Does Soy Decrease Testosterone and Increase Estrogen?

Soy MilkFollowing up on my recent article Drinking Milk Decreases Testosterone and Increases Estrogen, let’s look at one of the popular alternatives to cow milk: soy milk.

Soy is said to have feminizing properties when consumed as soy contains plant estrogens (phytoestrogens) called isoflavones1, so they should decrease testosterone and increase estrogen like mammalian estrogen as shown in my previous article about cow milk, but what does the research say?

According to a large study2 on the medline literature on soy isoflavones done in 2010, soy isoflavone exposure at levels even greatly exceeding reasonable dietary intake does not affect serum testosterone or estrogen levels in men or impair fertility in any way.

While there is one case study3 on a man who developed gynocomastia through excessive isoflavone consumption through soy products, it is speculated that he was sensitive to soy isoflavones which may have caused the increased estrogen. This is however, the exception, not the norm.

Conclusion

The clinical evidence overwhelmingly indicates that anyone with low to moderate soy intake shouldn’t be worried that their testosterone levels will plummet or their estrogen levels rise following soy product consumption.

References

1.
Soy Isoflavones. Linus Pauling Institute. http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/soy-isoflavones. Published April 29, 2014. Accessed June 3, 2017.
2.
Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril. 2010;93(7):2095-2104. [PubMed]
3.
Martinez J, Lewi J. An unusual case of gynecomastia associated with soy product consumption. Endocr Pract. 2008;14(4):415-418. [PubMed]

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