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Soy

Definition

The soybean has been a part of the human diet for almost 5,000 years. Unlike most plant foods, the soybean is high in protein and is considered equivalent to animal foods in terms of the quality of the protein it contains.

Function

Soy in your diet can lower cholesterol. There are many scientific studies that support this conclusion. In fact, the U.S. Food and Drug Administration (FDA) agreed that 25 grams per day of soy protein, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.

Soy may also reduce symptoms of menopause and the risk of osteoporosis. Soy products may possibly prevent certain hormone-dependent cancers, including breast cancer, endometrial cancer, and prostate cancer.

Food Sources

Not all soy protein products contain the same amount of protein. The following list ranks some popular products from greatest amount of soy protein to lowest:

  • Soy protein isolate (added to many soy food products, including soy sausage patties and soybean burgers)
  • Soy flour
  • Whole soybeans
  • Tofu

The best way to find out about protein content is to look on the product's Nutrition Facts label to see the percentage of soy protein. Also look at the list of ingredients. If a product contains isolated soy protein (or soy protein isolate), the protein content should be fairly high.

Some products also list how many grams of soy protein are in one serving of the product.

Note: There's a difference between soy supplements (commonly sold in tablets or capsules) and soy protein products. Soy supplements are generally made of concentrated soy isoflavones. These substances may help relieve symptoms of menopause but there is not enough evidence to support using soy isoflavones for any of the other health benefits, such as lowering cholesterol.

Side Effects

For individuals who are not allergic to soy, no serious short-term or long-term side effects have been reported from eating soy foods.

Common mild side effects include stomachaches, constipation, and diarrhea.

Soybeans also contain moderate amounts of a natural substance called purine. Consuming large amounts of purines can make gout worse. Persons with gout should not eat a lot of soy products.

Recommendations

In adults, 25 grams per day of soy protein may reduce the risk of heart disease.

Soy foods and soy-based infant formula are widely used in children, but no studies have shown whether isolated soy protein or isoflavone supplements are useful or safe in this population. Therefore, isolated soy products are not recommended for children at this time.

References

Sacks FM, Lichtenstein A, Van Horn L, Harris W, Kris-Etherton P, Winston M. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006 Feb 21;113(7):1034-44. Epub 2006 Jan 17.

Hasler CM. Position of the American Dietetic Association: Functional foods. J Am Diet Assoc. 2004;104(5): 814-26.

Nedrow A, et al. Complementary and alternative therapies for the management of menopause-related symptoms: a systematic evidence review. Arch Intern Med. 2006 Jul 24;166(14):1453-65.


Review Date: 5/3/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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