Summary: Energy expenditure is measured using an indirect respiration calorimetry system (CLAMS, Columbus Instruments, Columbus, OH). Air is drawn through calorimetry chambers and flow rate is controlled and measured with a mass flow controller. Oxygen consumption and carbon dioxide production are measured and used to calculate energy expenditure (or heat production, kilocalories (kcal)) and respiratory exchange ratio (RER: VCO2\/VO2). The calorimetry chambers are also equipped with sensors, which allow the measurement of physical activity, food intake and water intake. All calorimetry chambers are housed within a temperature and light controlled incubator. The system contains 8 calorimetry chambers. Animals are acclimated to the facility for at least 1 week. Animals are then acclimated to the CLAMS cages and powdered diet for 48 hours and to the light and temperature-controlled chamber for 24 hours prior to testing. Analyzed data constitutes data collected from 48 hours of continuous measurement (2 light\/2 dark cycles). To investigate the influence of exercise on energy expenditure and substrate oxidation, the chambers can also be fitted with running wheels or the animals can be placed in separate chambers containing treadmills.