Decreased glucose-induced thermogenesis at the onset of obesity.

To investigate the possible existence of a defect of thermogenesis at the onset of obesity, we studied glucose-induced thermogenesis (GIT) during an oral glucose-tolerance test (OGTT) (1 g/kg body wt) in 12 women who were at the onset of obesity (group A) compared with 12 long-standing obese women (group B) and 8 lean control subjects. During OGTT hyperinsulinemia and glucose intolerance were measured in group B, suggesting an insulin-resistant state, but not in group A. A similar defect in GIT occurred in both obese groups (8.9 +/- 1.5% in control subjects vs 4.2 +/- 1.1% in group A and 4.3 +/- 1.0% in group B, P < 0.05) despite the absence of alteration in nonoxidative glucose metabolism. We conclude that a decrease in GIT already exists at the onset of obesity, which supports the hypothesis of a possible involvement of this defect in the genesis of obesity.