Introduction
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.
This fact sheet highlights what is known about soy when used by adults
for health purposes.
Common Names—soy
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 (a condition in which bones become thin
and brittle), 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 on January 2, 2007.
Soy (Glycine max [L.] Merr.). Natural Standard Database Web site. Accessed on January 2, 2007.
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.
NCCAM Publication No. D399
October 2007
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