Leucine supplementation improves muscle protein synthesis in elderly men independently of hyperaminoacidaemia

J Physiol. 2006 Aug 15;575(Pt 1):305-15. doi: 10.1113/jphysiol.2006.110742. Epub 2006 Jun 15.


The present study was designed to assess the effects of dietary leucine supplementation on muscle protein synthesis and whole body protein kinetics in elderly individuals. Twenty healthy male subjects (70 +/- 1 years) were studied before and after continuous ingestion of a complete balanced diet supplemented or not with leucine. A primed (3.6 micromol kg(-1)) constant infusion (0.06 micromol kg(-1) min(-1)) of L-[1-13C]phenylalanine was used to determine whole body phenylalanine kinetics as well as fractional synthesis rate (FSR) in the myofibrillar fraction of muscle proteins from vastus lateralis biopsies. Whole body protein kinetics were not affected by leucine supplementation. In contrast, muscle FSR, measured over the 5-h period of feeding, was significantly greater in the volunteers given the leucine-supplemented meals compared with the control group (0.083 +/- 0.008 versus 0.053 +/- 0.009% h(-1), respectively, P < 0.05). This effect was due only to increased leucine availability because only plasma free leucine concentration significantly differed between the control and leucine-supplemented groups. We conclude that leucine supplementation during feeding improves muscle protein synthesis in the elderly independently of an overall increase of other amino acids. Whether increasing leucine intake in old people may limit muscle protein loss during ageing remains to be determined.

Publication types

  • Clinical Trial
  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Amino Acids / administration & dosage
  • Amino Acids / pharmacokinetics*
  • Breath Tests
  • Carbon Dioxide / metabolism
  • Carbon Radioisotopes
  • Dietary Supplements*
  • Humans
  • Insulin / blood
  • Leucine / administration & dosage
  • Leucine / pharmacokinetics*
  • Male
  • Muscle Proteins / biosynthesis*
  • Muscle, Skeletal / metabolism*
  • Phenylalanine / pharmacokinetics
  • Postprandial Period


  • Amino Acids
  • Carbon Radioisotopes
  • Insulin
  • Muscle Proteins
  • Carbon Dioxide
  • Phenylalanine
  • Leucine