PURPOSE OF REVIEW: Since the 1980s, hypocaloric feeding has been regularly proposed in the critically ill, although there is no clear definition available, nor evidence-based strategy to support it. We aim to define hypocaloric feeding based on indirect calorimetric data and to discuss patient-relevant clinical outcomes resulting from hypocaloric feeding. RECENT FINDINGS: Overfeeding and underfeeding both have proven deleterious effects and should be avoided, which requires determination of the patient's total energy requirement. Indirect calorimetry appears as the only precise method to determine such requirements in clinical settings. We define hypocaloric feeding as the delivery of 0.5-0.9 times the resting energy expenditure, isocaloric feeding as 1.1-1.3 times the resting energy expenditure, whereas hypercaloric feeding delivers more than 1.5 times the resting energy expenditure. Whether the patients are lean or obese, all the available predictive equations of energy requirements are grossly inaccurate in more than 30% of cases. SUMMARY: There is growing evidence that negative energy balances are associated with poor intensive-care-unit and hospital outcome. Using an evidence-based approach, hypocaloric feeding in the critically ill cannot be supported either. Whether the cutoff of tolerance for introducing feeding is 24 h or more is not yet defined and still awaits a prospective trial.