What is the optimal fast frequency?

Ask Dr. Jason Fung

What is the optimal fast frequency? Can you fast with low blood pressure? Is type 2 diabetes caused by fat plugging the pancreas or via high insulin levels in blood? And, can a low metabolic rate be reversed?

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

Fast frequency

I’ve found through various of your articles and videos that the 24-hour fast can be performed daily (Warrior Diet). I’ve also found the “mixing up” the duration of fasts is good so that the body doesn’t adapt. My question is on what frequency are three-day and seven-day fasts acceptable? For example, one 7-day fast per month and three 3-day fasts per month, 24-hour fasts the remainder? If you’re in general good health, a of couple weeks into the keto diet, 40 pounds (18 kilos) overweight having lost 20 pounds (9 kilos) already?


That’s a great question, but one with no easy answer. It all depends upon the person. It depends upon the specific reason you are fasting, how your body responds to it (some people do better than others), and how easy it is for you. I just saw somebody who did a 61-day fast, and the very next person said she couldn’t do 12 hours. The answer is different if you are at your ideal weight or severely diabetic and 100 pounds overweight.

Dr. Jason Fung

Fasting and low blood pressure

Hi Jason,

Is it safe to start fasting if you have low blood pressure?


It is not an absolute contraindication but you need to speak with your own doctor. Some people during fasting can feel faint, especially if they are not staying hydrated, so the low blood pressure may exacerbate that problem.

Dr. Jason Fung

Fat plugging pancreas vs. high insulin levels in blood

Dr. Fung: Your books are a revelation for a person with type 2 diabetes for many years. I’m now fasting.

One thing gnaws at me. You make great sense to me that the 0.6 g (I think you said) of fat clogging the pancreas is the reason beta cells are not performing.

But, contrarily, you indicate that there are already high levels of insulin in the blood and that it’s the insulin in the blood that’s the real problem – high blood glucose is a symptom.

How can both of these statements be true?

Again, “you had me at ‘reversible.'”

Thank you,
Steve Brock

The underlying problem of type 2 diabetes is too much insulin. This drives glucose into cells, and drives de novo lipogenesis. The liver exports the fat to the pancreas which gets clogged and this decreases insulin production. This is the body’s compensatory response.

Insulin is too high (usually due to diet) and the body is trying to fix it by clogging up the pancreas. This lowers insulin, but does not fix the root problem. In the mean time, glucose goes up in the blood, which then gets dumped out the kidney. This gives us the symptoms of diabetes. But again, this is the body trying to fix the problem.

There is too much glucose coming in (diet) so it is trying to dump it out through glucosuria. But neither of these compensatory responses fixes the root problem (diet).

Dr. Jason Fung

Can a low metabolic rate be reversed?

I have been a yo-yo dieter for years. last year, following a diagnosis of diabetes, I started on the BSD (800 calories a day). I have lost 50 pounds and my blood sugars are much improved. My metabolic rate is definitely low, it probably was before I started even on 800 calories. I have reached a plateau having been on 800 calories and low carb for nearly three months. I have just started intermittent fasting and generally understand that this, in itself, does not lower metabolic rate but what if you already have a low metabolic rate – can this be helped? I have your books on fasting, obesity and diabetes and they have helped me to understand the aetiology of diabesity, but I don’t think they address this specific enquiry. Could you elaborate?


Yes, the basal metabolic rate (BMR) is not fixed. If a specific diet can lower the BMR, then a different diet must be able to raise it. A severe calorie-restricted diet, such as 800 calories per day, is almost guaranteed to lower your BMR. I generally suggest fasting and LCHF diets.

Dr. Jason Fung

Q&A videos

Top Dr. Fung videos


Intermittent fasting for beginners

A keto diet for beginners

Earlier Q&A

Intermittent fasting Q&A

More with Dr. Fung

All posts by Dr. Fung

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

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Dr. Fung’s books The Obesity Code, The Complete Guide to Fasting and The Diabetes Code are available on Amazon.1

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