Soy isoflavones are found in soybean products such as tofu, miso, tempeh and soy milk. They contain powerful compounds called phytoestrogens, plant-based substances similar to the hormone estrogen. These phytoestrogens can bind to estrogen receptors in the cells and be beneficial when the hormone's levels are too high or low.
In Asian countries where soy is commonly consumed, rates of certain cancers including breast, prostate and endometrium cancers are significantly lower than in countries where it isn't a dietary staple. This is most likely due to the phytoestrogens blocking the overproduction of natural estrogen. When natural estrogen levels are low such as during menopause, phytoestrogens can kick in and possibly reduce symptoms like hot flashes and the bone loss that can lead to osteoporosis.
Some studies show that the soy isoflavones have anticoagulant benefits, can lower LDL (bad) cholesterol and increase HDL (good) cholesterol levels, and can even protect against coronary heart disease.