Abstract
Substrate utilisation, previously measured indirectly with Indirect Calorimetry (IDC), can now be measured directly using stable isotopes. IDC may underestimate fat utilisation due to the conversion of glucose into fat. We combined IDC with direct measurement of glucose oxidatior using U-13C-glucose. Glucose and fat utilisation was calculated from IDC (non-protein VO2 and RQ) over 5 hr. Simultaneously, a primed constant infusion of U-13C-glucose was given. Glucose oxidation was calculated from the 13CO2 excretion in breath at plateau, fat oxidation by subtracting the glucose oxidation from the non-protein metabolic rate. Sixteen AGA TPN fed infants were studied (x±SE). BW 2.7±0.2 kg, gest. age 36.6±1 wk, study weight 2.7±0.2 kg, age 13.7±0.3 d. Energy intake 87.0±1.6 kcal/kg/d, protein int. 3.2±0.2 g/kg/d, glucose int. 13.8±0.3 g/kq/d, fat int. 2.0±0.1 g/kq/d.
Conclusions: 1. IDC shows a significantly higher glucose and lower fat utilisation compared with 13C-data. 2. The 13C-data show that 92% of the fat intake is being utilised. 3. Fat oxidation is an important contribution to the energy expenditure during TPN with lipids.
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Sauer, P., Van Aerde, J., Smith, J. et al. SUBSTRATE UTILISATION OF NEWBORN INFANTS RECEIVING TOTAL PARENTERAL NUTRITION (TPN). Pediatr Res 19, 1081 (1985). https://doi.org/10.1203/00006450-198510000-00078
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DOI: https://doi.org/10.1203/00006450-198510000-00078
