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PHILADELPHIA — Compounds found in soy, called isoflavones, can decrease the risk of developing certain types of breast cancer, a new study suggests.
The finding is in line with previous studies which found breast cancer risk can be reduced by consuming soy, said study researcher Anne Weaver, a graduate student at the University at Buffalo, and contradicts others studies showing an increased risk of cancer with soy consumption.
"Isoflavones don't appear to be harmful, at least in this study," she told MyHealthNewsDaily.
The study found women who ate a small amount of soy isoflavones (217 micrograms, or less than half a serving) a day had a 30 percent decreased chance of developing invasive breast cancer than women who ate almost no soy (76 micrograms a day or less), Weaver said.
Soy's possible role in breast cancer stems from the fact that isoflavones may affect hormones by binding to estrogen receptors in the body, Weaver said.
The research was presented here at the Frontiers in Cancer Prevention Research Conference in Philadelphia, held by the American Association for Cancer Research.
In the new study, Weaver and colleagues compared 681 Caucasian women who had breast cancer with 611 women without breast cancer.
The women recorded the amount of soy isoflavones in their diets as high (217 micrograms or more a day), medium (76 to 216 micrograms) or low (less than 76 micrograms).
Researchers found the women who ate the most isoflavones had a 30 percent lower risk of having invasive breast cancer, and a 60 percent lower risk of developing a grade 1 tumor, which is the least aggressive type of tumor, compared with the women who ate the least.
Pre-menopausal women who ate the highest amount of isoflavones also had a 30 percent lower risk of developing stage 1 cancer, a 60 percent lower chance of developing stage 2 cancer and a 70 percent lower risk of having a tumor larger than 0.8 inch (2 centimeters) than women who ate the least.
Some animal and in vitro studies have linked soy with an increased risk of breast cancer , which could be due to isoflavones' binding to estrogen receptors and spurring tumor growth. However, those results haven't been found in humans, Weaver said.
When soy is eaten as a food, there is no evidence it is detrimental for health, said Dr. Gertraud Maskarinec, a researcher at the Cancer Research Center of Hawaii.
"The whole discussion that it's bad is confused by high-dose supplements," said Maskarinec, who was not involved with the new study. "Lots of people want supplements to treat things like hot flashes, but there's no monitoring of those supplements to see what their effects will be," as supplements aren't regulated the way drugs are.
The findings show that even when soy isoflavones are consumed at low levels, they can still have a protective effect, said study researcher Susan McCann, of Roswell Park Cancer Institute.
In fact, 75 percent of the women in the study didn't eat soy products, and instead got their isoflavones from greens, coffee and nutrient-enriched bread and deli meats, she said.
Most people don't consume several servings of soy a week, so the findings are significant because they mimic the actual diets of people, McCann said.
The findings agree with a 2008 study in the British Journal of Cancer of 35,303 Chinese women, which found that women who ate more soy had a decreased risk of breast cancer than women who ate less soy.
And a study published last month in the Canadian Medical Association Journal found a diet high in isoflavones could reduce the risk of cancer's recurrence in breast cancer survivors.