title: Co-ingestion of protein and leucine stimulates muscle protein synthesis rates to the same extent in young and elderly lean men.
abstract: BACKGROUND
  The progressive loss of skeletal muscle mass with aging is attributed to a disruption in the regulation of skeletal muscle protein turnover.
  
  
  OBJECTIVE
  We investigated the effects on whole-body protein balance and mixed-muscle protein synthesis rates of the ingestion of carbohydrate with or without protein and free leucine after simulated activities of daily living.
  
  
  METHODS
  Eight elderly (75 +/- 1 y) and 8 young (20 +/- 1 y) lean men were randomly assigned to 2 crossover experiments in which they consumed either carbohydrate (CHO) or carbohydrate plus protein and free leucine (CHO+Pro+Leu) after performing 30 min of standardized activities of daily living. Primed, continuous infusions with L-[ring-13C6]phenylalanine and L-[ring-2H2]tyrosine were applied, and blood and muscle samples were collected to assess whole-body protein turnover and the protein fractional synthetic rate in the vastus lateralis muscle over a 6-h period.
  
  
  RESULTS
  Whole-body phenylalanine and tyrosine flux were significantly higher in the young than in the elderly men (P < 0.01). Protein balance was negative in the CHO experiment but positive in the CHO+Pro+Leu experiment in both groups. Mixed-muscle protein synthesis rates were significantly greater in the CHO+Pro+Leu than in the CHO experiment in both the young (0.082 +/- 0.005%/h and 0.060 +/- 0.005%/h, respectively; P < 0.01) and the elderly (0.072 +/- 0.006%/h and 0.043 +/- 0.003%/h, respectively; P < 0.01) subjects, with no significant differences between groups.
  
  
  CONCLUSIONS
  Co-ingestion of protein and leucine with carbohydrate after activities of daily living improves whole-body protein balance, and the increase in muscle protein synthesis rates is not significantly different between lean young and elderly men.
authors.affiliation: Department of Human Biology, Maastricht University, Maastricht, Netherlands. r.koopman@hb.unimaas.nl
authors.forename: René
authors.initials: R
authors.lastname: Koopman
authors.forename: Lex
authors.initials: L
authors.lastname: Verdijk
authors.forename: Ralph J F
authors.initials: RJ
authors.lastname: Manders
authors.forename: Annemie P
authors.initials: AP
authors.lastname: Gijsen
authors.forename: Marchel
authors.initials: M
authors.lastname: Gorselink
authors.forename: Evelien
authors.initials: E
authors.lastname: Pijpers
authors.forename: Anton J M
authors.initials: AJ
authors.lastname: Wagenmakers
authors.forename: Luc J C
authors.initials: LJ
authors.lastname: van Loon
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism / Q000502:physiology; D002247:Carbon Isotopes; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D004311:Double-Blind Method; D006801:Humans; D007930:Leucine / Q000008:administration & dosage* / Q000378:metabolism; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D010649:Phenylalanine / Q000097:blood; D014443:Tyrosine / Q000097:blood
chemical_list: D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D009124:Muscle Proteins; D014443:Tyrosine; D010649:Phenylalanine; D007930:Leucine