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Guest Bio:

Jason Fung, MD, is a nephrologist and expert on the use of fasting as a clinical tool to promote patient health. Dr. Fung is also a New York Times bestselling author of many books, including The Obesity Code, The Diabetes Code, and The Cancer Code. He completed medical school at the University of Toronto and a fellowship in nephrology at UCLA. Dr. Fung continues to practice nephrology in Toronto, where he is the cofounder of the cardiometabolic health program The Fasting Method, which provides evidence-based support for natural weight loss and management of blood sugars through low-carbohydrate diets and intermittent fasting.

Transcript: 

Kalea Wattles, ND:
Intermittent fasting may be an appropriate therapeutic approach for some patients and has been associated with improved health across a range of areas. Research suggests that the potential benefits of fasting work through multiple pathways, from reducing oxidative stress to triggering autophagy. What are potential benefits when intermittent fasting therapies are used in the prevention and treatment of cardiovascular disease? 

In this episode of Pathways to Well-Being, intermittent fasting expert Dr. Jason Fung joins us to discuss the fasting/heart health connection and how personalized intermittent fasting treatments may help improve patient outcomes. Welcome to the show, Dr. Fung. 

Jason Fung, MD
Thank you so much, thanks for having me here. 

Kalea Wattles:
We know that you’re a fasting expert and I, my perspective is that you were talking about fasting before it was trendy, before it was all over in our pop culture. I mean, you published a book on this topic in 2016. So I just thought it would be fun to hear, what brought about this interest in fasting? How did you discover that you actually had a passion for this topic? 

Jason Fung:
It was really because I had—so I’m a kidney specialist, and I treat a lot of type 2 diabetes, so I became very interested in weight loss because it was very important for my patients to lose weight. So one of the things that had come up, this is probably back in 2012, something like that, somebody had talked about, you know, a cleanse that she was doing, which is, and I thought, okay, sounds very similar to fasting, which of course was a really bad idea, and everybody knew it was a bad idea. So then, but then I thought, well, you know, if you don’t eat for a period of time, you know, 16 hours, 18 hours, 24 hours, what really is so bad about that? So I really, because at that time, if you remember, this is about, you know, 10, 11 years ago, it was sort of well-accepted that you should eat 10 times a day sort of thing, right?  

And so I thought, well, where’s the scientific evidence, you know? Because, you know, I started to think about it more and more, and I started to think, it doesn’t sound like it’s actually that bad, because one, people have been doing it for thousands of years. We know that; it’s been mentioned in, you know, most major religious texts, it’s mentioned in the Bible. So we know that people have been doing it for at least 2,024 years. So if there was something bad about it, you know, we would’ve figured that out. But there’s actually nothing bad. And if you think about it from a physiologic standpoint, your body is able to store food energy, which is calories, in two forms. One is sugar, one is fat. That’s how your body stores calories. And it’s not a bad thing; it’s how we survived the winters, you know, when, you know, we were cave men and cave women, that kind of thing, right? So if you don’t eat, then really all that happens is that your body is going to use your body’s stored energy. So instead of using food, it’s going to use its stored food, right? No different than if you have nothing to eat, you go to your fridge and get whatever you stored there. Your body stores some as well. But if you have too much glucose, like type 2 diabetes, or if you have too much body fat, then your body will simply use it. And that’s natural and that’s normal and there’s nothing wrong with it. Animals do it, humans have done it for thousands of years.  

So as I started to sort of research more and more into the physiology of what happens during fasting, there’s all these other benefits, it turned out, that are beneficial. But in this sort of day and age, where we’re dealing with a lot of type 2 diabetes and a lot of obesity, this is a very, very useful thing to do, as opposed to say, 150 years ago when there was a lot less obesity, a lot less type 2 diabetes, and a lot more sort of people who didn’t have enough to eat. So that’s where I started talking about it and writing about it. Really, very, very few people had been talking about it at that point, and really, from a medical standpoint, really no doctors had been talking about it, very few nutritionists were talking about it. It was very much against the whole what people were thinking at the time. But, you know, people started to get interested in it.  

That’s why I published the book The Obesity Code in 2016, to point out some of these sort of facts and how fasting can be actually a very useful treatment for losing weight, for keeping the weight off, because it has a lot of sort of unique advantages compared to traditional calorie-restricted dieting, for example. You know, it’s flexible. That is, you can do it whenever you want. You can go however long you want. You can go, you know, 16 hours, you could go 20 hours, you could go 24 hours, you could go two days, three days, four days. You know, it’s free, it’s available to everybody. You don’t need special food. You know, there’s just so many different advantages, and it was completely different. That is, you could use whatever diet you wanted to. You could use a low-fat diet, you could use a low-carb diet, you could use a keto diet, you could use a vegetarian diet. You could use whatever diet you felt like you wanted because it didn’t impact the foods that you’re eating. It really aimed at a different part of the whole sort of spectrum, that is, the foods that you eat are important in terms of your weight but also how long you go, you know, and how often you’re eating was a completely separate thing that very few people had been talking about, but it is actually really important. 

