Ask Eirik: Does Intermittent Fasting Work as Well for Women as for Men?

woman-exercisingToday I received an e-mail from Cain Credicott, Co-Owner/Editor in Chief at Paleo Magazine. He contacted me because one of his editors had a question about an article on Intermittent Fasting (IF) I handed in a short while ago and that they’re now preparing to publish.

I thought the editor’s question was a great one, and one that revolves around a topic/issue that a lot of people are curious about, so I decided to put it up here on the blog.


Here’s the e-mail I got from Cain:

Hey Eirik –

Got a question from my editor on a section in this article.

(FROM YOUR ARTICLE) I would argue that we’re genetically adapted for an eating pattern that naturally incorporates periods of fasting. We should go hungry every now and then; eating all the time, and never giving our digestive machinery a rest, is unwise. This notion is supported by the evolutionary evidence, as well as a growing body of research linking IF with various health benefits, including fat loss, improved glycemic control, and reductions in blood pressure.1, 2, 5, 6

My editor is curious if you’ve examined the evidence that Stefani Ruper has brought to light re IF and women; i.e., the differential outcomes that women have on IF protocols (and the fact that most of the favorable findings involved male subjects)? Do you consider the benefits you list above to pertain to both men and women? If not, it would be great to add something about the difference between the sexes.

Cain Credicott

My reply:

Hey Cain,

That’s a really interesting question. I’ve come across a couple of articles in the past that claim there’s a difference in how men and women respond to fasting, but I haven’t really dug into the literature on this issue. I took a look at the blog post you just sent over. It seems to provide a good overview of the data.

Here are my general thoughts on this issue:

Most of the scientific evidence pertaining to the health benefits of fasting is derived from studies with male participants. There’s a paucity of data on IF in relation to women’s health. Hence, it’s very difficult to draw firm conclusions regarding the health benefits of IF for women. What we can do, however, is to make educated guesses based on the evolutionary evidence, as well as the few studies on IF that have been done in women.

The author of the article at concludes, based on the few studies that are available, that women respond differently to fasting than men. They don’t seem to experience the same health effects, at least not to the same extent as men.

This is exactly what I would expect, based on what I know about the differences between the evolutionary path that male members of our species have traveled upon and the one that women have journeyed.

As we all know, men were historically hunters, whereas women were gatherers. When you’re out on a hunt, it may take hours or even sometimes days before you manage to chase down your prey; hence, you may go long periods of time without eating. If you get a hold of some plant foods or small game along the way, you’ll likely eat it; however, the big meal doesn’t commence until you manage to bring down your primary prey.

Some indigenous, non westernized people (e.g., the San) are known to perform persistence hunting – a type of hunting that involves tracking animals over long distances, for long periods of time, in order to completely exhaust them. It’s generally believed that this was a common hunting strategy among our Paleolithic forebears as well.

As for gathering, there isn’t one big pay-off at the end, but rather, food is gradually collected – and sometimes eaten – over time. This, in combination with the fact that pregnancies and child-rearing activities would have made our female ancestors less mobile and more dependent on a stable food supply than men, may suggest that IF agrees more with the male physiology than the female one.

Other factors may be important as well, but these are probably the major ones. Over time, these differences in the way of life of men and women would have produced physiological differences between the two sexes. For example, men developed more muscle mass in certain areas of the body than women and may have evolved an enhanced capability to sustain high levels of physical performance while in a ketogenic state. Differences in nutritional requirements (e.g., men need more protein per kilogram of body weight than women) and metabolic and hormonal responses to different meal patterns (e.g., IF) would naturally result from these physiological differences between the sexes.

Those are my general thoughts anyway. I would have to take a closer look at the literature on the topic to give you a more thorough answer.

I hope that helps!

– Eirik


  1. One Women's IF Experience says:

    I loved the concept of intermittent fasting (in this case eating 5 hours, fasting 19/daily) and male friend had great success with it. Since IF was the only difference I adopted (still exercised same, ate same paleo type diet, no illnesses) I can only assume that it was the IF that threw my body for a loop. Previous to IF I had very consistent menstrual cycles (almost every 28 days exactly) after a few months of IF my cycles went crazy. I didn’t get my period at all, then I got it once for 18 days. I ended up with adrenal fatigue when it was all said and done and it’s taken me about 18 months to get back to “normal”. I still would like to try maybe fasting just one day a week?

