’re not talking about, as you mentioned, somebody who is underweight already. We are not talking about that. For somebody who is underweight or having issues around disordered eating or things like that. But for someone who is of normal healthy body weight or has more to lose. So that’s the question; how does our body know that that’s a different state? And I’m guessing what you’re saying is it’s the hormonal signals that are happening.

Dr. Jason Fung: It’s the hormonal signals, exactly. So again, people always have what I call a one compartment model of obesity. That is, they think that all calories go into a single sink, and all your calories come out of that. That’s not how the body works. The body is partitioned into different kind of areas. And I use an analogy that you have something similar to a refrigerator and a deep freezer. Like a basement freezer. So the refrigerator is like your glycogen. That is the food goes into the refrigerator, comes out of the refrigerator; it’s easy. It goes in, goes out, goes in, goes out.

But there’s limited storage. So your body has also a freezer, which is harder to get to, but has unlimited storage. It’s like your basement freezer. You can store a lot of stuff down there, and if you want you can buy a second freezer, a third freezer, and a fourth freezer. And that’s body fat. It’s a lot harder for the body to get at that body fat; but there’s a lot more storage. So you can store a lot of food energy. Even hundreds of pounds of body fat. So the difference between calorie restriction and intermittent fasting is how easy it is to get at that body fat.

Insulin is the key hormone here. When insulin stays high, you simply cannot get at that body fat. You’re closing the door to the basement freezer, you can’t get at it. And technically what we say is that insulin inhibits lipolysis. That is, lipolysis is the breakdown of fat. Lipo means fat, lysis is to break down. And insulin inhibits lipolysis; meaning when your insulin is high, you can’t burn body fat. That makes sense; because insulin is high, you think you’re eating, therefore you don’t want to be burning fat because you’re supposed to be storing food energy. So you’re storing it in your fridge, you’re storing it in your freezer, but you’re not taking it out of the freezer.

On the other hand, when insulin goes down, you can get at that body fat. Because that’s the signal to say go. So if you simply reduce your calories, but you eat from the minute you get up to the minute you go to bed, and you’re eating these foods. Refined grains, sugars, that continually stimulate your insulin. But you eat less of it; say, 1500 calories instead of 2000 calories, you continually eat it. Your insulin is always high because you’re eating all the time. Every time your insulin starts to drop you pop it back up. So you close the door on that body fat. You can’t access that body fat at all. But there’s not that much in your fridge, so you have to slow down your metabolism because you don’t have the energy. So every time you just kind of store a little energy, you’re keeping that door closed.

The whole point of fasting is to give yourself enough time for those insulin levels to drop. When you can drop it, now you can access that body fat. So there’s two compartments, and that’s the difference. Everybody has this one compartment model, because it’s been promoted for so long. Calories in, calories out. As if it’s all one big swimming pool of stuff. It all goes into the pool, it all comes out of the pool. It doesn’t. There’s some of it that is just locked away. And it’s locked away by insulin. The physiology has been worked out for like 60 years or something. It’s been a long time. I don’t know why people can’t understand that you’re not going to burn body fat if you’re eating. Why would your body store energy and burn energy at the same time? You can only do one or the other. So, eat all the time, insulin stays high. Therefore you’re not burning body fat. And that’s the difference. Therefore, if you’re not taking in enough calories you’re not going to burn enough calories to feel good because of this whole thing that you’ve still kept your body stores closed.

So now you go to zero calories, for example, all of a sudden you can burn body fat. Because insulin goes down, you open the door, the freezer is there. You’re like; “Whoa. There is a lot of food in here. Let’s just take it all.” So that’s the difference. Even if you keep calories the same. I always say, as soon as you talk about calories, I know that people are on the wrong track. Because your body does not respond to calories. It has no way of counting calories. It just is a very, very poor paradigm of understanding energy metabolism of the body. So if your body doesn’t care about calories, there is no. If I take calories, for example, it’s not like I metabolize them the same. So if you have 1000 calories of steak, and 1000 calories of brownies. They’re the same 1000 calories. The minute you put that in your mouth, the metabolic response is completely different. So how can you pretend that they’re the same? It’s the most ridiculous thing I’ve ever heard.

If you eat kale salad with salmon day in and day out, day in and day out, you’re going to lose weight. If you eat brownies day in day out, you’ll gain weight. It doesn’t matter that they’re same calories. And anybody who knows anything about real life will tell you. And that’s why I think some of these academic people are so out to lunch. Because they live in this research world where they pretend that, “Oh, hey. Those 1000 calories of brownies are the same as 1000 calories of kale salad.” They’re nothing the same. If you take the brownies, your insulin goes way sky high. You get all this sugar, which is fructose.

