Interest in soy’s hormonal effects has grown in recent years. A new review from researchers at the University of Minnesota, published in The Journal of Nutrition, looked at whether soy or its natural isoflavones influence reproductive hormones in premenopausal women and men. The goal: to clarify which concerns are backed by evidence - and which aren’t.

Study Overview

Researchers reviewed results from many human studies that tested soy foods or isoflavone supplements. They focused on hormonal markers such as menstrual cycle patterns, estrogen levels, and semen quality. By comparing findings across these studies, they evaluated whether soy meaningfully affects hormones in either women or men.

Key Findings

• In women, soy caused small hormonal shifts - like slightly longer menstrual cycles or small drops in certain estrogens - but the changes were minor.
• These effects pointed in a potentially beneficial direction but were too small to draw strong conclusions.
• In men, soy intake did not meaningfully change testosterone, estrogen, or semen quality.
• Across all studies, soy showed mild effects in women and minimal effects in men, with no evidence of harm at typical intake levels.

Why It Matters

This review helps settle common questions about soy and hormones. For women, soy may have gentle hormone-modulating effects, though they’re modest. For men, the evidence is reassuring - soy doesn’t lower testosterone or impact fertility. Overall, the research shows soy is safe for both sexes, and any hormonal effects are mild.

Takeaways

The research concludes that including soy as part of a balanced diet appears safe, and fears of major hormonal disruption aren’t supported by evidence: 

• Soy foods and moderate isoflavone supplements are unlikely to disrupt hormones in most people. 
• Women may experience very small hormonal shifts, but these changes are not clearly linked to major health outcomes.
• Men can consume soy without worrying about testosterone levels or semen quality.

Read the Research: The Journal of Nutrition. Hormonal Effects of Soy in Premenopausal Women and Men. March 2002. https://pubmed.ncbi.nlm.nih.gov/11880595/