If you’ve heard that intermittent fasting might mess with women’s hormones, a new study offers a more nuanced take, at least for women with PCOS.
Researchers found that women who followed a time-restricted eating plan lost weight and lowered testosterone levels, similar to those who simply cut calories. But the fasting group also showed improvement in a marker tied to how much active testosterone is circulating in the body.
The study, published in Nature Medicine, followed 76 premenopausal women with PCOS over 6 months. One group ate within a daily window from 1-7 p.m., while the other reduced calories without time limits.
Both groups ended up eating about 200 fewer calories per day and lost an average of about 10 pounds. Both also saw drops in testosterone levels.
That overlap is important. It suggests that weight loss itself likely explains much of the hormone improvement, regardless of how participants got there.
Still, the fasting group showed one additional change. Researchers saw a drop in free androgen index, a measure of how much testosterone is actively available to the body’s tissues. The group also improved A1C levels, a marker of long-term blood sugar control.
PCOS, or polycystic ovary syndrome, affects up to 18% of women of reproductive age. It is often linked to higher testosterone levels, insulin resistance, irregular periods and weight gain. Because of that, even modest weight loss can make a difference.
“We’re looking for other ways of lowering testosterone levels in these women,” said Krista Varady, a professor of nutrition at the University of Illinois Chicago. “One way is through weight loss. If someone loses around 5% of their body weight, they can actually help lower testosterone levels and sidestep any kind of drug intervention.”
The findings also push back on a common concern about fasting and women’s health.
“There’s a particular sentiment that intermittent fasting is really bad for women,” Varady said. “This study and several other studies published by our lab and others show that intermittent fasting can actually improve female hormone levels, particularly in women with PCOS.”
That does not mean fasting is better than other approaches, or that it will work for everyone. The study was small, and it focused only on women with PCOS. It also did not improve every symptom. Menstrual irregularity, for example, did not change over the 6-month period.
The study was supported by the Department of Kinesiology and Nutrition at the University of Illinois Chicago.