Definition: An amino acid is a molecule that is the basic ingredient necessary to create a protein. Amino acids link together in long chains to form proteins. Some amino acids are created by the body, but others can only be obtained by eating foods that contain them, such as meat, dairy products, or beans. Amino acids -- used both as the basic building blocks of proteins and an alternative source of energy in cells -- are necessary to all cells of all known living things. Inadequate intake of amino acids (and/or protein) can have extremely serious health consequences.