Glucose utilization and nitrogen balance in the obese on a protein-lipid hypocaloric diet

Glucose utilization and insulin and growth hormone responses were evaluated in eight obese women by three rapid intravenous glucose tolerance tests (IVGTT): during a control period, and after 1 and 3 weeks of a 750 kcal/day protein-lipid diet (1 kcal = 4.1855 kJ). Weight loss averaged 454 g/day during the 1st week and 238 g/day for the 2nd and 3rd weeks of the diet. Nitrogen balance was maintained in equilibrium. Plasma insulin concentrations fell by 50% within 1 week of dieting; growth hormone levels were not modified. The net rate of glucose disappearance dropped from 0.98 to 0.65 and 0.68% min, the glucose pool from 16.2 to 13.3 and 13.4 g, and glucose utilization from 158 to 88 and 87 mg/min during the control period, and at 1 and 3 weeks of dieting, respectively. The insulinogenic index decreased from 0.41 to 0.24 to 0.16 with successive IVGTT's. The glucose volume of distribution was not modified with dieting. It is concluded that a hypocaloric protein-lipid diet induces (i) a carbohydrate intolerance not related to a negative nitrogen balance and (ii) a rapid initial weight loss which cannot be ascribed to a depletion of the glucose volume.