DEAR DR. BLONZ: What are the concerns about the use of soy and flax if you have breast cancer? -- S.B., Chicago
DEAR S.B.: Soy and flaxseed contain substances that are similar in structure to the human hormone estrogen. In soy, these are the isoflavones, while in flax, they are the lignans. These plant versions of estrogens, called phytoestrogens, cannot take the place of our own, but they can play tricks on some of the estrogen receptors in our bodies.
Your question relates to the use of soy and flax with breast cancer patients. It is known that certain types of breast cancer grow faster when estrogen is around. These cancers are referred to as estrogen receptor positive (ER+) cancers. Research has found that phytoestrogens can block estrogen's ability to stimulate the growth of these estrogen-sensitive cancers. The cancer-fighting drug Tamoxifen is designed on this very principle.
When considering the use of soy and flax with a breast cancer patient, it's of primary importance to know if the cancer is ER+. A next consideration is whether Tamoxifen treatment is being used, which is more likely with estrogen-sensitive cancers.
In such instances, it would be unclear whether the presence of additional phytoestrogens from soy and flax would have a chance of making things better, or work at cross-purposes to the Tamoxifen. There are studies underway to determine if fixed intakes of phytoestrogens might be therapeutic, but the particulars have yet to be worked out. That means it would be wise to refrain from high intakes of these phytoestrogen-containing foods until you have discussed it with your oncologist, or a dietitian working with the practice. This is a relatively new area, where the reliable research evidence is somewhat limited.
Nobody wants to make a misstep. But if the breast cancer is not estrogen receptive, and there is no history of these types of cancers in the family, I am not aware of any reason why these whole foods can't be a part of your plant-based diet. Flaxseed contains fiber and omega-3 fats, while soy contains the essential omega-6 fats. A regular intake of soy protein has been shown to help decrease the risk of heart disease.
The American Cancer Society has a discussion of soy and the risk of breast cancer at tinyurl.com/hqgcxt7.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.