Soy: The Up and Coming Bean

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Vegetarians have always known about the low-fat, high-protein soybean—the one bean that contains all of the amino acids essential to the healthy functioning of the human body. Recent research, though, has catapulted the humble bean and products made from it into a health spotlight that’s glaring enough to have generated its own backlash.

Last fall, soy got a boost when the U.S. Food and Drug Administration (FDA) announced that products rich in soy protein could carry labels stating that the products may help lower cholesterol and reduce the risk of heart disease. According to its website, the FDA made its decision after reviewing dozens of controlled clinical studies showing that a low-fat, low-cholesterol, soy-rich diet (containing 25 g or more of soy protein a day) could benefit the heart. Additional research indicates that soy might help prevent some cancers, protect against osteoporosis, and reduce menopausal symptoms such as hot flashes.

Recently, though, conflicting studies have muddied the waters in terms of understanding exactly how soy affects the body. Most health professionals say that the benefits of soy are indisputable but that more research is needed to pinpoint how soy works and to determine who will benefit and who should refrain from eating soy. What is also required, they say, is a common-sense approach.

“There are no miracle foods,” says Marilynn Schnepf, Ph.D., R.D., and chair of the Department of Nutritional Science and Dietetics at the University of Nebraska—Lincoln. Soy, however, is “certainly a good addition to anyone’s diet. It is a high-quality protein and contains those isoflavones that we’re just starting to understand.”

Some practitioners fear that overconsumption of soy supplements—not soy foods—could backfire in some people, particularly postmenopausal women or women with a family history of breast cancer. 

Researchers believe that isoflavones act as weak, estrogen-like compounds in the human body. Naturally occurring estrogen—whether it’s made in your body or harvested from animals—can promote breast cancer. But scientists speculate that soy isoflavones, particularly two of them, genistein and daidzein, may offer estrogen’s benefits of reduced menopausal symptoms and bone protection without the cancer risks that estrogen carries.

Researchers also suspect that isoflavones are the key to soy’s potential ability to prevent other hormone-related cancers, including prostate cancer in men and possibly ovarian cancer in women.

Soy’s potential problems

However, some practitioners fear that overconsumption of soy supplements—not soy foods—could backfire in some people, particularly postmenopausal women or women with a family history of breast cancer. (The studies responsible for raising this concern involved products with concentrated soy isoflavones, including soy powder, a soy beverage, and isolated genistein—not soy foods such as tofu or tempeh.) Experts fear that such oversupplementation could actually stimulate the growth of cancer cells.

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