The male offspring of rats fed diets containing genistein, a chemical found in soybeans, developed abnormal reproductive organs and had sexual dysfunction as adults. This finding may indicate a need for further research to determine whether exposure to genistein while in the womb and during breastfeeding influences human reproductive development, according to researchers.

Researchers found that while the sperm counts of genistein-exposed males were normal, they had smaller testes and a larger prostate gland than unexposed rats. They also had lower testosterone levels and were less likely to ejaculate than unexposed rats.

The effects of genistein exposure continued long after the rats were exposed, leading researchers to say that exposure during reproductive development may have negative, long-term consequences in males.

It is thought that genistein may act as an estrogen or an anti-androgen, blocking the function of the sex hormones, known as endogenous androgens, necessary for males to develop a normal reproductive system.
(J urol2003;169(4):1582-6)