Kalea Wattles:
Beautifully said. Something I really appreciate about your work is that you highlight the versatility, as you just did, of fasting. And I think maybe there historically has been this perception that fasting means like three days of water only. But that’s not what you’re talking about, and you’ve done a great job of providing some education about that, and you’ve done it in a way that is really approachable. And I’ve heard you say that fasting is a tool, and using it in the right situations is really important. And you said, “You wouldn’t use a hammer for a job that needs a wrench.” So you can choose the right tool for the right job. And when it comes to cardiovascular disease, it seems like fasting can be one of those tools that we use appropriately. Will you talk to us a little bit about what are the most studied types of fasting specific to cardiovascular disease or cardiovascular treatment? 

Jason Fung:
Yeah, so in terms of cardiovascular disease, the types of fasting, there’s lots of different fasting, and, you know, the word itself sort of is interesting because for about, you know, most of human history, up until say the 1990s or 2000s, fasting was sort of this good thing, right? Sometimes it was called a cleanse, it was called a detox. It was something that you did, which wasn’t particularly fun, but it was, you did it because it was good for you. And that was the connotation. When you fasted, you know, for spirituality or for whatever it is, it’s like, oh, you’re doing something good for yourself.  

Then it, for some reason, and, you know, I think that a lot of it had to do with food companies that wanted us to eat all the time so that they could sell more food, it became this dirty word, and we were supposed to eat all the time. Then fasting became this sort of thing that you shouldn’t do. But you’ve got to remember that fasting, and all of its different types, because it mostly differs on the length and also what you eat during the fast, is actually just a normal part of the eating day, right? And so there’s a period of the day that you should eat. That’s when you feed, that’s when you eat, that’s when you store energy, which is calories. But there’s also part of the day that you’re not supposed to eat, right? And that’s when you’re going to use those calories, right? Because when you’re eating, you’re going to put in more calories than you’re going to eat in the half hour that you have lunch, for example. So you obviously have to store some. So therefore you must have a period of the day that you’re not eating in order for you to use those calories that you put in. Well, that’s your fasting period.  

And the whole, you know, the whole notion is that you have to keep those in balance, and that the fasting part is a part of the normal day. That’s where you get the word breakfast. That’s the meal that breaks your fast. What it means is you have to fast in order to break it, so therefore you should not be eating all the time, which was sort of what people believed up until about 2016, 2017, 2018. And the whole thing is that you can do different fasts. So for cardiovascular health, for example, if you think about a normal eating period, you might eat, you know, if you eat from 8:00 am to say 6:00 pm, that’s like, you know, 10 hours of eating and 14 hours of fasting. And that’s how people did it in the 1970s. They didn’t eat after dinner and they didn’t eat in between meals, three meals a day, nothing after dinner. If you wanted an afterschool snack, your mom said, “No, you’ll ruin your dinner.” If you wanted a bedtime snack, your mom said, “No, you should’ve ate more at dinner.” Right? And you just didn’t eat for that period, and that was supposed to be good for you. Then of course came the 2000s, 2010, where people thought you should really be putting food in your mouth all the time, even to lose weight, which is sort of ridiculous. So if you’re overweight, it’s like you should be eating all the time. It’s like, well how are you going to lose weight if you’re putting food in your mouth all the time? You can’t, because you never went into the fasting state where you’re using calories, right? You eat, you store calories, you don’t eat, you use calories.  

So for cardiovascular health, it’s really a matter of getting the sugars down, because type 2 diabetes, where your body has too much sugar, is a very, very high risk for heart disease. It’s actually one of the biggest risk factors for heart disease. And so you could do 16 hours of fasting a day, and that’s pretty good if you’re just trying to get it down a little bit. You can always push it if you really want to. As you said, it’s a tool, right? So you can use more and more powerful tools, but you have to be more and more careful, right? Just like if you use a hand saw, you have to be a little careful, but if you have a power saw, it’s much more powerful, but you have to be much more careful. So same thing with fasting. If you’re going to go longer, 20 hours, 24 hours, two days, three days, four days, whatever you feel like you need, then you just have to be more careful that you’re doing it mindfully, that you’re making sure that your medications are going to be adjusted properly, that you’re monitoring your sugars and that kind of thing. But mainly it’s about the results. So are you losing the weight? Because we know that, you know, if you lose the weight, your sugars get better, your type 2 diabetes gets better, which is going to reduce your risk of heart disease.   

The other thing that’s interesting about heart disease is that the hormone insulin, if it’s too high, that is a state of hyperinsulinemia, where you have too much insulin, is actually very atherogenic to the body. That is, if the high, high insulin levels, if they’re sustained over a long period of time, causes a lot of damage. I was just talking to a fellow who said that even in the 1930s, we knew that insulin is a very pro-atherogenic hormone. So they, take dogs, for example, and they infuse one leg with insulin and one leg without insulin, just salt water. What they found is that the arteries on the leg they infuse insulin started to develop the hardening, the stiffening, the smooth muscle growth, which causes that sort of stiffness. So too much insulin can cause these precursor lesions to heart disease. And one way to lower insulin is fasting. Because when you eat, insulin goes up. When you don’t eat, insulin goes down. So you got to make sure that you have enough of the period where your levels of insulin are low, and that’s what the fasting does for you. 

