According to a new study published by the American Society for Reproductive Medicine (ASRM), soyfoods and soy isoflavone supplements have no significant impact on male reproductive hormone levels in men. The literature review indicates that soy doesn't lower testosterone levels.

Headed by Jill M. Hamilton-Reeves of St. Catherine's University in St. Paul, Minn., researchers assessed the effects of soy protein and soy isoflavones on measurements of male reproductive hormones. The research, which has just been published online in Fertility and Sterility, a publication of the Birmingham, Ala.-based ASRM, shows no significant effect of soy protein or soy isoflavone intake on circulating levels of testosterone, sex hormone-binding globulin or free testosterone in men.

The comprehensive meta-analysis examined the existing scientific literature, including all clinical studies examining soy's effect on male reproductive hormones published before July 1, 2008. Fifteen placebo-controlled treatment groups with baseline and ending measures were analyzed, and 32 reports involving 36 treatment groups were additionally assessed in simpler statistical models.

"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," said reproductive endocrinologist William R. Phipps of the University of Rochester Medical Center, a co-author of the analysis. He added that some men have avoided soyfoods because of worries about estrogen-like effects of soy isoflavones, but noted that "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."

"Soy is often praised for the positive role it can play in the diets of women," observed Lisa Kelly of the United Soybean Board, a St. Louis-based organization comprising 68 farmer-directors who oversee the investments off the soybean checkoff on behalf of all U.S. soybean farmers. "But years of clinical research have shown that men stand to benefit from soy, too."

- Nielsen Business Media