While men have been warned away from soy, there are new reasons to believe it can save women's lives. A recent study from Tufts University in Massachusetts investigated the link between dietary intake of the isoflavones found in soy products and breast cancer mortality, and unearthed some surprising data.

Isoflavones are plant-based compounds that resemble estrogen. Previous studies indicated estrogen was inclined to help cancer cells multiply and spread - especially in hormone receptor-positive cancer, which is the most common form of the disease. Consequently, doctors have been concerned about the adverse health effect of soy on breast cancer patients.

The Tufts study is changing all of that. The researchers examined isoflavone intake in 6,235 women diagnosed with breast cancer from the US and Canada. The women were followed over a median period of 9 years, and the study examined the isoflavones that occur naturally in foods, not supplementary isoflavones. The scientists concluded that dietary soy intake was safe, and noticed a connection between high soy consumption and a decrease in the mortality risk for some breast cancer patients.

In fact, women with breast cancer who consumed isoflavones in large amounts were 21 percent less likely to die than their counterparts who consumed small amounts.

The only catch was that the drop in the mortality risk was noticed only in women who had hormone receptor-negative cancer and women who had not been taking anti-estrogen therapy. However, high amounts of isoflavone did not associate with higher mortality in women who did receive hormonal therapy.

"Based on our results, we do not see a detrimental effect of soy food intake among women who were treated with endocrine therapy. For women with hormone receptor-negative breast cancer, soy food products may potentially have a protective effect. Women who did not receive endocrine therapy as a treatment for their breast cancer had a weaker, but still statistically significant, association," wrote Dr. Fang Zhang, lead author of the study.

Receptor-negative breast cancer makes up 20 percent of all recently diagnosed cases of cancer.

The research has been published in journal of the American Cancer Society, Cancer.