Genistein Intake Does Not Alter Male Testicular Development

BIRMINGHAM, Ala.--Male exposure to dietary genistein does not negatively affect testicular development, according to animal research out of the University of Alabama that was published in the July issue of the Journal of Nutrition (133, 7:2287-93, 2003) (www.nutrition.org). Researchers compared the effects of a phytoestrogen, genistein, and a synthetic estrogen, diethylstilbestrol (DES), on rat testicular development.

For five weeks, rats were given dietary genistein in doses of either 250 mg/kg or 1,000 mg/kg, or 75 mcg/kg of DES. The dietary DES intake caused impaired testicular development, as well as reduced testicular weights, altered morphology and increased apoptosis in the seminiferous tubules (essential for testicular function). Conversely, dietary genistein intake--which caused rats to exhibit serum concentrations that approximate or exceed concentrations in Asian men on a soy-containing diet--did not significantly alter testicular weights or morphology. However, researchers did note that the high-dose genistein diet significantly reduced testicular aromatase activity, which may contribute to reduced estrogen concentrations and suppression of prostate cancer development.

This research opposes previous research out of the Johns Hopkins Bloomberg School of Public Health in Baltimore, which indicated when pregnant and lactating rats were fed a genistein-enhanced diet, male offspring developed smaller testes, had lower testosterone concentrations in adulthood and demonstrated long-term dysfunction in reproductive behavior (J Urol, 169, 4:1582-6, 2003). The Baltimore researchers concluded genistein exposure resulted in transient and lasting alterations in masculinization of the rats' reproductive systems.

Contrary to those findings, the Birmingham researchers concluded from their study that "exposure to genistein in the diet at concentrations that result in serum concentrations at the upper limit of humans consuming soy products does not adversely affect testicular development, but may provide health benefits."