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What is it? Overview Usage Side Effects and Warnings

What are Isoflavones?

Isoflavones are water-soluble chemicals found in many plants. In this article, we will discuss a group of isoflavones that are phytoestrogens, meaning that they cause effects in the body somewhat similar to those of estrogen. The most investigated phytoestrogen isoflavones, genistein and daidzein, are found both in soy products and the herb red clover . Soy additionally contains glycitein, an isoflavone that is more estrogenic than genistein and daidzein, but is usually present in relatively low amounts. Red clover also contains two other isoflavones: biochanin (which can be turned into genistein) and formonenetin (which can be turned into daidzein).

Certain cells in the body have estrogen receptors, special sites that allow estrogen to attach. When estrogen...

Soy products are known to improve cholesterol profile, but isoflavones may not be the active cholesterol-lowering ingredient in soy. 1 Isoflavones may, however, improve other measures linked to cardiovascular risk, such as levels of blood sugar, insulin, and fibrinogen. 2 According to some but not all studies, soy protein or concentrated isoflavones from soy or red clover may slightly reduce menopausal symptoms , such as hot flashes and vaginal dryness. 3 However, isoflavones have failed to prove effective for the hot flashes that often occur in breast cancer survivors. 4 There is conflicting evidence regarding whether soy or isoflavones may be helpful for preventing osteoporosis , but on balance the evidence suggests a modest beneficial effect. 5 One study...

Safety Issues

Studies in animals have found soy isoflavones essentially nontoxic. 6 The long history of the use of soy as food in Asia would tend to suggest they are safe as well. Even though absolute safety cannot be assumed from historical consumption of soy as food, it is reassuring to note that researchers found no evidence of ill effects when they gave healthy postmenopausal women 900 mg of soy isoflavones a day for 84 consecutive days. 7 In Japan, the maximum safe intake level of soy isoflavones has been set at a total of 70 to 75 mg daily (food plus supplement sources).

Still, concerns have been raised about estrogenic and other potential side effects of excessive soy isoflavone intake. Overall, the estrogenic effect of soy isoflavones in women appear to be fairly...