Diane Sanfilippo: And perhaps they’re only the same in the short-term. I mean, until the body has recognized, whoever it was that did the Twinkie diet. It’s like, yeah. In the short term; that’s not what we’re really looking for, though. We’re looking for a long-term approach.

Dr. Jason Fung: Yeah. And in the short term, everything works for 6 months. Which is what he knew already. And the funny part about that story, for the Twinkie diet, is that he was paid by Coca-Cola, which doesn’t ever get out there. So have you heard this story?

Diane Sanfilippo: I mean, I believe it.

Dr. Jason Fung: It’s very funny. He wasn’t outed until a few years later, so 2011 or something. He comes out with this Twinkie diet, he says, “I ate Twinkies but I controlled my calories and I lost…” I don’t know how much weight. So it’s like, “Oh wow, you can eat the Twinkie diet.”

Diane Sanfilippo: {laughs} How ridiculous.

Dr. Jason Fung: So, last year. Ridiculous, yes. Last year, Coca-Cola got into a lot of hot water. Because they were funding this so-called Global Energy Balance Consortium, which is pushing the idea of calories. The reason Coke loves to push the idea of calories is that you can take a can of Coke, 500 calories, and you can take broccoli at 500 calories, and as long as you get the same amount, you’re going to lose weight.

Diane Sanfilippo: Or you can drink diet Coke, and they’ll still be making money.

Dr. Jason Fung: Exactly. So they love this idea. So they gave a million dollars to the University of Colorado. Eventually they got found out, and the New York Times, they sort of outed them. So Coke says; “Ok. We’re going to be transparent. We’re going to publish a list of everybody we give lots of money to.” And somebody looked through and said, “Hey, that’s the Twinkie diet guy!” {laughs}

Diane Sanfilippo: That is so funny.

Dr. Jason Fung: So. Yeah, it’s funny. Because his story is a lot better as, professor proves that calories are all that matter. Rather than; oh hey, coke paid some guy to say that he ate Twinkies and lost weight. That’s a non-story. But the Twinkie diet was all over the place. It’s hilarious.

Diane Sanfilippo: It’s really funny.

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6. Benefitting from mini-fasting in combination with keto [46:37]

Diane Sanfilippo: So, we have some other questions here. And I wrote down a lot of notes. I don’t know if you could see that I was taking some notes over here. But I’m trying to see if there was anything that I wanted to cover with you specifically from these other notes.

So here’s a question. Again, a lot of our listeners eating a paleo type of diet, and for a lot of them when they first transition, it becomes when they drop a lot of carbs because they’re eating vegetables and proteins and healthy fats. And one of the things that we’ve described, and what you were talking about with eating, especially when you’re eating more carbohydrate and insulin going up and not being able to burn body fat. We get into details on that in our Balanced Bites Master Class, so our students who have gone through that are familiar with the stop and go mechanisms of what’s happening when we eat and when we eat different things. So there’s that.

So this idea of being able to burn fat when we’re not eating; are people actually achieving that with a reduced, low-carb, or ketogenic diet between meals?

Dr. Jason Fung: Oh absolutely.

Diane Sanfilippo: Ok, let’s just say you’re 2 hours postprandial after your meal. Until you eat your next meal, we are in that sort of; we’re reaching in the deep freeze, and then can come back. And that is one of the benefits of; that’s kind of a mini-fast, in between the meals. We’re not just every second we feel anything, the breeze blows and we’re eating something. We’re really waiting between meals. So that’s one of the big benefits of just this other lifestyle that may or may not even include a conscious fasting. It’s just that between meal time. That’s one of the benefits. Where we can go 4 to 6 hours between meals.

Dr. Jason Fung: Yeah. And that’s where fasting and sort of low-carbohydrate, high-fat, ketogenic sort of diets really work extremely well together. For two reasons. One, they both have the same goal of reducing insulin. Insulin is the main driver of obesity. It’s not calories. Your body actually just doesn’t care about calories. It has no way of tracking it. It has no way of knowing if you take calories or not. It just doesn’t care at all about calories. What it does care about is hormones, because that’s what carries information through our body. So when you get the hormonal signal to store fat, which is insulin, you store fat. So if I give you insulin, I can actually make anybody fat. I just give them insulin, insulin, insulin. And they will gain weight. If they stay on the same diet; they will still gain weight. Why? Because your insulin tells your body to store fat. You store fat, all your food energy goes into storing fat. You decrease your metabolism. So it’s very easy. Insulin is the key.

