Clinical nutrition for critically ill patients: a practical appraisal of guideline gaps and perspectives for future research.

Malnutrition and accelerated muscle wasting are frequent during critical illness and make nutritional support a central component of ICU care. Nutritional support is therefore central to ICU care, but its optimal timing, route, dose, and composition remain debated. Recent randomized trials have challenged the traditional objective of early full feeding and shifted practice toward progressive, phase-adapted, and tolerance-based nutrition. This narrative review compares current international guidelines for nutritional support in critically ill adults. Guidelines broadly agree that nutrition should be initiated early after clinical stabilization, acute-phase overfeeding should be avoided, energy and protein delivery should be increased progressively, and refeeding syndrome should be anticipated. However, important differences remain regarding acute-phase energy targets, protein dosing, enteral versus parenteral nutrition, supplemental parenteral nutrition, indirect calorimetry, and enriched enteral formulas. These discrepancies reflect differences in methodology, healthcare context, and interpretation of evidence largely derived from mechanically ventilated patients during the first ICU week. Several clinically important situations remain insufficiently addressed, including prolonged critical illness, obesity, sarcopenia, post-extubation nutrition, post-ICU rehabilitation, and nutrition after major surgery. Future research should move toward individualized strategies based on illness phase, metabolic trajectory, nutritional phenotype, tolerance, and recovery-oriented outcomes.