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Keywords:

  • obesity;
  • insulin sensitivity;
  • frequently sampled intravenous glucose tolerance test (FSIGT);
  • oral glucose tolerance test (OGTT);
  • body composition;
  • DXA scanning

SUMMARY

Aim  To evaluate the long-term effect of changes in body composition induced by weight loss on insulin sensitivity (SI), non-insulin mediated glucose disposal, glucose effectiveness (SG) and β-cell function.

Design  Glucose metabolism was evaluated before and after participation in a two-year weight loss trial of Orlistat vs. placebo, combined with an energy and fat restricted diet.

Subjects  Twelve obese patients (11 women, 1 man), age 45.8 ± 10.5 years, body weight (BW) 99.7 ± 13.3 kg, BMI 35.3 ± 2.8 kg/m2.

Measurements  At inclusion and 2 years later an oral glucose tolerance test (OGTT) and a frequently sampled intravenous glucose tolerance test (FSIGT) were performed. Body composition was estimated by a dual-energy X-ray absorptiometry (DXA) whole body scanning.

Results  The patients obtained varying changes in BW ranging from a weight loss of 17.8 kg to a weight gain of 6.0 kg. Corresponding changes in fat mass (FM) varied from a 40% reduction to a 19% increase. A significant decrease in both fasting (p = 0.038) and 2 h (p = 0.047) blood glucose at OGTT was found. The improvement in insulin sensitivity (SI) estimated by means of Bergmans Minimal Model, was significantly and linearly correlated to change in total FM (r = − 0.83, p = 0.0026). A multiple regression analysis showed that changes in truncal FM was the strongest predictor of change in SI explaining 67% of the variation. First phase insulin response (AIRg) remained unchanged whereas insulin disposition index increased significantly (p = 0.044). At inclusion five patients had impaired glucose tolerance of which four, who lost weight, were normalized at the retest 2 years later.

Conclusion  In obese subjects long-term minimal or moderate changes in weight were found to be linearly associated with changes in insulin sensitivity. In obese subjects with impaired glucose tolerance even a minor weight loss was able to normalize glucose tolerance.