Dietary Soy Phytoestrogens Alter Sexual Behaviors in Male Rats

Phytoestrogens are plant-derived estrogen mimics found in high quantity in soy products. Because almost all standard rodent chows are rich in soy, laboratory animals are constantly exposed to these hormonally active substances and have high plasma phytoestrogen levels. In addition, dietary phytoestrogens cause morphological changes in brain structures such as the sexually dimorphic nucleus of the preoptic area (SDN-POA). Sexual behavior, governed by hormonal balance and input from the SDN-POA, is thus susceptible to dietary phytoestrogens. This study fed male Sprague Dawley rats either a commercially available soy-rich (phytoestrogen-rich) diet or a soy-free (phytoestrogen-free) diet from day 21 until behavioral testing (day 90-116) and examined appetitive and consummatory sexual function. Soy rats were more active and exploratory in the appetitive test, but showed fewer copulatory behaviors in the consummatory test. Importantly, rats fed the soy diet mounted less and displayed a longer mount latency. This study is the first to examine the impact of dietary soy consumption on sexual behaviors but confirmed the ability of soy phytoestrogens to complicate laboratory behavioral analyses