Proteins are the building blocks of muscle, enzymes, and sonic hormones. They are made up of amino acids and are essential for growth and repair in the body. A gram of protein contains four calories. Those from animal sources contain the essential amino acids. Those from vegetable sources contain some but not all of the essential amino acids. Proteins are broken up by the body to produce amino acids.
digestible food components containing nitrogen composed of amino acids; protein is essential for tissue repair and growth and provides four calories per gram.