Energy substrate utilisation was evaluated over 21 days in two groups of malnourished children on total parenteral nutrition (TPN). Non-protein energy was infused as glucose (Group A; n = 7) or as a glucose/fat (1:1 v/v) mixture (Group B; n = 10). Results indicated that: 1) net glucose oxidation was related to glucose intake; 2) glucose storage was elevated in group A; 3) net fat synthesis occurred earlier in group B together with constant net fat oxidation which was inversely related to glucose intake (r = -0.89, p < 0.001); 4) lipogenesis from glucose occurred only when glucose intake exceeded 19.3g/kg/d; 5) energy expenditure increased by 36% (group A) and 18% (group B) during renutrition; 6) 73% and 82% of the energy administered in excess of energy required was stored in group A and B respectively. Hence, glucose/fat infusion appears to be more energy-efficient than glucose-alone in TPN of malnourished children.