So what you see from low-carbohydrate diets to fasting is that very low carb diets, ketogenic diets, actually get you about 70% of the way there. So you’re actually almost there. So for people who don’t have a lot of weight to lose or whatever, ketogenic diets will do the majority of your work. The other thing is, and a lot of people who do ketogenic diets have noticed this, a lot of times you’re just not hungry after a certain time, so you don’t have to eat. You can go sometimes 10 hours. Sometimes you go down to two meals a day, or one meal a day. Which is a sort of inadvertent fasting that happens with a lot of people on paleo diets.

Again, the physiologic reason is much easier to understand when you’re eating a lot of protein, when you’re eating a lot of fat, you actually stimulate the hormonal mechanisms of satiety. That is, there are certain hormones that get relieved. There are mechanical stretch receptors in your stomach that when you distend it out, it tells your body that you’re full and you can’t eat. And everybody has experienced this. Suppose you go to the all you can eat buffet. And you eat until you’re really, really, really full. You’re uncomfortably full. Now, if somebody sticks a steak in front of you, you’d be like, “Whoa! Take that away, I can’t even look at that thing!” Because you’re so full. But now if somebody says, “Do you want a sip of this Coca-Cola?” you’re like, “Ok.” And here you can take 500 calories of Coca-Cola no problem. Why? Because the refined carbohydrates, the same for a slice of apple pie or something. You’re so full, and you go, “oh, I’ll have a little bit more apple pie.” Because those refined carbohydrates; the sugar, don’t activate the satiety mechanisms. So your body doesn’t even really count them.

That’s why kids will; maybe I’m dating myself. But when I was a kid, I used to say, “Oh it’s like a second stomach.”

Diane Sanfilippo: No, I was just about to say the exact same thing! My dessert stomach is a totally separate thing. Because I was full, but then you brought that flourless brownie over here, and suddenly I feel like I could have some of that. {laughs}

Dr. Jason Fung: Exactly. {laughs} And they’re all very sugary because the sugar doesn’t activate your satiety. In fact, appetizers, for example, make you more hungry. So you absolutely get that. So that’s why they work so well together. And people find that when you go from a ketogenic diet to fasting, it’s very simple.

Diane Sanfilippo: Yeah. Very natural.

Dr. Jason Fung: The transition is seamless because your body is so used to burning fat. It doesn’t matter whether you’re burning dietary fat or body fat. To the body, it’s the same thing. Fat is fat. They’re triglycerides; you burn it. Whether it came from your stomach or whether it came from your hips; your hip fat. It’s all the same thing. So it burns just as easy. If you’re used to burning sugar, then you are going to have a bit more of a harder transition to go to fasting. So again, that’s why ketogenic, low-carb diets and intermittent fasting really they exist on the same sort of continuum. And one is kind of the ultimate version of the other one. But they really go well together. And that’s what we do in our clinic since we have low-carbohydrate diets and intermittent fasting. And we use them together. Some people; the point about fasting is not that you have to do it. You can do well on low-carbohydrate diets. Absolutely. But it represents options for people.

And this is the thing that always kind of strikes me as silly. We have an option to simply not eat, and we’ll lose weight. And it’s natural, and it’s healthy. And if you have say, severe obesity, severe type 2 diabetes, you will get a lot healthier by not eating for a period of time. Yet, we tell people that they should never, ever, ever do that. It’s like, what are you talking about? This is the most powerful tool in your weight loss arsenal, and we’ve told people to never even consider it. It’s like, if you do it and do well, good for you. If you do it and hate it, then don’t do it. It’s an option for you. Why are we taking away options when it’s so hard to lose weight already?

7. Who should not be fasting [53:41]

Diane Sanfilippo: So that’s a really good transition to this next. Who would you not recommend fasting to? Obviously we need to cover that. And as a follow-up to that, because we do have a lot of women who listen who are in their pre-pregnancy or fertility years and all of that. Who would you not recommend it to? And, are there some considerations for women especially in those years or in whether they’re pregnant or breastfeeding, etc. So I’m really curious about that, because it’s a huge percentage of our listener base.

