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Soy ; Soy Protein Extract; Hydrolyzed Soy Protein; Soy Protein

Proposed Uses: High Cholesterol; Allergic Rhinitis (Shoyu Polysaccharides); Cancer Prevention; Cyclic Mastitis; High Blood Pressure; Menstrual Migraines; Menopausal Symptoms; Osteoarthritis; Osteoporosis

The soybean has been prized for centuries in Asia as a nutritious, high-protein food with a myriad of uses, and today it's popular in the United States not only in Asian food, but also as a cholesterol-free meat and dairy substitute in traditional American foods. Soy burgers, soy yogurt, tofu hot dogs, and tofu cheese can be found in a growing number of grocery stores alongside the traditional white blocks of tofu, and soy is increasingly used as a protein filler in many prepared foods, including fast-food “hamburger.”

Soy appears to reduce blood cholesterol levels, and the U.S. Food and Drug Administration has authorized allowing foods containing soy to carry a "heart-healthy" label.

Soybeans contain isoflavones, chemicals that are similar to estrogen. These are widely thought to be the active ingredients in soy, although, as discussed below, there is substantial evidence that other constituents may be equally or more important.

Therapeutic Dosages
The FDA allows soy foods containing 6.5 grams of soy to carry a heart-healthy label. Evidence suggests that a daily intake of 25 g of soy protein is adequate to noticeably reduce cholesterol. This amount is typically found in about 2 1/2 cups of soy milk or 1/2 pound of tofu.

NOTE: Soy is increasingly added to foods in the U.S. as a protein filler, and there are concerns that some people here may be greatly exceeding the amount of soy eaten anywhere else in the world. Even the 25 g amount recommended for reducing cholesterol levels is relatively high. For comparison, in Asia, the average intake of soy is only about 10 g daily.

Therapeutic Uses
According to the combined evidence of numerous controlled studies, soy can reduce blood cholesterol levels and improve the ratio of LDL ("bad") versus HDL ("good") cholesterol. At an average dosage of 47 g daily, total cholesterol falls by about 9%, LDL cholesterol by 13%, and triglycerides by 10%. Soy's effects on HDL cholesterol itself are less impressive. Soy might also reduce blood pressure.

Soy may reduce the common menopausal symptom known as "hot flashes," but study results conflict. Soy has not been found helpful for improving the hot flashes that often occur in breast cancer survivors.

Unlike estrogen, soy appears to reduce the risk of uterine cancer. Its effect on breast cancer is not as well established, but there are reasons to believe that soy can help reduce breast cancer risk as well possibly by reducing estrogen levels and lengthening the menstrual cycle.

Safety Issues
Studies in animals have found soy essentially nontoxic. However, soy or its isoflavones could conceivably have some potentially harmful effects in certain specific situations.

Soy appears to have numerous potential effects involving the thyroid gland. When given to individuals with impaired thyroid function, soy products have been observed to reduce absorption of thyroid medication. In addition, some evidence hints that soy isoflavones may directly inhibit the function of the thyroid gland, although this inhibition may only be significant in individuals who are deficient in iodine.

Individuals with impaired thyroid function should not take large amounts of soy products except under the supervision of a physician.

One study found that soy products may decrease testosterone levels in men. This could conceivably cause problems for men with infertility or erectile dysfunction.

Soy may reduce the absorption of the nutrients zinc, iron, and calcium. To avoid absorption problems, you should probably take these minerals at least 2 hours apart from eating soy.

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