TOTAL AND EXOGENOUS CARBOHYDRATE OXIDATION IN OBESE PREPUBERTAL CHILDREN

The aim was to explore whether the origin of carbohydrate oxidation (e xogenous compared with endogenous carbohydrate) after consumption of a mixed meal was influenced by obesity in children. Ten obese prepubert al children 8 y of age (44.2 +/- 3.6 kg) were studied over 9.5 h and c ompared with eight normal-weight, matched control children (28.5 +/- 1 .6 kg). They were fed a mixed meal containing naturally enriched [C-13 ]carbohydrate (cane sugar and popcorn) providing 55% of the daily ener gy requirement as measured by 24-h resting metabolic rate. Total carbo hydrate oxidation was calculated by indirect calorimetry (hood system) whereas exogenous carbohydrate oxidation was estimated from carbon di oxide production (V over dot CO2), the isotopic enrichment of breath ( CO2)-C-13, and the abundance of [C-13]carbohydrate in the meal ingeste d. The time course of (CO2)-C-13 in breath-measured over 570 min-follo wed a similar pattern in both groups. Although total carbohydrate oxid ation was not significantly different among the two groups, exogenous carbohydrate utilization was significantly greater (P < 0.03) and endo genous carbohydrate oxidation was significantly lower (P < 0.05) in ob ese compared with control children. In addition, the rate of exogenous carbohydrate oxidation expressed as a proportion of total carbohydrat e oxidation was positively related to the body fat of the children (r = 0.68, P < 0.01). The study suggests that in the postprandial phase, a smaller proportion of carbohydrate oxidation is accounted for by gly cogen breakdown in obese children. The sparing of endogenous glycogen may result from decreased glycogen turnover already present at an earl y age.