Soy diet linked to fewer deaths in breast cancer survivors

Breast cancer survivors in China who ate tofu, soy milk and fresh soybeans had a lower risk of dying and less chance their cancer would return, a study found.

Those who ate the most soy protein had a 29 percent lower risk of dying and a 32 percent lower rate of their breast cancer returning than those who had the lowest intake of soy, research showed in the Journal of the American Medical Association. The foods included in the study were tofu, soy milk and fresh soy beans, all common choices in Asian meals.

The study, which followed women for an average of about four years, is the largest to examine the influence of soy intake on breast cancer survival and recurrence, the authors said. More than 192,000 women in the U.S. will be diagnosed with breast cancer this year, according to the National Cancer Institute.

"Women with breast cancer can be assured that consumption of moderate amounts of soy food is safe and may be associated with better outcomes," said the study's lead author Xiao-Ou Shu, a professor of medicine at Vanderbilt University in Nashville, Tenn. The researchers will follow the women to watch "the long-term effects of soy food intake on health among breast cancer survivors, including bone density, fracture and coronary heart disease," she said.

Soy foods are rich in isoflavones, which are estrogen-like compounds that occur naturally in plant foods. Soy isoflavones may compete with the body's estrogen in binding to cell receptors, reducing the amount of estrogen in the body and hindering the ability of cancers to grow. The most common types of breast cancer depend on estrogen to grow, Shu said.

The researchers said the results eased previous concern that isoflavones might interfere with tamoxifen, a cancer drug designed to block estrogen. The study found higher soy food consumption was beneficial regardless of whether a patient was taking tamoxifen, she said.

The researchers analyzed data from women in the Shanghai Breast Cancer Survival Study in China. The 5,033 women had been diagnosed with breast cancer from March 2002 to April 2006. They were followed for an average of four years through June 2009.

The four-year mortality rate was 7.4 percent for women with the highest consumption of soy protein compared with 10.3 percent for those with the lowest intake. The four-year breast cancer recurrence rates were 8 percent for those in the highest soy group and 11.2 percent for those in the lowest group, the researchers found.

Eating soy food that is the equivalent to 11 grams (0.39 ounces) of soy protein or 40 milligrams of soy isoflavone a day was enough to see a benefit, Shu said. In the study, the women consumed an average of 47 milligrams a day of isoflavone compared with the average U.S. intake of 1 milligram to 6 milligrams a day, the researchers said.

One cup of fortified soy milk contains 10 grams of soy protein, or 43 milligrams of isoflavone, while a half cup of a firm soybean patty called tempeh contains 16 grams, or 53 milligrams of isoflavone. A half-cup of tofu or about 1.5 cups of edamame, a green vegetable, also each contain 10 grams of soy protein.