Soy's anticancer surprise.

With many studies suggesting that soybeans possess anticancer activity, a team of midwestern scientists recently began probing the gooey wastes left over from the commercial extraction of oil and protein from soy. Their test-tube data now indicate that even this molasseslike muck contains agents with cancer-fighting potential.

Geneticist Michael Plewa of the University of Illinois at Urbana-Champaign and his colleagues incubated animal cells with dilute concentrations of the soy wastes and then exposed them to a known carcinogen. Cells treated with the soy wastes developed fewer of the precancerous changes called adducts than untreated cells did. Adducts occur when the carcinogen binds to DNA.

"We expected this anticancer activity would turn out to be due to soy isoflavones," such as genistein, observes chemist Mark A. Berhow of the Agriculture Department's Bioactive Agents Research Unit in Peoria, Ill. However, he observes, "it turned out to be more interesting than that."

Low doses of genistein, isolated from the waste, inhibited the formation of adducts, but higher doses fostered adducts. In contrast, genistin, a plant form of genistein contains an added sugar molecule, mildly inhibited adduct formation at all doses, Berhow notes.

The real surprise, he says, was the uniformly protective nature of saponins, cholesterol-like plant compounds being explored elsewhere for their potential to fight several diseases (SN: 12/9/95, p. 392). In contrast to genistein, the saponins inhibited adduct formation whether or not they had sugar molecules attached to them. Moreover, Berhow reports, the most active of these, soya sapogenin B, offered more cancer protection than any of the isoflavones.

His team plans to begin identifying foods rich in soy saponins. Based on preliminary data, Berhow says, isolated soy protein looks promising.