Kalea Wattles:
And would we expect to see that effect on insulin, no matter what type of a fasting routine we’re following, time-restricted eating, alternate-day fasting, the 5:2 method, fasting-mimicking? Will all of those have some effect on our insulin? 

Jason Fung:
Yeah, yeah. They all will to different degrees. Obviously, the longer you go, the more strict your fast is, then the more you’re going to lower it, because it really just reflects the foods that you eat. Fasting-mimicking diet, for example, where you’re still eating, but you’re not, you know, you’re trying to mimic the effect of the fast, what that’s trying to do is get you to eat foods that don’t stimulate a lot of insulin, so therefore you’re still getting a lot of those sort of benefits, but still sort of eating. Because different foods are going to stimulate insulin to different degrees, so they’ve tried to make it so that you’re getting the benefits without eating. So 5:2, you’re going to still be able to eat, you know, 500 calories in the day, so again, much less than normal; therefore, if you’re eating less, insulin is going to be stimulated less.  

Kalea Wattles:
So you’ve talked about the hyperinsulinemia, the lipid burden, and atherosclerosis risk. Another cardiovascular risk factor I wanted to ask you about was inflammation. Is there some anti-inflammatory effect of a fasting routine? 

Jason Fung:
It’s very likely. The data is not all there because it’s sometimes hard to get, and a lot of that’s because for many years people didn’t think fasting was good for you, so they didn’t really study it. But there does seem to be a lot of anti-inflammatory effect, especially if your body has sort of too much inflammation. So there are autoimmune diseases where your body has, it starts attacking itself for some reason that we don’t really know. But in those cases, there does seem to be some ability of a fast to sort of reset the immune system. So there’s a bit of studies on that. And probably what happens is that if you’re fasting, your body goes into sort of a resting state, because if you’re not putting, if you’re not eating, your body says, okay, well I need to start, you know, to conserve energy, and I need to make sure the energy is going to where I really need it to go. So a lot of stuff, instead of going into sort of a growth phase goes into more of a resting phase. And same thing with the inflammation. So if your body has sort of over-stimulated the immune system, then it’s going to ramp it down because it’s like, well, it’s got to pull back on a lot of other things.   

So anecdotally, we’ve seen a lot of people, like people have written into me and they’ve said, well, you know, I had all this, inflammatory bowel disease was one example, and he started doing the fasting. It was actually, he’s spoken about it, it’s Georges St-Pierre, who’s a very famous, he was an MMA fighter. And he had a lot of this inflammation, and when he started fasting, a lot of that just went away. It actually all healed up and so on. And that’s great, it’s like. So all these autoimmune diseases, all these diseases where there’s sort of excess, excess inflammation, because remember inflammation is not a bad thing, it’s just a reaction to an injury. But inside the body, if you have too much inflammation, it can be bad for you. And fasting seems to sort of ramp that down a lot, but the data is still all coming, 

Kalea Wattles:
You introduced this connection between fasting and the health of our gut with this person who healed their inflammatory bowel disease, or at least reduced their symptom load. Will you talk to us a little bit about this connection between fasting and the gut microbiome?  

Jason Fung:
Yeah, so the gut microbiome, which is all the different bacteria that you get in the gut, it actually changes depending on pretty much everything you eat or don’t eat. So if you eat certain foods, you’re going to have more of certain bacteria. If you eat other foods, you’re going to have others. When you fast, you’re going to change the microbiome because you’re going to, you’re going to be able to, you know, those bacteria that are able to survive in that setting can do it. So there’s two things that are very interesting because it may change the types of bacteria that are there. So that’s very useful.  

And the other thing is that some people who have bacterial overgrowth, so they have this thing called SIBO, S-I-B-O, which is small intestinal bacterial overgrowth, they have too much bacteria in their small intestines, which are actually supposed to be relatively sterile. And again, by denying them food and so on, it may actually help reduce that, the bacterial overgrowth. And some people feel that’s very important because if you have too much bacteria there, it can cause a bit of, you know, it can release inflammatory mediators, which can cause leaky gut, and leaky gut’s very dangerous because it allows things, so your gut, your GI system is not supposed to, you know, food and stuff is not sterile generally. So it has to be, your intestines have to be tight in that it’s not supposed to let anything through the gut wall. When you have leaky gut, stuff gets through the gut wall and causes all kinds of problems. And when you reduce the amount of bacteria, maybe get less of the SIBO and perhaps you get less of this leaky gut, which then causes less inflammation down the line, so that’s another pathway that fasting might be useful. I mean we use it in hospital all the time. People don’t realize this, but if you get like pancreatitis or any of these intestinal things, the first thing the doctor does is put you NPO, which is nil per os, which means nothing goes in your mouth. And basically, you’re resting the gut and they put you on an IV, and we do this for all kinds of different bowel diseases. And what you’re doing when you’re fasting is really doing something very similar, in that you’re not putting any food in your mouth and trying to give it a rest and let the body sort of heal itself. 

