Objective: To determine within the setting of isocaloric, isonitrogenous enteral diets whether a diet that supplies most of its calories from fat or carbohydrate would be most beneficial at limiting muscle protein wasting in catabolic illness.
Design: Prospective, randomized, crossover trial.
Setting: Academic pediatric burn unit in tertiary medical center.
Patients: Fourteen severely burned (>40% total body surface area) children underwent systemic metabolic and cross-leg muscle protein kinetic studies.
Interventions: All were treated clinically in a similar manner, including early excision and grafting, antimicrobial therapy, and isocaloric, isonitrogenous enteral nutritional support. Subjects randomly received either a high-carbohydrate enteral diet (3% fat, 82% carbohydrate, 15% protein), or a high-fat enteral diet (44% fat, 42% carbohydrates, 14% protein) for 1 week and then crossed over to the other diet for a second week.
Measurements and main results: On day 5 of each diet, muscle protein kinetics were determined from femoral arterial and venous blood samples during a primed-constant d5-phenylalanine infusion. Indirect calorimetry was used to determine systemic resting energy expenditure and respiratory quotient. The seven boys and seven girls were 7.1 +/- 1.1 (mean +/- sem) years old and suffered burns over 65 +/- 4% of their bodies, with 52 +/- 6% being third-degree burns. Muscle protein degradation markedly decreased (p <.01) with administration of the high-carbohydrate diet. Protein synthesis was unaltered. Endogenous insulin concentrations increased during the high-carbohydrate feeding period. No differences in energy expenditure were seen between study diets.
Conclusions: In severely burned pediatric patients, enteral nutrition supplied predominantly as carbohydrate rather than fat improves the net balance of skeletal muscle protein across the leg. This is attributable to decreased protein breakdown, suggesting a protein-sparing effect of high-carbohydrate feedings.