Isoflavones are like human estrogen in chemical shape and properties, but are much weaker than the human form.
Soybeans are concentrated sources of isoflavones.
Studies in laboratories have shown that genistein has a strong inhibitory ability in a number of breast and prostate cancer cell lines. The exact system that genistein works by is not fully understood. There is the belief that genistein blocks a key cellular pathway in cancer cells. Much of the interest in soy stems from the fact that Asian men who have diets high in soy have a lower rate of death for prostate cancer than American men do. Asian men tend to have higher levels of phytoestrogens in their bodies.