Nutrition Hotline
By Reed Mangels, PhD, RD
QUESTION: What's the latest thinking about soy and the risk of breast cancer or breast cancer recurrence?
S.A. via email
ANSWER: Soyfoods contain substances called isoflavones, which have a chemical structure similar to the hormone estrogen. This similarity is what initially led to concerns that soyfoods could increase the risk of breast cancer or of breast cancer recurrence. Recent research does not support these concerns. Asian women who eating traditional diets that typically include soy products, have a lower risk for breast cancer than do women in the United States who typically eat few soy products1. Of course, there are other differences between these groups that could explain the dissimilar breast cancer rates.
Studies focusing on soy intake during childhood and adolescence suggest that higher soy consumption in early life is associated with a lower risk of breast cancer2. This higher consumption was around 16 grams of soy protein per day, which means eating about a half cup of cooked soybeans or 3/4 cup firm tofu or drinking 2 cups of soymilk. Soy consumption later in life does not appear to increase or decrease the risk of breast cancer although it may be beneficial for older women who ate little or no soy when they were teens2.
Several large studies of women who had been diagnosed with breast cancer found that breast cancer survivors who ate soy actually had a lower risk of their breast cancer recurring than women who did not eat soyfoods3. Women eating soyfoods also had a lower risk of death3. There is some evidence that soy products may boost the effects of common drugs used to treat breast cancer such as tamoxifen1. Both the American Cancer Society and the American Institute for Cancer Research have said that it's fine for breast cancer survivors to eat soy4,5.
References
- Messina M. Impact of soy foods on the development of breast cancer and the prognosis of breast cancer patients. Forsch Komplementmed. 2016;23(2):75-80.
- Baglia ML, Zheng W, Li H, et al. The association of soy food consumption with the risk of subtype of breast cancers defined by hormone receptor and HER2 status. Int J Cancer. 2016;139(4):742-8.
- Chi F, Wu R, Zeng YC, et al. Post-diagnosis soy food intake and breast cancer survival: A meta-analysis of cohort studies. Asian Pac J Cancer Prev. 2013;14: 2407–2412.
- Rock CL, Doyle C, Demark-Wahnefried W, et al. Nutrition and physical activity guidelines for cancer survivors. CA Cancer J Clin. 2012;62:243-74.
- AICR. Soy is safe for breast cancer survivors. Cancer Research Update. November 21, 2012.
