Comparison of glucose, fructose, sorbitol, and xylitol utilization in humans during insulin suppression

During fructose, sorbitol, and xylitol perfusions, carbohydrate utilization was studied by continuous indirect calorimetry and compared with glucose utilization during pharmacologic inhibition of endogenous insulin secretion. The experiment was performed in 28 normal volunteers divided into 5 groups (glucose, fructose, sorbitol, xylitol, and saline), each subject being its own control. Insulin suppression was obtained by means of a constant infusion of epinephrine (6 microgram/min) and propranolol (0.08 mg/min). After 90 min, during plasma insulin steady state, each sugar or polyol was infused at a rate of 6 mg/kg/min for 120 min. In contrast with a rise in plasma glucose from 161 +/- 6 mg/dl) to 291 +/- 14 mg/dl during glucose infusion, glucose levels remained unchanged during infusion of the glucose substitutes. Carbohydrate oxidation showed a rise of 24, 65, 76, and 44 mg/min during infusions of glucose, fructose, sorbitol, and xylitol, respectively. Lipid oxidation rates decreased by 7, 20, 33, and 23 mg/min during the same infusions. These results indicate that fructose, sorbitol, and xylitol are oxidized at a higher rate than glucose during suppression of endogenous insulin secretion, without any significant rise in glycemia.