The seesaw popularity contest over soy has constantly been an ongoing debate among foodie skeptics. Is soy good for me or will it increase my risk for chronic disease? The question of whether soy is the superman or kryptonite to your health is reviewed in nearly 2,000 papers published annually.

Several epidemiological studies have argued that the daily consumption of soy is associated with a lower incidence of chronic diseases including cardiovascular disease, type two diabetes, breast and prostate cancer as well as even reducing menopausal symptoms. These studies have observed soy consumption in Asian populations where its intake is the highest. On average, these populations have about one to two servings of soy per day. Compared to the United States, Asia continued to demonstrate a lower incidence of cancer and researchers wanted to know why. They found that the isoflavones in soy play a key role in the suppression of tumor growth. When isoflavones, also known as phytoestrogens, pass through our digestive barriers unscathed and enter circulation, scientists believe that it interacts with human estrogen and as a result, decreases the development of cancers.

However, some studies have suggested that a daily intake of soy may actually heighten one’s risk for breast cancer by actually promoting tumor growth. Previous in-vitro studies looking at mice found genistein, one of the primary isoflavones in soy increased the growth of estrogen receptor-positive in breast cancers leading to growth. Even though advancements in future studies have managed to determine that mice process phytoestrogens such as genistein differently than humans, those at risk or those that that have been diagnosed with breast cancer, still find it hard to shake the belief in its harm.

One study recently published this past March in Cancer looked at more than 6,000 American and Canadian women with breast cancer and found that consumption of foods post-diagnosis containing soy’s main component, isoflavones, is associated with a 21% decrease risk of death. This decrease was only observed in women with hormone receptor-negative tumors as well as those who were not treated with endocrine therapy. A meta-analysis that included close to 10,000 breast cancer patients also found a positive correlation between consuming at least 10 mg of dietary isoflavones and a 25% reduced risk of breast cancer reoccurrence. The researchers believe that the consumption of isoflavones in their dietary form may even contribute to longevity.

Dietitians have a responsibility to try to resolve the ongoing debate about the effects of soy consumption. Soy is an excellent substitute for any meat protein, and the only legume that contains high amounts of omega-3 fatty acids. For years, many countries including the United States have recognized soy’s ability to lower cholesterol and have provided health claims to support their growing consensus. The benefits of soy remain clear and continue to surprise researchers. It may be worth incorporating soy onto your plate on a regular basis.

Contributed by Bryan Stengel, Dietetic Intern

Dietary Isoflavone Intake and All-Cause Mortality in Breast Cancer Survivors: The Breast Cancer Family Registry. (n.d.). Retrieved June 15, 2017, from

Hooper, L., Kroon, P. A., Rimm, E. B., Cohn, J. S., Harvey, I., Le Cornu, K. A., … Cassidy, A. (2008). Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. The American Journal of Clinical Nutrition, 88(1), 38–50.

Messina, M., & Messina, V. (2010). The Role of Soy in Vegetarian Diets. Nutrients, 2(8), 855–888.

Nechuta, S. J., Caan, B. J., Chen, W. Y., Lu, W., Chen, Z., Kwan, M. L., … Shu, X. O. (2012). 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. The American Journal of Clinical Nutrition, 96(1), 123–132.

Soyfoods & Cancer. (n.d.). Retrieved June 15, 2017, from