Women and fasting

Can women fast? Or is it – as many people still claim – somehow dangerous for them?

Not surprisingly, the use of fasting for weight loss has a long history, since it’s, kind of, like, obvious. I mean, everybody understands that if you do not eat, you are highly likely to lose weight. Duh. Which makes it even more surprising how much people fear missing even a single meal, let alone fast for a prolonged period of time.

They think that fasting (not eating) will make you fat. That’s kind of like saying that splashing water on your head will dry your hair. That’s modern dietetics for you. Kind of a Bizarro world.

There are still many doctors who argue that eating sugar isn’t bad for type 2 diabetics. Kind of makes you wonder how they got into medical school at all. Since it is quite obvious that missing meals leads to weight gain, the old bogeyman, ‘starvation mode’ is often invoked to instill fear.

Tales of people ‘ruining’ their metabolism abound. Food companies, of course have eagerly ‘educated’ medical professionals about the dangers of missing meals and the safety of eating sugar. Nobody makes money when you skip meals.

A long history of fasting


Fasting appeared in the medical literature over 1 century ago. Interestingly, they describe ‘professional fasters‘ who would fast for specific periods of time for exhibition. One professional faster went for 30 days and drank a quantity of his own urine.

Talk about being starved for entertainment. Kind of like watching paint dry. This was depicted in Franz Kafka’s short story “A Hunger Artist”. Fasting for entertainment was popular from 1883-1924. My guess is that it really is not that entertaining.

In the early 1900s, Drs. Folin and Denis described fasting as ‘a safe, harmless and effective method for reducing weight of those suffering from obesity’. Great. That’s exactly what we need. Something safe, harmless, and effective.

The fact that fasting has been performed (mostly for religious purposes) for several thousand years only reinforced the long history of safety. It’s hard to argue that fasting is dangerous if people have been doing for the 5,000 years. May as well argue that using soap is dangerous. Yet, myths about the dangers of fasting are everywhere.

By the early 1950’s, Dr. W. Bloom reignited interest in fasting as a therapeutic measure mostly using shorter fasting periods. However, many longer periods were also described in the literature.

Fasting for women?

Dr. Gilliland reviewed fasting in the revival of the 1950’s and 1960’s and reported his experience with 46 patients “whose reducing regime started with a standard absolute fast for 14 days”. Whoa. I love that. When I tell people to fast for more than 24 hours their eyes just about bug out of their head. These people had a ‘standard’ fast that lasted for 2 weeks! And that was just the beginning!

Of these, there were 14 males and 32 females. This is important because I constantly get questions about whether fasting works for females. This is primarily, I think due to a post found online that’s been viewed close to 100,000 times. What she wrote in 2012 is this – “Intermittent fasting and women: Should women fast? The few studies that exist point towards no.”

Nothing is further from the truth. There are hundreds of studies spanning over 100 years and clinical experience spanning 5,000 years that point to the fact that women and men respond more or less equally except in the underweight situation.

This is an easy problem. Should anybody who is seriously underweight, fast? Uh, no. You don’t have to be a genius to figure that out yourself. If you are severely underweight and fast, you could become infertile, yes.


Consider the past 2,000 years of human history. Are Muslim women ‘exempt’ from fasting? Are Buddhist women ‘exempt’ from fasting? Are Catholic women ‘exempt’ from fasting? No. So we have millions of person-years of practical experience with women and fasting. And there are no problems in 99.9% of cases.

In our own clinic, where we’ve treated close to 1,000 patients, I have noticed no significant difference between men and women. If anything, the women tend to do better. Men, it seems, are sometimes just big babies. I will mention here, too, that the highest success rates come when husband and wife do it together.

Exceptions and problems

However, pregnant women are, in fact ‘exempt’ from fasting in almost all human religion. As are children. In both situations, this makes entirely logical sense. These people need adequate nutrients for growth, and human populations have always acknowledged this.

