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. Some studies suggest that soy isoflavone supplements may reduce hot flashes in women after menopause. The safety of long-term use of soy isoflavones has not been established. Soy has been studied as an intervention for hot flashes in patients with cancer.