The Effects of Fasting and Caloric Restriction on Reproductive Hormones: A Systematic Review, Meta-Analysis, and...

Fasting and caloric restriction (CR) have shown promising effects in body composition management and metabolic health. Both CR and time-restricted eating (TRE) have been associated with improved insulin sensitivity and lipid profiles. Although dietary and lifestyle interventions for weight management may influence reproductive hormones, the specific impact of these dietary strategies on reproductive hormones is still unclear. This systematic review and meta-analysis assessed the effects of different types of fasting and CR on reproductive hormones in adults. Parallel or crossover randomized controlled trials published up to April 2025 were identified through PubMed, Scopus, and Google Scholar. Eligible studies included adult participants aged ≥ 18 years undergoing fasting (alternate-day, TRE, or full-day fasting) or CR (20%-30% energy reduction). The primary outcomes were changes in reproductive hormones, including testosterone, free testosterone, sex hormone-binding globulin (SHBG), dehydroepiandrosterone sulfate (DHEA-S), follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, estrogen, anti-Müllerian hormone (AMH), prolactin, and progesterone, analyzed using random-effects models. The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the certainty of evidence. Fifteen randomized trials (n = 954 participants) were included. Overall, both fasting and CR showed largely neutral effects on reproductive hormones, with no consistent evidence of either detrimental or beneficial changes. Fasting had a non-significant effect on testosterone (WMD: -0.88 ng/mL; 95% CI: -2.37 to 0.61; p = 0.24), with significant heterogeneity. However, a statistically significant effect on free testosterone was observed (WMD: -4.9 pg/mL; 95% CI: -9.22 to -0.59; p = 0.02), although this finding was based on some of the small trials. Similarly, CR had a non-significant effect on testosterone (WMD: -0.02 ng/mL; 95% CI: -0.13 to 0.08; p = 0.65), with significant heterogeneity. No significant effects were observed for other outcomes. Current evidence indicates that fasting and CR exert minimal to no statistically significant impact on reproductive hormones in adults. However, these findings should not be interpreted as evidence of clinical neutrality because we didn't assess changes in symptoms. Overall, these dietary strategies appear endocrinologically safe for weight management and metabolic health; however, larger, longer-term, and population-specific trials are needed to clarify subgroup-specific responses.