Summary
This controlled study used stable isotope tracers to examine protein digestion, amino acid absorption, and muscle protein synthesis in mechanically ventilated ICU patients compared with healthy controls following a 20 g milk protein meal. Despite normal plasma amino acid availability between groups, critically ill patients showed markedly blunted incorporation of dietary amino acids into myofibrillar protein (~60% lower than controls), indicating a selective impairment in the capacity to utilise ingested protein for muscle protein synthesis despite preserved digestive function.
UK applicability
The findings are relevant to UK intensive care nutrition practice and clinical guidelines for protein supplementation in critical illness, suggesting that standard protein dosing may not overcome the anabolic resistance observed in mechanically ventilated patients and that alternative nutritional or pharmacological interventions may be needed.
Key measures
Fasting and postprandial myofibrillar protein synthesis rates (%/h); plasma amino acid availability (%); incorporation of protein-derived phenylalanine into myofibrillar protein (mol percent excess)
Outcomes reported
The study quantified myofibrillar protein synthesis rates at rest and after protein administration in mechanically ventilated ICU patients versus healthy controls, and measured plasma amino acid availability and incorporation of dietary amino acids into muscle protein.
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