Abstract
Fat oxidation (FO) has previously been measured by indirect calorimetry (IDC). Due to conversion of glucose into lipid, true fat oxidation may be underestimated. In the present study, we combined IDC with direct measurement of glucose oxidation using U-13C-glucose. IDC was performed for 5 hrs. Simultaneously a primed constant infusion of U-13C-glucose was given. Glucose utilisation was calculated separately from IDC data (ie. protein free RQ + VO2), and from 13CO2 enrichment in breath at plateau. Fat oxidation was then calculated by subtracting the glucose utilisation from the non-protein metabolic rate. Ten AGA parenterally fed infants were studied (x±S.E.) BW 2.7±0.33 kg, gest. age 36.6±1.4 wk, study weight 2.7±0.31 kg, age 14.2±2.8 d., energy intake 86.2±2.35 Kcal/kg.d, protein intake 2.8±0.09 g/kg.d.
CONCLUSIONS: Due to lipogenesis, IDC overestimates glucose utilisation and hence underestimates fat oxidation. By measuring glucose utilisation directly, we have been able to demonstrate a significantly higher fat oxidation, approximately 90% of intake.
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Aerde, J., Sauer, P., Smith, J. et al. 747 FAT OXIDATION IN PARENTERALLY FED NEWBORN INFANTS. Pediatr Res 19, 235 (1985). https://doi.org/10.1203/00006450-198504000-00777
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DOI: https://doi.org/10.1203/00006450-198504000-00777
