These isoflavones may have some beneficial effects on breast cancer, which is the second most common cause of death among American women and is the leading cause of death in women between the ages of 35 and 44. Breast cancer is a complex disease and scientists don't yet understand exactly what causes it, but they do know that lifestyle affects risk. For example, both alcohol and smoking raise the risk for breast cancer. Certain dietary changes may lower that risk. Breast cancer rates vary dramatically among different groups of women.
American women are four times more likely to die of breast cancer than Japanese women.
Although there are a number of possible reasons for this difference, one reason may be that Japanese women consume soyfoods. Some research shows that women who eat soy have less breast cancer than those who don't. When estrogen attaches to sites on the breast tissue, it can induce the cancer process. Isoflavones look like estrogen so they can attach to the same sites on breast tissue. By occupying these sites, they may keep the more powerful estrogen from exerting its cancer-causing effects.