Does Soy Pose a Breast Cancer Risk?

download                There has been a lot of news attention about it and you have probably heard a family member or friend talking about it – the connection between soy and cancer.  More specifically, many people were worried for a time that there is a connection between soy consumption and breast cancer.  There are many foods that contain soy, such as tofu, edamame, soy sauce, tofu, soy flour, soybean oil, miso, soy milk, tamari, teriyaki sauce, tempeh and more.  Soy is a plant fiber full of important vitamins and amino acids. With soy being in so many foods, many women became very concerned they were increasing their risk of cancer.  The American Cancer Society explains the concern behind soy consumption to provide a more clear background for the discussion, “Soy foods (such as tofu, tempeh, edamame, miso, many veggie burgers, and other products made with soy flour) contain isoflavones, which are chemically similar to estrogens. Two major types, genistein and daidzein, can act like estrogen in the body, although at a very small fraction of the potency of circulating free estrogen in women.  These effects can be good or bad.  Let me explain.  It is well established that estrogen is linked to hormonally-sensitive cancers in women, such as breast and endometrial cancer.  Breast cells contain estrogen receptors, and when the “key” (estrogen) joins with the “lock” (the estrogen receptor), a series of signals are sent which can spur on estrogen-receptor (ER) positive breast tumor growth.”

What research is showing will give many people a lot of relief.  The American Cancer Society goes on to point to the research that shows that there is not a connection between soy and breast cancer and references research that was conducted in China because Chinese women tend to consume significantly more soy in their daily diets than women in the U.S. so it offered the best chance to examine a truly soy-rich diet, “In general, studies in Asian women have found a lower risk of breast cancer with eating more soy, whereas studies in the U.S. have tended to not find any association between how much soy a woman consumes and her risk of breast cancer.  Indeed, a recent study combined data from 14 epidemiologic studies on this topic and found that in Asian countries, women who ate the most (compared to the least) soy isoflavones had a 24% lower risk of developing breast cancer, while there was no association in Western countries such as the U.S… Keep in mind also that women in Asia likely have other cultural dietary patterns that may not be assumed in the U.S., such as lifelong consumption of soy and other foods that may have influenced breast development during adolescence in ways not yet fully understood.  A study in Shanghai found that women who ate a high amount of soy protein consistently during adolescence and adulthood had a significantly reduced risk of breast cancer before menopause, but not after menopause… What about women who have had breast cancer, especially ER-positive breast cancer? A recent study looked at soy consumption in the diets of more than 9,000 breast cancer survivors who were participating in 3 studies of eating habits and other lifestyle factors after breast cancer. Two of the studies were from the U.S. and 1 was from China. Women from both the U.S. and China who consumed 10 mg/day or more of soy had a 25% lower risk of breast cancer recurrence. These protective associations were slightly stronger in women with ER-negative tumors. In women with ER-positive tumors, the associations also seemed protective (though not strongly so) for women regardless of whether they were taking tamoxifen or not.”  So, fascinatingly, not only has a soy and breast cancer link been disproven but, in fact, increased consumption of soy may help reduce the risk of cancer diagnosis and recurrence.  As with anything, if you have concerns about your diet or intake of particular foods, talk to your physician who will be able to provide you with guidance based on your individual health history.

 

 

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