Soy

Background

This fact sheet focuses on the use of soy by adults for health purposes.

Soy, a plant in the pea family, has been common in Asian diets for thousands of years. Soy is also present in modern Western diets as a food and food ingredient.

Soy products are used for menopausal symptoms, bone health, improving memory, high blood pressure, and high cholesterol levels.

In addition to its food uses, soy is available in dietary supplements, in forms such as tablets, capsules, and powders. Soy supplements may contain soy protein, isoflavones (compounds that have effects in the body similar to those of the female hormone estrogen), or other soy components.

How Much Do We Know?

Although there have been many studies on soy products, there are still uncertainties about soy’s health effects.

What Have We Learned?

Consuming soy protein in place of other proteins may lower levels of LDL (“bad”) cholesterol to a small extent.
Soy isoflavone supplements may help to reduce the frequency and severity of menopausal hot flashes, but the effect may be small.

It’s uncertain whether soy supplements can relieve cognitive problems associated with menopause.

Current evidence suggests that soy isoflavone mixtures do not slow bone loss in Western women during or after menopause.

Diets containing soy protein may slightly reduce blood pressure.

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

Current National Center for Complementary and Integrative Health (NCCIH)-funded studies on soy and its components are investigating a variety of topics, including stroke outcomes, anti-inflammatory effects, and effects on diabetes.

What Do We Know About Safety?

Except for people with soy allergies, soy is believed to be safe when consumed in normal dietary amounts. However, the safety of long-term use of high doses of soy extracts has not been established.

The most common side effects of soy are digestive upsets, such as stomach pain and diarrhea.

Long-term use of soy isoflavone supplements might increase the risk of endometrial hyperplasia (a thickening of the lining of the uterus that may lead to cancer). Soy foods do not appear to increase the risk of endometrial hyperplasia.

Current evidence indicates that it’s safe for women who have had breast cancer or who are at risk for breast cancer to eat soy foods. However, it’s uncertain whether soy isoflavone supplements are safe for these women.

Keep in Mind

Tell all your health care providers about any complementary or integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

Key References

-NIH