Ethanol exerts acute protein-sparing effects during postabsorptive but not during anabolic conditions in man

Ethanol abuse is frequently associated with protein malnutrition. To assess the acute effects of ethanol on whole-body protein metabolism, [1-13C]leucine kinetics were measured in eight postabsorptive normal male subjects three times, ie, during administration of two doses of ethanol (dose 1, 0.52 g/kg during 2 hours and 0.3 g/kg during 3 hours; dose 2, 0.69 g/kg during 2 hours and 0.3 g/kg during 3 hours) and during saline (controls). During the last 2 hours of the studies, glucose, insulin, and amino acids were infused to assess the effects of ethanol on protein kinetics under anabolic conditions (euglycemic clamp). The decreases in leucine flux (reflecting whole-body protein breakdown) and nonoxidative leucine disappearance (a parameter of protein synthesis) during saline infusion were abolished in both ethanol protocols (P textless .05 or less v saline). The rate of leucine oxidation decreased during the higher dose of ethanol compared with saline (P textless .005), indicating an anticatabolic effect. During anabolic conditions (clamp), leucine flux and nonoxidative leucine disappearance were significantly higher in both ethanol studies compared with saline (P textless .05). Resting energy expenditure (REE) and oxygen consumption (VO2) during the euglycemic clamp increased to a greater degree during both ethanol studies than during saline (P textless .05 or less). Thus, an elevation of blood ethanol concentrations to the levels observed in social drinking results in a net anticatabolic effect (diminished leucine oxidation) when ethanol is administered alone. However, during administration of other nutritional substrates, the anticatabolic effect was not detectable, possibly because ethanol enhanced nutrient-induced thermogenesis.