Soy in diet may lower sperm concentration, male fertility

April 1, 2008

Higher intakes of soy foods and soy isoflavones were associated with reduced sperm concentrations in a Harvard study.

Washington-Contrary to a study reported at the American Society for Reproductive Medicine annual meeting in 2006, men interested in fathering children might do well to avoid soy food products. Higher intakes of soy foods and soy isoflavones were associated with reduced sperm concentrations, according to investigators at the Harvard School of Public Health and Massachusetts General Hospital in Boston, who presented their findings at the 2007 ASRM annual meeting here.

Found mainly in soybeans and soy-derived products, isoflavones have weak estrogenic activity. High isoflavone intake has been related to decreased fertility in animals; however, studies of their possible effects on human reproduction are limited.

Investigators found the mean isoflavone intake to be 5.3 mg per day. An inverse relationship was observed between soy intake and sperm concentration that remained significant after accounting for age, abstinence time, body mass index, caffeine and alcohol intake, and smoking, Dr. Chavarro reported.

In the multivariate analysis, men in the highest quartile of soy intake (median intake of 0.5 servings per day, or more than two servings per week) had 41 million sperm/mL less than men who never consumed soy foods (p=.03).