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Soy Isoflavones

Soy Isoflavones: Overview

Soy isoflavones are a type of nutrient derived from soybeans. Isofolavones occur naturally in many other plants such as red clover. Soy isoflavones are sometimes referred to as phytoestrogens; plant compounds able to affect estrogen receptors on human cells. Phytoestrogens are thought to occupy vacant estrogen receptors, theoretically reducing the effects of estrogen on those cells. In actuality, the interaction between soy isoflavones and estrogen receptors is very complex, so some experts now prefer to use the term SERM (Selective Estrogen Receptor Modulators).1 SERMs may be useful to those wishing to balance estrogen and overall hormone health. SERMs may or may not be advisable depending upon an individual's overall hormonal status, especially with respect to hormone-sensitive conditions like breast or prostate disease. See Using Soy Isoflavones below for more information. Soy isoflavones are found in most forms of soy-based foods such as tofu, soymilk, miso, or soy protein.

Health Benefits of Soy Isoflavones

Studies have shown that soy isoflavones have antioxidant properties.2 But most people using soy isoflavones do so based on research that suggests it may help preserve the health of hormone-sensitive aspects of the male and female reproductive systems and breast health.3 Soy isoflavones' SERM properties may also be of value in reducing symptoms associated with menopause, and reducing the risk of osteoporosis.4,5

Using Soy Isoflavones

SERMs such as soy isoflavones may not be appropriate for those at risk for, or with a history of hormone-sensitive cancer. In these circumstances it is best not use soy isoflavones without a doctor's supervision. A hormone panel (blood test) may enable you and your doctor to asses your current hormone status and whether or not a SERM such as soy is appropriate. Dosage varies. In addition to soy-based foods, soy isoflavones are available in capsule, liquid, powder and tablet supplements.

Side-effects and Cautions:

Those allergic to soy should not consume any soy-based products. Although consumption of soy in pregnant/nursing women is believed safe, more research is necessary to confirm this. Soy isoflavones may interfere with the breast cancer drug tamoxifen, as well as the osteoporosis drug raloxifene. A diet high in fiber may inhibit the absorption of soy isoflavones; soy consumption should be increased in this case. Soy isoflavones may be associated with some cases of hypothyroidism.

1. Journal of the American College of Nutrition, Vol. 20, No. 90005, 354S-362S (2001).
2. J Agric Food Chem. 2007 Nov 28;55(24):9811-6. Epub 2007 Oct 26.
3. Br J Nutr. 2008 May;99 E Suppl 1:ES78-108.
4. J Manag Care Pharm. 2008 Apr;14(3 Suppl):14-9.
5. Menopause. 2008 Feb 14.