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.
Latin Names—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
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
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.
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.
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.
Soy. Natural Medicines Comprehensive
Database Web site. Accessed on January 2, 2007.
Soy (Glycine max [L.]
Merr.). Natural Standard Database Web site. Accessed on January 2, 2007.
For More Information
“What’s in the Bottle? An Introduction to Dietary
“Herbal Supplements: Consider Safety, Too”
Toll-free in the U.S.: 1-888-644-6226
TTY (for deaf and
hard-of-hearing callers): 1-866-464-3615
CAM on PubMed
Web site: nccam.nih.gov/camonpubmed/
NIH Office of Dietary Supplements
Web site: ods.od.nih.gov
NIH National Library of Medicine’s MedlinePlus
Soy Listing: www.nlm.nih.gov/medlineplus/druginfo/natural/patient-soy.html