Effect of initiating enteral protein feeding on whole-body protein turnover in critically ill patients

Am J Clin Nutr. 2015 Mar;101(3):549-57. doi: 10.3945/ajcn.114.091934. Epub 2015 Feb 4.


Background: Critically ill patients are susceptible to protein catabolism. Enteral feeding may ameliorate protein loss, but its effect is not well characterized in terms of protein kinetics.

Objective: We established a method of quantifying the effect of enteral protein feeding on whole-body protein turnover and studied critically ill patients receiving early enteral nutrition.

Design: In a proof-of-concept study, we established, in healthy subjects (n = 6), a method of measuring the effect of continuous enteral protein feeding on whole-body protein turnover by using ¹³C-phenylalanine (¹³C-Phe) intrinsically labeled casein by a nasogastric feeding tube and an intravenous ²H₅-Phe tracer. The protocol was applied to study critically ill patients (n = 10) during the initial hypocaloric-hyponitrogenous dose of enteral nutrition.

Results: Patients were catabolic with a negative protein balance. The median splanchnic extraction fraction of hourly dietary Phe intake was 92% (range: 86-99%); that is, the availability of dietary Phe in arterial plasma was low. In patients with a stable parenteral amino acid supply (n = 7), the median net protein balance improved during enteral feeding from -8.6 to -5.8 μmol · kg body weight⁻¹ · h⁻¹ (P = 0.018).

Conclusions: Whole-body protein turnover and the contribution of dietary protein can be quantified in critically ill patients by using intravenous and enteral stable-isotope Phe tracers. The whole-body protein balance improved during early hypocaloric-hyponitrogenous enteral protein feeding in these patients.

Keywords: critical illness; intrinsically isotope-labeled casein; nutritional support; stable isotope tracers; whole-body protein turnover.

Publication types

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

MeSH terms

  • Aged
  • Caloric Restriction / adverse effects*
  • Carbon Isotopes
  • Cohort Studies
  • Critical Illness*
  • Deuterium
  • Diet, Protein-Restricted / adverse effects*
  • Energy Metabolism*
  • Enteral Nutrition / adverse effects*
  • Feasibility Studies
  • Female
  • Hospitals, University
  • Humans
  • Intensive Care Units
  • Kinetics
  • Male
  • Protein Biosynthesis*
  • Protein Stability
  • Proteolysis*
  • Sweden


  • Carbon Isotopes
  • Deuterium

Associated data

  • ANZCTR/ACTRN12614000333617