Impact of Feeding Time and Duration on Body Mass and Composition in Young, Exercising Mice

Time-restricted feeding (TRF) has increased in popularity among various groups, including fitness enthusiasts. The ideal timing of TRF in relation to daily exercise is unknown. Most fitness enthusiasts consume meals immediately or soon after exercise to improve body composition (e.g., lean mass). We compared two different TRF approaches, as well as an ad libitum control diet, with regards to body mass and body composition in C57BL/6 mice. Young, healthy, male mice exercised five days per week and were assigned to consume food ad libitum (control), or to follow a 6-hour TRF that began immediately after exercise (TRF-I) or 5 hours after exercise (TRF-D); n = 12 mice per group. Body mass, lean mass, and fat mass were assessed weekly. Due to animal deaths, only 10 animals were included in the analysis for each TRF group, with 8 animals included for the control group. When computing the 8-week average, body mass varied between groups (p < 0.0001), with the TRF-I (25.4 ± 1.7 g) weighing less than the TRF-D (26.3 ± 2.3 g) and control (26.9 ± 2.3 g). Lean mass also differed (p < 0.0001), with control (22.8 ± 1.9 g) higher than TRF-I (21.4 ± 1.7 g) and TRF-D (21.7 ± 1.8 g). Additionally, fat mass differed between groups (p < 0.0001), with the TRF-D (2.7 ± 0.9 g) higher than the TRF-I (2.2 ± 0.9 g) and control (2.0 ± 1.2 g). Finally, percent body fat differed (p < 0.0001), with TRF-D (10.5 ± 3.3%) higher than TRF-I (8.6 ± 3.7%) and control (7.5 ± 4.3%). At the end of the 8-week intervention, TRF-I was lower in fat mass and percent body fat than TRF-D (p < 0.05), while body mass and lean mass were higher for control as compared to both TRF groups (p < 0.05). These results indicate that when combined with regular exercise, ad libitum feeding may be more beneficial (greater overall and lean mass gain) than TRF, regardless of feeding timing.