Addition of carbohydrate or alanine to an essential amino acid mixture does not enhance human skeletal muscle protein anabolism1-3

Erin L. Glynn, Christopher S. Fry, Kyle L. Timmerman, Micah J. Drummond, Elena Volpi, Blake B. Rasmussen

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


In humans, essential amino acids (EAAs) stimulate muscle protein synthesis (MPS) with no effect on muscle protein breakdown (MPB). Insulin can stimulateMPS, and carbohydrates (CHOs) and insulin decrease MPB. Net protein balance (NB; indicator of overall anabolism) is greatestwhenMPS ismaximized andMPB isminimized. To determinewhether adding CHO or a gluconeogenic amino acid to EAAs would improve NB compared with EAA alone, young men and women (n = 21) ingested 10 g EAA alone, with 30 g sucrose (EAA+CHO), or with 30 g alanine (EAA+ALA). The fractional synthetic rate and phenylalanine kinetics (MPS,MPB, NB) were assessed by stable isotopic methods onmuscle biopsies at baseline and 60 and 180 min following nutrient ingestion. Insulin increased 30 min postingestion in all groups and remained elevated in the EAA + CHO and EAA+ALA groups for 60 and 120 min, respectively. The fractional synthetic rate increased frombaseline at 60 min in all groups (P < 0.05; EAA = 0.053 6 0.018 to 0.090 6 0.039% h-1; EAA+ALA = 0.051 6 0.005 to 0.087 6 0.015% h-1; EAA+CHO = 0.049 6 0.006 to 0.1156 0.024% h-1).MPS and NB peaked at 30min in the EAA and EAA+CHO groups but at 60 min in the EAA+ALA group and NB was elevated above baseline longer in the EAA+ALA group than in the EAA group (P < 0.05). Although responses were more robust in the EAA+CHO group and prolonged in the EAA+ALA group, AUCs were similar among all groups for fractional synthetic rate, MPS, MPB, and NB. Because the overall muscle protein anabolic response was not improved in either the EAA+ALA or EAA+CHO group compared with EAA, we conclude that protein nutritional interventions to enhance muscle protein anabolism do not require such additional energy.

Original languageEnglish (US)
Pages (from-to)307-314
Number of pages8
JournalJournal of Nutrition
Issue number3
StatePublished - Mar 2013

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics


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