Kalea Wattles:
As we’re talking about these high-level mechanisms that explain how fasting can be helpful for a variety of treatments, will you review the concept of autophagy? And then I’ll add a layer to it, which is mitophagy, which I think may be an even more novel term for many of our listeners. So will you give us the breakdown of those descriptions? 

Jason Fung:
Yeah, so autophagy is this sort of recently described mechanism whereby the body, when you fast or when you eat very low protein, actually starts to break down certain subcellular organs. And that sounds really bad, it’s like, oh, you’re getting breakdown and stuff. But that’s actually not bad at all because if you think about how people, remember cells are turning over in your body all the time, right? Some cells are dying, some cells are being grown. But the way that you rejuvenate yourself, the initial process is destructive. That is, if you’re to, say, renovate your bathroom, the first thing you’ve got to do is throw stuff out, right? You got to get rid of that, you know, lime green tub and lime green sink from the ’70s, then you can put new stuff in. If you don’t get rid of stuff, you can’t put more stuff in, right? So you can’t, if you have an old toilet, you can’t put a new toilet in, right? So you can’t refresh, you can’t, you know, renovate without destruction first. So even though destruction always sounds bad, it’s actually a good thing.  

So what happens during fasting is that, again, as the body senses that there’s less food coming in, it starts to say, okay, let’s get rid of some of the old stuff, right? So anything that’s really old, these subcellular organs, it’s going to actually break it down for energy. But what happens during fasting is that not only does insulin go down, but growth hormone goes up. So if you look at fasting over, you know, three, four days, you know, the level of growth hormone goes up three, four, or five times normal, so that when you eat again, your body is now primed to rebuild. So what you’re doing is getting rid of that old junky protein. And then, when you eat again, because of course you can’t fast forever, then your body is now primed, it’s got growth hormone, it’s got nutrients, and it’s going to detect where is it that you need and it’s going to rebuild it. So basically, you’re getting rid of the old stuff, you’re bringing in new stuff, which is exactly what rejuvenation is, right? So it’s an anti-aging process, this sort of cyclical sort of fasting and eating, right? Because obviously, at some point you have to eat again, and that’s the whole point. This autophagy sort of is part of this process and, you know, it was very topical because in 2016 the Nobel Prize for Medicine was awarded to one of the sort of key initial researchers. So it became very interesting, and it sort of dovetailed with a lot of the interest in fasting as well. 

Kalea Wattles:
Right, you talked about this cellular rejuvenation effect, and I’ve seen you talk about this, that we’ll have patients who are in their 60s or 70s and they implement fasting and their perceived health and their quality of life and their ability to have freedom in their health and feel good in their body actually improves, even though they might be in their 70s. 

Jason Fung:
Yeah, exactly. And it’s probably this little bit of low-level chronic inflammation, as well as the autophagy and stuff that’s being improved. It has cognitive benefits. So there’s a whole lot of stuff, and it’s not that you should do, you should eat all the time or you should fast all the time, it’s a cycle, right? So you should eat sometimes and you should not eat sometimes. So it’s always cycling. Even if you look at the way that people used to do fasting, it’s not like you fast all the time. It’s like once a year you’d have, you know, Ramadan or Yom Kippur or Lent or, you know, whatever it is that, whatever religion it is. It’s not like all the time you do it, it’s like you do it sometimes and you don’t do it sometimes. And that’s going to keep you healthy by this sort of cycle of rejuvenation. 

Kalea Wattles:
Right. A question, a common question that I see in regard to fasting is, do I have to be in ketosis to reap the benefits of fasting? And I’d love to get your perspective on that. 

Jason Fung:
You don’t have to. Oh, before we get there, you asked about mitophagy before, so just to finish off the thought about that. So mitophagy is actually the process of autophagy as applies to mitochondria. So mitochondria are the sort of powerhouses, they generate the energy in your body. And turns out that they’re a lot more important than people used to realize. And a lot of diseases might actually be related to poor mitochondrial health. And what fasting does, which is very good, is that the mitochondria are always sort of, you know, they break off, they form new ones, and so on. And mitophagy is this sort of rejuvenation process of autophagy as applied to mitochondria. So keeping those mitochondria young can be very important. And sorry, you’re asking was the, I’ve forgotten… 

Kalea Wattles:
Yeah, the question is, do we need to be in ketosis to experience the benefits of fasting?  