    • Hi,

      Thanks for sharing your experience.

      I suspect that you may have overdone things. 19 hours is a pretty long fast. Maybe you would see better results with a somewhat shorter fast and longer eating window.

      Also, I wouldn’t exclude the possibility that IF wasn’t the primary cause of your problems. Other factors may be involved.

      Did you frequently exercise on an empty stomach?

      • One Women's IF Experience says:

        Yes, re: exercise on empty stomach … my window was usually 4-9pm at night and then I would do crossfit usually around 12pm noon. I agree, I think I may have overdone it. I need to find that happy middle ground of getting the benefits of fasting and not stressing my body so much.

        • Yep, then I suspect you took the whole thing a bit far.

          Crossfit is pretty taxing, at least if you’re doing a lot of high intensity stuff.

  2. Hi Eirik. Interesting article. I’m not sure what health benefits men derive from IF that women don’t also benefit from. It would seem likely that the feast-and-famine existence of our early ancestors necessarily evolved into a normal eating pattern for the human species, including women, whereas the modern way of eating every few hours goes against our ancestral grain.

    I’ve never seen any valid reason to fast for long periods, but I regularly fast overnight between an early dinner and a late breakfast/lunch. This is generally a 16-hour (or longer) time period that I do on a daily basis. This type of IF comes naturally to me since I’m not a snacker and rarely eat between meals. If I get sufficient sleep, my energy level is good so I’m not sure what actual health benefits this type of IF provides me, as a woman, other than it does help keep my weight at a normal level.

    I would say to other women, if IF is at all unpleasant or doesn’t feel right to you, then don’t do it. Optimal health can and should be achieved in ways that are appropriate to each of us as individuals.

    • Hi Shary,

      My intention with this article was absolutely not to scare women away from trying IF. I’m a proponent of IF, as I’ve pointed out many times where on the blog. I was only addressing the notion/concern that men and women respond differently to fasting.

      It’s almost comical that IF has become such a “big thing”/controversial topic in the health/fitness community, considering that it may represent the default eating pattern for Homo sapiens. Intermittent periods of fasting were undoubtedly a natural part of our ancestors’ life. It’s the modern way of eating (early breakfast followed by several meals spread out over the day) that we should be skeptical to, IMO.

      On a side note, I really like your IF protocol. I think a lot of people may find such a set-up to work well for them.

      • Hi Eirik. I wasn’t criticizing your article or the points you were making. I’m only saying that IF might not work for all women–or all men, for that matter–for whatever reason. The comment regarding messed-up menstrual cycles due to IF is a prime example. Good health isn’t necessarily a one-size-fits-all proposition.

        For instance, back when protein drinks first became popular, I tried to stick with them, convinced by others that I would greatly benefit–and I immediately got sick each time I drank one. The lightbulb came on and I realized that not everything deemed “healthful” is right for all of us. The reverse is equally true. I definitely feel best on a diet that contains quite a bit of red meat, for example–FATTY red meat–well-marbled steaks and the like, even though red meat in general has been frowned upon in recent years. I tend to agree with your last sentence here, but ultimately, it has to be about paying attention to our own individuality to see what works best for each of us?

        • I agree, to an extent šŸ™‚

          Ancestry, epigenetic programming, and lifestyle will all affect a person’s metabolism, gene expression, nutritional needs, and so forth.

          That said, all Homo sapiens have a similar (not identical) set of basic nutritional requirements, which have been passed down to us from our ancestors.

          I suspect that interindividual variability in microbiota composition can help explain why there’s so much variability with regards to how people respond to different diets.
          The best way to address this issue is probably not to prescribe person A a diet that is very different from the one that’s prescribed to person B (“personalized nutrition”), but rather to intervene at the level of the microbiota.

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