Dr. Jason Fung: Yeah. So there are certain people who shouldn’t, and those are the people where nutrition is really very much more important. So if you’re a child, for example, you shouldn’t really be fasting. At least not for a long time. It doesn’t mean you should never skip a meal, but you shouldn’t do it deliberately just for weight loss. Pregnancy, breastfeeding; if there’s any concern about malnourishment or malnutrition. So a body mass index, for example, less than 18.5 is considered underweight. And I say that anybody under a BMI of 20 really shouldn’t be. And if there’s any other concern about malnutrition, yes. Fasting is obviously not good for you.

Anorexia nervosa is very interesting, because again a lot of people come back and say, “Oh, you’re promoting disordered eating.” It’s like, no. Anorexia nervosa is a psychiatric disorder of body image. People have fasted for thousands of years. Anorexia nervosa didn’t exist for the most part of human history. You don’t see it in the 1800s. But people were fasting all the time. So fasting does not lead you to anorexia. It’s the other way around. Anorexia makes you not eat. It’s not the not eating that gives you a psychiatric disorder.

That’s kind of like if I say to you, “You know, obsessive compulsive disorder, people wash their hands a lot. You should really stay away from washing your hands because you could develop obsessive compulsive disorder.” It’s like, no. Washing hands does not give you a psychiatric disorder. The conscious act of not eating does not give you an eating disorder. It means you have decided not to eat. That being said, there are some studies that show yes, fasting does not cause anorexia nervosa. But if you have a history of disordered eating, you should probably be a little bit careful. That’s just common sense. So that’s a fairly small group. Everyone else in the world can fast, safely.

The point about women. I hear this a lot. Is that women don’t benefit, or women can’t do it. And again, the very idea is pretty ludicrous, honestly. Because throughout history, women have fasted along with the men. All the times. If you look back at studies in terms of average weight loss for women and men, they’re about the same. There’s no difference between women and men. They lose fat at roughly the same rate. It’s not quite the same, because women’s metabolic rate tends to be a little bit lower than men. So, there’s a slight difference. But it’s still the same. We have experience with hundreds of women, so at least half. Probably slightly more than half of our clinic is women. And they do just as well. We don’t see any problems.

So the people that say women should never fast; one, do you have any experience with women fasting? Because we have fasted 6, 7, 800 women and seen no more problems than the men. Are there problems? Yes. I’m not saying it’s a cure-all or it’s everything, all that. I’m saying women have problem fasting, so do men. But some of the people who do the best in our clinic are women. It’s an option for them. So why do we tell people these things? What is it that you think is different about women’s physiology that makes them not able to fast? And there’s nothing. We have millions of years of experience of the human species, female version of fasting. Hey, if there was a problem, maybe Jesus Christ and the prophet Mohmmed would not have told their women followers to fast. They would have said; “Whoa, all women are exempted!” {laughs}

8. Hypothyroid and fasting [58:22]

Diane Sanfilippo: Well. I mean, I think that’s fair to say from a physiological standpoint. But if we look at modern society in levels of perhaps hypothyroidism that are happening today. And not necessarily in obese women. This is where I would have the question. You did mention before what happens when we lower calories and we lower metabolism, and perhaps become cold, right? And we feel that suppressed metabolism. That’s also often a symptom of low thyroid. Which is going to come hand in hand with low metabolism, or the low thyroid is what’s actually causing the low metabolism. This is something where we do have quite a number of listeners, also who are dealing with hypothyroidism, and they may or may not be overweight to any significant level. So those are people who are also asking, should they not fast?

Again, back to that question of the 16-hour fast, 8-hour feeding window, is it not so much about the fasting as it is perhaps they’re skipping a meal or they’re skipping nutrition. This is something my cohost, who is not on this episode with us, we’ve talked a lot in the almost 300 episodes we’ve had, where our take over the years would have been, the fast is the fast. Right; those 16 hours without food, do it. But in the 8 hours that you’re supposed to eat; eat the food you’re supposed to eat. We don’t want you then skipping nutrition during that time, because the point is not that you miss nutrition. Your body does need vitamins and minerals and everything from your food. So these are the other questions; what is the situation if someone is dealing with thyroid issues? Should they ignore fasting until they feel they’re in balance? Is it not something they really need to worry about causing more problems for them?