Jason Fung:
You don’t have to, although fasting will stimulate ketosis, but you don’t necessarily have to be in ketosis. So they are two different processes entirely. So ketosis is when your body runs out of carbohydrates, basically. So your body has two fuels that it can use, it can use glucose, which is sugars, which is carbs, or it can use fat. So those are the two fuels the body can run on. The body doesn’t run on protein, for example. Protein is used for structural tissue, like muscles and so on. But carbs and fat are the two main sources of energy. If you don’t eat carbs, like you eat a ketogenic diet, then your body will then produce ketones, ketone bodies. Your liver will take the fat and will turn it into a ketone body so that that can cross the blood-brain barrier and provide fuel for the brain. So it’s really a period where your body has very low carbohydrates. And fasting of course helps stimulate ketosis. If you have enough carbohydrate stores while fasting, well then, you’ll not go into ketosis. You’ll still generate some of the benefits, you’ll have the lower insulin, you’ll have the decreased inflammation, all that.  

Some people like to eat a low carbohydrate diet and then do the fasting, in which case if your carbohydrate stores are not that low, then you’re going to burn through all the carbohydrate stores, then you’re going to start to burn fat. And, you know, it’s important because some people like to measure that, they use breath tests and stuff so that they know that they’re in ketosis so that they know they’re burning fat. That’s how you know. You don’t necessarily have to be in ketosis to get the benefits, but on the other hand, some people find it’s something that they can measure, that they can make sure that they’re staying in that sort of fat-burning state so that they, you know, if they’re trying to lose weight particularly, if you’re burning sugar, you’re not burning fat, then you’re not going to lose body fat because that’s what body fat is. 

Kalea Wattles:
Right. As we talk about all these mechanisms that play a role in the benefit of fasting, we know that mitochondrial dysfunction, which you introduced with this concept of mitophagy, and oxidative stress can play a role in the pathogenesis of cardiovascular disease. Will you tell us a little bit about how intermittent fasting can actually help to ameliorate some of the detrimental effects of oxidative stress, for example? 

Jason Fung:
Yeah, fasting has a lot of different benefits. I mean, oxidative stress is, it’s sometimes a little bit hard to measure exactly because it’s this, you know, this sort of…oxidation is the process of combining with oxygen, that’s where it comes from. And you get these sort of reactive free radicals and stuff in your body and, you know, some of the excess inflammation is thought to be a big source of oxidative stress. And that’s where fasting can be really beneficial in terms of reducing it and reducing, and sort of dealing with all that excess oxidative stress. But the whole, you know, they’re all sort of tied in together, because, you know, if you’re eating constantly and not giving yourself adequate fasting period, then you’re just going to put more stress on the body because a lot of these foods can lead to more oxidative stress. 

Kalea Wattles:
And as we’re reading about these topics and doing our own research, we might encounter this term, chrononutrition, and we even have an article about chrononutrition on the IFM website. Will you just tell us what that term means if we find it when we’re on the internet doing our search? 

Jason Fung:
I’m not sure if there’s a formal definition. I mean, chrono- means time, and one of the things that people had always sort of talked about was the foods that you eat, the calories you eat, the nutrients, the vitamins, and so on, which is very important without a doubt. But what they hadn’t talked about was the time aspect of those foods. So, you know, my understanding, I mean, and again, other people may have a different definition, is that what impact does it have, to have the same, you can take the same nutrients, but if you eat them in a different time, does it make a difference? If you eat them all at one time versus not at one time, does it make a difference?  

And I think the answer is yes, because our body has a natural circadian rhythm, so that certain hormones go up and down depending on what time of day it is. And there are certain times of day that are more conducive than others to weight loss and weight gain. For example, if you take the same, so we know that insulin is a storage hormone. So insulin, you eat, insulin goes up. Insulin actually tells your body to store those calories because that’s its job to do. If you store those calories, of course you’re going to have more stored forms of calories, which includes body fat. If you take the same meal in the morning versus the evening, what we can see is that the effect later, the later on you eat tends to have a higher insulin effect. So if it’s higher insulin effect, then you’re actually going to have more stored energy, which is body fat. So the same meal can have different effects, depending on the time of day that you actually take it. Same thing with the, you know, with the fasting, like is there a difference if you eat small meals all throughout the day, versus eating sort of discrete meals? And I think that there is, because again, if you constantly stimulate your body, if you’re constantly eating a little bit and putting yourself into the sort of fed state, then you keep telling your body to store energy because you’re never getting into the fasted state, right? And that’s the only time that you can actually use calories.  

So remember in the fed state, when you eat, insulin goes up. Insulin inhibits lipolysis, which means that insulin blocks you from burning fat. Why? Because insulin is a hormone that tells you to store energy. You don’t want to store energy at the same time you’re pulling energy back out, right? So insulin, which is, again, this is just logical, insulin is telling you to store energy so therefore stops you from taking energy back out, right? So body fat cannot be burned for energy while insulin is high. So if you continually stimulate insulin, well, you’re blocking yourself from burning body fat. You’re telling your body you can’t burn body fat, right? So if you constantly eat, but only a little bit, you don’t get enough calories, your body can’t take that, so say you eat all the time, you eat 1,500 calories, but because you’re eating all the time, you’re keeping your insulin high. Well insulin says, well, you can’t take any calories out of storage, right? You want to put calories into storage, so therefore your body has to reduce its metabolic rate from 2,000 calories, for example, to 1,500, in order to balance that equation. So it, you know, this idea is that the timing of the meals, what time of the day you eat it, how you eat it, how often you eat it, still plays a very, very important role in nutrition. And just talking about the foods and the nutrients and the macros is not giving you the complete picture. 

