Intermittent fasting is frequently touted for its weight loss benefits, but some experts say it could negatively affect overall health, including sex hormones and fertility. However, new research suggests otherwise.
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Intermittent fasting has steadily grown in popularity over the last decade. Supporters of the trend claim that it provides several benefits, such as helping to improve metabolism, maintain healthy body weight, lower blood pressure and reduce chronic disease risk. While adding periods of fasting or calorie restriction throughout the day might lead to some health improvements, some critics have cautioned that intermittent fasting can do more harm than good. For example, some research indicates fasting may disrupt reproductive hormone production, leading to potential fertility issues.

However, a new study published in Obesity in October 2022 found that concerns over intermittent fasting's adverse effects on fertility may not be a universal phenomenon. Read on to learn more.

What the Study Found

In this secondary analysis, researchers at the University of Chicago gathered a small group of females with obesity who had just finished an eight-week time-restricted eating (TRE) program. Of the 23 participants, 12 were premenopausal, 11 were postmenopausal and all had body mass index (BMI) scores ranging between 30 and 49.9. The TRE programs the participants followed included eating windows of four to six hours with 18 to 20 hours of fasting daily. Participants who consumed calories in a four-hour window were permitted to eat anything they wanted between 3 PM and 7 PM with only water and calorie-free beverages during the fasting period. Similarly, those eating in a six-hour window consumed their daily calories between 1 PM and 7 PM while being allowed to eat whatever they liked while drinking only water and calorie-free drinks during the 18-hour fasting window.

Twelve-hour fasting blood samples were taken from participants at the start of the TRE programs and after eight weeks. The researchers then measured the differences in hormone levels between the two groups. Among the postmenopausal participants, researchers measured blood concentrations of the sex hormones androstenedione, dehydroepiandrosterone (DHEA), estradiol, estrone, progesterone, testosterone and SHBG. Some of these hormones—estradiol, estrone, and progesterone—weren't measured in premenopausal participants since concentrations tend to fluctuate during the menstrual cycle. Matthew Macer, M.D., medical director of Halo Fertility, tells EatingWell, "Post-menopausal is defined as not having any menstrual cycle for 12 months and is synonymous with no longer growing eggs in the ovaries. So no matter the change in sex hormones, TRE will not affect fertility outcomes."

Both groups ended up losing weight during the study. The premenopausal group lost an average of 3% of their body weight, while the postmenopausal group lost 4%. Additionally, researchers saw reductions in insulin resistance, which might suggest that time-restricted eating can help with prediabetes and diabetes.

What It Means

The argument that intermittent fasting interferes with reproductive hormones would lead one to believe that blood concentrations of these sex hormones would have decreased after eight weeks. But interestingly, the only hormone that dropped was DHEA. All other hormone concentrations weren't affected by the TRE programs. DHEA, a steroid hormone essential for ovarian function and egg quality, decreased significantly in both groups after the trial period with a 14% reduction. However, DHEA levels returned to the normal range by the end of the eight weeks for both pre and postmenopausal participants.

Since the study was conducted on females with obesity over a short period, further research is larger scale and more diverse is needed to substantiate the findings. "The study was small and not a randomized control study, with a short follow-up time of only eight weeks," says Deena Adimoolam, M.D., an endocrinologist and specialist in obesity medicine with Summit Health. "Also, important hormones weren't studied in the premenopausal group that significantly impact fertility. Specifically, estradiol and progesterone."

The Bottom Line

A new study out of the University of Chicago found that females with obesity who followed four- and six-hour time-restricted eating programs didn't experience fertility issues or significant disruption to sex hormone production. The only reduction was in DHEA, a critical hormone for fertility, but concentrations returned to normal after the eight-week program concluded. While this study suggests that intermittent fasting may not affect your sex hormones, more research is warranted to determine its impact on a broader population and over extended periods.

Additionally, some research shows that restricting eating patterns like intermittent fasting could promote disordered eating, increased irritability and fatigue and difficulty concentrating. Also, talk to your health care provider to determine the best healthy and balanced eating pattern for you.