Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein

Exp Gerontol. 2006 Feb;41(2):215-9. doi: 10.1016/j.exger.2005.10.006. Epub 2005 Nov 23.


To counteract the debilitating progression of sarcopenia, a protein supplement should provide an energetically efficient anabolic stimulus. We quantified net muscle protein synthesis in healthy elderly individuals (65-79 yrs) following ingestion of an isocaloric intact whey protein supplement (WY; n=8) or an essential amino acid supplement (EAA; n=7). Femoral arterio-venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion of L-[ring-2H5]phenylalanine. Net phenylalanine uptake and mixed muscle fractional synthetic rate (FSR) were calculated during the post-absorptive period and for 3.5 h following ingestion of 15 g EAA or 15 g whey. After accounting for the residual increase in the intracellular phenylalanine pool, net post-prandial phenylalanine uptake was 53.4+/-9.7 mg phe leg-1 (EAA) and 21.7+/-4.6 mg phe leg-1 (WY), (P<0.05). Postabsorptive FSR values were 0.056+/-0.004% h-1 (EAA) and 0.049+/-0.006% h-1 (WY), (P>0.05). Both supplements stimulated FSR (P<0.05), but the increase was greatest in the EAA group with values of 0.088+/-0.011% h-1 (EAA) and 0.066+/-0.004% h-1 (WY), (P<0.05). While both EAA and WY supplements stimulated muscle protein synthesis, EAAs may provide a more energetically efficient nutritional supplement for elderly individuals.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Administration, Oral
  • Aged
  • Aging / physiology*
  • Amino Acids / administration & dosage*
  • Amino Acids / analysis
  • Amino Acids / metabolism
  • Analysis of Variance
  • Female
  • Humans
  • Leg / blood supply
  • Male
  • Milk Proteins / administration & dosage*
  • Milk Proteins / chemistry
  • Milk Proteins / metabolism
  • Muscle Proteins / biosynthesis*
  • Phenylalanine / analysis
  • Phenylalanine / blood
  • Regional Blood Flow
  • Whey Proteins


  • Amino Acids
  • Milk Proteins
  • Muscle Proteins
  • Whey Proteins
  • Phenylalanine