Kalea Wattles:
Hmm, this is so fascinating. I’ve thought about this a lot, I’m excited to ask you this next question, just to get your opinion. I have seen people ask, let’s say they want to do an eating window that is six or eight hours during the day, and they’ll ask, should I front-load it and eat breakfast and lunch and skip dinner? Or would it be better to skip breakfast and eat lunch and dinner? Do you have a preference for how that eating window is shifted, or is it so personalized for everyone? 

Jason Fung:
Yeah, I actually… that’s a really good question, and I did a whole YouTube video on this actually. So on YouTube I think I said, should you skip breakfast or dinner, which is exactly the same question. And as an aside, I have a lot of videos on YouTube, if people want more information, just look under Jason Fung. The simple answer is that if you’re trying to lose weight, then skipping breakfast is easier but not as effective as skipping dinner. So if you want to skip dinner, you’re going to do better than skipping breakfast. However, you have to balance that out because skipping breakfast is a lot easier than skipping dinner. Why? Because in the way that most people live in sort of Western society, we, dinner is a very social meal. That is, you’re with your family, you’re with your friends, you go out, you have dinner meetings, you have, you know, whatever it is you do, a lot of people have that at dinner as opposed to breakfast. Therefore, if you skip dinner on a regular basis, well, you may miss dinner with your family, you know, a lot, which is difficult because it’s more than just the food. We’re sharing our lives, we’re sharing our stories, we’re sharing a meal together. So therefore, skipping dinner, while it’s better for weight loss because of what we talked about, that is, you get less insulin effect at breakfast, you get more insulin effect at dinner, so skipping the dinner, even if it’s the same meal, gets you better effect for weight loss. But it’s just so much harder to do because if you skip breakfast, virtually nobody knows or cares. I know because I skip breakfast a lot and it’s not that social a meal. It’s, you know, it’s, for a lot of people, it’s whatever you eat on the run. So instead of eating on the run, just get a coffee on the run. And virtually nobody cares if you skip breakfast because it’s not like people are like, well, you know, can’t meet with you because I’m fasting, right? If you’re skipping dinner and then your friends are like, “Let’s go out,” you know, “get something to eat.” You’ll be like, “Well, I can’t, I’m fasting.” Or you go with them and then you’re just staring at the food all day. It’s no fun for them, it’s no fun for you, and you’ll be hungry because you’ll be in a place that you’re smelling food. So it’ll be really difficult.  

So the quick answer is that skipping dinner is better but a lot harder from a social standpoint, from a societal standpoint. So therefore, you have to balance the effect of the two. Because if it’s always very hard and you’re missing dinner with your family every, you know, three days, well, that’s not good for your social life, that’s not good for your family life. So you have to balance those two because they’re real considerations. If you’re to just go with pure physiology, yeah, eat breakfast and lunch, skip dinner. But, you know, I don’t do that a lot because it’s just so disruptive, if I were to do that all the time. Like I skip breakfast probably at least five or six days of the week, especially now that like my family is used to skipping breakfast as well. So it’s super easy to skip breakfast. So it doesn’t disrupt my life in any way. Whereas skipping dinner would be sort of highly disruptive, because I work, my kids go to school, so when are we going to sit down as a family? Dinner time. Absolutely. After dinner they go do their stuff, I’ll do my stuff, right? So it’s like, it’s not like you can skip dinner and then still have that quality family time. Very difficult. So that’s why you have to just be cognizant of that, because you don’t want to be, oh yeah, you’re losing weight, but, you know, you’ve let all these relationships go, right? 

Kalea Wattles:
Yeah, that makes great sense. And I’ve noticed in my observations, as we’re talking about the circadian patterns as seasonal, I’ve observed a seasonal change in myself as well. We’re in the Seattle area, and right now, it’s getting dark at 4:00 pm, and so it’s a lot easier to stop eating earlier in the day and then kind of curl up and be done for the night, where in the summer it’s light until 9:00 pm and you feel like you’re out and you’re doing more social things and eating much later into the day. And that’s an interesting observation. 

Jason Fung:
Yeah, yeah. And there’s other eating patterns that work as well. So in Europe, for example, they will eat very late at night, I mean. And they’re not particularly overweight compared to us, but the way that they eat is different because the lunch is their major meal. So Spain, for example, they’ll have a big lunch, and then yes, they will eat at like 10:00 pm, but it’s just very light, like not a lot at all. So that’s the way that they get around it. So yes, they’re eating, but it’s not very much. And how much you eat does play a role because, you know, if you’re eating a lot late at night, your body has nothing else to do, like you take in a certain number of calories late at night, your body has nothing else to do with it but store it, right? And it stores it as body fat. Whereas you take that big meal in the morning time, then your body can use it throughout the day and keep you less hungry during the day. So certainly there’s a difference, so eating late at night is probably best avoided. But yeah, skipping dinner all the time is just difficult. But with season, yeah, absolutely. If it’s easy then push it up earlier, it certainly works. 

