New data on how intermittent fasting affects female hormones

Krista Varady

A new study led by Krista Varady, professor of nutrition, found that intermittent fasting did not change the levels of certain kinds of female reproductive hormones and caused a decrease within normal ranges for another hormone.

“I think this is a great first step,” said Varady about the eight-week study, funded by the National Institute of Diabetes and Digestive and Kidney Diseases.

The study followed a group of pre- and post-menopausal obese women who maintained an intermittent fasting diet that involved eating during a four-hour or six-hour period each day without calorie limits, then consuming only water until the same time next day.

The researchers compared the differences in hormone levels with those of a control group that followed no diet restrictions.

They found that levels of a protein that carries reproductive hormones throughout the body was unchanged in the dieters after eight weeks. The same was true for steroid hormones related to the production of testosterone and estrogen.

However, another hormone, DHEA, that fertility clinics prescribe to improve ovarian function and egg quality, dropped by about 14% but remained within normal range.

Women in the four-hour and six-hour dieting groups lost 3% to 4% of their baseline weight compared with the control group, which had almost no weight loss. The dieters also saw a drop in insulin resistance and biomarkers of oxidative stress.

“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,” Varady said.

“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.”

This article has been edited for length and clarity by Sonya Booth.