Variable Intensity Exercise Increases Protein Requirements in Active Male and Female Adolescents as Determined by the Indicator Amino Acid Oxidation (IAAO) Technique
Authors: Brooks Jahmal C , Volterman Kim A , West Daniel W , Courtney‐Martin Glenda , Pencharz Paul B , Moore Daniel R 
Published: November 2023

Adolescence is characterized by the greatest increase in linear growth and accrual of fat‐free mass (FFM) during the life cycle. This growth spurt is optimized by adequate energy and protein intake. Active adolescents also display a greater FFM than their sedentary peers with the sexual dimorphism of puberty leading to a greater total gain in males than females. Given current evidence which suggest that protein requirement is higher in active adults than their sedentary counterparts, we aimed to determine the protein requirements of active, growing adolescents by utilizing the minimally invasive Indicator Amino Acid Oxidation (IAAO) technique. Fourteen active male (n=7; 13±0.6 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) and female (n=7; 11±0.4 years; 159±3.3 cm; 51.6±8.1 kg; 41.5±6.7 kg FFM; 0.5±0.4 years from PHV; means±95% CI) participants each underwent 6 metabolic trials that included an acute bout of a variable intensity exercise (modified Loughborough Intermittent Shuttle Test) 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 to match habitual intake. Protein was provided as crystalline amino acid mixtures modeled on the basis of egg protein, with the exception of 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). After the determination of breath 13CO2 enrichment by continuous‐flow isotope ratio mass spectrometry and CO2 production by indirect calorimetry, the estimated average requirement (EAR) was determined from the breakpoint of the 13CO2 excretion (F13CO2) after application of a bi‐phase linear regression. Preliminary analysis of F13CO2 revealed breakpoints of 1.53 g·kg−1·d−1 (r2 = 0.57) and 1.34 g·kg−1·d−1 (r2 = 0.69) for males and females respectively. When normalized to FFM, the breakpoints were 1.97 ± 0.33 g·kg FFM−1·d−1 (r2 = 0.68) and 1.45 ± 0.22 g·kg FFM−1·d−1 (r2 = 0.63) for males and females, respectively. The breakpoints derived herein exceed current estimated breakpoint values using the IAAO method for sedentary adults and children (0.93 g·kg−1·d−1, and 1.3 g·kg−1·d−1 respectively). Adjusting for the upper 95% CI, a recommended dietary allowance (RDA) was determined to be 1.83 g·kg−1·d−1 and 1.54 g·kg−1·d−1 for males and females respectively. Our estimate of the RDA in active adolescents exceeds the current protein RDA based on the factorial estimate of nitrogen balance for adolescents (0.9 g·kg−1·d−1), suggesting that variable intensity exercise increases daily protein requirements in active adolescents (and especially males) to potentially support greater FFM development and/or the replenishment of exercise‐induced oxidative losses.Support or Funding InformationSupported by the Ajinomoto Innovation Alliance Program.