Circadian and metabolic effects of light-phase time-restricted feeding with a Western-style diet in young female rats

Young adulthood is a critical period for the development of metabolic disorders. Time-restricted feeding (TRF) has been proposed as an intermittent fasting strategy to mitigate these effects. However, its impact when feeding occurs out of sync with the biological clock remains uncertain. This study aimed to investigate the effects of mistimed time-restricted feeding during the light phase on metabolic and circadian outcomes in young female Wistar rats maintained on a pre-existing Western-diet background. Post-weaning rats (n = 24) were divided into a control group (standard chow diet) (C) and an western group (Western-style diet) (W) ad libitum for 8 weeks. The western group was further split into two subgroups: western ad libitum (WA) and western time-restricted (WR, 12-hour feeding window - light phase). Body weight, fat deposition, food intake, locomotor activity, glycemic and lipid profiles, hepatic lipid content, and circadian parameters were evaluated. At the end of the experimental period, Western-style diet exposure was associated with increased visceral adiposity and metabolic disturbances, consistent with a diet-induced obese phenotype. TRF during the light phase reduced visceral adiposity but paradoxically increased plasma glucose levels and relative liver weight, altered feeding patterns, disrupted glycemic rhythms, and reduced robustness of locomotor activity rhythms. Overall, these findings suggest that mistimed TRF may promote circadian misalignment and metabolic alterations under Western-diet conditions, highlighting a dissociation between metabolic and circadian responses.