Can soy affect testosterone or fertility in men?
The Question
Do males who consume soy (foods or supplements) have more fertility/reproductive problems than males who do not consume soy?The Recommendation
Soy or isoflavone-rich foods or supplements do not affect testosterone or estrogen levels and do not appear to affect semen parameters or breast tissue in men.
If soy is consumed, a suggested reasonable adult recommendation is 15-25 g/day of soy protein and 50-100 mg/day of isoflavones.
Grade of Evidence: A and C
*Grade A - The conclusion is supported by good evidence.
*Grade C - The conclusion is supported by limited evidence or expert opinion
Remarks
The estrogen-like effects of isoflavones have raised concerns about the impact of soy food consumption in males as highlighted in case reports and animal research.
There was a high variance in the forms and amounts of soy in the included studies of the 2022 review. However, based on studies in all populations, a suggested reasonable adult recommendation provided was 15-25 g/day of soy protein and 50-100 mg/day of isoflavones. Intakes greater than this level do not appear to be associated with adverse effects, but there is little research for consuming more than these amounts.
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