Amino acids are organic compounds that contain nitrogen, carbon, hydrogen, and oxygen. They form long chains via peptide bonds: proteins.

Essential amino acids are amino acids that cannot be formed by animal organisms from other compounds. They must be supplied through external sources, such as food or supplements. For humans, there are nine, including L-leucine, L-isoleucine, and L-valine.

Non-essential amino acids can be synthesized by cells of animal organisms from other amino acids or nitrogen-containing compounds. Examples are alanine, asparagine, and glutamine (under normal circumstances).

Conditionally essential amino acids may not be produced sufficiently by the body under certain circumstances and can then be supplemented through diet.

BCAAs are branched-chain amino acids: L-leucine, L-isoleucine, and L-valine. The molecular structure of these amino acids contains a branched side chain, which chemically distinguishes them from other amino acids.