"Soy has been correlated with low rates of breast cancer in Asian populations, but soy foods in Asia are made from minimally processed soybeans or defatted, toasted soy flour, which is quite different from soy products consumed in the U.S.," said William G. Helferich, a professor of food science and human nutrition, in a study presented online May 6 in advance of regular publication by the journal Carcinogenesis.
"Isoflavone-containing products consumed in the U.S. may have lost many of the biologically active components in soy, and these partially purified isoflavone-containing products may not have the same health benefits as whole soy foods," he said.
Soy isoflavone products are marketed as dietary estrogens to women over age 50 as a natural alternative to hormone replacement therapy (HRT), but this is the age group in which most breast cancers occur.
Seventy-five percent of breast cancer cases are diagnosed in women over 50, and the majority of these cases are estrogen-dependent. For these women, Helferich said, consumption of highly processed isoflavone products may pose a risk.
Helferich used an animal model that has been used extensively to evaluate breast cancer therapies such as tamoxifen. "The results of this preclinical investigation are especially relevant to postmenopausal women with estrogen-responsive breast cancers who are looking for alternatives to HRT," he said.
In the study, mice were fed equal concentrations of the soy isoflavone genistein, allowing Helferich to determine the influences that various bioactive soy compounds had on genistein's ability to stimulate estrogen-dependent breast tumor growth. "As bioactive compounds were removed, we observed
Contact: Phyllis Picklesimer
University of Illinois at Urbana-Champaign