Isoflavones are a subclass of flavonoids, which have mild estrogen-like properties and other biological attributes that are purported to reduce the risk of some chronic diseases, including cancer and osteoporosis. Found mainly in soybeans and soy-based products, isoflavones, particularly the compounds genistein, daidzein, and glycitein, are present in much smaller amounts in a wide variety of processed food items.
Isoflavones
Soy isoflavones have weak estrogen effects. Estrogen receptors are present in reproductive organs -- for example, the breast, prostate and uterus -- in addition to the bone, liver, heart and brain. In some organs, isoflavones mimic estrogen, while at other sites these compounds have opposing, or anti-estrogenic, effects. For example, while estrogen promotes the development of certain breast cancers, it strengthens bone and influences memory and learning. The precise effects of isoflavones on these and other organs, and its effect on cholesterol, is currently a focus of intense research.
Major Sources
Soybeans have the highest amounts of isoflavones. Through processing, as occurs when soybeans are made into tofu or soymilk, or converted to soy burgers and dogs, the isoflavone content diminishes markedly. For example, a serving of soy protein concentrate has 100mg of isoflavones. Washing it with alcohol, as can occur in the preparation process, reduces that amount by 90 percent. Boiled soybeans contain 50mg of isoflavones. A cup of soy milk has 30mg; a serving of tofu has 20mg. One ounce of soy cheese has only 2mg of isoflavone.
Other Sources
Soy-based infant formulas are also a significant source of isoflavones, containing levels comparable to that found in tofu. There are also a number of soy supplements on the market, including protein powders. Generally, any food that lists as an ingredient soy protein concentrate or isolate contains these isoflavones to some degree, though generally less than the values found in the whole and soy-based foods listed above.
Evidence
Studies suggest that substituting 50g/day of soy protein for animal protein can help lower cholesterol; however, these benefits are not seen with supplementation. In addition, isoflavone consumption at levels less than 90 mg/day may strengthen bones and inhibit osteoporosis. The affects of soy products and other foods containing isoflavones on cancers of the breast and prostate is still unclear based upon the results of clinical research to date. Although diets containing soy appear beneficial, the affects of supplementation are not clearly understood and further research is needed.
Member Comments