Protein-metabolism kinetics and energy-substrate utilization in infants fed parenteral solutions with different glucose-fat ratios

The relative effect of glucose and lipids an whole-body protein-metabolism kinetics was assessed in seven infants undergoing parenteral feeding. Protein intake was kept constant and nonprotein energy was either provided as glucose alone or as an isoenergetic glucose-lipid mixture according to a randomized crossover trial. Protein metabolism and energy- substrate utilization were assessed by a primed, constant L-(13C)leucine infusion, combined with indirect calorimetry. There was a significant difference in the pattern of energy-sub- strate utilization according to regime. Protein turnover ( 1 1.3 ± 0.7 vs 9.8 ± 0.4 g- kg' -d'; P < 0.05), protein breakdown (8.4 ± 0.6 vs 7. 1 ± 0.4 g - kg ' . d ' ; P < 0.05), and amino acid oxidation rates (2.7 ± 0.4 vs 1.4 ± 0.5 g - kg� - d�: P < 0.05) were higher for the glucose than the glucose-lipid treatment, whereas protein-synthesis rates did not significantly differ. These results suggest that the nature of energy substrates delivered to parenterally fed infants may affect protein metabolism. Am J Clin Nutr 199 l;54:370-6.