These include common bean, caraota, feijao, french bean, kidney bean, haricot bean, field bean, poroto, snap bean, string bean, frijol, and wax bean. One different food species is the tepary bean, P. acutifolius , native to the Southwest U.S. and Mexico, a heat tolerant and drought resistant plant, that was an important part of the Native American diet. The center of origin of beans is obscure, with some experts citing the Mediterranean area, and others claiming South America. Bean fossils have been found in Egyptian tombs, American caves, and Asian prehistoric sites. The beans used for human food are separated into two broad agronomical categories, green and dry.
All beans are annuals.
The plants produce pods which contain the seeds. While beans are inexpensive, easy to prepare, tasty, and loaded with protein and carbohydrates, many humans avoid them because of the problem of intestinal gas. Gas is caused by the body's inability to digest the complex carbohydrates found in beans. Before any carbohydrate can be absorbed from the intestines into the bloodstream, it must be broken down into a single sugar. If it can't be broken down, it can't be absorbed, and will pass whole into the lower intestinal tract where bacteria ferment it, causing gas.