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

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

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From the Department of Anesthesiology and Intensive Care, Karolinska University Hospital Huddinge and Karolinska Institutet, Stockholm, Sweden (FL, JW, and OR), and NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, Maastricht, The Netherlands (LJCvL).



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.


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.


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.


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).


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.


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

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