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.

The study involved pregnant rats that were fed one of three diets: a genistein-free diet, a diet supplemented with a low dose of genistein, and a diet with a high dose of genistein. The male offspring were, therefore, exposed to genistein indirectly through their mothers’ diets during pregnancy and lactation.

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.

Further studies are needed to determine whether exposure to genistein during gestation, lactation, or both caused the long-term effects seen in the study, researchers noted.

This is an important issue when a parent is considering the use of soy-based infant formula. The evidence is rich. It demonstrates repeatedly that soy products deliver estrogen-like substances to the people who consume them. In the case of infants, the hormone substitute can have serious, long-term effects.

While doctors would not generally agree, there is an opportunity for parents to make infant formula at home that doesn’t provide harmful substances to their child. Marie Bishop, Sally Fallon and Mary G. Enig, PhD have published full information on the internet http://www.soyonlineservice.co.nz/articles/alternativeformula.htm

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12629420&dopt=Abstract