Soy's Not All Bad
But if some studies point to dangers from soy, others suggest important benefits. For instance, isoflavones may prevent the growth of estrogen-dependent breast cancer cells, according to findings published in the March 2000 issue of the journal Cancer Research. That's because isoflavones appear to encourage the body to break down estrogen more quickly -- before it can stimulate cancer cells to grow. Instead of lingering in the blood, bits and pieces of estrogen molecules wind up in the urine.
Isoflavones can also slow prostate cancer cells from growing, according to a study published in the June 2000 issue of the International Journal of Oncology. Other studies hint that eating soy may help prevent heart disease, endometriosis, and even osteoporosis in women, Gillespie says. However, if you think you may have any of these conditions, see your doctor before making any substantive changes to your diet.
Soy's biggest impact is on cholesterol levels, according to a mound of studies. One published in the December 1998 issue of the American Journal of Clinical Nutrition found that men who ate a low-fat diet and relied on soy as their main protein source for five weeks saw their "bad" (LDL) cholesterol levels decrease by as much as 14% and their "good" (HDL) levels increase by as much as 8%. Men who ate a low-fat diet but instead relied on meat as protein also saw their cholesterol levels significantly improve, though not as much as the soy-eaters.
In the Kitchen
So what's the verdict on soy? Health experts say that although there's no need to give up your favorite frosty shake made with soft tofu, frozen strawberries, and a dab of honey, you may not want to eat soy for breakfast, lunch, and dinner. Yet there's nothing wrong with incorporating soy into a healthy diet of fruits, vegetables, and whole grains.
Messina, for instance, recommends a daily serving of soy: perhaps 1 cup of soy milk or 3 to 4 ounces of tofu. "If 20 years from now researchers don't find any benefits to soy, then you've lost nothing," Messina says. "If they do find some benefits, then you've got a great trade-off."
As for my grandma, she successfully fought off breast cancer at the age of 80, and she couldn't be healthier now at 93. She still memorizes Bible passages and spends afternoons sweating to the beat of an exercise video. Researchers can't tell her what role, if any, soy has played in her life and health. It doesn't, however, seem to have done her any harm.