Although once controversial, evidence increasing highlights the potential benefits of soyfoods for breast cancer patients. The latest support for soy comes from the World Cancer Research Fund International. On behalf of the WCRFI, an independent panel of scientists evaluated an extensive body of literature relating to lifestyle and the survival of breast cancer patients.
The panel concluded that because of limitations in either the design or execution of much of the research that exists, the evidence is still not strong enough to make specific recommendations for breast cancer survivors. However, they concluded there are indications of links between better survival after breast cancer and: 1) a healthy body weight 2) being physically active 3) eating foods containing fiber 4) eating foods containing soy 5) a lower intake of total fat and, in particular, saturated fat.
In regard to soy, the panel identified three follow-up studies on isoflavone intake 12 months or more after a diagnosis of primary breast cancer and all-cause mortality, and two on soy protein intake and all-cause mortality. For isoflavone intake, one study reported a significant inverse association when comparing the highest versus the lowest category of intake, and two reported a non-significant inverse association. All three studies identified were included in the dose-response meta-analysis (n = 794), which found a 9% reduction associated with the consumption of 10 mg isoflavones per day, although the results were not quite statistically significant (relative risk = 0.91; 95% confidence interval: 0.83-1.00). Two of the three studies had more than 100 deaths. Two of the studies were from China and one was from the United States.
World Cancer Research Fund International. Continuous Update Project Report: Diet, Nutrition, Physical Activity, and Breast Cancer Survivors. 2014. Available at: www.wcrf.org/sites/default/files/Breast-Cancer-Survivors-2014-Report.pdf