Ask the Nutritionist: Does Intermittent Fasting Work the Same for Men and Women?

Hi Dan, Is intermittent fasting good for women? I have heard that research focuses only on men and therefore intermittent fasting doesn´t work the same way for women.

I can see where you’re coming from with this question. Differences in sex is one of many variables that need to be considered when conducting a scientific study.

How much sex influences a potential study can vary a lot and is often up for debate. For example, breast cancer is far more common in women than it is in men, whereas the effect of protein on muscle growth is determined more strongly by other factors. 

Diving into the research there appears to be some minor differences in how intermittent fasting affects men and women. In one study resting energy expenditure decreased slightly more in women (if you’re trying to lose weight this isn’t a good thing) but no other markers were different and in another study plasma glucose levels were lower in women after an extended period of fasting.

Some studies have looked at alternate day fasting, where a day of eating is followed by a day of no, or very low, food intake. The 5:2 diet is a popularised example of this. When focussing on weight loss we find no significant differences over 3 months. 

Looking at the effects on androgenic (growth and reproductive) hormones it appears that intermittent fasting can affect these hormones in all participants. Interestingly, this could be a positive in women with PCOS but a negative for men’s libido, I will caveat this is based on very limited research. 

There is definitely a lack of good quality research in the intermittent fasting area, this is also true for women in general because often participants are middle class Caucasian men. Combine these two factors and you can see why it becomes difficult to answer your question with any confidence.

Not only that, but pre- and post-menopause participants may react entirely differently in a trial, digging deeper so can participants based on the stages of the menstrual cycle and this has contrasting effects on individuals because hormones are weird and that’s without considering people taking hormones to transition. So even if we had lots of well designed trials with female participants we may still struggle to draw conclusions.

At this point I still think it’s difficult to determine some of the top level claims around intermittent fasting, so trying to work out the influence of sex is beyond our current understanding. 

TL;DR

Based on the data we have, I think it largely does. However this question highlights the need for better designed research focussed on women, and more of it.