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 synthesized by animals from other compounds. They must be obtained from 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 the cells of animals from other amino acids or nitrogen-containing compounds. Examples include alanine, asparagine, and glutamine (under normal conditions).

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