‘How many times should I eat during my eating window?’

Ask Dr. Jason Fung

Do longer fasts decrease metabolism? How long should you fast to reverse insulin resistance? And how many times should you eat during your eating window?

It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:

What’s the best duration of fasting for lowering insulin resistance?

Hello, Dr. Fung!

I have insulin resistance, from what I learned the duration of fasting for lowering insulin resistance should be as long as possible, but less than 14 days. However, someone told me that many researches and studies have said the best is 18 to 96 hours.

Do you have any opinion on this?

Thank you,

There is no real ‘best’ duration. It all depends upon your own circumstance and what you prefer. Some people love the longer fasts and others hate them. It’s neither right nor wrong. Similarly, some people get great results with shorter fasts and others do terribly. I’d try all different regimens and decide for yourself which suits you best. Our basic principle in the IDM program is to start with a ‘standard’ sort of regimen and then individualize it to achieve your goals.

Dr. Jason Fung

Long fast and decreased metabolism?

Do longer than 48 hours of fasting decrease metabolism?


No. Metabolic rate increases at least up to 4 days according to the studies. This is the result of the release of counter-regulatory hormones by the body during fasting that includes the increase in sympathetic nervous system and noradrenalin. However, this only applies in general, and individuals may differ substantially.

Dr. Jason Fung

Should I worry about HOW MANY times am I eating during my eating window?

A little bit of context:

I literally just started intermittent fasting (yesterday), so this is my second day. I stopped eating at 8 pm last night and had my first meal at 12:30 today and I will stop again at 8 pm tonight. I plan to do this Mon-Fri and will give myself permission to eat more freely on weekends (but only if I feel I need to, otherwise I plan to keep the fasting).

My problem:

I like snacking, even if I’m not hungry. So I’m worried (without any justification, yet) that eating too often during my eating window may make the overall process less effective.

For example, today I had my lunch at 12:30. I started with some fruit (a cup of grapes). Then I had a salad with shrimp (spinach, bell peppers, carrots, shrimp… the healthy part), and then a small plate of rice and chicken (to feel more satiated). Then, one hour later at 13:30 I was sitting at my desk, and I felt like eating a cup of grapes WHILE I work. I tend to do this, i.e. eating while at my desk typing (I’m a software engineer, btw).

So, should I restrict myself to eat a certain number of times during my window? or does that not matter?


Yes, it does make a difference, but not a huge difference (depending upon what you eat). Everything you eat will stimulate insulin unless you eat pure fat. The more times you eat, the more insulin you stimulate. So, yes, it is better to eliminate snacking.

However, it is equally important to individualize to a plan that you can stick with. Is eating a small salad with shrimp a big deal? Probably not. Start with an eating window and see how you do. If you get the results you are looking for, then continue. If not, tighten the window.

Dr. Jason Fung



Intermittent Fasting for Beginners

Earlier Q&A

Intermittent Fasting Q&A

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More with Dr. Fung

Dr. Fung has his own blog at intensivedietarymanagement.com. He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code

His new book, The Complete Guide to Fasting is also available on Amazon.


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