Insulin sensitivity during very-low-calorie diets assessed by minimal modeling.

The time course of plasma glucose, insulin, and C-peptide after intravenous glucose (300 mg/kg body wt) injection was analyzed with minimal model approach in nine normal females and seven obese females. Glucose tolerance, estimated by glucose assimilation coefficient (KG), was positively correlated with glucose effectiveness (SG), but not correlated with peripheral insulin sensitivity (SI) in obese females as well as normal females. These factors were estimated before and after weight loss with 1.8-MJ (420-kcal) very-low-calorie diets (VLCDs) or with 2.5-3.3-MJ (600-800-kcal) low-calorie diets in two obese subjects. KG and glucose effectiveness decreased after acute weight loss with VLCD, although insulin sensitivity increased. Weight loss with low calorie diets resulted in improvement of KG and glucose effectiveness. These results suggest that a significant amount of glucose is taken up through insulin-independent mechanisms during the intravenous glucose tolerance test (ivGTT) in these subjects. This insulin-independent glucose uptake may be an important determinant of the fate of glucose in obese females as well as normal females.