Soya and male reproductive hormones in clinical studies
What it found
In men, eating soya or taking isoflavones made no difference to testosterone, estradiol, estrone or sex hormone binding globulin levels.
The authors looked at 41 clinical studies.
What they found
Studies in people
Testosterone levels
Soya protein or isoflavone intake had no significant effect on total or free testosterone in men. This held regardless of the statistical model used.
Estrogen levels
Soya protein or isoflavone intake had no significant effect on estradiol or estrone levels in men.
Sex hormone binding globulin
Soya protein or isoflavone intake had no significant effect on sex hormone binding globulin levels in men.
Dose and duration
When the data were split by isoflavone dose and by how long the studies lasted, there was still no effect on any of the hormones measured.
What the authors conclude
“This updated and expanded meta-analysis indicates that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects TT, FT, E 2 or E 1 levels in men.”
Also in their conclusions
- They conclude that neither soy protein nor isoflavone exposure affects total testosterone, free testosterone, estradiol or estrone levels in men.
- They say this holds regardless of dose and study duration.
How it was done
Concerns continue to be raised that the isoflavones in soya may feminize men. Some studies and case reports have described effects such as lower testosterone and higher estrogen in men.
They pooled 41 clinical studies in which adult men ate soya foods, soya protein or isoflavone extracts from soya or red clover. Total testosterone was measured in 1753 men, free testosterone in 752, estradiol in 1000, estrone in 239 and sex hormone binding globulin in 967.
What it can’t tell you
- We summarised it from the abstract only.
- The studies measured hormone levels in the blood, not whether men noticed any feminizing effects.
- The analysis cannot show what happens with very long-term soya intake beyond the study durations included.
Who paid
- Authors work at
- University of Essex, United Kingdom; University of Kansas Medical Center, United States; Kansas University Department of Urology and Department of Dietetics & Nutrition, United States
The paper
- Title
- Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies
- Type
- Meta-analysis
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Reed KE, Camargo J, Hamilton-Reeves J, Kurzer M, Messina M (2021). Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reproductive toxicology (Elmsford, N.Y.). doi:10.1016/j.reprotox.2020.12.019PubMed 33383165DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error