Amino Acid Metabolism and Protein Requirements in Active, Adolescent Males Using the Indicator Amino Acid Oxidation (IAAO) Technique

We aimed to determine the protein requirements of active adolescents by utilizing the minimally invasive, Indicator Amino Acid Oxidation (IAAO) technique. Seven male participants (n=7; 13.8±0.5 years; 171±2.8 cm; 57.3±4.2 kg; 48.4±5.0 kg FFM; 0.3±0.2 years from peak height velocity (PHV); means±95% CI) each underwent 6 metabolic trials that included an acute bout of a variable intensity exercise, followed by the ingestion of 8 hourly meals providing a variable amount of protein (0.2 – 2.67 g·kg−1·d−1), 6 g·kg−1 of carbohydrate, and sufficient energy. Protein was provided as crystalline amino acid mixtures, modeled after the contents of egg protein, apart from tyrosine (40 mg·kg−1·d−1) and phenylalanine (30.5 mg·kg−1·d−1 of which 5.46 mg·kg−1 was L-[13C] phenylalanine over the final 4 drinks). 13CO2 enrichment in breath was determined by continuous-flow isotope ratio mass spectrometry and CO2 production by indirect calorimetry. Bi-phase linear regression indicated a breakpoint of the 13CO2 excretion (F13CO2) equivalent to an estimated average requirement (EAR) of 1.48 g·kg−1·d−1 (r2 = 0.54), with the upper 95% CI, which approximates the recommended dietary allowance (RDA) of 1.78 g·kg−1·d−1. Our estimate exceeds the current protein RDA based on the factorial estimate of nitrogen balance for adolescents (0.9 g·kg−1·d−1). Therefore, suggesting that variable intensity exercise, as well as, the incorporation of a new determining method, increases daily protein requirements in active adolescents.M.Sc