photo of Craige Wrenn
Craige Wrenn

Study shows soy-based diet for moms changes reproductive anatomy, spatial learning skills of male offspring

A soy-based diet in pregnant and nursing rats has been shown to cause changes in the reproductive anatomy and spatial learning skills of their male offspring, according to Drake research presented last month at the national conference of the Society for Neuroscience.

Craige Wrenn, Drake assistant professor of pharmacology, and former Drake faculty member Amy Wisniewski conducted the study. They found that male rats, whose mothers were fed genistein, a phytoestrogen found in soy, took longer to find a submerged platform in an opaque liquid maze than male rats that were fed a regular diet.

“The genistein-exposed rats took a day or two longer to consistently find the platform,” said Wrenn, co-author of the study. In addition, the study found that male rats whose mothers were fed a soy diet had a significantly shorter anogenital distance, increasing their anatomical similarity to female rats.

The research was conducted at Drake by Wrenn and Wisniewski, now associate professor of pediatrics at the University of Oklahoma, and Drake seniors Evan R. Ball and Karla Overton and Jenna Wilcox, AS’07.


PHOTO OF amy Wisniewski
Amy Wisniewski

In two previous studies, Wisniewski also found that male offspring of female rats on a diet containing genistein had smaller testes and exhibited demasculinized sexual behavior.

“The findings from those studies essentially were that, beyond having smaller testes, if you put one of these male rats in a cage with a female rat they were less enthusiastic and mated less often,” Wrenn said.

Based upon the latest findings, the National Institute of Health’s Center for Complementary and Alternative Medicine has awarded Wrenn and Wisniewski a $191,672 grant to further examine the link between soy diets, pregnancy, and the impact on the behavior and physiology of offspring.

In Wisniewski’s previous studies, the female rats ate food containing genistein throughout gestation and nursing. The new study will feed one group of rats only during pregnancy, a second group only during nursing and a third group during both pregnancy and nursing. A fourth group will be fed no genistein at all.

Based on their findings so far, Wrenn said he’d be reluctant to recommend a heavily soy diet for pregnant vegetarian mothers.

“If my wife were pregnant, I would not want her exclusively eating soy as her source of protein,” Wrenn said. “Natural products are not healthy just because they’re natural. What differentiates a toxin from a medication is dose. Eating large amounts of soy because you’re avoiding the deleterious health properties of meat may be bad as well because it contains estrogen-like compounds that could have biological effects.”

In the studies they conducted, Wrenn said the soy dosage was 5 mg of genistein per kilogram of food, a concentration that results in genistein consumption comparable to that of a typical Japanese diet.

“It’s a physiologically relevant dose,” he said.