1. Indirect calorimetry and primed constant infusion of [U-13C]glucose were combined in 16 appropriate-for-gestational age newborn, parenterally fed infants, in order to measure glucose utilization and glucose oxidation respectively.
2. Glucose intake ranged between 10.0 and 24.1 g day−1 kg−1 and energy intake between 156.9 and 439.3 kJ day−1 kg−1.
3. Glucose utilization (P < 0.001), glucose oxidation (P < 0.001) and metabolic rate (P < 0.005) increased significantly with rising glucose intake.
4. The significant difference between glucose utilization and oxidation (P < 0.001) can be accounted for by an increasing storage as fat.
5. As lipogenesis from glucose consumes 15-24% of the original glucose energy, the increasing metabolic rate accompanying rising glucose intake is probably due to increasing lipogenesis.