How permanent is the effect of intermittent fasting on insulin resistance?

Ask Dr. Jason Fung

There are tons of questions about intermittent fasting, like these:

  • How permanent is the effect of intermittent fasting on insulin resistance?
  • Does whey protein supplements help lower blood sugars?

Dr. Jason Fung is one of the world’s leading experts on fasting for weight loss or diabetes reversal. Here are a his answers to those questions and more:

Fasting and insulin resistance

Dr Fung,
I have a few questions:

1. How permanent is the IF on the insulin resistance? After you lower the insulin resistance through a regimen of fasting, is it sustainable or you have to do it for life. As you mentioned, most weight loss diet are not reversible. So I wonder whether IF is sustainable.

2. In this study, it is mentioned that whey protein helps to lower blood sugar. For me, I take Whey after a gym regimen to help to build muscles. I am TD2. Is it harmful to take whey (not excessive – just about one spoonful provided by the Whey protein can).

3. What about Monk Fruit (natural – not processed). Is it OK to drink that or mix it with your drink?

Dr. Jason Fung:

1. It is not permanent. It’s like taking a bath. You can’t do it once and expect to be clean forevere.
2. I don’t recommend it. Stick to real food.
3. No.


Dr. Fung, thanks for the reply to previous questions, now have one about baby aspirin. I’ve been taking a daily baby aspirin in addition to all the oils for blood lubricity, and with all the bad press I’ve been reading lately I’m beginning to question the wisdom of that. I’m thinking the oils I’m taking : fish oils, avocado oils, olive oils, Vit E in tocotrienol form, and Vit. D’s, are enough to keep blood lubed up plenty good. Question is do I really need the baby aspirin. I know from your book “The Obesity Code” that you don’t seem to hot on the idea of aspirin. Whats the verdict?
1. Does aspirin artifically stimulate insulin?
2. Is aspirin a good thing to be taking regularly to help prevent heart attacks?
3. Other then use for a say, monthly headache is aspirin something a person wants in their diet?

Thanx in advance Doc !

Dr. Jason Fung:

1. No
2. No. Only in secondary prevention. The recommendation that everybody of the age of 60 take an aspirin a day is old and has since been retracted. It is a drug and has use in specific patient groups, not everybody willy-nilly.
3. No.

Intolerance to dairy and fasting tricks

Hi Dr Fung – thank you for your reply to my previous questions.
I’m now on Day 3 of my fast and feel good.
I introduced double cream (15mls) to each of my 3 coffees today, and it is becoming clear that I am intolerant to dairy products as my skin has already deteriorated after improving over the first 2 days of the fast. So:
1) Could I substitute canned coconut milk for the double cream? (15mls / serving x 3)
2) Are micronutrients stored within fat cells in the body. If not, how do you maintain electrolyte balance whilst fasting?
3) Would taking 2 tbsps raw organic apple cider vinegar daily be a good idea whilst fasting?
4) You suggested alternate day fasting at the end of a fast. – would this be a water fast or 500 calories as suggested by Dr Krista Varady in The Every Other Day Diet?


Dr. Jason Fung:

1. Yes. Try coconut cream instead of coconut milk. It’s delicious.
2. A general multi-vitamin supplement for extended fasts.
3. Yes
4. Either works.



Intermittent Fasting for Beginners

More questions and answers

Many more questions and answers:

Intermittent Fasting Q&A

Read Dr. Jason Fung’s new great book The Obesity Code for many more insights:

The Obesity Code

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Full IF Course >


  1. 1 comment removed
  2. Natalie
    I am new to your website but have been doing LCHF for about 18months. I am keen to try Intermittent fasting, I did 2 days last week and found I had no problem and liked the results.(I did no exercise on those days). I do quite a bit of running and have just completed a marathon. My runs at the moment are not long as I am still recovering.
    I normally run early in the mornings in a fasted state. My question is, is it ok to do Intermittent fasting while exercising or should I be consuming a meal of good carbs, fats and protein post exercise even if it's of short duration (30 minutes).

    Thank you

  3. Zepp
    Do as you feel good of!

    30 minutes is what everbody should do.. att least!

  4. Earle Wignall
    The above analysis leads to several prospects for the intermittent faults dependability enhancement strategy. Comprehensive fault injections have been conducted to characterize the effects of transient faults on processors. As semiconductor technology scales into the nanometer regime, a resurgence of interest in intermittent faults has c 858 ome forth in recent years.
  5. Trevor
    I've seen it mentioned that cream in coffee during a fast is acceptable. What about other fats like butter and/or coconut oil? Also, would buttered broth be acceptable?
    Reply: #6
  6. Peter Biörck Team Diet Doctor
    Hi Trevor!

    If you use small amounts of "pure" fat it's even better than cream. :)

    I've seen it mentioned that cream in coffee during a fast is acceptable. What about other fats like butter and/or coconut oil? Also, would buttered broth be acceptable?

  7. Amy
    I've been told to take an aspirin a day for cancer risk. Can I continue to do this while fasting? Or should I stop while fasting and resume afterwards? (My main reason for fasting is also to reduce cancer risk due to familial genetic risk)
  8. Juddee’
    Dr. Fung:
    Your book is excellent. I have been fasting every other day for 36 hours or more. On the fasting days I have not been doing any insulin. My blood sugar climbs back up to around 122 on fasting days. On food days I take insulin, 15 ml twice daily. Should I be taking any insulin on my fasting days? Thank you.
    Reply: #9
  9. Kristin Parker Team Diet Doctor
    Please work with your doctor regarding any questions about medication dosage.
  10. Steven Svoboda
    Hello, I have a question about if fasting causes temporary insulin resistance? Dr. Peter Attia talked about how after a long fast, he took an oral glucose tolerance test and found he had significant postprandial glucose elevation but wasn't quite sure why this would be... Would this transient insulin resistance possibly be because you have cortisol around when fasting which is needed to stimulate gluconeogenesis in order to maintain basal blood glucose levels. Then, when you refeed with a carby meal, it appears as if you are insulin resistant bc it takes a little while for cortisol to decrease and for your cells to switch back to utilizing glucose. However, its only transient because fasting increases AMPK which increases GLUT4 receptors ultimately increasing insulin sensitivity in the long run. Thus the transient insulin resistance that occurs from cortisol during fasting really wouldn't matter if you aren't consuming any carbs. The glucose being produced in your liver is only really supplying cells that require it such as RBCs and brain cells to a small degree. Thus this insulin resistance that occurs may be a mechanism to ensure that glucose is preferentially utilized by cells that require it? Does this make sense mechanistically?

    Thank you,
    highly curious medical student

  11. Renn Van Niekerk
    Hi I have Lupus SLE and take many meds. Is it ok for me to take meds on the 16/8 intermittent fasting? Thanks
    Reply: #12
  12. Kristin Parker Team Diet Doctor

    Hi I have Lupus SLE and take many meds. Is it ok for me to take meds on the 16/8 intermittent fasting? Thanks

    Please check with your doctor regarding the safety of fasting with Lupus and timing of your medications.

  13. Mark W.
    Just dropped in to say 'thank you' for your work.

    I've lost nearly 10% of my body weight in the last six weeks, and I've never felt more in control of my body weight and food intake in my life. Your books have been life-changing for me, and there are no words to adequately communicate my gratitude.

    I've been telling EVERYONE about your books. The unofficial sub-title I've given both The Obesity Code and The Complete Guide to Fasting is 'an owner's manual for your mouth'. Yours to use in publication without attribution, should you so wish.

    Thank you, so much, Dr. Fung.

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