Kalea Wattles:
Well you’ve presented some pretty compelling research and data and concepts to encourage us all to experiment with fasting. Where does the research need to go from here? I mean, what future research would best inform our personalized clinical interventions and would inspire us to prescribe fasting more often? 

Jason Fung:
I think that the most important thing, I think, is how to get people to do it successfully. And I think that that’s the big thing, because there’s, you know, you can tell people, well, fasting will help you lose weight. Obviously, if you don’t eat, then your body will use up, you know, body fat. So that’s fine. But it doesn’t mean that they’ll do it, right? It’s just like if I say, “Don’t eat cookies.” That’s great advice, right? No question. Every diet, you know, will say cookies are not that good for you for weight loss. But it doesn’t mean I won’t eat cookies, right? Because there’s different reasons why you eat cookies. Same as fasting, right? So I can say, “You should fast.” That’s great, but actually getting people to do it is more difficult. So what I think needs to happen is we need to figure out ways, or do research, into ways to make it more easy for people to do, right? Whether it’s, you know, different societal norms or different groups or whatever. I think that’s where it needs to go because we need to get away from the thought that, oh, we just need to tell people to do this. I mean, it’s sort of like alcoholism. I can solve alcoholism. I just tell people, “Don’t drink alcohol.” It’s like, that doesn’t mean they’re actually going to do it, right? So then you have to figure out, how is the best way to deal with it? Like, you know, there’s the Alcoholics Anonymous, there’s groups, there’s counseling, there’s therapy. So that’s the same with fasting. What’s the problem, what’s the holdup?  

So, for example, one area of big research is food addictions. So there are certain foods that people actually become addicted to, and it’s become more recognized. So if you’re addicted to certain foods, and mostly we’re talking about highly processed carbohydrates, right? So some people, when they eat, they just become addicted to it. And it’s a similar, it’s similar in the way that people get addicted to cigarettes or drugs or whatever, and they can’t stop themselves. Even though they know it’s bad for them, they can’t stop themselves. Well, if that’s the reason you can’t fast, because of the addiction, then you have to figure out how to deal with that addiction.  

So that’s one example of research where you say, okay, well, now we’re getting into stuff that can actually help people more than just understanding that fasting is useful. So for those people that can do it, great, but if people can’t do it, why can’t they do it? And what can we do to help them? Let’s get into that sort of deeper understanding of, you know, whether it’s food addiction is one example. Emotional eating is another example, you know. There we could really do a lot by trying to investigate why are people eating. Because people eat for different reasons. So one is the reward, you know, is called hedonic pleasure, which is that you eat because it’s enjoyable. It lights up, and it’s enjoyable, because it lights up the reward pathways in your brain. Well, if you are slightly depressed, for example, then you might go to food to sort of medicate yourself by giving you this pleasure, because you’re missing it in another aspect of your life because of, you know, seasonal affective disorder or whatever it is. Or, you know, you have something happen, you break up and then you’re just eating all the time, right? All these sorts of things happen. But that’s important because there, you’re getting into the sort of deeper understanding of like, okay, well, we tell people to fast, but they won’t. Why? Because they’re actually a little bit depressed. Well, what can we do about that? What can we do about emotional eating? Do we need to have groups, do we need to have counseling, do we need to have therapy? All of those things are going to be more successful than just saying, which is unfortunately what happens a lot with medical research and nutrition research is, you know, we took a bunch of people and we fasted one, you know, 20 hours, and we fasted one 12 hours, and we compare the difference. They’re like, okay, that’s fine. It’s all decent research, but you don’t need, like, it’s not practical in that way, right? So trying to understand the sort of forces behind it, I think that would be very, very interesting and useful research to help people directly. That is, you know, can we develop tools to identify emotional eating? Can we identify tools to identify food addictions? Can we then develop treatments for those that are easy for people to, like, you have to know about it before you can treat it, and then you have to be able to treat it. 

Kalea Wattles:
Right, that makes great sense. And I wonder if part of that process is also identifying misconceptions that people have about fasting. And I’ve seen you, I’ve watched videos that you’ve done about myth-busting about fasting. For example, the fear that you’ll lose all your lean muscle mass if you do fasting. Do you think that’s part of it, the education piece, to help people understand where they can safely fast? 

