Is Soy The Recipe For What Ails You?Pam Black
Ever since the humble soybean gained prominence as a health food in the 1970s, its products have found their way into mainstream supermarkets, stacked right next to the heads of lettuce and bunches of parsley. Even former junk-bond king Michael Milken is promoting soy's potential to fight prostate cancer in his book, The Taste for Living Cookbook: Mike Milken's Favorite Recipes for Fighting Cancer. There is also new evidence suggesting that soybean derivatives can protect against heart disease, breast cancer, osteoporosis, and the hot flashes that accompany menopause.
For a long time, nutritionists have suspected that soy-rich diets might explain why Asians have lower rates of heart ailments, reproductive cancers, and menopausal symptoms than Westerners. Over the past decade, scientists have discovered that estrogen-like active ingredients called isoflavones or phytoestrogens may be responsible for soy's health effects.
Using these compounds, researchers have proven that soy has cardiovascular benefits. Soy helps the heart primarily by reducing low-density lipoprotein, or LDL, commonly referred to as "bad" cholesterol. It's not clear how soy works. It may keep LDL from being oxidized to form artery-clogging plaques. It also increases flexibility in the arteries, which stiffen with age.
In one study, researchers at Wake Forest University School of Medicine in Winston-Salem, N.C., fed soy to people on low-fat diets who continued to exhibit moderate to high levels of cholesterol. Among those getting the most soy protein (62 mg of isoflavones), LDL levels dropped by as much as 10%, compared with the 8% drop among subjects who were fed only 37 mg. Those with the highest cholesterol (between 160 and 210) showed the most dramatic results. People with levels above 210 were not included in the study because their condition was risky enough to require drugs.
Soy's effects on cancer are less conclusive. Studies have shown that genistein, the main soy phytoestrogen, can slow cancer-cell growth in test tubes and increase the time it takes for mice exposed to carcinogens to develop prostate tumors. Exposing rats to genistein in the womb or just before puberty protected them from developing breast tumors later. There is debate about whether soy can stimulate cell growth in breast tissue. But most researchers doubt soy has harmful effects.
Soy has great appeal to the large numbers of women in their late 40s and 50s who are approaching menopause. As their estrogen levels decrease, they face increased risk of heart disease, fractures from osteoporosis, and discomfort from hot flashes. These symptoms are usually treated with Premarin, an animal-based estrogen. However, most women don't take because it may increase the risk of breast cancer. Nutritionists think soy phytoestrogens could be a safer alternative.
So far, soy has prevented bone loss in mice whose ovaries have been removed and increased bone density in the lower spines of post-menopausal women. "I'm optimistic, but we need more data from longer tests," says Susan Potter, a senior nutrition scientist at Protein Technologies International, a St. Louis soy producer that funds research. Studies are also ongoing into soy's effects on hot flashes, where "a high placebo effect causes interference," says Tufts University School of Medicine researcher Margot Woods.
All this suggests that adding soy foods to your diet can't hurt. At best, they will live up to their health claims; at the least, they provide a rich source of protein. Based on the typical Asian diet, scientists recommend consuming 7 to 10 grams of soy protein with 30 to 60 milligrams of phytoestrogens a day. "Some amount of soy protein is required for the phytoestrogens to exert cardio-protective benefits," notes Thomas Clarkson, professor of comparative medicine at Wake Forest. "I emphasize that because some pills on the market are just soy phytoestrogens."
Drinks and powders are the most efficient way to add soy to your diet. An 8-ounce glass of soy milk or 1 ounce of soy protein powder provides roughly the recommended daily dose (table). So does about 3 ounces of tofu or tempeh (which some people prefer for its burger-like texture). And for those of you who've always turned up your noses at tofu, there's good news: Soy is available in such guises as hot dogs, burgers, cheeses, and ice cream.