Soy Isoflavones, Estrogens and Growth Factor Signaling

By Stephen Barnes, Ph.D. and Helen Kim, Ph.D.

Soybeans are unique among beans because they contain compounds called isoflavones. Because these molecules have structures very similar to the body’s natural estrogens (hence the name plant- or phyto-estrogens), major research efforts are directed at understanding what isoflavones do in our bodies when we eat soy.

Soy Isoflavones

How do soy isoflavones fit in? Genistein, the most abundant isoflavone in soybeans, binds only weakly with ER alpha, but complexes with ER beta almost as well as estrogen does (5). This probaby explains genistein’s ability to support bone health in ovariectomized rats (6). The predominance of ER beta in the cardiovascular system suggests that soy isoflavones may be partly responsible for the lower incidence of heart disease in soy-consuming countries (the FDA has approved an official claim that 25 grams of soy protein per day, as part of a healthy diet low in cholesterol and saturated fat, may reduce risk of heart disease).

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Korzenik JR, Barnes S, White RI, Jr. A pilot study of soy protein isolat in the treatment of hereditary hemorrhagic telangiectasia (HHT): possible efficacy in HHT associated epistaxis, gastrointestinal hemorrhage and migraine. Am J Clin Nutr, accepted for publication.

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Kim H, Peterson TG, Barnes S. Mechanisms of action of the soy isoflavone genistein: emerging role of its effects through transforming growth factor beta signaling pathways. Am J Clin Nutr, accepted for publication.

About the authors

Stephen Barnes, Ph.D. is professor in the Department of Pharmacology & Toxicology, University of Alabama at Birmingham. He is also director of the UAB Comprehensive Cancer Center Mass Spectrometry Care Facility. He obtained his Ph.D. in biochemistry in 1970 from the Imperial College of Science and Technology, University of London.

Helen Kim, Ph.D. is research associate professor in the Dept. of Pharmacology & Toxicology at the University of Alabama at Birmingham. Her Ph.D. in biophysics was obtained from the University of Virginia in 1983.

Reprinted with permission from The Soy Connection newsletter, Volume 6, No. 2, Spring 1998. More information about the newsletter can be obtained by writing to:

Editor, The Soy Connection
P.O. Box 237
Jefferson City, MO 65102