Essential Amino Acid Definition

Methionine is an essential amino acid.
Methionine is an essential amino acid. Todd Helmenstine

An essential amino acid is an amino acid which an organism needs to ingest because it is necessary for nutrition and cannot be synthesized in the body. It is also known as an indispensable amino acid.

List of Essential Amino Acids

In humans, several amino acids are considered essential:

  • Histidine (H)
  • Isoleucine (I)
  • Leucine (L)
  • Lysine (K)
  • Methionine (M)
  • Phenylalanine (F)
  • Threonine (T)
  • Tryptophan (W)
  • Valine (V)


  • Fürst, P.; Stehle, P. (June 1, 2004). "What are the essential elements needed for the determination of amino acid requirements in humans?". Journal of Nutrition. 134 (6 Suppl): 1558S–1565S. doi:10.1093/jn/134.6.1558S
  • Young, V.R. (1994). "Adult amino acid requirements: the case for a major revision in current recommendations." J. Nutr. 124 (8 Suppl): 1517S–1523S. doi:10.1093/jn/124.suppl_8.1517S