Phytoestrogens in the Human Diet

One of the major sources of phytoestrogens in the human diet is the soybean. Genistein is the major phytoestrogen in soybeans. It is present in some soybean products such as tofu, although it is not present in soy sauce. Genistein, extracted from soybean plants, can also be obtained as a dietary supplement. Dietary supplements, which are often pills, powders, or tinctures containing plant-derived products, can be purchased over the counter. In the United States, the manufacture and sale of such products, classified as "dietary supplements," is far less closely regulated and standardized than the manufacture and sale of food and drugs.

Genistein has been promoted as a possible preventive treatment or therapy for several diseases and conditions. There are claims that it reduces hot flashes associated with menopause, that it can prevent or delay the onset of osteoporosis in post-menopausal women, and that it can lower blood cholesterol levels. In each instance the potential effectiveness of genistein would be attributable to its acting as an estrogen replacement in older women, in whom the level of estradiol is naturally low. Genistein may also be effective in the treatment of certain breast cancers that require estrogen in order to grow. In this case it is theorized that the genistein, with weak estrogen activity, acts to reduce cancer growth by competing with the more potent estradiol for the estrogen receptor.

Some of the evidence for the role of phytoes-trogens in women's health is circumstantial. It is based, in part, on observations that women who live in countries such as Japan and China, where soy products are widely consumed, have a lower incidence of diseases such as osteoporosis and breast cancer. Clearly, other factors, genetic and environmental, may be contributory. Health claims attributed to phytoestrogens, including genistein, need further evaluation in well-designed clinical trials before such claims can be accepted by the scientific and medical communities or relied upon by those using dietary supplements.

Valerie M. Sponsel

See also: Medicinal plants; Metabolites: primary vs. secondary.

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