Indicator Amino Acid Oxidation (IAAO)
Stable isotope tracer method that determines amino acid or protein requirements by feeding graded levels of the test amino acid and measuring oxidation of an isotopically labeled indicator amino acid.
Also: IAAO
When the test amino acid is limiting, its supply constrains protein synthesis and the indicator amino acid is oxidized; when test intake meets requirement, oxidation drops sharply. IAAO has produced protein requirement estimates ~30-50% higher than nitrogen balance, especially in older adults, athletes, and pregnancy, motivating reconsideration of the protein RDA in MNHD Ch 1.
How one textbook covers it
Modern Nutrition in Health and Disease, 12th ed. — Ch 1: Proteins and Amino Acids
When the test amino acid is limiting, its supply constrains protein synthesis and the indicator amino acid is oxidized; when test intake meets requirement, oxidation drops sharply. IAAO has produced protein requirement estimates ~30-50% higher than nitrogen balance, especially in older adults, athletes, and pregnancy, motivating reconsideration of the protein RDA in MNHD Ch 1.
Related terms
Nitrogen balance, Protein, RDA