Soy Foods in Moderation Safe for Breast Cancer Survivors

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Women who have been diagnosed with breast cancer don’t need to worry about eating moderate amounts of soy foods, according to AICR 2011 Research Conference speaker Bette J. Caan, DrPH, Senior Research Scientist at Kaiser Permanente in Northern California.

Soy foods contain compounds called isoflavones, phytochemicals found to behave like the sex hormone estrogen, which is linked to promotion of breast cancer. Yet soy foods have for the most part been associated with a lower risk of breast cancer — especially in Asian countries where unprocessed  soy foods like tofu are a regular part of the diet from an early age.

There has also been concern because of the estrogen-like qualities of soy foods that in survivors, these foods might interfere with the benefits of tamoxifen therapy. That’s why some doctors caution breast cancer patients against eating soy foods like tofu, edamame, tempeh and soy milk.

Today, at AICR’s annual conference session on Cancer Treatment and Survivorship, Dr. Caan stated that enough evidence seems to have accumulated from human studies of breast cancer survivors to relieve fears that soy foods may increase breast cancer risk or recurrence.

In her review of seven studies she said that, despite large differences in levels and types of soy consumption between US and China, in both populations, soy food intake after diagnosis did not appear harmful and, to some degree, appeared to improve prognosis among breast cancer survivors, even those receiving tamoxifen therapy.

In another presentation, Leena Hilakivi-Clarke, PhD, of Georgetown University, pointed out that research on the effects of soy phytochemicals on each of the four types of breast cancer has not yet yielded enough evidence. Dr. Hilakivi-Clarke, an AICR grantee, said that women who ate soy before a breast cancer diagnosis could enjoy a moderate amount of soy after diagnosis, while women who had never eaten soy probably should be cautious about how much they ate after diagnosis.

Both researchers agreed that soy foods should be just a small part of an overall healthful diet and that the amount of soy phytochemicals in foods would be unlikely to exceed healthful levels. They advised people not to rely on supplements of soy phytochemicals and rather to get them from whole soy foods.

“These findings are great news for women who want to use soy as a source of protein while cutting back on animal protein such as red and processed meat for better health and lower cancer risk. Soybeans and their products are nutritious and versatile,” Dr. Caan commented.

AICR advises eating soy as part of a cancer-fighting diet that includes a wide variety of plant vegetables and fruits, and mostly consists of vegetables, fruits, whole grains and beans, including soy.



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