Patient Information
By Phyllis Woodson, MS, RD, CDE

Soy is one of the most versatile foods. It has been reported that only about two percent of the estimated two billion bushels of soybeans grown in the US is consumed as human food. The remainder is used for products including livestock feed, soaps, glue, bottle caps, pencils, paint, plastics, and detergents.

Can we appreciate soy more as a health food? Over time some studies have suggested that soy may be helpful in reducing your risk for certain diseases including heart disease, cancer, osteoporosis, and even decreasing the symptoms of menopause. More research, however, is needed to confirm these claims.

Soy protein contains phytoestrogens and isoflavones, nutrients that may have estrogen-like effects. Phytoestrogens have been likened to a weak form of plant estrogen. It has been suggested that the effectiveness of isoflavones can be enhanced by a daily intake of soy foods containing about 50 mg of isoflavones (3/4 cup soybeans), the amount consumed in the traditional Japanese diet. The potential effects of these substances are wide-ranging and require further scientific study. The following are some claims from studies and reports:

Heart Disease

Some studies have reported that isoflavones in soy protein may lower LDL or low density lipoprotein (bad cholesterol) and raise HDL or high density lipoprotein (good cholesterol). Isoflavone may have an antioxidant effect similar to that of vitamin C. Some studies report that phytosterol, a plant's counterpart to cholesterol, may help lower cholesterol levels by reducing cholesterol absorption. Soybeans are an excellent source of phytosterols.

Cancer

Some studies report that isoflavones in soy may inhibit the growth of breast, endometrial, prostate, and colon cancers. These studies report that phytosterols may reduce colon cancer risk. High levels of estrogen have been related to escalated risks for breast cancer and other hormone-related cancers. By mimicking and interfering with estrogen, these studies report that isoflavone may prevent estrogen from binding to cell receptors and thereby inhibit the cancer process.

Osteoporosis

Soy protein contains less sulfuric amino acids and phosphorus than animal proteins. Large amounts of sulfur and phosphorus can cause the body to lose calcium, one of the most important minerals in retaining healthy bones. Some studies report that isoflavone in soy may inhibit bone loss and stimulate bone formation. This may reduce the risk for osteoporosis, the bone-thinning process so common in postmenopausal women. Preliminary reports suggest that daily consumption of about 40 grams of soy protein (1 cup soymilk) may increase bone density, yet well-controlled studies are needed to confirm these claims.

Menopause

Studies claim that isoflavone in soy foods may relieve symptoms of menopause, including vaginal dryness and the inability to regulate body temperature, which often leads to sweats and hot flashes. Hot flashes occur in a significant number of pre- and perimenopausal women. Some studies have suggest that 80 mg of isoflavones (about 1 cup of tofu) per day may reduce the frequency of hot flashes.

There are no well-controlled studies documenting the safety or appropriate dosage of soy in the prevention or treatment of the above health issues. Many scientists and physicians are concerned about the lack of scientific evidence regarding how little soy, for example, may be necessary to reduce hot flash symptoms but not present a risk for breast or endometrial cancer. Since we are unsure how much soy is needed to provide a beneficial response without a potentially harmful response, no specific dosage can be safely recommended. Remember, just because a product is sold at a grocery or health food store, doesn't mean that the product is safe.