Influence of alcohol and sucrose consumption on energy balance and brown fat activity in the rat

Voluntary intake of solutions of alcohol (7%) and sucrose (10%) represented 20% and 25% of total metabolizable energy intake, respectively, in young male rats maintained on a stock diet, but total energy intake was similar to that of controls drinking water. Body weight and energy gains were similar for control and sucrose-treated rats but were significantly reduced in the group drinking alcohol, and energy expenditure, corrected for body size (kJ/kg0.75/day), was elevated in rats drinking alcohol (17% above control) or sucrose (18%). Gross and net energetic efficiencies were markedly depressed by consumption of alcohol but not by consumption of sucrose. Resting oxygen consumption, before and after injection of norepinephrine (25 micrograms/100 g body weight) was similar for all groups. Brown adipose tissue (BAT) mass and mitochondrial protein did not differ between groups, but the activity of the mitochondrial proton conductance pathway, assessed from the binding of 3H-guanosine diphosphate, was significantly elevated by alcohol and sucrose consumption. Thus, the increased energy expenditure associated with alcohol and sucrose ingestion may involve BAT thermogenesis, but this alone cannot explain the larger effects of alcohol on metabolic efficiency.