Soy

© Steven Foster

This fact sheet provides basic information about soy—common names, 

what the science says, potential side effects and cautions, and 

resources for more information. The following information highlights 

what is known about soy when used by adults for health purposes.

Common Name—soy

Latin Name—Glycine max

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. 

Traditional or folk uses of soy products include menopausal symptoms, 

osteoporosis, memory problems, high blood pressure, high cholesterol 

levels, breast cancer, and prostate cancer.

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.

What the Science Says 

• 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.

• NCCAM supports studies on soy, including its effects in 

cardiovascular disease and breast cancer, and on menopauserelated symptoms and bone loss.
Side Effects and Cautions 

• Soy is considered safe for most people when used as a food or when taken for short periods as a 

dietary supplement.

• 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). Studies show no effect of dietary 

soy on risk for endometrial hyperplasia.

• 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 all your health care providers about any complementary health practices you use. Give them a 

full picture of what you do to manage your health. This will help ensure coordinated and safe care. 

For tips about talking with your health care providers about complementary and alternative 

medicine, see NCCAM’s Time to Talk campaign at nccam.nih.gov/timetotalk/. 

Sources

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):98-108.

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 www.naturaldatabase.com on July 23, 2009.

Soy (Glycine max [L.] Merr.). Natural Standard Database Web site. Accessed at www.naturalstandard.com on July 23, 2009.

For More Information

Visit the NCCAM Web site at nccam.nih.gov and view Using Dietary Supplements Wisely

(nccam.nih.gov/health/supplements/wiseuse.htm).

NCCAM Clearinghouse

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

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

E-mail: info@nccam.nih.gov

PubMed®

Web site: www.ncbi.nlm.nih.gov/sites/entrez

NIH Office of Dietary Supplements

Web site: www.ods.od.nih.gov

This publication is not copyrighted and is in the public domain. Duplication is encouraged.

NCCAM has provided this material for your information. It is not intended to substitute for the medical expertise and advice of 

your primary health care provider. We encourage you to discuss any decisions about treatment or care with your health care 

provider. The mention of any product, service, or therapy is not an endorsement by NCCAM.

National Institutes of Health

♦♦♦

U.S. Department of Health and Human Services

D399

Created October 2007

Updated April 2012