Nutrition-wise blog

Soy and breast cancer — What's the connection?

By Katherine Zeratsky, R.D., L.D. May 17, 2016

Does eating soy put women at higher risk of developing breast cancer? Does the type of breast cancer, defined by hormone receptor type, change the advice to eat or avoid soy? These questions reflect growing confusion among women about soy and breast cancer risk.

A recent study found that soy foods lower women's risk of breast cancer. The study reviewed food intake questionnaires from 70,578 Chinese women, 40-70 years of age, participating in the Shanghai Women's Health Study.

This study's results are in line with previous research demonstrating that soy foods lower a woman's risk of developing breast cancer. The greatest benefit appears to be in premenopausal women. Among women who developed breast cancer during the study period, soy foods appeared to delay the onset by 2-5 years.

However, the influence of soy on the risk of breast cancer appears to vary by hormone receptor status, with soy significantly reducing the risk for some types of breast cancer but not others.

Eating soy foods appears to lower the risk of estrogen receptor positive and progesterone receptor positive (ER+/PR+) breast cancer in all women, with the greatest reduction occurring in postmenopausal women. Soy intake appears to be especially protective in premenopausal women at risk for estrogen receptor negative and progesterone receptor negative (ER-/PR-) breast cancer. There doesn't appear to be an association with human epidermal growth factor receptor 2 (HER2) status and soy intake.

In a review of the available research, the American Institute for Cancer Research notes that 1-2 servings of soy foods a day do not increase and may decrease breast cancer risk. A serving of soy is:

  • 1/3 cup soy nuts
  • 1/2 cup edamame
  • 1 cup soy milk

Soy foods are nutritious. If you want to cut back on red meat, soy can be a good substitute because it's a complete protein. Soy foods are also excellent sources of calcium, manganese and selenium. Do you include soy in your diet? How?

May 17, 2016