title: Leucine co-ingestion improves post-prandial muscle protein accretion in elderly men.
abstract: OBJECTIVE
  It has been speculated that the amount of leucine in a meal largely determines the post-prandial muscle protein synthetic response to food intake. The present study investigates the impact of leucine co-ingestion on subsequent post-prandial muscle protein accretion following the ingestion of a single bolus of dietary protein in elderly males.
  
  
  METHODS
  Twenty-four elderly men (74.3±1.0 y) were randomly assigned to ingest 20 g intrinsically L-[1-(13)C]phenylalanine-labeled casein protein with (PRO+LEU) or without (PRO) 2.5 g crystalline leucine. Ingestion of specifically produced intrinsically labeled protein allowed us to create a plasma phenylalanine enrichment pattern similar to the absorption pattern of phenylalanine from the ingested protein and assess the subsequent post-prandial incorporation of L-[1-(13)C] phenylalanine into muscle protein.
  
  
  RESULTS
  Plasma amino acid concentrations increased rapidly following protein ingestion in both groups, with higher leucine concentrations observed in the PRO+LEU compared with the PRO group (P<0.01). Plasma L-[1-(13)C]phenylalanine enrichments increased rapidly and to a similar extent in both groups following protein ingestion. Muscle protein-bound L-[1-(13)C]phenylalanine enrichments were significantly greater after PRO+LEU when compared with PRO at 2 h (72%; 0.0078±0.0010 vs. 0.0046±0.00100 MPE, respectively; P<0.05) and 6 h (25%; 0.0232±0.0015 vs. 0.0185±0.0010 MPE, respectively; P<0.05) following protein ingestion. The latter translated into a greater muscle protein synthetic rate following PRO+LEU compared with PRO over the entire 6 h post-prandial period (22%; 0.049±0.003 vs. 0.040±0.003% h(-1), respectively; P<0.05).
  
  
  CONCLUSIONS
  Leucine co-ingestion with a bolus of pure dietary protein further stimulates post-prandial muscle protein synthesis rates in elderly men.
authors.affiliation: Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, PO Box 616, Maastricht, 6200 MD, The Netherlands.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Wall
authors.forename: Henrike M
authors.initials: HM
authors.lastname: Hamer
authors.forename: Anneke
authors.initials: A
authors.lastname: de Lange
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kiskini
authors.forename: Bart B L
authors.initials: BB
authors.lastname: Groen
authors.forename: Joan M G
authors.initials: JM
authors.lastname: Senden
authors.forename: Annemie P
authors.initials: AP
authors.lastname: Gijsen
authors.forename: Lex B
authors.initials: LB
authors.lastname: Verdijk
authors.forename: Luc J C
authors.initials: LJ
authors.lastname: van Loon
mesh_terms: D000368:Aged; D001786:Blood Glucose / Q000032:analysis; D002247:Carbon Isotopes / Q000097:blood; D002364:Caseins / Q000008:administration & dosage / Q000737:chemistry; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage; D006801:Humans; D007328:Insulin / Q000097:blood; D007930:Leucine / Q000008:administration & dosage* / Q000097:blood; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D010649:Phenylalanine / Q000008:administration & dosage / Q000097:blood; D019518:Postprandial Period / Q000187:drug effects*
chemical_list: D001786:Blood Glucose; D002247:Carbon Isotopes; D002364:Caseins; D004044:Dietary Proteins; D007328:Insulin; D009124:Muscle Proteins; D010649:Phenylalanine; D007930:Leucine