Does Intermittent Fasting Affect Adult Female Hormones?

The Warrior Diet is a version of intermittent fasting, and this dietary practice prescribes a time-restricted feeding window of around 4 hours per day, and within this time frame, people can eat without counting calories after which they return to following a water fast until the next day. This may also put your body into ketosis, which is a metabolic state in which your body gets its fuel from fat rather than sugar, according to research published in Ageing Research Reviews. This diet plan promotes exercising and undereating during the day as our ancestors would have likely done, then eating one large meal in the evening without restrictions on how much or what kind of food you eat within the time restriction. 

For this study, the researchers followed a group of pre and post-menopausal women for 8 weeks who followed the warrior diet intermittent fasting plan, and perimenopausal women who are typically in their 40s were excluded from this study. Participants were divided into groups of a 4-hour eating window, a 6-hour eating window, and a control group with no diet restrictions. The team measured the differences in hormone levels which were obtained by analyzing blood sample data. 

After 8 weeks the researchers found that levels of sex-binding globulin hormones were unchanged, as well as testosterone and androstenedione. Sex-binding globulin hormone is a protein that carries reproductive hormones throughout the body, and androstenedione is a steroid hormone that the body uses to produce estrogen and testosterone. 

However, DHEA (dehydroepiandrosterone) levels were found to be significantly lower in pre and post menopausal women, with levels dropping by 14%. DHEA is a hormone that is commonly prescribed to help improve ovarian function as well as egg quality in women. Although the drop was the most significant finding, the levels remained within the normal range by the end of the 8-week study period. As a benefit to this decrease, high levels of DHEA are linked to breast cancer, a moderate decrease may be helpful in decreasing the risk of cancer in women. 

"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," Varady said. "The drop in DHEA levels in post-menopausal women could be concerning because menopause already causes a dramatic drop in estrogen, and DHEA is a primary component of estrogen. However, a survey of the participants reported no negative side effects associated with low estrogen post-menopause, such as sexual dysfunction or skin changes."

Estradiol, estrone, and progesterone levels were also measured, but only in post-menopausal women due to the changing levels of these hormones throughout the menstrual cycles of premenopausal women. Results show that there were no changes in these hormones, which are all hormones that are vital to pregnancy, at the end of 8 weeks. 

Those in the 4 and 6-hour eating window groups experienced a 3-4% weight loss of their baseline weight compared to the control group which experienced almost no weight loss. Those in the eating window groups also experienced a decrease in insulin resistance and in biomarkers of oxidative stress.  

"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,” said Varady.