The soybean (also called soja or soya bean) is an annual legume cultivated in many types of soil. A branching plant ranging in height from several centimeters to over 2 meters, the soybean has broad, heart-shaped leaves and white or pale-purple blossoms. At maturity, the plant bears irregular, oblong pods containing one to four seeds a piece. The seeds (soybeans), which may be yellow, green, brown, black, or bicolored, are a staple in the diet of people and animals in many parts of the world. Soybeans were introduced into the United States in 1804, and became a major agricultural commodity by the mid-20th century. By the 1980s, the U.S. became the world's leading soybean producer, followed by Brazil and China. Ninety-eight percent of the U.S. crop is used for livestock feed.
Although the origins of the modern soybean plant remain obscure, many botanists believe it is a derivative of Glycine ussuriensis, a legume native to central China. For more than 5,000 years, the Chinese have used soy as a food and for medicinal purposes. Over the years, soy has proven to be a remarkably versatile food, and it is now consumed in a variety of forms including soy milk, tofu, tempeh, miso, soy flour, concentrated soy protein, and soy sauce. Soybean oil can be processed to make food products such as shortening, margarine, and vegetarian cheese, and industrial products such as ink, paints, fertilizers, and adhesives.
Commonly used as a meat substitute because of their high protein content, soybeans are also rich in lecithin, potassium, phosphorus, magnesium, and iron; and contain significant amounts of thiamin, riboflavin, niacin, and vitamin C. In addition to these basic nutrients, soybeans contain compounds called isoflavones, which have been shown to have unique biological activity. The two best-known soy isoflavones, genistein and daidzein, are often referred to as "phytoestrogens" because of their estrogen-like activity in the body.
Soy is consumed widely as a food and has not been associated with any toxicity. Daily soy intake providing the equivalent of 25 grams soy protein or more are recommended for lowering cholesterol levels.