An RER of 0.7 during the fasting period for TRF mice indicated that fat was the major source of fuel, whereas ALF mice burn a mixture of fats and carbohydrates, and NC mice burn mainly carbohydrates. Data for the respiratory exchange ratio (RER) (panels A and B); the volume of oxygen consumed (panels C and D), the volume of carbon dioxide produced panels (E and F), the heat generated (panels G and H), and the cage temperature (panels I and J) were collected and analyzed by two-way ANOVA and Tukey's multiple comparisons test. *p<0.05, **p<0.01, ***p<0.005 and **** p<0.001.