Amaranth has been cultivated as a grain for 8,000 years. The yield of grain amaranth is comparable to rice or maize. It was a staple food of the Aztecs, and was used as an integral part of Aztec religious ceremonies. The cultivation of amaranth was banned by the conquistadores upon their conquest of the Aztec nation. Because the plant has continued to grow as a weed since that time, its genetic base has been largely maintained. Research on grain amaranth began in the US in the 1970s. By the end of the 1970s, a few thousand acres were being cultivated. Much of the grain currently grown is sold in health food shops.