Soy impact on reproduction?

Is it possible that soy foods could influence human reproductive development? A new study released this week reports that male rats whose mothers were fed diets containing genistein - a chemical found in soybeans - developed abnormal reproductive organs and experienced sexual dysfunction as adults.

While these findings do not indicate that genistein has a similar effect in humans, researchers say the increasing popularity of soy and soy-based foods, such as tofu and some infant formulas, may warrant further research to determine if genistein exposure in the womb and during breast-feeding influences human reproductive development.

In the study, published in the April issue of the Journal of Urology​, pregnant female rats were randomly assigned to one of three regimens: a genistein-free diet, a diet supplemented with a low dose of genistein, and a diet with a high dose of genistein.

Male offspring were exposed to genistein indirectly through maternal consumption during pregnancy and lactation.

When the genistein-exposed offspring matured, researchers found the males had smaller testes and a larger prostate gland compared to unexposed rats. Although their sperm counts were normal, exposed adult males had lower testosterone levels and were also less likely to ejaculate when presented with the opportunity to mate with a female.

"The effects of genistein continued long after the rats were exposed, leading us to believe that exposure to this plant-derived oestrogen during reproductive development can have long-term detrimental effects in males,"​ said the study's lead author, Amy B. Wisniewski, a researcher at the Johns Hopkins Children's Center in the US.

"Genistein may act as an oestrogen or an anti-androgen, blocking the function of endogenous androgens - the sex hormones necessary for males to develop a normal reproductive system - and ultimately leading to the reproductive abnormalities and sexual dysfunction we saw in the exposed rats,"​ added study co-author Sabra L. Klein, of the School of Public Health. "However, additional research is needed to determine if this is the case."​

Whether the long-term effects of genistein on the reproductive development of male rats are caused by exposure during gestation, lactation, or both also requires further investigation, Wisniewski said.