Effects of glucose on fuel utilization and glycerol turnover in normal and injured man

Rates of fat mobilization (glycerol turnover), and fuel utilization and energy expenditure (indirect calorimetry) were measured in normal subjects and injured or septic patients maintained on high or low iv intakes of glucose as their sole nutrient source during 3-day periods. Regimens were given consecutively to each subject in random order. Concentrations of glucose, glycerol, fatty acids, 3-hydroxybutyrate, urea, insulin, and glucagon were determined in plasma, and of epinephrine and norepinephrine in urine. In normal subjects, there was no increase in energy expenditure with increasing glucose, although estimated costs of glucose storage as glycogen or fat could account for an increase of 4%. Thus, storage costs of glucose do not necessarily constitute an obligatory increase in energy expenditure. Rates of glycerol turnover and fat oxidation, and plasma glycerol concentrations were lower with the high than the low rate of glucose infusion, and lower than values reported by others during fasting or glucose infusion. Rates of fat oxidation were higher and glucose oxidation lower in patients than in controls, even though insulin concentrations were more than twice as high in patients. This confirms previous studies comparing injured and septic patients to depleted patients or historical controls. Triglyceride cycle activity was higher in the injured and septic patients than in normal subjects, and could account for from 6% to 15% of the increase in energy expenditure, in agreement with reports for burn patients.