About a soy... masculine traits affected by eating soy?

Dear Alice,

Is it true, according to studies, that taking a lot of soy may make a man more feminine?

Dear Reader,

Mmmmmm, soy… Eating soy from food sources at recommended levels, such as soybeans or soy milk, won't have many notable effects on the body. That said, several studies show positive effects from eating soy, including a reduced risk for both cardiovascular disease and different cancers (including those of the breast, prostate, and ovaries). It's unclear what you mean by "feminine," — defining femininity and masculinity can be quite subjective and can be inclusive of varying tangible and intangible traits. However, a few case studies have shown that if eaten in excess — significantly over the recommended daily values — there may be physical effects (such as erectile dysfunction or the growth of breast tissue). It's worth noting, though, that these results were reversed when soy consumption was reduced.

Soy is a rich source of phytoestrogens, also called isoflavones, which mimic the effects of the hormone estrogen. Both people assigned male and female at birth typically have estrogen — those assigned female just have more. So, does eating a lot of soy cause a hormonal imbalance in people assigned male at birth? No! Research has indicated that soy consumption doesn't increase estrogen levels in humans. Besides mimicking the hormone, phytoestrogens actually help moderate the levels of estrogen in the body — that is, when estrogen levels are low, phytoestrogens act like estrogen, but when levels are high, phytoestrogens act as anti-estrogen agents. This helps maintain a balance in the body. There’s been research examining the effect of soy on hormone concentrations (including estrogen and other reproductive or sex hormones) in those assigned male at birth, and found negligible changes in hormone levels. 

In addition, studies that have looked at sperm quality suggest that eating soy doesn't have an effect on any related measures, including ejaculate volume, sperm concentration, total sperm count, and motility. All this to say, there's not evidence to suggest that soy affects the body in that way you've inquired. So, whether there was interest in gaining particular traits or maintaining others, it may be helpful to investigate other possible factors. However, if this was a concern that was resulting in the avoidance of soy, having learned more about this food may be an opportunity to add it back in and reap what nutritional benefits soy has to offer.

Enjoy the soy!

Last updated Oct 26, 2018
Originally published Nov 20, 2009

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