['In pediatric cardiac surgery, fluid-restricted low-protein (LoProt) diets account for cumulative protein deficits with increased morbidity. In this setting, we aimed to inhibit proteolysis by a high-carbohydrate (HiCarb)-intake-induced hyperinsulinemia and improve protein balance.', 'The effect of a HiCarb/LoProt (glucose 10 mg · kg(-1) · min(-1)/protein 0.7 g · kg(-1) · d(-1)) versus a normal-carbohydrate (NormCarb)/LoProt (glucose 7.5 mg · kg(-1) · min(-1)/protein 0.3 g · kg(-1) · d(-1)) enteral diet on whole-body protein breakdown and balance was compared in a prospective, randomized, single-blinded trial in 24 children after cardiac surgery. On the second postoperative day, plasma insulin and amino acid concentrations, protein breakdown (endogenous rate of appearance of valine), protein synthesis (non-oxidative disposal of valine), protein balance, and the rate of appearance of urea were measured by using an isotopic infusion of [1-(13)C]valine and [(15)N(2)]urea.', 'The HiCarb/LoProt diet led to a serum insulin concentration that was three times higher than the NormCarb/LoProt diet (596 pmol/L, 80-1833, and 198 pmol/L, 76-1292, respectively, P\xa0=\xa00.02), without differences in plasma glucose concentrations. There were no differences in plasma amino acid concentrations, non-oxidative disposal of valine, and endogenous rate of appearance of valine between the groups, with a negative valine balance in the two groups (-0.65 μmol · kg(-1) · min(-1), -1.91 to 0.01, and -0.58 μmol · kg(-1) · min(-1), -2.32 to -0.07, respectively, P = 0.71). The serum cortisol concentration in the HiCarb/LoProt group was lower compared with the NormCarb/LoProt group (204 nmol/L, 50-544, and 532 nmol/L, 108-930, respectively, P = 0.02).'] Does high-carbohydrate/low-protein-induced hyperinsulinemia improve protein balance in children after cardiac surgery?