Ask the Nutritionist

Q: I am 7 years out from Stage 1 estrogen + breast cancer. I have lost 30 pounds on Medifast. Is this mostly soy protein diet ok for me or should I transition off now that I have lost the weight?

Ellen Lamonoff, New York, New York 

A: Estrogen receptor positive breast cancer (ER+) may possibly be affected by concentrated sources of soy isoflavones, a phytoestrogen creating weak estrogen-like effects, although research on this is inconclusive. As described in this soy lecithin and breast cancer question, whole soy foods such as soymilk, tofu, edamame and soy nuts can be healthy in moderation as a lean source of protein.

However, soy products like supplements, pills, powders and soy-based bars contain higher, concentrated levels of phytoestrogens, which may be of concern for survivors of ER+ breast cancer. It seems that the Medifast products have soy protein isolate as either the first or the second ingredient, but the amount is not listed on the labels. There is controversial evidence about the impact of this type of soy so we would suggest being cautious and transition off Medifast.

Maintaining a healthy weight is important for breast cancer survivors. Exercising and eating a plant-based diet (including vegetables, fruits, whole grains and lean protein) can help to promote both a healthy weight and survivorship. Learn more about healthy diet and exercise tips for breast cancer patients.