Proteins are 1 of the 3 primary macronutrients in the body and are synthesized from individual building blocks called amino acids (AAs). Amino acids are bound together by peptide bonds, which link the amino end of one AA to the carboxy end of the next AA, generating a protein's primary structure. The strand of AAs then undergoes additional folding, ultimately generating complex 3-dimensional structures. Proteins have a wide variety of functions, including catalytic, structural, regulatory, transport, storage, and immunologic functions. They are digested by proteases and peptidases secreted by the stomach and pancreas and absorbed as individual AAs in the small intestines through specialized transporters. There are countless medical conditions related to protein abnormalities, including abnormalities related to enzymes, receptors, membrane channels, hormones, accumulation of proteins, and autoimmune disorders.