Moderate soy intake is not related to a negative breast cancer prognosis

Should women be concerned about the potential of soy foods to either cause breast cancer or decrease the survival rate for women who have been diagnosed with breast cancer? 
Here is a report that suggests there is not a connection.

At a Glance

Recent epidemiologic studies report no adverse effects of soy foods on breast cancer survival or prognosis.  Read more about this research below. 

Contrary to earlier clinical studies and some popular media suggesting that soy may promote breast tumor growth, three recent studies show that moderate intakes of soy-containing foods are not adversely related to breast cancer prognosis.

In the most recent study researchers used data from the Women’s Healthy Eating and Living (WHEL) study to examine the effect of soy intake on breast cancer prognosis. Soy isoflavone intake was assessed in 3,088 breast cancer survivors diagnosed between 1991 and 2000. After an average follow-up of 7.3 years, it was found that as isoflavone intake increased, risk of death decreased. Women whose intake was >16.3 mg of isoflavones had a 54% reduction in the risk of death.

This is the third recent epidemiologic study to report no adverse effects of soy foods on breast cancer prognosis. Because these studies varied by ethnicity and the level and type of soy consumed, the investigators stated that when taken together, these studies provide evidence to suggest that it may not be necessary for clinicians to advise against moderate soy consumption for women with a diagnosis of breast cancer.

Caan BJ et al. Soy food consumption and breast cancer prognosis. Cancer Epidemiol Biomarkers Prev. 2011 May;20(5):854-8.

The following is a summary of a previous Essentials of Health from Jan 27, 2010. Also included are two more recent study references with similar outcomes.

“In a large prospective study of female breast cancer patients treated surgically, moderate soy intake was associated with a significant decrease in death and cancer recurrence during a 4 year follow-up. Women whose intake of soy protein was among the top 25 percent of participants had a 29 percent lower risk of death during follow-up and a 32 percent lower risk of recurrence compared to those whose intake was in the lowest quarter.  This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer.”

Shu XO et al. Soy food intake and breast cancer survival.  JAMA 2009;302(22):2437-2443

Zhang YF, et al. Positive effects of soy isoflavone food on survival of breast cancer patients in China.  Asian Pac J Cancer Prev. 2012;13(2):479-82.

Nechuta SJ et al. Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women.  Am J Clin Nutr. 2012 Jul;96(1):123-32.