Co-ingestion of protein and leucine stimulates muscle protein synthesis rates to the same extent in young and elderly lean men.
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.
Koopman
René
R
Department of Human Biology, Maastricht University, Maastricht, Netherlands. r.koopman@hb.unimaas.nl
Verdijk
Lex
L
Manders
Ralph J F
RJ
Gijsen
Annemie P
AP
Gorselink
Marchel
M
Pijpers
Evelien
E
Wagenmakers
Anton J M
AJ
van Loon
Luc J C
LJ
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
D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D009124:Muscle Proteins; D014443:Tyrosine; D010649:Phenylalanine; D007930:Leucine