Soy is a subtropical plant native to southeastern Asia. This member of the pea family (Fabaceae) grows from 1-5 feet tall and forms clusters of 3-5 pods that each contain 2-4 beans. Soy has been a dietary staple in Asian countries for at least 5,000 years. During the Chou dynasty in China (1134-246 B.C.), fermentation techniques were discovered that allowed soy to be prepared in more easily digestible forms such as tempeh, miso, and tamari soy sauce. Tofu was invented in 2nd Century China. Soy was introduced to Europe in the 1700s and to the United States in the 1800s. Large-scale soybean cultivation began in the United States during World War II. Currently, Midwestern U.S. farmers produce about half of the world's supply of soybeans. Soy and components of soy called "isoflavones" have been studied for many health conditions. Isoflavones (such as genistein) are believed to have estrogen-like effects in the body, and as a result, they are sometimes called "phytoestrogens." In laboratory studies, it is not clear if isoflavones stimulate or block the effects of estrogen or both (acting as "mixed receptor agonists/antagonists").