TIME-COURSE OF INCREASED LIPID AND DECREASED GLUCOSE-OXIDATION DURINGEARLY PHASE OF CHILDHOOD OBESITY

To determine the time course of metabolic dysfunctions in recent activ e obesity, we studied basal energy expenditure and lipid and glucose o xidation in 31 obese children (duration of obesity 1-11.5 yr), compare d with 14 lean age-matched control subjects. Using indirect calorimetr y in basal overnight fasting conditions, we found that obese children produced 15% more energy than control subjects. Obese children oxidize d twice as much lipid (56 +/- 4 mg/min) as normal children (25 +/- 5 m g/min, P < 0.0005), so that lipid oxidation provided 61 +/- 6% of over all energy production (vs. 33 +/- 3% in control subjects, P < 0.0005). This increase of lipid oxidation was already present in the earlier s tages of obesity. Glucose oxidation was diminished in the obese (93 +/ - 6 mg/min) compared with the control children (136 +/- 6 mg/min, P < 0.0005) and accounted for only 39 +/- 3% of energy production (67 +/- 6% in control subjects, P < 0.0005). This decrease was not present ini tially and appeared after approximately 4 yr and worsened with obesity duration (r = 0.72, P < 0.0005). The results were similar when lipid and glucose oxidation were normalized to body surface area or lean bod y mass. We hypothesize that increased lipid oxidation is one of the ea rlier dysfunctions observed in recent-onset obesity and that lipid oxi dation may induce a progressive decrease of glucose oxidation, insulin resistance, and increased fasting insulin secretion.