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"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.," Helferich said.
"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 continued.
Soy isoflavone products are marketed as
dietary estrogens to women over age 50 as a natural alternative to
hormone replacement therapy, 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 risk.
Helferich used a preclinical 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.
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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 an
increase in estrogen-dependent tumor growth," he said.
If genistein had been the only
biologically active compound, all diets would have resulted in
similar tumor growth, but that was not the case, he said.
A soy flour and mixed isoflavones diet
and a mixed isoflavone diet each contained equal amounts of
genistein but differed in the amount of other bioactive components
originally present in the soy flour. Tumors neither grew nor
regressed in animals fed these diets. "The minimally processed soy
flour used in these diets is more like the soy foods in the Asian
diet," Helferich said.
"Dietary soy products that contained
isoflavones in more purified forms were associated with greater
tumor growth. These products are similar to the materials used in
isoflavone-containing dietary supplements, which is how many
Americans consume these compounds," he added.
Other researchers contributing to the
study were Clinton D. Allred, Kimberly F. Allred, Young H. Ju, Tracy
S. Goeppinger and Daniel R. Doerge.
The study
was funded by grants from the National Institutes of Health and
USDA.
[University of Illinois news release]
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