Soy and Breast Cancer Prevention
Breast cancer incidence is higher in Western countries than in Asian countries. In addition, migrant populations from Asia to the United States have increased incidence of breast cancer. Known risk factors of breast cancer are reproductive factors, dietary factors, family history of breast cancer, benign breast disease history, and body size, and low physical activity. In addition to its antiestrogenic effects such as suppressing estrogen levels and prolonging menstrual cycles, isoflavone may contribute to breast cancer risk reduction by its effect on cancer cell growth inhibition. Animal experiments examining the effect of soy or its ingredients on breast cancer development are not as numerous as in vitro studies. The highest evidence comes from the randomized controlled trial with sufficient statistical power to show the difference in breast cancer incidence between the soy-rich food group and no soy-rich food group to which subjects are randomized.