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Soy Consumption and Breast Cancer Risk

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Soy Consumption and Breast Cancer Risk

Is it safe to eat soy? It’s a question our Cooper Clinic Nutrition Services team receives often from female clients. 

For many years, women were advised not to consume soy because it was believed to increase the risk of breast cancer, specifically estrogen-receptor-positive (ER-positive) breast cancer. Soy contains isoflavones, weak phytoestrogens (plant estrogens), which were thought to behave much like the estrogen our bodies make by binding to estrogen receptors. Because of this, there was fear that eating soy might increase the risk for hormone-related breast cancers.

Research now shows this is not true. In fact, soy may even offer protective properties against breast cancer. It is important to know that phytoestrogens (found in soy) are not the same thing as female estrogens. Below, Cooper Clinic's registered dietitian nutritonists answer a few of the most commonly asked questions regarding soy and the risk for breast cancer. 

1. Is soy safe for women in general?

Yes. In fact, the American Institute for Cancer Research (AICR) includes soy in its “Foods That Fight Cancer” list. Consuming a daily moderate amount of soy from whole soy foods (such as edamame, tofu, soy nuts and soymilk) may actually reduce your risk for colorectal cancer. 

Regarding breast cancer risk among cancer-free women, AICR studies on soy consumption either show no link or a slightly protective link to breast cancer. 

Nutritionally, soy is low in saturated fat, is a good source of polyunsaturated fat (both in the form of omega-3 and omega-6) and is rich in fiber and high-quality protein (one serving averages about 7 g). Additionally, soy contains key nutrients and phytochemicals well studied for their cancer prevention properties. 

In addition, the U.S. Food and Drug Administration (FDA) has determined including 25 g of soy protein a day may lower your risk for coronary heart disease. 

2. Is soy safe for women who have or have had ER-positive breast cancer?

Determining whether it is safe for breast cancer survivors to eat soy has been one of the most common questions studied. AICR nutrition advisors say research shows consistent evidence soy is in fact safe. 

Research also shows consuming moderate amounts of soy may even reduce your risk of recurrence for breast cancer survivors. 

3. Are all soy products considered the same? (i.e., whole soy foods vs. soy protein isolates)

Soy protein isolates found in soy supplements, soy-based protein powders and soy-based protein bars generally contain a more concentrated amount of soy isoflavones compared to the amounts in whole-soy foods. 

The numerous studies that have shown safety with soy inclusion and even protective benefits from soy have been studies that include whole-soy foods, not supplements.  Therefore, it is advised that whole soy foods be incorporated into a healthy diet, not soy-based supplements, which contain concentrated soy protein isolates.  

If you are a woman concerned about breast health and you enjoy soy, focus on healthy whole soy foods. As The Academy of Nutrition and Dietetics Oncology Nutrition Practice Group advises, the occasional soy protein bar or snack food is fine, but as with all plant foods, less processed is better.

4. Are there specific amounts that have been deemed safe?

Yes. According to AICR, a moderate consumption of soy–defined as 1 to 2 standard servings a day–is considered safe and may even reduce your risk of breast cancer.

Examples of one serving of soy include:

  • ½ cup of edamame – 11 g  protein
  • ¼ roasted soy nuts – 11 g  protein
  • 3 ounces tofu  – 8 g protein
  • 1 cup soymilk – 7 g  protein

One serving averages about 7 g of protein and 25 mg of isoflavones. Some studies have shown up to 3 servings a day is safe. Foods containing soy include tofu, soymilk, soy nuts and edamame.

To schedule a one-on-one consultation with a registered dietitian nutritionist or for more information on Cooper Clinic Nutrition Services, visit or call 972.560.2655.

Article provided by Cynthanne Duryea, RDN, LD, and Cooper Clinic Nutrition Services.