Question: Soy products have been the protein source for people with prostate cancer. Yet lately, soy has been thought to be bad for this type of cancer. What are your thoughts?

Answer: On balance, soy is a wonderful food for people with prostate cancer and for those trying to prevent it.

Earlier this year, for example, researchers at Harvard Medical School presented their findings from a new study showing that mice inoculated with cancer cells had their tumors sharply reduced with a soy diet. After eight weeks, tumor size was reduced by 68%, and the spread of tumors to lymph nodes reduced by 50% in the soy-treated mice, compared to the untreated group.

A study tracking 12,395 Seventh-day Adventist men found that those who drank soy milk more than once a day were 70% less likely to get prostate cancer. Estrogen promotes cancers of the prostate, breast, ovaries, and endometrium, and soy may diminish estrogen's activity. The phytoestrogens in soy have a structure similar to that of regular estrogen, so the soy phytoestrogens bind to the estrogen receptors but do not turn these receptors on to the same degree as regular estrogen. Once the soy phytoestrogens bind to these receptors, they keep regular estrogen from binding to it, thereby lessening estrogen's effects.

Soy products also can reduce cholesterol levels and promote healthy hearts. When you switch from eating a cheeseburger to a soy burger, for example, you get a double benefit: you're not eating the large amounts of saturated fat, cholesterol, and animal protein found in the cheeseburger and you're getting additional benefits from the soy protein itself.

Nutrition expert Andrea Dunn of the Cleveland Clinic's department of nutritional services says, "People should get on the bean -- the soybean -- and get in on soy's health benefits.''

Evidence that soy can lower cholesterol is so strong the Food and Drug Administration now allows the claim on food labels. (The FDA says: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.") A new study at Wake Forest University Baptist Medical Center in North Carolina found that a daily soy beverage containing 37 milligrams of isoflavones (the amount in 1 1/2 cups of soy milk) lowered high cholesterol by 8%. A daily drink with 62mg isoflavones decreased cholesterol 9%, but a drink with 27mg isoflavones had no benefit.

The higher your cholesterol, the greater the impact. A recent review of 38 studies in The New England Journal of Medicine showed that soy protein (average 47 grams daily) depressed high cholesterol (above 335) by 24%, compared with 8% when cholesterol was 200 or less. Soy worked regardless of levels of dietary fat.

While the phytoestrogens and isoflavones bind to the estrogen receptors and only weakly stimulate these receptors (and keep regular estrogen from more strongly turning them on), too much of even the weakly-stimulating phytoestrogens and isoflavones may be unwise. One study showing that women who took purified isoflavones in pill or powder form consumed excessive amounts of these and thus increased their risk of breast cancer. If you have breast cancer, it's probably a good idea to eat soy but avoid purified isoflavone supplements, keeping under 25-50 mg of isoflavones per day.

Several years ago, I began using nonfat soy milk in place of cow's milk on my breakfast cereal. You can add tofu cubes to salads, stews, soups, and casseroles. Tofu takes on the flavor of whatever else is in the dish, so you can substitute it for meat in most recipes.

An excellent discussion of the benefits of soy and prostate cancer can be found in Dr. Bob Arnot's book, The Prostate Cancer Prevention Book.

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