D

Soy 

This fact sheet provides basic information about soy—uses, potential side 

effects, and resources for more information. 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. The following information highlights what is known about soy when 

used by adults for health purposes. 

Common Name—soy 

Latin Name—Glycine max 

What It Is Used For 

People use soy products to prevent or treat a variety of health conditions, 

including high cholesterol levels, menopausal symptoms such as hot flashes, 

osteoporosis, memory problems, high blood pressure, breast cancer, and 

prostate cancer. 

How It Is Used 

•	 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 is supporting ongoing studies of soy, including its effects on 

women’s arteries and bones after menopause. 

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 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. This will help ensure 

coordinated and safe care. 

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):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 http://www.naturaldatabase.com on 

January 2, 2007. 

Soy (Glycine max [L.] Merr.). Natural Standard Database Web site. Accessed at http://www.naturalstandard.com on 

January 2, 2007. 

For More Information 

Visit the NCCAM Web site at nccam.nih.gov and view:

•	 What’s in the Bottle? An Introduction to Dietary Supplements at nccam.nih.gov/health/bottle/ 

•	 Herbal Supplements: Consider Safety, Too at nccam.nih.gov/health/supplement-safety/ 

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 

CAM on PubMed 

Web site: nccam.nih.gov/camonpubmed/ 

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 March 2008 

D399