Let’s be clear here. This point is made that several problems come up with fasting in women. Well, they come up with men and fasting, too. Sometimes women don’t lose weight the way they want. Well, that happens with men, too. The problem of amenorrhea arises when body fat is too low. Yeah, that’s not a problem we treat with fasting.

If amenorrhea or any other problems appear during fasting – stop immediately. The women and fasting issue is just another myth designed to discourage fasting. Virtually all case series of the past 100 years have included both men and women.

Back to the study

Gilliland1Anyway, back to the study. The patients were hospitalized into a metabolic ward during the first 14 days and only water, tea and coffee were allowed. After that, they were discharged and asked to follow a 600-1,000 calorie diet.

Funny enough, 2 patients asked(!) to be readmitted for a second 14 day period of fasting because they wanted better results. Did it work? Was there ever any doubt?

Average weight loss was 17.2 pounds (8 kg) in 14 days. This is in excess of the roughly 1/2 pound (0.2 kg) per day of fat loss seen in more prolonged fasting. This indicates that some of the initial early weight loss is water weight. This is confirmed by the rapid regain of weight upon refeeding.

It is important to understand this in order to avoid the disappointment that often accompanies the weight gain upon eating again. That quick weight loss and regain is water weight and not a reflection that the fasting ‘failed’. 44 of 46 patients completed the 2 week fasting period. One developed nausea and one simply decided against it and dropped out.

That’s a 96% success rate even for a regimen as long as a 2 week fast! This is our clinical experience as well. People always think they cannot do it without ever having tried it a single time. Once we start with fasting, patients in our Intensive Dietary Management (IDM) program quickly realize that it’s actually quite easy.

However, after the fasting period, patients were instructed to go on a low calorie diet. This was terribly unsuccessful. 50% of patients did not adhere to this diet over the ensuing 2 year follow up period. Instead of applying successful intermittent techniques, they returned to the unsuccessful constant energy restriction we discussed at the last post.

The key point here is that the natural rhythm of life is Feast and Fast. There are times that you should feast (weddings, celebrations), and there are times that you should fast. Intermittent. To constantly restrict calories for years on end is unnatural and ultimately worse, unsuccessful.

Drenick1Ketones appeared in the urine starting on day 2 and persisted throughout the fasting period. All 3 diabetic patients were all off insulin by the end of the 2 weeks. One patient with severe congestive heart failure was able to walk without breathlessness by the end. This 2 week fast was not harmful, as we have been told, but extremely beneficial.

Was it hard? In fact, Dr. Gilliland describes a ‘feeling of well being’ and ‘euphoria’. Hungry? Well, no. “We did not encounter complaints of hunger after the first day. We did not meet anorexia.” These experiences were echoed by other researchers of the time.

Dr. Drenick, from the VA centre in Los Angeles, also wrote extensively about therapeutic fasting. His experience was published in 1968. This was a time of renewal of interest in fasting for weight loss. He published his experience of 6 men and 4 women (yes, again there were women in the study). Did it work? In a word, yes.

Should women fast? Yes

Should men fast? Yes


Intermittent fasting for beginners

Top intermittent fasting videos

  • How to maximize fat burning
  • The most common questions

Full IF course >

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


  1. Marion
    The reason why people ask wether fasting doesn't make you fat is because it is well established that fasting whilst dieting the 'old way' (ie: the 'high carb, counting calories, eat less and exercise more' way) *does* make you fat. Because what you *do* eat is carbs so your body will produce insulin. The high insulin will lock the fat in your fatcells and so, if your body thinks you're starving, it will slow down your metabolism, and when you go back to 'normal' eating again, your metabolism never quite forgets that it was in starvation mode and so will a) try to eek out the calories it does get and b) because it's high carb, the body will desperately stuff fat in fatcells even faster to prepare for the next 'starvation period'.

    This is well established.

    The difference with HFLC fasting is that a) it's low carb so your insulin is low so your body will be able to access the fuel in your fatcells and b) because your body gets fuel (from your fatcells) and does *not* get the signal that it's starving, it will *not* lower your metabolism.

