Soya and male reproductive hormones in 41 studies
What it found
In men, eating soya or taking isoflavones made no difference to total testosterone, free testosterone, estradiol or estrone.
The authors looked at 41 studies.
What they found
Studies in people
Total testosterone
Soya or isoflavone intake made no significant difference to total testosterone levels in men. This held true whether the data were analysed by comparing treatment with control groups or by looking at change over time.
Free testosterone
Free testosterone levels in men showed no significant change with soya or isoflavone intake. The result was the same under both statistical models used.
Estradiol and estrone
Levels of estradiol and estrone in men were not significantly affected by soya or isoflavone intake. There was little actual change over time in the active treatment arms.
Dose and duration
When the data were split by isoflavone dose (under 75 mg per day versus 75 mg per day or more) or by study length (12 weeks or less versus more than 12 weeks), still no effect on any hormone was found.
Sex hormone binding globulin
Sex hormone binding globulin levels in men were not significantly changed by soya or isoflavone intake.
DHT not examined
The authors did not analyse dihydrotestosterone (DHT) because blood levels of DHT give only a hint of tissue levels. They note that the evidence on isoflavones and DHT is mixed, with some studies finding changes and others not.
What the authors conclude
“In conclusion, extensive clinical data published over the past two decades shows that in men neither soy nor isoflavone intake, even when exposure occurs for an extended period of time and exceeds typical Japanese intake, affects levels of total testosterone, free testosterone, estradiol or estrone.”
Also in their conclusions
- They conclude that neither soy nor isoflavone intake affects total testosterone, free testosterone, estradiol or estrone levels in men.
- They say this holds even when exposure occurs for an extended period of time and exceeds typical Japanese intake.
- They state that extensive clinical data published over the past two decades supports this conclusion.
How it was done
Some people worry that the plant estrogens in soya might feminize men, and some studies and case reports have described effects like lower testosterone or higher estrogen. The authors wanted to check the clinical data on this.
They searched medical databases for studies published between 2010 and April 2020 where adult men consumed soya foods, soya protein or isoflavone extracts. They included 41 studies. Total testosterone was measured in 1753 men, free testosterone in 752 men, estradiol in 1000 men, estrone in 239 men and sex hormone binding globulin in 967 men.
What it can’t tell you
- This paper combined results from many studies, so it cannot show what happens in an individual man.
- The authors had to make assumptions when full data from individual studies were not available.
- Many trials did not say whether the isoflavone dose was in aglycone equivalent or glycoside weight, so there was uncertainty about the exact doses.
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
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- 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.2020.12.019Free full textPubMed 33383165DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error