Q:
I finished chemotherapy for estrogen receptor positive (ER-positive) breast cancer this past April. I take tamoxifen and have been advised by my doctor to avoid foods that contain estrogen. Although avoiding all estrogens in foods is probably impossible, I would still like to know what are some common foods with high amounts of estrogen or phytoestrogens, such as soy, flax and wild yams, that I should avoid?
A:
You are certainly on the right track. The goal for people who have had breast cancer and/or are taking tamoxifen is to avoid a diet high in phytoestrogens, but not to avoid all sources, as more than 300 foods have been found to contain some level of these substances. Depending on the source (both food or supplement) and its preparation, the phytoestrogen content of similar products can vary widely. Phytoestrogens are naturally-occurring substances found in plants that can either mimic the actions of estrogen in the body or work against the body's estrogen. Because phytoestrogens can cause tissue growth, women who have had breast cancer are cautioned against ingesting large amounts of these compounds. Additionally, studies have found that genistein, a type of phytoestrogen, prevented the tumor suppressive action of tamoxifen.
There are three classes of phyoestrogens:
- Isoflavonoids, found in legumes, with soybeans being the major dietary source of this compound.
- Lignans, found in cereal bran, beans, fruits and vegetables, with flaxseed having the highest amount.
- Coumestan, found in peas, pinto and lima beans, with alfalfa and clover sprouts having the highest amounts.
Always talk to your health care provider before taking any supplement. You should definitely avoid taking phytoestrogen-based supplements, such as soy isoflavones or black cohosh. Also, reduce your intake of soy products (e.g., tofu, miso, tempeh, soymilk), flaxseed, alfalfa and clover to keep your phytoestrogen intake close to the United States average, which is considered quite low.
More information on diet and cancer prevention and therapy can be found at:
- American Institute of Cancer Research: www.aicr.org
- American Cancer Society: www.cancer.org