    Now, in stead of making fun of people, why not simply... explain this to them?

  2. Patty
    Yes Marion, I was wondering why Mr. Fung needs to be condescending to explain his views. I think your post makes a very important point about lchf and fasting.
    Reply: #10
  3. Adele Hebert
    Dr. Fung is a highly educated kidney specialist and a very informative speaker. He has a great sense of humour as well. I totally recommend his book - The Obesity Code.
  4. Angele
    Question for Dr. Fung-
    I had a partial hysterectomy about 10 years ago due to uterine fibroids. I kept my ovaries and cervix. I also have Hashimoto's Thyroiditis. I have been strictly following a LCHF diet for just over 4 weeks. In my fourth week I completed a 22 hour fast and several shorter fasts of about 16-18 hours. On my second day of LCHF, I experienced cramping and a very light discharge for about 24 hours. Today, on my 33rd day of LCHF, the cramping returned but this time with a true menstruation. The 30-day timing is highly suspect as it resembles a regular monthly cycle...is this common? Other women eating LCHF report in the Ketogenic Success Facebook group that irregular monthly bleeding is common and attribute it to fat cells releasing estrogen. Most say that their cycles return to normal after 3-6 months. What is the cause? Should I be concerned? Otherwise, I'm feeling fantastic. I'd love to know your thoughts on this. Thank you so much!
    Reply: #6
  5. Janknitz
    I think that there ARE some issues that women face with fasting:
    1) Some women (men too, to a lesser degree) have very distorted body images and are at risk for developing eating disorders--or already have them. Prolonged fasting and failure to "feast" intermittently with nutritious foods can feed in (no pun intended) to this problem. I'm beginning to see some of the IF group forums start to read like the forums that encourage anorexia and bulimia in teens. The type of fasting Dr. Fung recommends is healthy fasting, but it can be twisted into some very unhealthy practices.
    2) When menses cease as a result of fasting, as Dr. Fung says "Stop Immediately". But some people don't stop. One member of a FB fasting group (named after Dr. Fung and supposedly quoting him) claimed Dr. Fung said that "there's nothing wrong with not menstruating regularly--it's a natural form of birth control". IMHO, that is just wrong. Healthy women of child-bearing years menstruate regularly as they should. As a person with PCOS who struggled long and hard against insulin resistance to be able to menstruate regularly and have normal fertility, I don't see this as something to be taken lightly. When your body shuts down fertility, other harm is occurring. Some women will sacrifice their own health for the almighty scale, and it's easy to do by taking fasting too far.

    Many women fast successfully, but some may ignore their body's signals and take it too far.

  6. Peter Biörck Team Diet Doctor
    Hi Angele!

    If you are a member you can direct your question to dr Fung here (after july 4.)

    Question for Dr. Fung- I had a partial hysterectomy about 10 years ago due to uterine fibroids. I kept my ovaries and cervix. I also have Hashimoto's Thyroiditis. I have been strictly following a LCHF diet for just over 4 weeks. In my fourth week I completed a 22 hour fast and several shorter fasts of about 16-18 hours. On my second day of LCHF, I experienced cramping and a very light discharge for about 24 hours. Today, on my 33rd day of LCHF, the cramping returned but this time with a true menstruation. The 30-day timing is highly suspect as it resembles a regular monthly cycle...is this common? Other women eating LCHF report in the Ketogenic Success Facebook group that irregular monthly bleeding is common and attribute it to fat cells releasing estrogen. Most say that their cycles return to normal after 3-6 months. What is the cause? Should I be concerned? Otherwise, I'm feeling fantastic. I'd love to know your thoughts on this. Thank you so much!

