Can intermittent fasting cause hormonal imbalances in women?

Ask Dr. Jason Fung

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

  • Can intermittent fasting cause hormonal imbalances in women?
  • As Metformin prevents your liver from producing sugar, will your liver be able to clean out the accumulated sugar?

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:

I’ve read that IF can cause hormone imbalances with women, is this true?

While I know this is one study1, I didn’t know if you’ve come across this through your program with other women? I’ve read about similar problems online with other women.

The reason I am asking is because I have been doing IF, 36-hour fasts every other day for 8 weeks with success. I have lost 15 lbs (7 kg) and my blood pressure has dropped. However, I am noticing hormonal problems with missed periods, and dry skin. Also a friend of mine, who is also doing IF, has begun to experience hot flashes. We are both in our late 40’s, and while we are getting close to menopause, it seems a bit early, and for us to suddenly start experiencing these symptoms when we began IF seems too coincidental.

While I am pleased with the results and I intend to continue with IF, I am wondering if you have any recommendations or suggestions? Perhaps a more modified intermittent-fasting approach?

Thank you,

Women can fast. That study is on rats. If you are a young rat, then maybe you shouldn’t fast. If you are a human adult, then yes, you may fast. We have had several thousand years of human history to guide us that yes, women may fast with equal efficacy to men. I’ve treated hundreds of women. Yes, some have problems fasting, but so do some men. There’s no difference.

Dr. Jason Fung

Learn more about women and fasting

Since Metformin prevents your liver from producing sugar, will your liver be able to clean out the accumulated sugar?

I’ve been on strict LCHF for 5 months religiously per page 4 eating plan. Lost 20 lbs (9 kg) during the first 6 weeks, then stopped. I stuck with it and finally decided to go on Metformin a couple of weeks ago per Dr. William Wilson in Keto Clarity.

I read your info on Dawn Phenomenon and I’m concerned that Metformin will prevent my liver from dumping all the stored sugar. Just started intermittent fasting yesterday to jolt my system. Blood glucose was 165 mg/dl (9.2 mmol/l) before metformin and is now hovering around 135-155 mg/dl (7.5-8.6 mmol/l). I’ve never taken any other medicines for type 2 diabetes and don’t have any other symptoms of type 2 diabetes.


Metformin blocks gluconeogenesis. It is neither particularly harmful nor helpful for type 2 diabetes. It lowers blood glucose but does nothing for diabetes.

Dr. Jason Fung

Learn more about the dawn phenomenon – why are blood sugars high in the morning?



Intermittent Fasting for Beginners

Earlier Q&A sessions with Dr. Fung:

Many more questions and answers:

Intermittent Fasting Q&A

Q&A videos

    Is low carb bad for exercise?
    Is low carb bad for the kidneys?
    Everything in moderation?

Top Dr. Fung videos

  • Diet Doctor Podcast #64 with Jason Fung
    Part 8 of Dr. Jason Fung's diabetes course
    The essential problem with type 2 diabetes

More with Dr. Fung

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.



  1. Bb
    I enjoy listening to dr. fung and I bought his book, but in this case I am disappointed that he did not answer the question. Is it possible for IF to cause hormonal changes? Not if IF causes problems. I too experience much more intense hot flashes when fasting and I am 57. I have asked several experts but none have addressed the question.
  2. RT
    I would have to agree with Bb. A more straightforward response would be, for example, something like "Yes, IF can can cause such issues and here's what you can do about it." Or "No, there's no evidence of IF being a cause of hormonal issues for women. The cause must be something else." Or "I don't know." With respect to Dr. Fung for his great contributions to human health, I do not think the question was adequately answered.
  3. Apicius
    I read through the material above, and I thought he did answer the question. The way it reads to me is that IF does not cause hormonal imbalances per se. He says he has treated many women without issue, except for some that had issues specific to those patients alone. From this, I would conclude that any woman experiencing issues during trying out IF needs to dig deeper...either an issue that would have come up anyway, or specific medical reasons that pertain only to that patient. Is it possible for two women, close to menopause age to experience issues at the same time...I would say yes...I wouldn't consider it statistically improbable. two cents...
  4. Jason
    The answer to your question Marci is that, yes, IF can cause hormonal issues in women. Fasting is perceived as a stress by the body and women under too much stress have their homrones get messed up. If you want to keep doing IF I suggest not skipping food for 36 hours but instead doing your fasting day as about 1/4 to 1/3 of normal daily food spread out like normal meals.
  5. RT
    Thank you, Dr. Fung. You are a stellar example of medical ethics and intellectual honesty in a world of officially sanctioned junk science. And you're not afraid to take on the disinformation-spewing vested-interest machines.
  6. Bb
    Thank you Dr. Fung and Marci for the question. That makes so much sense.
    Sorry spell check got me!!
  7. Apicius
    Peter Biorck, can you confirm that the response #4 above by "Jason" was indeed by Dr Jason Fung? Typically, responses from members of team dietdoctor tend to be in blue font, and typically complete name spelled out, too. Just exercising extra this is an open forum.
    Reply: #8
  8. Peter Biörck Team Diet Doctor
    Good question, Apicius!

    I will check this out. My best guess is that this is not a comment from Dr Jason Fung.

    Peter Biorck, can you confirm that the response #4 above by "Jason" was indeed by Dr Jason Fung? Typically, responses from members of team dietdoctor tend to be in blue font, and typically complete name spelled out, too. Just exercising extra this is an open forum.

  9. RT
    Good point, Apicius. I should not have automatically assumed that "Jason" = "Dr. Jason Fung."
  10. Dr. Andreas Eenfeldt, MD Team Diet Doctor
    It's not Dr. Jason Fung, just another amazing Jason. :)
  11. Judy Baker
    There have been reports about women losing their periods when they cut down on carbs and the diet usually takes the blame. The real culprit in many cases may be the amount of flax they are eating in their low-carb food. Flax is now a popular ingredient in "healthful" foods, such as zero-carb breads and crackers. It is used to replace gluten and eggs in baked goods and to increase the amount of omega-3s and fiber. Flax contains more estrogen than any plant food and can have serious side effects for both men and women and especially children.
  12. Erika
    The doctor didn't answer the question, in fact the answer is misleading. Not surprising with regard to women's health.

    Yes, women can fast, though not necessarily in the same intervals as men. That's ok! We should be cautious with extended fasts, for the reasons already mentioned here. Me -- a woman, I fast 23 hours each day. I have however done longer fasts like 48/72 but, do not recommend in frequent intervals, for the side effects aforementioned. I did however clear a vaginal infection with a 72 hour fast in combination with boric acid and lots of rest.

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