Increased consumption of soy products after a breast cancer diagnosis improves mortality in some breast cancer patients. For other patients, increased consumption has no effect. No association was found between increased dietary soy and increased mortality.
Dietary Isoflavone Intake and All-Cause Mortality in Breast Cancer Survivors: The Breast Cancer Family Registry
Authors: Zhang, F. et. al.
Source: Cancer 2017 doi: 10.1002/cncr.30615
Many women with breast cancer wonder if dietary soy is helpful or detrimental. Soy contains isoflavones, which are plant-based estrogens (phytoestrogens). These substances are known to bind to breast tumor estrogen receptors. Recent studies strongly suggest that isoflavones actually mimic the anti-tumor activity of tamoxifen and raloxifene. There are few studies that explore the association between dietary soy and outcomes with specific types of breast cancer (estrogen and progesterone receptor positive or negative).
The investigators in this study surveyed over 6,000 women in North America who were diagnosed with breast cancer. These women reported their dietary soy intake before and after breast cancer diagnosis. Other factors, such as cancer specifics, ethnicity, body mass index (BMI), alcohol consumption and level of physical activity were recorded.
Follow up was approximately 9 years. Women who consumed the most soy had a 21% lower rate of death than women who consumed moderate or low amounts. This decrease was statistically significant for women who had greater soy consumption after their breast cancer diagnosis as opposed to before it.
The association between increased soy intake and reduced mortality existed among the women with estrogen and progesterone receptor negative disease and in women who did not take endocrine therapy as part of their breast cancer treatment. There was no association between level of soy intake and mortality among the patients with estrogen and progesterone receptor positive breast cancer.
This study did not show a negative impact between dietary soy and overall mortality in women with breast cancer, implying that women with hormone receptor positive disease may be unaffected by dietary soy. On the other hand, women with hormone receptor negative disease may have improved mortality by eating soy.