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Soy, Flax, and Breast Cancer

Published: January 2, 2010

My breast cancer was estrogen receptor-positive. I’ve heard that eating soy and flax might cause a recurrence. But many cereals and vitamins contain soy, flax, or both, which really limits my food choices. Your help, please?


Pocatello, Idaho

Don’t give up soy and flax yet! While it’s true that estrogen can increase cancer risk—especially when abnormal cells have “docking stations” (called receptors) for the powerful hormone—the estrogen-like compounds in soy and flax may actually provide health benefits. Post advisor Dr. Walter Willett, chairman of the Department of Nutrition at the Harvard School of Public Health, explains:

“Soybeans and flaxseed contain phytoestrogens, which react with the same receptors as estrogen from ovarian or fat tissue. Phytoestrogens, which are sometimes called ‘plant hormones,’ may have estrogen-like effects. However, they trigger a far weaker response than do the estrogens produced by the body. In fact, consuming soy and flax may prevent stronger-acting estrogens from binding to the receptor sites and produce an overall antiestrogenic effect, similar to the way tamoxifen, a breast cancer drug, works.

“The potential benefit has caused many to question whether the high soy consumption in Asian populations contributes to the low breast cancer rates in those countries. Although studies have not been conclusive, some of the data suggest increasing soy intake during adolescence or early adulthood may decrease cancer risk. Alternatively, studies do not show a direct correlation between high soy consumption and the risk of breast cancer.

“While I wouldn’t recommend loading up on large amounts of flax, tofu, soy milk, and other soy products, I don’t think it’s necessary to completely avoid them. Stay away from phytoestrogen supplements, though. They may increase your consumption too much. Instead, focus on staying lean and physically active to reduce body fat, which is a major source of estrogens. And of course, schedule regular checkups with your physician to discuss treatment options and answer any questions that may arise.”

Of the foods that Americans eat, soy and flax have the highest content of phytoestrogens. Other sources (with lesser amounts) include: sesame seeds, wheat, berries, oats, barley, dried beans, lentils, yams, rice, alfalfa, mung beans, apples, carrots, pomegranates, and wheat germ.

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  • jackiec

    I am a chinese and have breast cancer ER+ & PR+. Who said Asian has low rate of breast cancer. The medical system is not like us in Western world. Records are not accurate and many poor people died in villages and have no money to go to hospital. Many women in China has breast cancer and most of them eat soy products and thinking they are good. I moved to China in 2009 and started eating more soy, flaxseed and oats almost everyday to lower my cholesterol from 698 to 510. It works on cholesterol but after 9 months…. I was diagnosed Breast Cancer in January, 2010. My mammogram was normal in March 2009. I wish somebody warmed me not to eat SOY and FLAXSEED. Or at least told me to watch out. I am undergoing Chemo right now and was told by my medical term not to eat SOY.