Isoflavones are a class of compounds that occur naturally in plants, specifically beans, the majority of which act as phytoestrogens. Genistein and daidzein, found prominently in soy, are the most investigated isoflavones. See: Phytoestrogens.

Health considerations

In the absence of sufficient estrogen, isoflavones can cause weak estrogenic acivity by attaching to estrogen receptors in the body. In the presence of excess estrogen, isoflavones can still attach to estrogen receptors, but their weak activity lowers overall estrogenic activity, reducing the excess estrogen-associated risks such as breast cancer. Isoflavones are associated with reduced cardiovascular risk, improvement of symptoms of menopause, reduced breast and prostate cancer risk, and prevention of osteoporosis. In animal studies isoflavones have stimulated breast cancer cells, though isoflavone intake from moderate consumption has not been firmly associated with increased breast cancer risks. Isoflavones may impair thyroid function by reducing iodine uptake. See: Phytoestrogens, Soy.

Keep in mind

Isoflavones in raw and minimally processed soy are in a different form than those in fermented soy products such as miso and tempeh. Fermented soy isoflavones are thought to be the most effective. Studies of soy isoflavones are most commonly modeled on Asian cultures’ consumption rather than North American intake of processed soy products and derivatives.

May be found in

Soy, soy products, soy milk, miso, tempeh, soy sauce, tofu, edamame, soy beans, soy flour, soy protein powder, red clover


NYU Langone Medical Center
Mayo Clinic Proceedings
Current Opinion in Clinical Nutrition and Metabolic Care
Nutrition Reviews

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