If you’re trying to get pregnant now or in the near future and you’re worried that intermittent fasting might affect your level of fertility, research shows that it has no negative effects at all, and in some cases even improves your fertility levels.
While you should always discuss fasting with your doctor if you’re concerned, here’s some interesting research to help put you at ease. Some articles or studies out there tell us that intermittent fasting will affect our ability to conceive due to a decrease in reproductive hormones if fasting just prior to ovulation. But, most of these studies have been been done with other animal species, like rats and mice, not humans. And the results have depended on the nutritional status of the animal at the time.
These studies are not relevant to human because rats and mice are ‘foragers’ (so therefore rarely go without food for any length of time) compared to us, human hunter-gatherers. Fasting for any period of time in a species who forage for food is likely to trigger a decrease in reproduction hormones because the message their body is receiving is that ‘food is scarce’. Throughout the Paleolithic era (which is the majority of the time humans have been on earth) we human beings naturally ate intermittently, when we could find and hunt for food. So it is unlikely to trigger the same stress in our human bodies.
If you’re fasting correctly (eating well on non fasting days/parts of the day when not fasting) you should be well nourished from your meals and these hormonal effects are unlikely to occur. It’s actually the chronic dieters who restrict calories and put their body under stress who are poorly nourished and have problems conceiving.
So here’s some evidence in humans. A study in the International Journal of Fertility and Sterility (2010) looked at the effect of intermittent fasting on ovulation and fertility hormones such as follicle stimulating hormone, estradiol and progesterone, in 24 women with normal menstrual cycles. They found that there were no changes in these hormones when fasting compared with not fasting, and no changes at all in ovulation.
Another study in the ‘Reviews of Reproduction’ Journal (1996) showed that women who fasted intermittently for short periods were actually more fertile in the follicular phase of menstruation (days 1 to 4 of their period) and from day 14 (at ovulation) until day 28 they showed slightly and insignificantly less, reproductive hormones during each fast. However as soon as they ate again after the fast these hormones normalized again. It concluded that there was no evidence of a decrease of reproductive hormone and fertility due to short-term fasting.
So, bearing in mind this research is about ‘short fasts’ and ‘intermittent’ fasts, if you’re fasting correctly and responsibly, your fertility levels shouldn’t be affected by intermittent fasting. But if you’re concerned and you are trying to get pregnant, talk to your doctor about taking a break from intermittent fasting completely, or avoid fasting in the a few days leading up to ovulation.