Q.Please help clear up the confusion. Do soy foods prevent or promotebreast cancer? I?ve heard both.
A.The effect soy foods have on breast cancer risk is hotly debated right now,because the evidence points in opposite directions simultaneously. A clearanswer is not likely any time soon. In the meantime, though some experts urgecaution, it’s probably safe?maybe even beneficial?for most women toconsume soy foods at least a few times a week.
Soy foods are a primary source of plant compounds calledphytoestrogens, which are structurally similar to human estrogens, but much lesspotent. The two most studied phytoestrogens are the isoflavones genistein anddaidzein found in soy. Because phytoestrogens mimic the structure of humanestrogens, the plant compounds can bind to estrogen receptors in the body, thusblocking human estrogens and their cancer-causing potential. On the otherhand, adding any estrogen-like compound?even small amounts ofphytoestrogens?might, theoretically, increase cancer risk.
Interest in soy as a breast cancer protector originatedwith population studies that found low breast cancer rates in Asian countries,where soy consumption is high. However, not all human studies show such a link;lab and animal studies are even more inconsistent.
How to explain the dichotomy? Some researchers believe soy’seffect on breast cancer depends on the level of human hormones present in thebody. Soy may be protective in premenopausal women when estrogen is high, butharmful after menopause when estrogen is low. Or perhaps consumption at puberty(typical in Asian countries) affords greater protection than consumption thatstarts in adulthood (typical in the U.S.).
The Bottom Line. Leading soyexpert Mark Messina, Ph.D., of Loma Linda University in California, is confidentthat soy will ultimately prove to be of more help than harm where breast canceris concerned. But don’t go overboard, he cautions, increasingly easy thesedays, with all the soy added to foods, energy bars and supplements.
For the general population, health benefits may be safelyachievable with one to two daily servings of soy foods (up to 100 milligrams ofsoy isoflavones from food or supplements), says Messina. If you have a historyof estrogen-dependent breast cancer, however, limit soy foods to three or fourservings a week.
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