An essential nutrient is a nutrient required for normal human body function that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health (e.g., niacin, choline), and thus must be obtained from a dietary source.
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo (from scratch) by the organism being considered, and therefore must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H).
- "What is an essential nutrient?". NetBiochem Nutrition, University of Utah.
- Robert S. Goodhart and Maurice E. Shils (1980). Modern Nutrition in Health and Disease (6th ed.). Philadelphia: Lea and Febinger. pp. 134–138. ISBN 0-8121-0645-8.
- Young VR (1994). "Adult amino acid requirements: the case for a major revision in current recommendations" (PDF). J. Nutr. 124 (8 Suppl): 1517S–1523S. PMID 8064412.
- Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, published by the Institute of Medicine's Food and Nutrition Board, currently available online at http://fnic.nal.usda.gov/dietary-guidance/dietary-reference-intakes/dri-reports