Ask the Nutritionist
Q: I was diagnosed a year ago with DCIS, ER/PR+. I have read that people with this type of breast cancer should not consume products containing soy protein isolate. Is the same true for products with soy lecithin?
B.A., Harford, Connecticut
A: The relationship between soy intake and cancer is a topic that has been studied extensively. However, to date, the results have been inconclusive as to whether consumption of soy products, particularly excessive intake of isoflavones, can stimulate the growth of ER+ tumors.
Soy is naturally rich in isoflavoves, a phytoestrogen, that can bind to estrogen receptors (ER) and create weak estrogen-like effects. Chemical components of soy isoflavones have non-hormonal properties that have been associated in numerous prostate and breast cancer studies with decreased cancer cell growth. The majority of studies showing a benefit to soy intake have used "whole soy" products such as soy milk, tofu, soy nuts, tempeh, and edamame, which are all healthful, lean protein sources. Moderate consumption of foods high in phytoestrogens is unlikely to have any adverse effects, such as 2-3 servings per week. What should be avoided are soy products that are concentrated sources of phytoestrogen such as dietary supplements, pills, powders, and soy-based protein bars, as you mentioned in your question.
Soy lecithin, extracted from soy-bean oil, is often used in numerous foods, like chocolate to help keep ingredients emulsified. Many food labels will list a soy-based emulsifier like lecithin. The amounts are generally minute and don't contribute a substantial level of phytoestrogens. Products with soy lecithin do not need to be avoided because they have such minor amounts.