A recent meta-analysis that will be published in the journal Fertility and Sterility showed that neither soy foods nor isoflavone supplements from soy affect testosterone levels in men. Researchers looked at more than 50 treatment groups from articles in peer-reviewed journals for this meta-analysis. Soy foods contain phytoestrogens, including isoflavones, which have weak estrogen-like qualities.

Other research has shown that soy consumption decreases the risk of some forms of cancer and heart disease.

Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS, Messina MJ. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. June 11, 2009. DOI:10.1016/j.fertnstert.2009.04.038.

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