Acutely Decreased Thermoregulatory Energy Expenditure or Decreased Activity Energy Expenditure Both Acutely Reduce Food Intake in Mice

Despite the suggestion that reduced energy expenditure may be a key contributor to the obesity pandemic, few studies have tested whether acutely reduced energy expenditure is associated with a compensatory reduction in food intake. The homeostatic mechanisms that control food intake and energy expenditure remain controversial and are thought to act over days to weeks. We evaluated food intake in mice using two models of acutely decreased energy expenditure: 1) increasing ambient temperature to thermoneutrality in mice acclimated to standard laboratory temperature or 2) exercise cessation in mice accustomed to wheel running. Increasing ambient temperature (from 21 degrees C to 28 degrees C) rapidly decreased energy expenditure, demonstrating that thermoregulatory energy expenditure contributes to both light cycle (40 +/- 1%) and dark cycle energy expenditure (15 +/- 3%) at normal ambient temperature (21 degrees C). Reducing thermoregulatory energy expenditure acutely decreased food intake primarily during the light cycle (65 +/- 7%), thus conflicting with the delayed compensation model, but did not alter spontaneous activity. Acute exercise cessation decreased energy expenditure only during the dark cycle (14 +/- 2% at 21 degrees C; 21 +/- 4% at 28 degrees C), while food intake was reduced during the dark cycle (0.9 +/- 0.1 g) in mice housed at 28 degrees C, but during the light cycle (0.3 +/- 0.1 g) in mice housed at 21 degrees C. Cumulatively, there was a strong correlation between the change in daily energy expenditure and the change in daily food intake (R-2 = 0.51, p<0.01). We conclude that acutely decreased energy expenditure decreases food intake suggesting that energy intake is regulated by metabolic signals that respond rapidly and accurately to reduced energy expenditure.