A comprehensive meta-analysis of prior scientific literature was performed to determine whether soy protein and soy isoflavones affect male reproductive hormone levels. Led by Jill M. Hamilton-Reeves of St. Catherine's University in St. Paul, MN, the researchers examined a variety of clinical studies conducted prior to July 1, 2008, which looked at the effect of soy, which contain phytoestrogens, on male reproductive hormones. In total, the investigators analyzed 15 placebo-controlled treatment groups with baseline and ending measures. In addition, they assessed 32 reports involving 36 treatment groups in simpler statistical models. Their research, which has recently published online in Fertility and Sterility, showed no significant effect of soy protein or soy isoflavone intake on circulating levels of testosterone, sex hormone-binding globulin or free testosterone in men.

"As a high-quality source of protein that is relatively low in saturated fat, soy can be an important part of a heart-healthy diet and may contribute to a decreased risk of coronary heart disease," says reproductive endocrinologist William R. Phipps of the University of Rochester Medical Center, a co-author of the analysis. "Some men have avoided soy-based foods because of worries about estrogen-like effects of soy isoflavones. But it is important for the public to understand that there is no clinical evidence to support these ideas. After conducting a comprehensive review of the existing literature, we found no indication that soy significantly alters male sex hormone levels."

Citing the research study, Lisa Kelly, MPH, RD, of the United Soybean Board, says, "Soy is often praised for the positive role it can play in the diets of women. But, years of clinical research have shown that men stand to benefit from soy, too. I encourage men to incorporate soyfoods into a balanced and varied diet and talk to their healthcare provider about their own unique nutritional needs."

News Release: Soy safe for men: study www.gourmetretailer.com July 26, 2009