Leucine Is More Readily Oxidized When Ingested as an Isolated Nutrient versus Incorporated in Its Whole-Food Matrix

Abstract

\n \n \n The ingestion of free amino acids, or isolated sources of protein, results in faster postprandial release of dietary amino acids into circulation, which stimulates muscle protein synthesis rates. However, indirect evidence suggests that this rapid release of dietary amino acids after the ingestion of free amino acids is coupled with higher amino acid oxidation rates when compared to a whole-food source. Whole food protein results in a reduced peak amplitude and prolonged postprandial aminoacidemia. This study aimed to assess the effects of eating a whole food source of protein on the stimulation of whole-body leucine oxidation rates versus eating these same nutrients in isolated form in healthy young adults.\n \n \n \n In a crossover design, 10 recreationally active adults (24\xa0±\xa04\xa0y; 5\xa0M, 5 F) performed an acute bout of resistance\n exercise followed by the ingestion of salmon (SAL) (20.5\xa0g protein and 7.5\xa0g fat) or its matched constituents as crystalline amino acids and fish oil (ISO). Participants received priming doses of NaH13CO2 and L-[1–13C]leucine before initiating a constant L-[1–13C]leucine infusion. Blood and breath samples were collected at rest and after resistance exercise at regular intervals for the measurement of whole-body leucine oxidation rates and plasma leucine profiles. Data were tested using linear fixed effects models with time and group as fixed factors with Bonferroni s post hoc test.\n \n \n \n Postprandial plasma leucine concentrations did not differ between the SAL and ISO conditions (P\xa0>\xa00.05).\xa0Time to peak plasma leucine concentrations was faster in ISO (50\xa0±\xa027\xa0min)\xa0vs. SAL (114\xa0±\xa064\xa0min, \xa0P\xa0=\xa00.022) condition. Postprandial leucine oxidation rates were elevated from baseline at t\xa0=\xa030\xa0min to t\xa0=\xa0120\xa0min in ISO and t\xa0=\xa060\xa0min to t\xa0=\xa0180\xa0min in SAL (P\xa0<\xa00.001), with no total differences between group (P\xa0=\xa00.129). Time to peak leucine oxidation occurred sooner in ISO (66\xa0±\xa022\xa0min; \xa01.358\xa0±\xa00.699\xa0nmol · kg−1 · min−1) when compared to the SAL condition (105\xa0±\xa020\xa0min; \xa01.067\xa0±\xa00.3076\xa0nmol · kg−1 · min−1; P\xa0=\xa00.002).\n \n \n \n We show that the ingestion of a whole-food source of protein resulted in a delayed stimulation of leucine oxidation when compared to free amino acid ingestion, but a similar net increase in oxidation during the 5\xa0h postprandial period in healthy young adults.\n \n \n \n USDA National Institute of Food and Agriculture Hatch project 1017928\n