(A) Schematic outline of the four feeding regimens used in this study. Time-restricted-fed mice were allowed access to food from ZT13 through ZT21. Food availability is indicated by light beige boxes.

(B–E) Shown are (B) food ingested, (C) respiratory exchange ratio (CO 2 exhaled/O 2 inhaled), (D) average activity, and (E) whole-body energy expenditure as measured by volume of O 2 consumed in 2 hr bins plotted against time (+SEM, n = 4 mice). Since the high-fat diet (HFD) is energy rich (5.51 Kcal/g), the mice on HFD consume an amount of energy equivalent to that of the mice on normal chow (NC) (3.36 Kcal/g).

∗p < 0.05). Given the differences in body composition, metabolic activities in different organs, and heterogeneity of substrate uses in different groups of mice, both food intake and energy expenditures were expressed relative to individual animal or unit body weight. (F) Area under the curve analyses of energy expenditure (from Figure 1 E) (+SEM, n = 4,p < 0.05). Given the differences in body composition, metabolic activities in different organs, and heterogeneity of substrate uses in different groups of mice, both food intake and energy expenditures were expressed relative to individual animal or unit body weight.

(I) Average energy intake (+SEM) normalized to unit body weight shows no difference at the beginning of the experiment. In the subsequent weeks with gradual increase in body weight, this value progressively declines. By the end of 16–18 weeks, mice on tRF consume more energy/unit body weight than the ad lib counterparts.

(J) Representative FT mouse was remarkably leaner than the FA mouse.