Dr. Jason Fung’s Intermittent Fasting Schedule

Jason Fung, nephrologist, and bestselling author, shares his experiences utilizing an individualized approach to fasting to successfully treat thousands of overweight metabolically ill and diabetic patients. Being a doctor who specializes in kidney disease gives him a unique indication into early indications of metabolic disease.




The funny part I think is that people have known this for thousands of years, because if you go back and look at all major religions, they all have periods of fasting. Long periods of fasting; 40 days and 40 nights, it is crazy. Nobody in history has decided to restrict by eating small frequent meals, the much easier thing to do is to cut out a bunch of meals, like why would you want to cook and clean and prep six times a day when you could do it once a day. Doesn’t it make more sense from a logistical standpoint?

Another thing that is crazy, and I see this all the time because we do a lot of fasting in our clinic as well, is that people come back and say ‘I thought it would be terrible but it is easy’.
Because once you get into that mode of not eating, there’s no inertia there.

When you start eating it is really hard to stop. If you start by not eating, you might as well ride that until it is time, and it is a lot easier.

How many hours do you go? What’s your intermittent fasting schedule?

I completely go 24 hours a couple of times a week, although it depends on how busy I am. When I am really busy, I do a lot more, because it saves me 45 minutes of lunch time. I don’t worry about not having energy, there’s a whole thing that I won’t be able to concentrate. It is funny people think that.

 It is obvious if you don’t eat, your brain works better. If you think about it, you had a giant thanksgiving dinner, are you super sharp or are you sluggish on the couch watching television?

 It is pretty clear eating a lot doesn’t make you mentally sharp. On the other hand, when you say someone is hungry for something, does it mean they are sluggish and have no energy? It means you have a lot of energy and you are willing to do what it takes. That is what the body does, it fuels you. We have done so many studies on the fasting, it is well established. Your adrenaline levels go up, your growth hormones levels go up and your metabolism doesn’t go down. So you are more energetic. Everybody worries about metabolic slowdown that you see with caloric restriction, you don’t see that in intermittent fasting.
You can fast for four days and the resting metabolic rate at the end of the four days is actually 15% higher than at the beginning. So your metabolism is actually revving up but you have switched your energy sources from food to fat. Most days you are eating 1 – 2 meals a day, you are going, and how long do you go?

“I rarely eat breakfast, I eat breakfast on the weekends. On weekends I find that I am not actually hungry but I do eat because my family is there and I usually eat breakfast, there are social things I go along with but because it is nice right? This is what I say about fasting, you really have to find what fits into your life, because what fits into my life may not fit into someone else’s life.
So on the weekends, it is nice to enjoy that time in the morning, have a little something with the kids and the wife, and I like that. I find that I am not hungry often, but once I start, I can eat a full breakfast. That is what I mean, sometimes it is easier to go right through, Monday to Friday I don’t eat breakfast anymore. Some weeks I wind up doing it 4 out of 5 days, it depends on my work schedule when I get really busy I know that those are days I am going to. It is just not worth it for me, the body gets so used to it, it gets too easy to skip that meal, it is far more precious for me to get the 45 minutes or an hour and to get home earlier than eating something. And that is everyday right! That is 3-4 hours extra time. On days it isn’t busy, I will eat more. “


We warn people ahead of time that the first few times they do this, it is going to feel really bad. It is the same for ketosis, people talk about keto flu etc, as you make that shift in your metabolism what it takes is a bit of time, during that time you have to understand that things are not abnormal. If they do it twice, and it is bad both times, they say they can’t do it and give up. You have to give your body a chance.
If you want to learn to play the piano, you don’t give up after two times. It is the same thing; you have to let your body get used to it. We warn them before they start it.
Most people do fine once they get started, then they have to find their niche because some people feel great with 24-36 hrs, some people find they do better with long fasts. If you like it then do it, if you like the other, do it, as long as you are getting results.

When people have trouble, I ask them to go for a long period, like 5 or 7 days, kind of like Desert Island, you are forcing your body to actually do it. It takes a bit of motivation, and it takes people who are willing to do it, when they do that their bodies usually make that adjustment, then they know you kind of force your body to get used to it, ‘there’s no food coming, you better start shifting your metabolism ‘ and when it does, they find it much easier.

Those who are into low carb and are also eating a lot of ketogenic diets, they actually do much better, they find the fasting really easy, so it is kind of a natural segue when they are already in the high fat diet, they switch over very well. So sometimes it helps to switch them to that diet first.

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