Are soy products healthy additions to a person's diet, safe alternatives to hormone-replacement therapy or cancer-causing agents" The answer, according to University of Illinois food science and human nutrition professor William Helferich, is, "It depends."
He reviews the science linking breast cancer, soy and dietary supplements that contain soy phytoestrogens this month at a conference on "Diet and Optimum Health" sponsored by the Linus Pauling Institute at Oregon State University.
Helferich has spent a decade evaluating the health effects of isoflavones, a class of plant estrogens present in high concentrations in soy. Much of his work has focused on a single isoflavone, genistein, which occurs in varying concentrations in soy products or ingredients such as tofu, soy protein isolates, soy flour and some estrogenic dietary supplements.
Genistein is of interest because it is the most active of the soy isoflavones, and because it activates estrogen receptors in cells, including some breast tumor cells.
Dozens of studies of the role of human and plant estrogens in breast cancer have yielded seemingly contradictory findings. Some found that feeding genistein to female rats prior to puberty reduced the number of chemically induced mammary tumors. Other studies showed that estradiol, a primary human estrogen, spurs the growth of existing estrogen-dependent breast tumors.
Helferich and colleagues demonstrated that like estradiol dietary genistein stimulates the growth of estrogen-responsive tumors. They also found that dietary genistein interferes with treatments, such as tamoxifen, that target estrogen receptors in breast tumors. (About 70 percent of women with breast cancer have estrogen-responsive tumors.)
"The resolution of this paradox may lie in the timing of estrogen administration," Helferich said. Exposure to genistein, an estrogen, before puberty causes mammary gland differentiation. "A different
Contact: Diana Yates
University of Illinois at Urbana-Champaign