1. Both increased and decreased sensitivity to insulin has been proposed to precede the development of obesity. Therefore, insulin sensitivity was measured during a 2 h hyperinsulinaemia (100 m-units min−1 m−2) euglycaemic (4.5 mmol/l) glucose clamp combined with indirect calorimetry in nine weight-stable post-obese women and in nine matched control women preceded by 12 h fasting after 48 h on a standardized diet.

2. Both glucose disposal rate (post-obese women, 9.5 ± 2.2 mg min−1 kg−1, control women, 11.2 ± 1.4 mg min−1 kg−1, not significant) and glucose oxidation (3.6 ± 0.5 mg min−1 kg−1 versus 4.0 ± 0.7 mg min−1 kg−1, not significant) were similar in the two groups during the last 30 min of the clamp. Lipid oxidation also decreased similarly during the clamp in the post-obese women (from 30.4 ± 12 to 2.0 ± 7 J min−1 kg−1) and in the control women (from 33.6 ± 11 to 5.4 ± 8 J min−1 kg−1, not significant). Basal plasma concentrations of free fatty acids were similar, but at the end of the clamp free fatty acids were lower in the post-obese women than in the control women (139 ± 19 and 276 ± 48 μmol/l, P = 0.02).

3. We conclude that the insulin sensitivity of glucose metabolism is unaltered in the post-obese state. The study, however, points to an increased antilipolytic insulin action in post-obese subjects, which may favour fat storage and lower lipid oxidation rate post-prandially. The results suggest that alterations in lipid metabolism may contribute to the explanation of the propensity to obesity in susceptible individuals.

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