The ignored estrogen in soy.

Over the past decade, the plant estrogens genistein and daidzein have become darlings of health food enthusiasts. Scores of studies have suggested that these compounds, members of a family known as isoflavones, may underlie many of soy's reputed health benefits. These include defense against cancer (SN: 10/11/97, p. 230), reductions in cholesterol (SN: 5/30/98, p. 348), protection against age-related bone loss (SN: 1/2/99, p. 15), and perhaps even mitigation of menopausal hot flashes.

The two isoflavones constitute 90 percent of the estrogen-mimicking, or estrogenic, material in soy. Seldom mentioned is glycitein, which makes up the remaining 10 percent.

Glycitein's presence at just trace levels in the whole soybean has discouraged most researchers from working with it, notes Patricia A. Murphy of Iowa State University in Ames. However, she notes, glycitein makes up fully 40 percent of the plant estrogens in soy germ.

In terms of estrogenicity, glycitein appears to top both daidzein and genistein, the Iowa scientists report in the April JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. A companion paper in the May JOURNAL OF NUTRITION notes that the body takes up glycitein more readily than it does soy's other isoflavones. This alone could explain glycitein's greater estrogenicity, says Murphy. "We just absorb it better."

Noting glycitein's potency and the growing market for soy germ, Murphy believes that researchers should begin investigating any health effects of glycitein. Recent data on genistein have pointed out that whether a plant estrogen is beneficial or detrimental may depend on when it's ingested or other factors (SN: 4/24/99, p. 262).