Dr. Jason Fung: Thyroid doesn’t really get affected. If you look at the hormonal changes of fasting, it’s really insulin and the counter-regulatory hormones. That’s the main effect. Thyroid has very little to do with the short-term amount that you eat. Obviously, if you don’t eat and you become malnourished, this is a totally different story. And again, the same thing with the nutrients. You have to really be clear about what you’re treating. Are you treating nutrient deficiency? Or are you treating obesity? That is weight loss. If you’re treating nutrient deficiency, then you need to take nutrients. If you’re treating obesity, then that’s not any kind of consideration. I have the same thing. When you eat, you should eat well. But it’s not like you can go out there, and “Oh I ate a bagel.” Which has very little nutrients. Or “I ate white bread.” Which has very little nutrients. “Therefore, I’m ok because I ate some white bread.” There’s no nutrients in that. So if you’re worried about nutrient deficiency, eating that white bread or the cereal and toast with jam, it doesn’t give you any nutrients, anyways. So why are you better off eating that as opposed to just skipping it and fasting.

The whole point is that people get these two conditions completely mixed up. If you’re worried about nutrient deficiency, treat it with nutrients. If you’re worried about obesity, then treat it. But don’t say, “Oh, well I’m not eating therefore I’m going to develop nutrient deficiencies.” As a physician, I’m like, “Ok. Nutrient deficiency. What nutrient are you worried about? Vitamin C? You think you’re going to get scurvy? Beriberi? Osteomalacia? It’s like, these are nutrient deficiencies. Modern, especially in this kind of society. We don’t have a lot of nutrient deficiencies, yet we still sort of pretend that we do because the supplement market is very lucrative and you can sell a lot. Really, if you can take a multivitamin, you’ll get almost all the vitamins that you need. I mean, the recommended daily amount of all those things on the side. The vitamin B, the vitamin A, all that sort of thing. You’ll get that in a general multivitamin. So if you’re worried about nutrient deficiency, you could take that.

Now, it’s not the same as eating real food. But again, I don’t worry so much about nutrient deficiency unless that’s the disease that I’m treating. But obesity is not a nutrient deficiency state. So don’t pretend they’re the same. So again, when you eat, eat well. When you don’t eat, don’t eat. And let your body use up some of that energy that’s stored away. It’s an energy issue, not a vitamin issue. And they’re separate.

Diane Sanfilippo: And I think the short answer to the hormone question is; lowering calorie and lowering the intake of food is a totally different state from fasting. And that’s where you’re talking about the benefits that we get from fasting. That’s not having the same; it’s having a positive hormonal impact when done in these ways, and it’s not about a diet. Fasting is not the same. So it’s not affecting us in the same way, and has a lot of positive benefits for us.

9. How to exercise while fasting [1:03:29]

Diane Sanfilippo: There were a couple of questions; I know we’re just about out of time here. But I don’t want to leave our listeners hanging, because I know they’re going to wish that I had asked this. There are two, and then we can wrap it up. Because you already answered a lot of our questions here. One is; how to exercise or tying your exercise or what have. My guess is you will say, “See how you feel.” That would be my guess.

Dr. Jason Fung: {laughs}

Diane Sanfilippo: It seems like a pretty scientific answer. Balancing exercise.

Dr. Jason Fung: So for exercise, there are two ways to approach it, actually. Generally for most people, if you’re not concerned about performance athletics, then we say you should do everything you normally do at the same time you normally do it. Because your body is going to use your energy from your body fat to power you through the exercise. Now, there is a period of adaptation, again. So there’s a two-week period where if you’re not used to eating low-carb diets or fasting, you’re going to feel a little bit more tired. But in general, for most people, you should do it whenever you normally do it. And carry on as normally as you would. Again, we tell people to pretend that what they’re doing is they’re eating a meal of their body fat, and that’s it. They keep going.

The other thing for performance athletics is that there’s a lot of interest in something called training in the fasted state. Which is where people will fast for 24 hours, and then train, and then eat. So it’s actually a very powerful way to do things, because this sort of thing maximizes the hormonal benefits. So when you fast, your noradrenaline goes up. Your growth hormone goes up. So what happens is you’re all pumped up full of adrenaline, is that you can actually train harder than you ever have before. Because you’re all pumped up. Then after you finish training, you break your fast, you eat. Your growth hormone levels are high, so you rebuild faster. So what you’re doing is you’re giving yourself the ability to train harder and recover faster. Which is a huge, huge, huge benefit if you’re talking about milliseconds and so-on with these people in performance athletics.

So actually it makes a lot of physiologic sense, so that’s one of these sorts of things that is starting to pop up on the radars of a lot of endurance athletes, ultra-endurance athletes, performance athletics.

