WEDNESDAY, Oct. 20, 2004 (HealthDayNews) -- The plant estrogens found in soy don't impair fertility in female monkeys.
That's the conclusion of a study by researchers at Wake Forest University Baptist Medical Center and Emory University School of Medicine.
The study was designed to test a theory that diets with lots of soy might affect women's fertility.
"Our results suggest that a high-soy diet probably won't compromise fertility in women. But our results confirmed earlier findings that fertility may be affected by stress levels," lead researcher Jay Kaplan, of Wake Forest Baptist, said in a prepared statement.
Asian women, who consume a lot of soy, have lower breast cancer rates than American women. One theory is that the isoflavones in soy reduce ovarian hormones or increase menstrual cycle length. Both of these effects would reduce a woman's lifetime exposure to estrogen. But it's believed that such changes in the menstrual cycle may impair fertility.
"Our study was designed to determine whether a soy supplement containing twice the level of plant estrogen consumed by Asian women would alter any aspect of the menstrual cycle or ovarian function in monkeys," Kaplan said.
Female monkeys have a menstrual cycle similar to women.
During the year-long study, half the monkeys ate a high-soy diet and the other half got their protein from animal sources.
"Soy treatment did not change any characteristics of the menstrual cycle, including length, amount of bleeding or hormone levels. This suggests that any protection that soy may provide against breast cancer does not come from changes in the menstrual cycle," Kaplan said.
The study was presented Oct. 19 at the annual meeting of the American Society for Reproductive Medicine in Philadelphia.
The National Infertility Association has more about women and fertility.