strates, surpassing the capacity for synthesis [15, 16]. Amino acids extracted from muscle tissue serve as essential reserves for hepatic gluconeogenesis, a process leading to the endogenous production of glucose [ protein in critically ill patients has been suggested to attenuate the catabolic shift of the protein synthesis-proteolysis balance [17]. However, achieving this goal requires the body’s ability to absorb and metabolize these substrates under acute stress, yet early acute-illness-associated stress is known to impair protein–energy metabolism and its responsiveness to exogenous nutrients. Two studies, employing the analysis of amino-acid tracers, have reported that administering supplemental intravenous amino acids to critically ill patients improved whole-body net protein balance, and this effect was sustained for at least 24 h [18, 19]. Chapple et al. demonstrated that despite a preserved amino-acid digestion and absorption, muscle protein synthesis was severely attenuated [20]. These data suggest a so-called anabolic resistance to dietary protein in the acute phase of critical illness. Expanding our unders tanding of metabolic pathways, the potential toxicity of early amino-acid provision may stem from its stimulating effect on glucagon secretion. This catabolic ho rmone is known to be associated with hyperglycemia and hypercatabolism when upregulated. Addi­tionally, experimental data from a critically ill mice model shows that administering amino acids increases markers of hepatic amino acid catabolism without affecting markers of muscle atrophy [21].