Functional impact of high protein intake on healthy elderly people

Am J Physiol Endocrinol Metab. 2008 Oct;295(4):E921-8. doi: 10.1152/ajpendo.90536.2008. Epub 2008 Aug 12.


Decline in muscle mass, protein synthesis, and mitochondrial function occurs with age, and amino acids are reported to enhance both muscle protein synthesis and mitochondrial function. It is unclear whether increasing dietary protein intake corrects postabsorptive muscle changes in aging. We determined whether a 10-day diet of high [HP; 3.0 g protein x kg fat-free mass (FFM)(-1) x day(-1)] vs. usual protein intake (UP; 1.5 g protein x kg FFM(-1) x day(-1)) favorably affects mitochondrial function, protein metabolism, and nitrogen balance or adversely affects insulin sensitivity and glomerular filtration rate (GFR) in 10 healthy younger (24+/-1 yr) and 9 older (70+/-2 yr) participants in a randomized crossover study. Net daily nitrogen balance increased equally in young and older participants, but postabsorptive catabolic state also increased, as indicated by higher whole body protein turnover and leucine oxidation with no change in protein synthesis. Maximal muscle mitochondrial ATP production rate was lower in older people, with no change occurring in diet. GFR was lower in older people, and response to HP was significantly different between the two groups, with a significant increase occurring only in younger people, thus widening the differences in GFR between the young and older participants. In conclusion, a short-term high-protein diet increased net daily nitrogen balance but increased the postabsorptive use of protein as a fuel. HP did not enhance protein synthesis or muscle mitochondrial function in either young or older participants. Additionally, widening differences in GFR between young and older patients is a potential cause of concern in using HP diet in older people.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphate / biosynthesis
  • Adult
  • Aged / physiology*
  • Amino Acids / metabolism
  • Citrate (si)-Synthase / metabolism
  • Cross-Over Studies
  • Dietary Proteins / pharmacology*
  • Double-Blind Method
  • Energy Intake / physiology
  • Female
  • Glomerular Filtration Rate / physiology
  • Hormones / blood
  • Humans
  • Insulin / physiology
  • Insulin Resistance / physiology
  • Kidney / drug effects
  • Kidney / physiology
  • Male
  • Mitochondria, Muscle / drug effects
  • Muscle Proteins / biosynthesis
  • Oxidation-Reduction


  • Amino Acids
  • Dietary Proteins
  • Hormones
  • Insulin
  • Muscle Proteins
  • Adenosine Triphosphate
  • Citrate (si)-Synthase