The EPaNIC trial addressed a long-standing nutritional question: should parenteral nutrition be started early when enteral feeding is insufficient, or can it safely be delayed? More than 4,600 critically ill adults were randomised to early or late initiation of parenteral nutrition. Late initiation was associated with faster recovery from the ICU and hospital, fewer ICU infections, less cholestasis and shorter durations of mechanical ventilation and renal-replacement therapy. Mortality was not significantly different. The study challenged the assumption that rapidly closing a calorie deficit with parenteral nutrition necessarily improves outcomes. Instead, in patients who were not chronically malnourished and were receiving early enteral nutrition, the strategy of tolerating a period of nutritional deficit appeared beneficial. EPaNIC therefore influenced modern approaches to nutrition timing and highlighted the importance of distinguishing patients at high nutritional risk from those who can safely receive progressive enteral feeding. For clinicians, the practical message is not to withhold nutrition but to prioritise enteral feeding when feasible and avoid reflexive early parenteral supplementation simply to achieve a prescribed calorie target. Nutritional plans should consider baseline status, illness severity, gut function, metabolic tolerance and expected duration of critical illness. The trial remains central to discussions of nutrition and metabolism in the ICU.