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How Healthy Is Soy Really?

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By Amy Paturel, "How Healthy Is Soy Really?,"January/February 2011

The pros and cons of soy for your body.

Packed with high-quality protein, fiber and other good-for-you phytochemicals, soy seems to be a naturally healthful choice. But despite its healthy halo, some experts say soy isn’t a good choice for every condition. Here, we outline the pros and cons.

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Pros & Cons to Eating Soy

+Heart: You may be able to significantly lower your “bad” LDL and total cholesterol levels by eating 25 grams of soy protein each day (e.g., about 1⁄2 cup soy nuts; 11⁄4 cups of tofu or edamame; 31⁄2 cups soymilk), suggests a review of 30 studies. According to one hypothesis, soy protein directly lowers cholesterol levels by helping the liver clear more LDL from the body, says Mark Messina, Ph.D., adjunct associate professor at Loma Linda University and executive director of the Soy Nutrition Institute. You reap an even greater heart benefit when you replace meat and full-fat dairy with soy as you’ll naturally eat less saturated fat—and research shows that saturated fat increases LDL.

+Menopause: Good news, ladies! A new analysis of 17 studies—presented at the international soy symposium in October 2010—shows consuming isoflavones from soy (compounds that act as weak estrogens) cuts both the frequency and severity of hot flashes in half.

+Prostate: Studies in Asia show that men who consume about two servings of soy per day are about 30 percent less likely to develop prostate cancer than those who eat less. And for men who already have prostate cancer, preliminary research suggests that soy may inhibit the progression of the disease.

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Pros & Cons to Eating Soy

-Thyroid: Soy is high in isoflavones, compounds that may inhibit the body’s ability to make thyroid hormones, which play a role in controlling everything from metabolism to body temperature. Some studies suggest that over time, soy could cause thyroid problems, such as hypothyroidism (a condition characterized by weight gain, fatigue and cold intolerance). Other studies, however, say that soy only affects thyroid function when a person is low in iodine—a deficiency rare in the U.S.

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Pros & Cons to Eating Soy

+/-Bones: Some studies suggest that because soy isoflavones can mimic estrogen (which helps maintain bone mass), eating soy helps protect against bone loss, particularly in postmenopausal women whose estrogen levels are declining. But recent research doesn’t show any protection.

A yearlong study showed that getting 110 milligrams of isoflavones (about 11⁄2 cups tofu or 1 cup shelled edamame) each day did not prevent bone loss in postmenopausal women. Researchers reviewing 17 studies in peri- and postmenopausal women reached the same conclusion. What’s more, soybeans (like all beans) contain phytic acid, a natural plant substance that interferes with the absorption of bone-building calcium, magnesium and iron.

+/-Breasts: While there have been concerns about soy and breast health, recent research has shown that women who ate as little as one daily serving of whole soyfoods—such as edamame or tofu—throughout childhood and adolescence lowered their breast-cancer risk later in life by as much as 50 percent. Too bad eating soy as an adult doesn’t offer the same protective benefits: “The evidence suggests that adult soy consumption does not decrease risk,” says Messina.

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The Bottom Line About Soy

A little soy each day can be good for you. Most experts recommend eating just one to two servings a day. (One serving = 1⁄2 cup tofu or shelled edamame or 1 cup soymilk.) You can be a bit more liberal with fermented soyfoods like tempeh and miso as fermentation helps neutralize the calcium-interfering phytic acid in soy.

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