Should You Eat Soy?

I came late to soy, the Julia Roberts of the nutrition scene. I was drawn first to chocolate Tofutti, then sucked in by miso soup. Pretty soon, edamame replaced popcorn as my late-night Law & Order snack, and I even learned to like the hard stuff, tossing tofu into salads and scrambled eggs. Thanks to all the glowing health benefits attributed to the legume, which had racked up about 7,000 medical-research citations, soy was the little black dress of the American health-food set: It could make everybody look—or feel, at least—like Pretty Woman.

Here's why: The only common plant food that contains complete protein, soy—popular in China for at least 5,000 years—is also fortified with ninja-like isoflavones. These are phyto (plant) estrogens very similar to, albeit far less potent than, estradiol, the mammalian estrogen human beings produce. Soy has been proven to reduce the risk of coronary heart disease. It's proven promising in promoting bone health. Over the years, various studies have linked soy to breast-cancer prevention both in animal studies and in large-scale epidemiological research, which has found lower breast-cancer rates linked to soy consumption among Asian women. In 1990, the year Pretty Woman was released, a National Cancer Institute workshop identified no fewer than five potential anticarcinogens in soybeans.

Soy has special allure among women in their forties and fifties: Marketers tout it as a natural remedy for menopause symptoms, including night sweats, hot flashes and even forgetfulness. With so many Baby Boomers marching toward menopause, soy is a star—especially since the Women's Health Initiative linked conventional hormone replacement therapy to breast cancer and stroke. (In 2002, the National Institutes of Health halted its estrogen-plus-progestin trials, citing breast-cancer risks; within months, increased risks of dementia were established. And in 2004, NIH halted its estrogen-alone research, citing a greater likelihood of stroke and deep-vein blood clots, usually in the legs). By 2003, the most recent year for which data is available, Americans were spending $3.9 billion on soy-based food products.

But, like movie stars, vegetables can stay on top for only so long. Now there are hints that soy might have a downside. For instance, in women who have had breast cancer, some researchers speculated that soy, like estradiol, might actually encourage cancer cells to grow. In addition, one study found that soy phytoestrogen reduced sexual drive in rats; another linked soy to endometrial hyperplasia, a condition that causes abnormal vaginal bleeding. And those who ate vegetarian for environmental as well as health reasons had to consider the damage done by industrial soy farms (see sidebar, below right).

With all that in mind, should you eat soy? You betcha, especially if you like it. Just keep your intake at reasonable levels—no more than a few servings a day. But do make sure you let your doctor know, since it may affect her decision to prescribe hormone or calcium supplements. And there are two important caveats:

*Check with your doctor if you have had breast cancer; some scientists worry that when soy is consumed in large amounts, its weak estrogenic effect may raise the risk of recurrence.

*Steer clear of soy supplements: "We just don't know enough about them to know if they are safe," says Melanie Polk, R.D., director of nutrition education for the American Institute for Cancer Research.

In other words, eat soy moderately, as you would other foods. Don't treat it as a drug. Below, a case-by-case soy strategy.

If you want to . . .

Lower cholesterol: Eat up. The Food & Drug Administration says that 25 grams of soy protein a day can raise the levels of high-density lipoprotein (HDL)—aka "good"—cholesterol. In a study of 65,000 Shanghai women, those who ate 11 grams of soy protein a day were 86 percent less likely to have a heart attack.

Prevent breast cancer: While there's still no conclusive evidence that adult women can eat soy and lower their risk of breast cancer, says Polk, "it does appear that lifetime soy intake, as is true in Asian populations, may in fact be protective against breast cancer, especially when soy intake starts at an early age." What's more, she points out, soy is a plant-based food, "and we have evidence that a moderate amount of soy may be protective against a variety of cancers."

If you've got a teenage girl, do turn her on to tofu: A study published in Carcinogenesis found that Asian-American women who ate soy four times a week or more during adolescence and adulthood were nearly 50 percent less likely to develop breast cancer than those who ate soy less than once a month.

Battle cancer: If you have had or currently have an estrogen-dependent cancer—including breast or ovarian cancer—talk to your doctor about eating soy. "There's at least a theoretical concern that soy could actually promote the cancer's growth," says Nanette Santoro, M.D., a reproductive endocrinologist at Albert Einstein College of Medicine in New York and a member of the North American Menopause Society. This is especially important if you're taking Tamoxifen: Some researchers have found preliminary evidence that soy may interfere with the drug's effect on cancer cells; others have found that it might be beneficial.

Lose weight: Go easy! People often assume that all vegetables are low in fat, but soy isn't. A single serving of Edensoy Extra Vanilla, for example, has 150 calories and 40 mg of isoflavones. Although switching to the equally tasty Light version will save you 30 calories, you'll also get only 15 mg of isoflavones.

Strengthen bones: The research on bone health is promising. Do try to love tofu: Because it's often processed with calcium sulfate, it's generally a rich source of calcium (equivalent to milk).

Manage menopause symptoms: Although it won't hurt to try tempeh, soy's power to tame the change has been somewhat overrated. "At most, studies found that hot flashes were reduced from about 8 to 5 a day," says Santoro. But some women may well find that helpful.

The upshot? Okay, so maybe soy isn't Pretty Woman, the miracle food of the millennium. How about Notting Hill? Pass the edamame, please.