Intermittent fasting lowers testosterone through weight loss in PCOS, study finds

A study has found intermittent fasting to have potential benefits for polycystic ovary syndrome (PCOS), as weight loss decreased testosterone levels. 

PCOS occurs when the female body produces too much androgens — a group of hormones, mainly testosterone. It affects 18% of women of reproductive age and may cause obesity, menstrual irregularity, and infertility.

The research team studied intermittent fasting, also known as time-restricted eating, where the participants ate only during a six or eight-hour window and fasted with only water and calorie-free beverages during the remaining hours.

Nutrition Insight sits down with the lead author of the study, Krista Varady, Ph.D., professor of Nutrition at the University of Illinois Chicago, US, to discuss stigmas around intermittent fasting, how weight loss could lower testosterone levels, and what benefits the research found for PCOS.

Fasting vs. weight loss

Varady says that testosterone levels drop in those suffering from PCOS if they lose at least 5% of their body weight. However, critics have previously expressed concerns about intermittent fasting for women, as it may disrupt female hormones.

She argues that this sentiment is not true and that intermittent fasting can actually improve female hormones, especially for women with PCOS.

“This sentiment seems to have come from early animal studies that observed disrupted hormonal function, but more recent studies in humans don’t support this,” Varady tells us.

“Depending on the study population, human trials find that intermittent fasting has either little to no effect on sex hormones, such as in pre- and postmenopausal women with obesity, or that it leads to improvements, such as in individuals with PCOS. Ultimately, our guidance to women should be based on the results of human trials, not animal trials.”

Varady says that testosterone levels drop in those suffering from PCOS if they lose at least 5% of their body weight.She says there are very few studies that have studied the impact of intermittent fasting on women’s hormones, and therefore, no firm conclusions can be drawn. 

“Our lab’s analysis of sex hormones in pre- and postmenopausal women with obesity showed a slight decrease in dehydroepiandrosterone or DHEA — a precursor to testosterone — in postmenopausal women after eight weeks, but in our longer-term 12-month study, we did not see any changes.”

Varady further notes a 2021 trial where participants only ate during an eight-hour window each day for three months and found no changes in thyroid hormones or estradiol — a form of estrogen.

“If women are fasting for multiple days in a row, there’s some evidence this could alter hormone levels, like cortisol, in a negative way, but daily intermittent fasting does not seem to have these same effects,” she notes.

Contradicting findings

Time-restricted eating could cut one’s daily calorie consumption by 300 to 500. Varady says the method makes people eat less, similarly to counting calories. The benefits observed come from weight loss resulting from reducing calories, rather than the fasting itself. 

“To the best of our knowledge, it is the reduced calories. By shortening the eating window each day, people tend to simply eat less. When we look at studies comparing time-restricted eating to daily calorie restriction, we see very similar results in calorie intake and weight loss, which suggests that it comes down to reduced calories in both diets,” says Varady.

“It’s a way of reducing energy intake without having to do really complicated calorie counting.”

The randomized controlled trial has been published in Nature Medicine, involving 76 premenopausal women with PCOS. They either ate only between 1 PM and 7 PM or counted calories for six months. Both groups lost on average 10 lbs and reduced their average daily calorie intake by 200. 

Both groups showed lower testosterone concentrations. However, only the intermittent fasting group reduced the free androgen index — a ratio between testosterone and the protein that transports testosterone in the blood. This is the marker of how much testosterone reaches body tissue. The fasting group also showed a decreased risk of developing diabetes.

Prior studies similarly demonstrated that intermittent fasting does not lead to measurable metabolic or cardiovascular improvements, but the weight loss is solely attributable to reducing calorie intake.

Experts recently debated a study suggesting that intermittent fasting is unlikely to lead to weight loss in obese and overweight adults. It compared intermittent fasting to traditional diets, alongside making no dietary changes. Intermittent fasting did not appear to have a clinical effect on weight loss in either comparison. 

Multiple experts disagreed on these findings, some praised the study for its conductability and accuracy, while others claimed it to be vague and misleading.

In the long term

In Varady’s study, intermittent fasting did not decrease PCOS symptoms, such as menstrual irregularity, but she says it might improve over time, and if more weight is lost. 

She adds that there is a lack of long-term data on the sustainability of intermittent fasting, as the longest trials last only around a year. She notes that the existing data suggest that it could be a sustainable long-term diet.

Intermittent fasting did not decrease PCOS symptoms, such as menstrual irregularity.“In a study that our lab did in adults with obesity, those following intermittent fasting were able to maintain the diet on six out of seven days per week over the course of a full year.” 

“In another study that looked at intermittent fasting rates after the conclusion of a trial, close to half of the participants were still following the diet six months after the trial had ended. And in our PCOS trial, the majority of our intermittent fasting participants rated the diet as easy to follow, whereas our calorie restriction participants were more likely to rate their diet as difficult to follow,” she says.

Varady argues that these combined findings suggest the possibility of good long-term adherence. 

“Regardless of what kind of diet someone is following, whether it be intermittent fasting, calorie restriction, or something else, if someone goes back to their original diet, they will typically return to their original weight. Similarly, any other benefits they may have seen while following the diet, such as improved blood sugar, will reverse.”

Out of the study participants, 80% in the intermittent fasting group reported that they will continue their time-restricted eating. 

Caution of cortisol

Another factor to consider is cortisol. Fasting can increase cortisol, which is likely the body’s normal reaction to delaying food, and cortisol can also increase someone’s hunger drive. 

Multiple days of fasting can cause big increases in cortisol in females, so a prolonged multi-day fast would not be recommended, stresses Varady.

“But daily intermittent fasting does not seem to have these same drastic effects. To our knowledge, only one trial looked at intermittent fasting and cortisol in both men and women, finding that while morning cortisol increased, nighttime cortisol decreased, and in both cases, cortisol was still within normal range.”

Varady says the concern around fasting and cortisol in females may come from a breakfast-skipping study done over 10 years ago, which showed women who skipped breakfast had higher morning and afternoon cortisol than those who did not. 

“However, this study was observational, which means we can’t draw cause-and-effect from it, and the cortisol levels were still within normal range for those who skipped breakfast. In short, while cortisol can increase from intermittent fasting, it likely has little or no meaningful effect,” she concludes.

In other women’s health news, Nutrition Insight recently sat down with the creator of the Cycle Syncing Method, who told us that dietary patterns, including fasting, must be adapted to a woman’s natural cycle, as it may be beneficial during some weeks of the month, while in other phases it may disrupt overall health.