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Soy

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Updated July 10, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

A plant in the protein family, soy (Glycine Max) produces seeds known as soybeans. Soybeans contain protein, vitamins, minerals, fiber and isoflavones (estrogen-like compounds thought to offer various health benefits).

Soybean-based foods include tofu, soy milk, tempeh and miso. Soy also is available in supplement form.

Health Benefits of Soy

Scientific studies show that soy may be beneficial in treatment of the following conditions:

1) High Cholesterol

Research indicates that intake of soy protein may slightly lower levels of LDL ("bad") cholesterol. For instance, a 2004 study of 1,033 people concluded that moderate intake of soy-based foods as part of a regular diet is associated with favorable blood cholesterol concentrations.

2) Hot Flashes

Although results have been inconsistent, some studies have demonstrated that soy isoflavone supplements may reduce hot flashes in women going through menopause.

According to the National Center for Complementary and Alternative Medicine, there is not enough scientific evidence to determine whether soy supplements are effective for any conditions besides high cholesterol and hot flashes. However, preliminary research suggests that soy may slow bone density loss and protect against osteoporosis.

Soy and Breast Cancer

A meta-analysis published in 2006 concluded that soy intake may be associated with a small reduction in breast cancer risk. However, the study's authors caution that "recommendations for high-dose isoflavone supplementation to prevent breast cancer or prevent its recurrence are premature," partly due to experimental studies suggesting certain adverse effects caused by soy.

Until more is known about soy's possible role in breast cancer risk, the National Center for Complementary and Alternative Medicine recommends that women who have or who are at increased risk of developing breast cancer (or other hormone-sensitive conditions) discuss their use of soy with their health care providers.

Common Uses for Soy

Soy is purported to help treat these health problems:

  • high cholesterol
  • cardiovascular disease
  • menopausal symptoms
  • osteoporosis
  • memory problems
  • breast cancer
  • prostate cancer

In addition, soy is said to be useful in cancer prevention.

Side Effects of Soy

Although soy is generally considered safe for most people when consumed as a food (or taken for short periods as a supplement), it may cause a number of adverse effects (including nausea, bloating, and constipation.

Is Soy Safe?

The safety of long-term use of soy isoflavones has not been established, according to the National Center for Complementary and Alternative Medicine. If you're considering the use of soy in treatment of a specific health condition, make sure to consult your doctor first.

Sources:

Marini H, Minutoli L, Polito F, Bitto A, Altavilla D, Atteritano M, Gaudio A, Mazzaferro S, Frisina A, Frisina N, Lubrano C, Bonaiuto M, D'Anna R, Cannata ML, Corrado F, Adamo EB, Wilson S, Squadrito F. "Effects of the phytoestrogen genistein on bone metabolism in osteopenic postmenopausal women: a randomized trial." Ann Intern Med. 2007 19;146(12):839-47.

National Center for Complementary and Alternative Medicine. "Soy [NCCAM Herbs at a Glance]" [link: http://nccam.nih.gov/health/soy/]. NCCAM Publication No. D399. Created October 2007.
Updated March 2008.

Rosell MS, Appleby PN, Spencer EA, Key TJ. "Soy intake and blood cholesterol concentrations: a cross-sectional study of 1033 pre- and postmenopausal women in the Oxford arm of the European Prospective Investigation into Cancer and Nutrition." Am J Clin Nutr. 2004 80(5):1391-6.

Trock BJ, Hilakivi-Clarke L, Clarke R. "Meta-analysis of soy intake and breast cancer risk." J Natl Cancer Inst. 2006 5;98(7):459-71.

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