Large randomised controlled trials have shown that early supplemental parenteral nutrition in patients admitted to adult and paediatric intensive care units (PICUs) is harmful. Overdosing of energy with too little protein was suggested as a potential reason for this. This study analysed which macronutrient was associated with harm caused by early supplemental parenteral nutrition in the Paediatric Early versus Late Parenteral Nutrition In Critical Illness (PEPaNIC) randomised trial.