Nutrition support in the ICU: current evidence and evolving standards.

Nutritional support is a cornerstone of care in critically ill patients, yet the optimal delivery of macronutrient across phases of critical illness remains controversial. During the acute phase, profound metabolic alterations including anabolic resistance, enhanced proteolysis and endogenous energy production contribute to rapid muscle wasting. Recent large randomized trials have challenged the traditional paradigm of early full nutritional replacement, which may cause harm through overfeeding, refeeding syndrome, impaired autophagy, and metabolic intolerance. Low-calorie and low-protein strategies during the first week of critical illness, particularly in mechanically ventilated patients requiring organ support, may improve recovery and reduce complications. Increasing protein delivery has not consistently improved survival or functional recovery and may even be harmful, especially in patients with acute kidney injury. Current evidence therefore supports a cautious, individualized approach, with avoidance of overfeeding and consideration of low-calorie, low-protein feeding strategies while carefully monitoring gastrointestinal tolerance, metabolic complications and electrolyte disturbances. During the recovery phase, as inflammation resolves and anabolic processes emerge, nutritional priorities shift toward restoration of lean body mass and functional recovery. However, evidence defining optimal macronutrient targets remains limited. Observational studies consistently report inadequate energy and protein delivery after the acute phase due to feeding interruptions, gastrointestinal intolerance, and swallowing disorders. A multidisciplinary, protocol-driven approach emphasizing individualized nutritional support is therefore recommended. Future research should focus on defining phase-specific nutritional targets, identifying biomarkers of metabolic demand, and evaluating the impact of ICU and post-ICU nutrition on long-term functional outcomes.