Indicator Amino Acid Oxidation Protein Requirement Estimate in Endurance-Trained Men 24h Post-Exercise Exceeds both the EAR and Current Athlete Guidelines.

Despite studies indicating increased protein requirements in endurance-trained (ET) individuals, the Institute of Medicine has concluded, that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise" and the controversy regarding exercise effects on protein requirements continues. The objective of this study was to determine the dietary protein requirement of healthy young ET men (≥1 y training experience) 24h post-exercise (to minimize any acute effects of the previous training session) by measuring the oxidation of ingested L-[1-13 C] phenylalanine to 13 CO2 in response to graded intakes of protein [Indicator Amino Acid Oxidation (IAAO) Technique]. Eight men (V ̇O2max , 64.1±3.7 ml•kg-1 •min-1 ) were each studied 24h post-exercise repeatedly with protein intakes ranging from 0.3 to 3.5 g•kg-1 •d-1 . Protein was fed as an amino acid mixture based on the protein pattern in egg, except for phenylalanine and tyrosine, which were maintained at constant amounts across all protein intakes. For two d prior to the study day, all participants consumed 1.6 g protein•kg-1 •d-1 . The estimated average requirement (EAR) for protein was determined by applying a non-linear mixed-effects change-point regression analysis to F13 CO2 (label tracer oxidation in 13 CO2 breath), which identified a breakpoint in the F13CO2 in response to the graded amounts of protein. The EAR for protein and the upper 95% CI were 2.1 and 2.6 g•kg-1 •d-1 , respectively. These data suggest that the protein EAR for ET men, 24h post-exercise exceeds the Institute of Medicine' EAR and established athlete guidelines by ~3.5 and 1.3 fold, respectively.