There are twenty different amino acids and it is these twenty molecules that our bodies use to build proteins.
Eight of these twenty amino acids are essential nutrients making it imperative to our health that we obtain these eight from our diets because all twenty must be available in the body in order for it to use any of them.
All animal products contain ample amounts of all twenty amino acids because animals use the same twenty amino acids to build their proteins as we do.
Also, combining any grain with any legume will deliver all eight essential amino acids. Most grain based cultures have intuited this; in Mexican foods rice and beans are staples, chickpeas and whole wheat in Middle Eastern foods, and soy beans and rice in Asian cuisines.