Does Intermittent Fasting Negatively Affect Female Hormones?

By Jiri Kaloc

Proponents of intermittent fasting claim it helps with weight loss and improves health. Critics point out potential negative impacts on female reproductive hormones. A new study from the University of Illinois Chicago offers new evidence on the matter.

They tested eating only once a day

The study followed 12 pre-menopausal and 11 post-menopausal obese women for a period of 8 weeks. The participants were on an intermittent fasting protocol where they ate only once per day. They only had a window of 4-6 hours for eating and had to fast for the rest of the day. The researchers measured the differences in hormone levels of the participants and compared them against a control group that followed no diet restrictions.

Hormones were unaffected, except for one

The results of the study show that most of the monitored hormones were unaffected after the 8-week period. This includes the sex-binding globulin hormone, a protein that carries reproductive hormones throughout the body, testosterone, and androstenedione, a steroid hormone that the body uses to produce oestrogen. The study also showed no differences in levels of oestradiol, estrone and progesterone but only in post-menopausal women. These pregnancy-related hormones were not measured in pre-menopausal women due to their changing levels throughout the menstrual cycle.

The researchers observed a change in only one hormone. Dehydroepiandrosterone (DHEA), a hormone that fertility clinics prescribe to improve ovarian function and egg quality, decreased by about 14% in both pre-menopausal and post-menopausal women at the end of the trial. It’s important to note that the DHEA levels remained within the normal range even after the decrease.

“This suggests that in pre-menopausal women, the minor drop in DHEA levels has to be weighed against the proven fertility benefits of lower body mass. The drop in DHEA levels in post-menopausal women could be concerning because menopause already causes a dramatic drop in oestrogen, and DHEA is a primary component of oestrogen. However, a survey of the participants reported no negative side effects associated with low oestrogen post-menopause, such as sexual dysfunction or skin changes,” said co-author Krista Varady, a professor of nutrition at the University of Illinois Chicago.

Possible reduced risk of breast cancer

There is one more relevant effect of the DHEA hormone. Previous research links DHEA to breast cancer risk. The moderate decrease of this hormone observed in this study may lower the risk of this cancer type in both pre- and post-menopausal women.

Weight loss and improved biomarkers

This study confirmed some of the health and weight-loss benefits of intermittent fasting. Participating women experienced weight loss of 3-4% of their baseline weight over the 8 weeks compared with the control group, which didn’t lose weight. They also saw reductions in oxidative-stress biomarkers and insulin resistance.

“I think this is a great first step. We’ve observed thousands of pre- and post-menopausal women through different alternate-day fasting and time-restricted eating strategies. All it’s doing is making people eat less. By shortening that eating window, you’re just naturally cutting calories. Much of the negative information on intermittent fasting reported has come from studies on mice or rats. We need more studies to look at the effects of intermittent fasting on humans.”

We will need more and larger studies to confirm these results but so far it seems that intermittent fasting can be beneficial and safe for women.