Ask the Nutritionist
Q: My tumor is extremely estrogen sensitive. I've been reading that there is quite a bit of estrogen in meat and dairy products, so I now avoid them. Soy is reputed to behave like estrogen, so I am avoiding soy, although there is some question about whether or not soy may actually be helpful. There is even more conflicting evidence about other plant-based estrogens (phytoestrogens). There seems to be no way to know if phytoestrogens will help or hurt. I am particularly interested in your opinion about ground flaxseed. Is this something I should avoid, or is there no way to know, or is it something I should try to eat?
Valerie, Worcester, Massachusetts
A: A tremendous amount of controversy exists over the role of dietary plant-based or phytoestrogens in women with a history of estrogen-receptor positive breast cancer.
To first address your question on dairy and red meat: while there is no conclusive evidence that hormones in meat or dairy contribute to breast cancer risk, it makes sense to choose a low-fat version of these foods and to keep red meat intake to 4-6 ounces per week at most. Hormones are fat soluble so choosing a low-fat variety can help to reduce any potential exposure. Furthermore, weight gain and high body weight are correlated with risk for breast cancer recurrence, so choosing lower fat dairy and animal protein is helpful in this regard as well. You may also consider organic, low-fat dairy and meat.
In terms of soy-based foods and phyto- or plant-based estrogens, the data is unclear. Here at Dana-Farber, we recommend that women with a history of estrogen-positive breast cancer consume 2-3 servings of natural, whole soy foods per week to keep intake at a "moderate" level. You may choose to avoid soy altogether, however soy is a good source of protein, calcium, iron and other nutrients, so it need not be completely eradicated from the diet if you were already accustomed to eating soy. One does not need to begin eating soy, but can choose to do so in moderation without concern of harm.
Natural soy foods (i.e. tofu, edamame, soy nuts, soy milk) are the best choices because they have a lower concentration of phytoestrogen, as compared to concentrated soy foods containing ingredients such as Soy Protein Isolate (i.e. soy protein powder, most nutrition or protein bars, soy-based or vegetarian "meats"). Please avoid all soy-based dietary supplements such as those promoted to ease menopause symptoms.
Ground flax seed is a healthy source of Omega-3 fats and, when consumed at 1-2 tablespoons per day, does not pose any risk to breast cancer survivors.
Eating a plant-based diet, engaging in daily physical activity such as walking, limiting or avoiding alcohol, getting enough sleep and incorporating stress reducing behaviors into your life are the best way to promote health as a breast cancer survivor.