Current recommended parenteral protein intakes do not support protein synthesis in critically ill septic, insulin-resistant adolescents with tight glucose control

Objective: To investigate the effects of insulin infusion and increased parenteral amino acid intakes on whole body protein balance, glucose kinetics, and lipolysis in critically ill, insulin-resistant, septic adolescents. Design: A single-center, randomized, crossover study. Setting: A medicosurgical intensive care unit in a tertiary university hospital. Patients: Nine critically ill, septic adolescents (age 15.0 ± 1.2 yrs, body mass index 20 ± 4 kg m^-2) receiving total parenteral nutrition. Interventions: Patients received total parenteral nutrition with standard (1.5 g•kg ^-1•day^-1) and high (3.0 g•kg ^-1•day^-1) amino acid intakes in a 2-day crossover setting, randomized to the order in which they received it. On both study days, we conducted a primed, constant, 7-hr stable isotope tracer infusion with [1-¹³C]leucine, [6,6-²H₂]glucose, and [1,1,2,3,3-²H₅]glycerol, in combination with a hyperinsulinemic euglycemic clamp during the last 3 hrs. Measurements and Main Results: Insulin decreased protein synthesis at standard amino acid and high amino acid intakes (p < .01), while protein breakdown decreased with insulin at standard amino acid intake (p < .05) but not with the high amino acid intake. High amino acid intake improved protein balance (p < .05), but insulin did not have an additive effect. There was significant insulin resistance with an M value of ∼3 (mg•kg^-1•min ^-1)/(mU•mL^-1) which was 30% of reported normal values. At high amino acid intake, endogenous glucose production was not suppressed by insulin and lipolysis rates increased. Conclusion: The current recommended parenteral amino acid intakes are insufficient to maintain protein balance in insulin-resistant patients during tight glucose control. During sepsis, insulin decreases protein synthesis and breakdown, and while high amino acid intake improves protein balance, its beneficial effects may be offset by enhanced endogenous glucose production and lipolysis, raising concerns that insulin resistance may have been exacerbated and that gluconeogenesis may have been favored by high amino acid intakes. Dose-response studies on the effect of the level of amino acid intakes (protein) on energy metabolism are needed.