To characterize the abnormalities of glucose homeostasis and insulin action early in the course of human obesity, we studied in vivo glucose kinetics in seven children who were recently massively overweight. At time of study they were gaining weight at a rate of 13.5 ± 1.4 kg/yr. They were compared with six age-matched control subjects. Six adults with long-term obesity and five normal adults were studied in parallel. The obese children and adults were normoglycemic and hyperinsulinemic. We found that glucose production and utilization were remarkably higher in obese children (295 ± 18 mg/min; 7.6 mg · kg−1 lean body mass · min−1) than in control children (129 ± 13 mg/min; 4.4 mg · kg−1 lean body mass · min−1P < .01) and obese adults (151 ± 8 mg/min; 3.1 ± 0.3 mg · kg−1 lean body mass · min−1 , P < .01). Obese adults had normal rates of glucose production and utilization. Insulin- and non-insulin-mediated glucose uptake, estimated with somatostatin-induced suppression of endogenous insulin secretion, contributed almost equally to the excess glucose utilization observed in the obese children. When studied with the euglycemic-hyperinsulinemic clamp, obese children could not increase glucose disposal to the same extent as normal children and were not able to adequately suppress their endogenous glucose production. Recently obese children are therefore characterized by an increased basal glucose turnover rate and an already established insulin resistance of the liver and probably the skeletal muscles.

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