Intermittent fasting has taken off as a way to lose weight without having to limit types of a food a person eats.
But there was little research on how eating only during a few hours of the day and then only drinking water might affect female reproductive hormones.
A new study shows that while hormones do change with intermittent fasting, it might not harm fertility.
"We've observed thousands of pre- and postmenopausal women through different alternate-day fasting and time-restricted eating strategies. All it's doing is making people eat less," said Krista Varady, a professor of nutrition at the University of Illinois Chicago. "By shortening that eating window, you're just naturally cutting calories."
Much of the negative information on intermittent fasting has come from studies on mice or rats, she said, calling for more research of the effects on people.
For this study, the researchers followed women with obesity for eight weeks. They ate a "warrior diet," which was four or six hours of eating without counting calories followed by 18 or 20 hours of water and nothing else.
Researchers then compared the women's hormone levels to those of a control group.
Levels of sex-binding globulin hormone, a protein that carries reproductive hormones throughout the body, did not change. Neither did levels of testosterone and androstenedione, which the body uses to produce both testosterone and estrogen.
Dehydroepiandrosterone, or DHEA, levels did change.
That hormone is sometimes used by fertility clinics to improve ovarian function and egg quality. During the trial, it dropped by about 14% in both premenopausal and postmenopausal women.
Even so, DHEA levels remained within the normal range.
"This suggests that in premenopausal women, the minor drop in DHEA levels has to be weighed against the proven fertility benefits of lower body mass," Varady said in a university news release.
She added that the drop in DHEA levels in postmenopausal women could be concerning, however, because menopause already causes a dramatic drop in estrogen and DHEA is a primary component of it.
"However," she added, "A survey of the participants reported no negative side effects associated with low estrogen postmenopause, such as sexual dysfunction or skin changes."
High DHEA has been linked to breast cancer risk, Varady noted, so a moderate drop in levels might reduce risk.
During the study, dieters lost 3% to 4% of their baseline weight. The comparison group had almost no weight loss.
Researchers did not measure levels of estradiol, estrone or progesterone, all vital to pregnancy, in premenopausal women because those levels vary throughout the monthly menstrual cycle. Postmenopausal women saw no changes in those hormones.
The findings were recently published in the journal Obesity.
The U.S. National Library of Medicine has more on hormones.
SOURCE: University of Illinois Chicago, news release, Oct. 25, 2022