10. How to tell if we’re really hungry [1:06:07]

Diane Sanfilippo: Just in case Usain Bolt is listening to our podcast. Make sure he hears that one. Ok, the very last question I have for you, and this might seem pretty, well I don’t know if it’s out of left field or not. But how can we really tell when our body needs food versus kind of just this little pang of what we think is hunger, because we’ve gone so many years experiencing that little thing that we feel a couple of hours after we eat, and we just so quickly respond with more food. How do we know when we really hit that point? And I would say this is not necessarily while we’re on a fast, but just kind of in our everyday lives. When do we know we’re actually hungry? How are we mistaking this feeling?

Dr. Jason Fung: I think that is very difficult, actually. We can look at studies of ghrelin, which is the hunger hormone. And if you look at it and measure people, actually there are 3 peaks, which correspond to breakfast, lunch, and dinner. So therefore, obviously over time, most people have developed an entrained rhythm where their ghrelin is actually going up. They’re actually hungry, and it’s also lunchtime.

What you have to understand is that hunger doesn’t keep rising. Again, you see this when you look at studies of ghrelin. That it goes up and up and up; and if you don’t eat, it doesn’t keep going up. It goes back down. In fact, it goes right down to baseline. Which is very interesting, because again, most people have had this experience. When you’re super, super busy and you didn’t even have time for breakfast or lunch.

Diane Sanfilippo: That is interesting.

Dr. Jason Fung: So you missed lunch; at 12 o’clock, you’re hungry. At 1 o’clock, you get a bit of hunger but you’re just swamped. So you just keep working. By 3, you’ve basically forgotten that you missed lunch. Because the hunger has completely dissipated and it’s as if you ate lunch. And you did; you ate your lunch from your own body stores. And again, we tell people that hunger is actually a wave. It doesn’t just keep building. If you just ride it out, have a big cup of coffee, have a big cup of tea and let it pass, then it will just go right back down to baseline. Then you’ll know, you weren’t actually all that hungry. Because your ghrelin just kind of went back down. And if you ride it out longer, then what happens is your body then switches to body fat, and again that hunger starts to dissipate.

It’s interesting when you talk to a lot of doctors. Because I’ll tell this to doctors. Who, of course, have been brought up on this “You should eat 10 evenly spaced meals throughout the day.” And I’ll tell them, there’s actually no reason why you have to. Our bodies are not really that stupid. If we were required to eat 10 meals a day, none of us would be sitting here because we would not have made it out of the cave, right, as cavemen. They say, that’s really interesting. Because we all have done this for years as medical students, as residents. We were swamped a lot of times. We’d be just swamped. And they would miss their lunch, and they knew that one, nothing bad happened. And two, that hunger just kind of went away after a while.

It’s very interesting. You don’t actually know if that’s real hunger or just kind of a psychologic hunger. I don’t think there’s actually a real difference between the two. But if you just ride it out, everything just kind of disappears. It’s not always comfortable. You may have to figure out a routine. Staying away from food, for example, is a good way to start. Because if the food is right in front of you, obviously it’s a lot harder to not eat. But if you simply stay busy, for example, then you’re not going to be staring at the hamburger. You’re going to be away, doing your work, and it’s not going to enter your mind. And if it does then you can just keep going. So there are ways to get around it once you understand it.

Diane Sanfilippo: Thank you so much for taking extra time to answer those last couple of questions for me. I know our listeners are really going to appreciate this episode. And will have learned so much. I learned so much from you today, and The Complete Guide to Fasting is your book. We’ve got a link for you guys, if you want to check it out. You can go to and you’ll go right to the order page on Amazon. You can get it there. And it was co-authored with Jimmy Moore, who was just on the podcast a couple of weeks ago. I think that was probably one of our most popular episodes in a long time, on keto. Which he and I were laughing, because we’ve been talking about that together for years on previous episodes. But it’s just kind of hitting a critical mass again. And I think fasting is something that I think people are really interested in more now. So thank you so much for joining me today. Really awesome to talk to you.

Dr. Jason Fung: Yeah, thanks for having me. This was great.

Diane Sanfilippo: Alright, that’s it for this week. You can find me, Diane, at And Dr. Fung at, we’ll link to that in our show notes. Join our email lists for free goodies and updates you don’t find anywhere else on our websites or on the podcast. While you’re on the internet, please leave us an iTunes review. It helps new listeners find the show, and we really, really appreciate it. We know lots of you have been listening for many, many years. And some of you might be new listeners. So we’d love to hear from you. We’ll see you next week.

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