Figure 6.

Rates of heat production (HP) in 13-week-old male Sprague-Dawley rats (Charles River Laboratories) fed a high-fat (LF) diet (blue line) between 4 and 13 weeks of age. There were 16 rats in the LF group, with the animal identification number (#1 to # 16) being shown at the top of each subplot. The experiment also involved 16 male Sprague-Dawley rats (Charles River Laboratories) fed a high-fat (HF) diet between 4 and 13 weeks of age. See Table 2 for experimental detail. At 13 weeks of age, rats were placed in a computer-controlled Oxymax instrument (an open circuit calorimeter; Columbus Instruments, OH) to measure 24-h O2 consumption, CO2 production, and HP (34). HP is calculated according to the Brouwer equation (61): HP (Kcal) = 3.82 × VO2 (in L) + 1.15 × VCO2 (in L). The overall average trajectory (magenta line) for HP of the 32 rats (16 in the LF group and 16 in the HF group) at each time point is shown in each subplot. This aids in identifying which rats in the LF group had HP values above or below the average and, therefore in interpreting data on the principal scores. The x-axis represents time during 24 h of the day, where time point “0” = 12 AM and time point “23” = 11 PM.