Soy – Know What Herbs Do What

Latin NameGlycine max

Soy - Know What Herbs Do What

Illustration of a soybean plant by Engelbert Kaempfer, 1651-1716, who helped introduce soy to the West.

Soy, a plant in the pea family, has been common in Asian diets for thousands of years. It is found in modern American diets as a food or food additive.


Soybeans, the high-protein seeds of the soy plant, contain isoflavones—compounds similar to the female hormone estrogen. Soy is available in dietary supplements, in forms such as tablets and capsules. Soy supplements may contain isoflavones or soy protein or both.


Soybeans can be cooked and eaten or used to make tofu, soy milk, and other foods. Also, soy is sometimes used as an additive in various processed foods, including baked goods, cheese, and pasta.


The following highlights information about soy when used by adults.


Research on Benefits of Soy


  • Research suggests that daily intake of soy protein may slightly lower levels of LDL ("bad") cholesterol.


  • Some studies suggest that soy isoflavone supplements may reduce hot flashes in women after menopause. However, the results have been inconsistent.


  • There is not enough scientific evidence to determine whether soy supplements are effective for any other health uses.


  • The National Center for Complementary and Alternative Medicine (NCCAM) supports studies on soy, including its effects in cardiovascular disease and breast cancer, and on menopause-related symptoms and bone loss.


Side Effects and Cautions Summary

Soy - Know What Herbs Do What


  • Minor stomach and bowel problems such as nausea, bloating, and constipation are possible.


  • Allergic reactions such as breathing problems and rash can occur in rare cases.


  • The safety of long-term use of soy isoflavones has not been established. Evidence is mixed on whether using isoflavone supplements over time can increase the risk of endometrial hyperplasia (a thickening of the lining of the uterus that can lead to cancer).


  • Soy’s possible role in breast cancer risk is uncertain. Until more is known about soy’s effect on estrogen levels, women who have or who are at increased risk of developing breast cancer or other hormone-sensitive conditions (such as ovarian or uterine cancer) should be particularly careful about using soy and should discuss it with their health care providers.


  • Tell your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health to help ensure coordinated and safe care.  Complementary or alternative therapy should not be used in place of conventional medical care or to delay seeking that care.




  • Balk E, Chung M, Chew P, et al. Effects of Soy on Health Outcomes. Evidence Report/Technology Assessment no. 126. Rockville, MD: Agency for Healthcare Research and Quality; 2005. AHRQ publication no. 05-E024-1.
  • Low Dog T. Menopause: a review of botanical dietary supplements. American Journal of Medicine. 2005;118(suppl 12B):98S–108S.
  • Sacks FM, Lichtenstein A, Van Horn L, et al. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006;113(7):1034–1044.
  • Soy. Natural Medicines Comprehensive Database Web site. Accessed at on July 23, 2009.
  • Soy (Glycine max [L.] Merr.). Natural Standard Database Web site. Accessed at on July 23, 2009.


For More Information



NCCAM Clearinghouse


The NCCAM Clearinghouse provides information on CAM and NCCAM, including publications and searches of Federal databases of scientific and medical literature. The Clearinghouse does not provide medical advice, treatment recommendations, or referrals to practitioners.


Toll-free in the U.S.: 1-888-644-6226


TTY (for deaf and hard-of-hearing callers): 1-866-464-3615


Web site:
E-mail: Contact NCCAM
NIH Office of Dietary Supplements
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Source: National Center for Complementary and Alternative Medicine, Soy Fact Sheet,
Created October 2007, Updated July 2010



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