Fig. 1

Metabolic trial day schematic. Following an overnight fast, participants completed the LIST and subsequently consumed eight hourly isoenergetic mixed meals with protein provided as crystalline amino acids. The final four test drinks contained L-[1-¹³C]phenylalanine to model steady-state phenylalanine kinetics. Breath and urine samples were collected at baseline and isotopic plateau and were analyzed for ¹³CO₂ enrichment and L-[1-¹³C]phenylalanine enrichment, respectively. Steady-state CO₂ production (VCO₂) was measured for 20 min after the fifth test drink by indirect calorimetry. Urinary urea and creatinine excretion was determined by enzymatic assay