Isoflavones are phytochemicals, or plant chemicals, that are found in some legumes, grains and vegetables, and are particularly concentrated in soybeans and some soy food products. Because of their estrogen-like hormonal activity in the body, isoflavones are more specifically known as phytoestrogens, or plant estrogens. Soy isoflavones have been credited with various health benefits, but the results of clinical studies have been mixed.
Effect
Phytoestrogens such as soy isoflavones have a mild, hormone-like effect in your body. Soy isoflavones act like the hormone estrogen in your body, and attach themselves to estrogen receptors in your brain, bone, liver, heart and reproductive organs. By attaching themselves to these receptors --- which are proteins on cells that receive the hormone and allow it to become active --- isoflavones sometimes function like a mild version of estrogen. At other times, however, they can prevent your actual estrogen from becoming active.
Sources
Soy isoflavones are found in soybeans and food beverages made from soybeans. Some of the highest concentrations of isoflavones are found in dry roasted soybeans, miso, tempeh, soy milk, tofu and soy yogurt. The isoflavone content of soy foods varies among brands, but edamame, or green soybeans, and soy-based meat and cheese substitutes generally contain fewer isoflavones than other products. Soy isoflavones are also available as dietary supplements.
Evidence
A 2005 evidence report published by the U.S. Department of Health and Human Services reviewed the body of studies performed on soy isoflavones and their effects on bone and reproductive health, kidney and heart diseases, menopause symptoms, cancer, diabetes and cognitive function. With the possible exception of a minimal effect of lowering LDL cholesterol and reducing menopausal hot flashes, the reviewers found no evidence that soy isoflavones have any effect on health. Because many of the studies reviewed were small, short-term or of poor quality, the reviewers point out that more carefully structured and controlled studies are necessary to determine not only whether or not soy isoflavones are effective at treating this variety of medical conditions, but which forms of soy are most effective.
Risk
Although soy isoflavones are available as dietary supplements, the long-term safety of these products has not been studied. According to Iowa State University's Soybean Extension and Research Program, the amount of isoflavones in these supplements is unregulated and varies from pill to pill. Because no safe or effective dose has been established, and because it is not fully clear whether isoflavones or other components of soy are more beneficial to your health, the best way to get isoflavones in your diet is in the form of food.
References
- Oregon State University: Linus Pauling Institute; Soy Isoflavones; Jane Higdon, Ph.D; January 2006
- U.S. Department of Health & Human Services: Agency for Healthcare Research and Quality: Effects of Soy on Health Outcomes; E. Balk, et al.; August 2005
- Iowa State University Soybean Extension and Research Program: Soy Isoflavones; 2007
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