Objective: To compare the respiratory quotient in infants with chronic lung disease before and after receiving a modular diet with slightly lower carbohydrate content.
Material and Method: Infants with chronic lung disease from the King Chulalongkorn Memorial Hospital were enrolled and assessed for nutritional status, severity of chronic lung disease and dietary intake. Indirect calorimetry was performed using a custom-made airtight canopy with O2 and CO2 sensors. Respiratory quotient (RQ) was calculated from VCO2/VO2 during the period they were fed low carbohydrates (37% of total calories) for at least 24 hours vs. a standard diet (47% carbohydrate). These two formulas were similar in terms of caloric density and protein content. Each patient received at least 100-150 kcal/kg/day during the study period. Respiratory quotients of the same patient receiving the two diets were compared by using Wilcoxon signed-rank test.
Results: A total of 14 patients (median age 7 months, range 1-26 months) were recruited. Twelve children had weight for age Z-score below-2SD. Their median weight for age Z-score, length for age Z-score and weight for length Z-score were -2.89,
-3.08 and -1.24, respectively. The median RQ measured during the low carbohydrate diet was 0.96 (interquartile range 0.95-
0.97), significantly lower than the median RQ during the standard diet, which was 1.04 (0.97-1.10). However, the respiratory rate revealed no significant difference. Two participants with underlying gastroesophageal reflux disease showed higher RQ after low carbohydrate formula feeding, which might be a result of hypersecretion due to its high fat content.
Conclusion: Diet with slightly lower carbohydrate content can reduce the RQ in infants with chronic lung disease compared
to the standard enteral formula. A 10-percent reduction of carbohydrate content may provide a sizeable effect in this group of patients. Nevertheless, the clinical significance of this finding requires further investigation.

Keywords: Respiratory quotient, Chronic lung disease, Low carbohydrate formula