Protein is made up of essential and non - essential amino acids. A chain of amino acids is called a polypeptide. The human body can make the non - essential amino acids, whereas the essential amino acids must be ingested through food.
Protein is found in food, and is most highly concentrated in animal sources than other sources.
It is digested by the human body, and broken down into its amino acid components, beginning in the stomach. An enzyme disassembles the protein polypeptide chains into smaller components, which are broken down again and again in order to facilitate the digestion process. Once the protein has been broken down sufficiently, it can be absorbed and stored for the body to use. Protein can be inefficiently used as energy by converting amino acids to glucose, but it is primarily used by the body to build and repair tissues. If too much protein is taken in, the excess may be stored as fat.