Amino acids, often referred to as the building blocks of proteins, are compounds that play many critical roles in your body. Amino acids are concentrated in protein-rich foods such as meat, fish, and soybeans. The elements present in every amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N); in addition sulfur (S) is present in the side chains of cysteine and methionine, and selenium (Se) in the less common amino acid selenocysteine.