Is fasting every single day counterproductive?

Ask Dr. Jason Fung

Is fasting every single day counterproductive? Is it OK to have high fasting glucose while pregnant? And once you’ve become insulin resistant, will you always be insulin resistant?

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

Is fasting every single day counterproductive?

I’m seeing a lot of conflicting information on appropriate fasting frequency. Generally speaking, is fasting, for say, 16 to 20 hours everyday a bad idea?


There are no right or wrong answers. The term ‘break-fast’ as the meal that breaks your fast implies that fasting should be done every day, as you cannot break a fast if you did not fast. Up to the 1970s, people would have a 12-14 hour fast every day. If you finish dinner by 6 pm and ate breakfast a 8 am, that is a 14 hour fasting period done every day.

That may have helped maintain weight in a healthy range, but what if you want/need to lose weight? Extending this fasting period may be beneficial. You can then extend this to 16, 18, 20 hours or whatever suits you. Find what works for you in your lifestyle (job, family etc.) and your body (bodies respond differently)

If you do, for example, one meal a day (OMAD) or a roughly 23 hour fast daily, you may do very well. In that case, continue. On the other hand, we see many people start to stall at a weight higher than they like. In that case, it is good to shake things up a little, to keep your body from adapting too much to this. Try alternating longer and shorter fasts, for example.

Dr. Jason Fung

Is it OK to have high fasting glucose while pregnant?

I am on a very low-carb diet (probably up to 30 grams a day) with intermittent fasting (short only up to 24 hours) and have high glucose readings in the morning (between 95–115 mg/dl – 5.3–6.4 mmol/L).

I understand this is normal, but what about during pregnancy? During my last pregnancy I had the same issue and they wanted to put me on insulin. Is it OK to have high glucose in the morning when pregnant? I am pre-diabetic and really cannot tolerate carbs, it shoots my fasting blood glucose up even higher.

Thank you!

Gestational diabetes is a completely different kettle of fish. Type 1 diabetes is caused by the destruction of the pancreatic beta cells. Type 2 diabetes is caused by hyperinsulinemia/ insulin resistance. But gestational is totally different. Before the pregnancy, the woman does NOT have diabetes. After pregnancy, she does. Obviously, it is not a matter of weight gain since this is normal during pregnancy. Obviously she has not significantly changed her lifestyle/ food/ exercise since getting pregnant.

The only thing that has changed significantly is the hormonal status. During pregnancy, there are all kinds of changes, mainly to sex hormones, estrogen and progesterone. It is these hormonal changes that have caused the blood glucose to go up. Since it is not a dietary disease, dietary changes are not going to reverse the disease. They may make it slightly better, but will not treat the root cause – the pregnancy itself. LCHF and short intermittent fasts are OK during pregnancy. Avoid longer fasts.

What’s the best treatment? I don’t have a good answer for you. Leaving the blood glucose high exposes the fetus to risk. Taking lots of insulin to get blood glucose down also exposes the fetus to risk. It seems that dietary management is the least worst option but it is a temporizing solution at best.

Dr. Jason Fung

Once you’re insulin resistant, will you always be insulin resistant?

1. I am already seeing that the LCHF diet is lowering my blood sugar and I’m losing weight, but I heard you say something in an interview that made me wonder if I will remain insulin resistant?

2. I feel the tingling, burning, soreness in my feet, should that stop and be corrected by properly staying on the LCHF diet and fasting for 24 hours twice per week and a 12-hour fast every other day.


1. Insulin resistance is a reversible condition, but it sometimes takes a long time. It often takes years/ decades for hyperinsulinemia/ IR to manifest and can take years to reverse. It can be done. But it is not easy

2. This may be caused by diabetic nerve damage. I have heard anecdotes of it reversing but only in the very early stages. Once it becomes well established, it is often irreversible.

Dr. Jason Fung



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Dr. Fung has his own blog at 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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