Effect of Mixed Meal and Leucine Intake on Plasma Amino Acid Concentrations in Young Men

Dietary protein intake is critical for the maintenance of skeletal muscle mass. Plasma amino acid concentrations increase with protein intake and increases in muscle protein synthesis are dependent on leucineconcentrations. We aimed to investigate the effect of a mixed mealand free amino acids intake on plasma leucineconcentrations. In this randomized crossover study, 10 healthy young men (age 25 ± 1 years, height 1.73 ± 0.02 m, weight 65.8 ± 1.5 kg) underwent tests under different conditions—intake of 2 g of leucine(LEU), intake of a mixed meal( protein27.5 g, including 2.15 g of leucine, protein: fat: carbohydrate ratio—22:25:53) only ( MEAL), intake of 2 g of leucineimmediately after a mixed meal( MEAL-LEU) and intake of 2 g of leucine180 min after a mixed meal( MEAL-LEU180). Blood samples were collected within 420 min (240 min for LEU only) after intake and changes in amino acid concentrations were evaluated. Although the maximum plasma leucineconcentration increased to 442 ± 24 µM for LEU, it was lower at 347 ± 16 µM (p 0.1). The observation that rapid elevations in plasma leucineconcentrations are suppressed when leucineis ingested at the same time as a mealsuggests that the timing of its intake must be considered to maximize the anabolic response.