Soy isoflavones
A plant-based substance chemically similar to estrogen that is found in soybean products. Although isoflavones are weaker than estrogen, they can block human estrogen receptors in the cells, helping to prevent the development of such hormone-related diseases as breast cancer, osteoporosis and heart disease. They also seem to ease hormone-related symptoms such as menopause's hot flashes. The major isoflavones in soybeans include genistein and daidzein.