Repeated light-dark shifts speed up body weight gain in male F344 rats.

This study is aimed at verifying the causal relationship of chronic circadian desynchronization and changes in body weight control. Eight male albino F344 rats aged between 12-15 wk were subjected to twice weekly 12-h shifts of the daily light-dark (LD) cycle for 13 wk (3 mo). Continuous circadian phase shifts consisting of intermittent phase delay and advance and reduced circadian amplitudes were consistently displayed in all five experimental rats implanted intraperitoneally with heart rate, body temperature, and activity transponders. The experimental rat maintained a greater body weight during LD shifts and even after 10 days of recovery than that of the age-matched control rat, which was maintained on a regular LD cycle. Body weight gain was greater in the first 2 mo of LD shifts in the experimental rat than in the control rat. Relative to the baseline, food intake and activity percentages were increased and reduced, respectively, for the experimental rats. Features of these results, such as increased body weight gain and food intake, and reduced activity, suggest a causal relationship of chronic circadian desynchronization and changes in body weight control in male albino F344 rats.