  7. 1 comment removed
  8. Mechelle
    Today is my 49th B-day, and I have been High Fat Low Carb Mod Protein for just over 4 years now. In this lifestyle all of my health measures greatly improved, but I gained 40 pounds during this time--taking me from a normal weight to obesity. Ironically, although I hadn't eaten sugar in 4 years, I looked like I started each day with a donut! I avoided intermittent fasting as I believed the myth that it would make me gain more weight. On May 5th of this year I watched a video on this site with Jason Fung, finally got good information, and I immediately started my first fast--and it lasted 4 days. Since then, I have fasted for a minimum of 16 hours each day, and I often fast longer. Sometimes days, sometimes just a few additional hours. I could not be happier with the results! In 6 weeks I have lost 15 pounds, 2 inches around my waist, and my fasting glucose went from 125 to 86! If you are a woman, and you are unsure--please just give this a try. Take is one minute at a time. Start and stop as necessary. Every single minute is a new minute to choose what you want to do. Dr. Fungs videos are very, very helpful. So is his blog. Insulin goes down when you fast 12 hours or longer.
  9. wendy
    Female - age 40 - no issues fasting at all. Love the simplicity of it ! I feel great and once I got used to the first week of two 24 hour fasts, I've never looked back
  10. Apicius
    I don't find Dr Fung condescending at all. I do sense an undercurrent of rage in his narrative. And I don't blame him. He sees the insanity of his medical peers, getting away with murder....literally murder, if you think of the decades of bad advice and Big Pharma mis guiding us all into the bad eating habits of today. He is pissed off, and he has the courage to swim against the current and try to reverse the insanity. If it takes a bit of banter and quirky sense of humour to keep up his will to continue fighting...then so be it! I hope he keeps fighting...we need more doctors like him to put up a good fight!
  11. Netty
    I have just been given some disturbing news re maybe secondary melanomas, day 4 of my fast is nearly completed and I hope it will reset my body clock
  12. gbl
    Sure banter and quirky sense of humour: but fat shaming? It's unacceptable in any physician, but one who makes his living off people who are overweight and/or have Diabetes..that's deplorable. People posting here should know.
  13. Wendy
    I think Dr Jason Fung is just great! Makes the info fun to read. You people are being too sensitive. Fat shaming boo hoo! No he's not. A Doctor called Dr. Oz is more condescending and treats women like they're idiots and everyone just loves him. I don't fall for it. What do you want Dr. Fung to do? Sugar coat it? Butter it up? PUNS INTENDED! Boom!
  14. Olive
    My question is, by IF do women stop ovulating? I am torn between trying to cure some of my insulin resistance for the sake of getting to a more normal weight for pregnancy and possibly not being able to get pregnant once I get there.
    Reply: #20
  15. 1 comment removed
  16. Adele
    They are probably overeating the rest of the day and not putting themselves in a calorie deficit.
    Reply: #26
  17. PRM
    Hi Doc, a friend of mine recently posted your YouTube video on fasting. I have been doing intermittent fasting on and off for a while BUT controlled my calories also AND worked really hard in the gym.

    I am 37year old mum of 2 and i weigh 61.5kgs at a height of 168.91cm.

    However after 4 months of personal training i saw absolutely no change in my weight nor muscle definition nor inches lost. My holistic dr said that my body fat has gone up to 28% and my muscle mass has dropped!!!! However differnt centres/gyms show diff results!!!

    Past 3 days i have revamped my intermittent fasting with only 2 meals a day. No more snacks. I break my fast at 1pm with lunch followed by dinner at around 7.30pm or later depending on my schedule.

    My goal is to get to a min 21%body fat or less. I run (love it) 3xweek and do yoga and some resistance training on the other days.

    With too many unsolicited opinions and mostly all personal trainers being nutrition experts i am hoping to seek the right guidance from you in my goal of fat burning and lowering my body fat

    Am i on the right track? Pl pl help.

  18. 1 comment removed
  19. Linda
    It just amazes me how some people will believe or disbelieve everything, i.e. follow like sheep. It’s a fact that low fat, high carb diet has only increased diabetes, heart disease and heart attacks, and not to mention the obvious result, obesity.

