To date, studies into the role of human and plant estrogens in breast cancer have yielded seemingly contradictory findings. While there is little consensus on the existence of a link between soy products and breast cancer, one nutritional expert believes that the answer depends on how the soy is consumed. Professor William Helferich, from the University of Illinois, has spent a decade evaluating the health effects of isoflavones, a class of plant estrogens present in high concentrations in soy. His work has focused on a single isoflavone, genistein, which occurs in varying concentrations in soy products.
Genistein is the most active of the soy isoflavones and it can activate estrogen receptors in cells, including some breast tumor cells. Helferich demonstrated that - like estradiol - dietary genistein stimulates the growth of estrogen-responsive tumors. He also found that dietary genistein interferes with cancer treatments, such as tamoxifen.
Because exposure to genistein before puberty causes mammary gland differentiation, Helferich thinks the effects may be related to the timing of estrogen administration. "A differentiated cell undergoes less proliferation and therefore is less likely to progress through the cancer process," he explained. "However, if the estrogen is administered to an animal after the development of an estrogen-responsive tumor, the growth of this tumor will be stimulated."
Helferich is most concerned about the use of genistein and other isoflavones in supplements sold as "natural" alternatives to hormone-replacement therapy. He notes that midlife women who consume these products perceive them as natural and safe. But women aged 50 and older are also most at risk of developing breast cancer.
Helferich notes that the incidence rate of breast cancer in women aged 50 and over in the U.S. dropped significantly after use of HRT declined in 2002. While purified genistein is not as potent as HRT, Helferich cautioned, it still poses a risk to midlife women because the amount consumed is much higher.
But genistein is only one component of soy, Helferich said, and studying its effects in purified form may lead to misleading conclusions about the health consequences of soy in the diet. In fact, studies have shown that foods like soy flour have a very different effect. "The complex mixture found in soy flour doesn't make the tumor grow," he noted. "Whole soy contains a lot of biologically active ingredients, but together they may have multiple effects that can reduce the negative outcomes. When the whole food is consumed you get a very different effect than if you consume the concentrated constituents individually."
Helferich concludes that the whole soybean is healthier than many of its individual chemical parts. "That raw food can be consumed for less than a dollar a serving and is likely better for you than that thing you pick up at the health food store for $30 a pound," he said.
Related articles:
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HRT Confusion Drives Search For Alternatives
Alternative Therapies For Menopause Lack Research
Source: University of Illinois at Urbana-Champaign