Jason Fung:
I think so. There were a lot of myths, and I talk about them, you know, in my books, you know, The Obesity Code, The Complete Guide to Fasting. People had a myth that you couldn’t use it for type 2 diabetes, for example. So I talked about that in The Diabetes Code. So there are a lot of myths that go around, like there’s a myth that you’ll lose all your muscle, for example, and again, if you look at the data, it’s not actually true because, you know, it’s always interesting to me because when you fast, you lose weight, but you lose a little bit of protein at the same time. And losing protein is not the same as losing muscle, because there’s a lot of protein in your body. The skin is protein, connective tissue is protein. That’s the connective tissue is what, you know, connects everything. So if you just lose fat, for example, you might have a lot of excess skin, and, you know, if you watch those, you know, shows on TV, they do those skin removal surgeries, it’s like 20, 30 pounds of skin. That’s all protein. None of that is fat, right? So therefore, when you lose weight, you actually lose fat, but you should also lose protein because you need less protein to support the fat mass. So there will always be a bit of lean mass lost.  

The thing about muscle is that you gain or lose muscle based on how much you use it, not what you eat or don’t eat. Assuming that you’re not like very, you know, very, very low body weight, right, if your body mass index is like 14 or something like that, yeah, you don’t have enough protein to build muscle. But assuming that you’re sort of regular or overweight, then your muscle is going to go up or down depending on how much you use it, not what you eat. It’d be great if I could just eat and gain muscle. That will never happen. It’s not like I eat steak and protein and stuff and all of a sudden I can bench press 10 pounds more. I can only bench press 10 pounds more if I bench press. That’s it. You gain muscle because you use it, you lose muscle because you don’t use it. It doesn’t really have anything to do with the foods you eat. Again, not counting the extremes, like if you’re extremely protein deficient, if you’re extremely thin, then yes, but for most people, that’s not the case, right? So why conflate the two, right? If you’re overweight, your body will use body fat. People say you’re going to burn protein. And it’s like, so think about it this way. Your body stores energy in the form, which is calories, in the form of sugar and fat, right? So why would the body, as soon as you don’t eat, want to burn protein, specifically muscle protein. That’d be stupid. Like you’d have to think the human body is so incredibly stupid as to store sugar, but the minute you need it, to burn protein. It’s like storing firewood for the winter, and then as soon as it gets cold, you chop up your sofa, right? And throw it into the fire. Why would you do that? Like, it doesn’t make any sense at all. We wouldn’t even have survived as a species if that’s what we did.  

So the whole point is that, yeah, muscle loss is sort of one of these big myths of fasting. The other one is starvation mode and so on. There’s a whole lot of these different myths that happen, and, you know, most of them are just myths. The truth is that for most people, fasting is a highly beneficial sort of activity for weight loss. So if you have too much sugar, again, remember, sugar is just a way that you store energy. If you have too much sugar, it’s type 2 diabetes. If you fast, your body will burn off that sugar, and then you can reverse your type 2 diabetes. Body fat is also a way that the body stores energy, calories, so if you don’t eat, your body will burn fat. So if you’re overweight or obese, your body will burn the fat and you’ll go back to normal weight. So that’s all very good. 

 Kalea Wattles:
You’re very skilled at giving us these visuals that we can use as we’re describing these processes. That’s my biggest takeaway from this episode. But for our functional medicine primary care doctors who are listening, what do you want them to take away from our conversation today? 

Jason Fung:
I think the main thing is that one, fasting is just a part of the normal eating pattern, right? It’s not something cruel and unusual, it’s just something that is normal. And if you need to, if you have too much of the glucose effect, then you can extend that fasting period to use it. And it’s completely normal and it’s completely natural. And it’s something that you can use. And what it does is it gives you a very, very powerful tool for disease, right? So if you’re treating different diseases, it’s as varied as, you know, type 2 diabetes, which is obviously very important. Weight loss, which is very important for all kinds of things. You know, high blood pressure, for heart disease, we know it’s a risk factor for strokes, as we know, it’s a risk factor. So type 2 diabetes, obesity, but also these other things such as, you know, inflammatory diseases and other things. It’s all very, it gives you a tool to use other than medications and stuff, right? So we know all about how to give medications and surgeries and all that stuff. What most doctors don’t have as much skill is giving people advice like, hey, why don’t you try this, because it could help you. And, you know, we’ve seen so many people at thefastingmethod.com like reverse their diabetes, you know, people who had been on, you know, 20 years of diabetes, you know, five years of insulin, and within a month and a half, they’re off all their medications and they’re non-diabetic, right? So it’s like, it’s a very powerful tool. So therefore, for us, as people who want to help other people, it’s up to us to have the skill to use that tool, right? If you don’t tell people, they won’t use it, but we have to have the knowledge to, of what it can do, where you have to be careful, all these sorts of things. And so that’s the biggest takeaway. It’s a very powerful tool for us. 

Kalea Wattles:
Well, Dr. Fung, thank you so much for sharing all these clinical insights. With longevity trending in the functional medicine ecosystem, I know that we’ll have our eye on the research and are looking forward to learning more and more about the therapeutic uses of fasting. Thank you so much for your time today. 

Jason Fung:
Thank you. 

Kalea Wattles:
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