    I’d like to address another poster who said she/he was aware of some obese people who fast for long periods of time, eat and haven’t lost any weight. IMHO, most of these people obviously break they “fasts” with high carbs and sugar, i.e., pancakes, bread, potatoes, soda, beer, high protein, dairy, etc. There is no way in May, that these people are practicing a keto lifestyle accompanied with their “fasting”. The reason I can opine is experience. My mother (died at over 400 lbs) would eat like this. She wouldn’t eat until noon and when she did, it was a very high carbohydrates with heavy protein and milkshakes, and alcohol. She tried low fat, but that lasted as long as the food on her plate before she was reaching for a sugary soda.

    I’m moving onto week 3 of the 16:8 fasting protocol and while I have not weighed myself yet, I am noticing my body is redistributing my composition, which is fine with me. I’m going to wait until I complete my first 6 week mark to weigh-in. My starting weight was 182.3 lbs at my last medical check up. My goal weight (or appearance is fine with me) is 130-135 lbs. I am 62 years old and 5’6”.

    My take on Dr. Fung is a huge round of applause for his knowledge of newfound health discoveries and if his colleagues are still touting archaic theories that have kept us in poor health, on medications that are quickly being recalled, due to a million and one side effects, almost as quickly as they’re introduced on tv, instead of recommending a person with type 2 diabetes simple change the way they eat, they push a pill at them that may kill them.

    Rock on, Dr. Fung!

    Reply: #21
  20. Carli
    Id love to know this too
  21. Karen
    Hi Linda,
    I would really like to try this. It makes so much sense. I have similar stats. What exactly is the 16:8 fasting protocol. Would love some help. I'm low carb, high protein, low fat at the moment.
    Reply: #23
  22. 1 comment removed
  23. Samantha
    Karen - 16:8 represents a breakdown of the 24 hour day. 16 hours represents your fasting period and 8 hours represent your feasting period. Thus, for 16 hours you abstain from eating and eat all your meals within the 8 hour window. You'll sleep for part of the 16 hours and the remaining time only drink water, coffee or tea. When your 16 hours are up, you 'break-fast' - but be careful to maintain a high fat, low carb, moderate protein diet so you don't undo everything you accomplished during your fast.
  24. ella franzén
    Hey! I love IF but have had issues with becoming extreeemely tired/sleepy once I eat (eating window ca 8 h’s - I skip breakfast). I think I may be having some blood sugar problems? I eat healthy - No sugar, GI-low carbs. Im not overweight, but have some pounds to lose; 44 years old, female. I feel great while fasting - and Im doing it for the health benefits. But I’m a bit worried about this blood sugar issue as I think I may be prediabetic because of all the years eating sugar sugar sugar
  25. Carol
    "Keep calm and keto on" quote The Dudes.
  26. Beck
    Calorie deficits are long debunked for the “what goes in, must come out” mentality.
    Weight loss and metabolic disorders are not so simple.

    What is likely is that the people you are referring to, either leave their bodies malnourished because they are so ashamed of their size that they do not eat at all- and so their body stores all energy it can as fat.

    Also- after decades of being told obesity is caused by excess fat, these people eat once a day, a low fat meal- which is the opposite of what you should do when LCHF IF.

    Years and years of contradicting medical and nutrition advice and compounding societal pressure to look a certain way has absolutely demolished any self worth, motivation and drive of countless people struggling with understanding their own metabolism and why they are actually obese.

  27. jazzycarolanne
    Dr Fung never fat shames people...in fact he does the opposite. He explains that most folks have been following what diet experts have been promoting , CICO, low fat diets etc and that has made us fat. He is very empathetic and encouraging and just delightful in person! I should know...he is my doctor.
  28. Bella
    What about when a woman is on her period? You mentioned Muslims, well, a woman is not supposed to fast on her period I read. I developed nausea a few days before. Is that from progesterone levels or unrelated? Thank you.
    Reply: #29
  29. Kristin Parker Team Diet Doctor
    Dr Fung addresses this in the article. A woman doesn't need to stop fasting unless she loses her period, which is usually related to very low body weight and underweight people shouldn't fast in any case.

Leave a reply

Reply to comment #0 by

Older posts