Sweet treats before sleep disrupt the clock system and increase metabolic risk markers in healthy rats

Aim: Biological rhythms are endogenously generated natural cycles that act as pacemakers of different physiological mechanisms and homeostasis in the organism, and whose disruption increases metabolic risk. The circadian rhythm is not only reset by light but it is also regulated by behavioral cues such as timing of food intake. This study investigates whether the chronic consumption of a sweet treat before sleeping can disrupt diurnal rhythmicity and metabolism in healthy rats. Methods: For this, 32 Fischer rats were administered daily a low dose of sugar (160 mg/kg, equivalent to 2.5 g in humans) as a sweet treat at 8:00 a.m. or 8:00 p.m. (ZT0 and ZT12, respectively) for 4 weeks. To elucidate diurnal rhythmicity of clock gene expression and metabolic parameters, animals were sacrificed at different times, including 1, 7, 13, and 19 h after the last sugar dose (ZT1, ZT7, ZT13, and ZT19). Results: Increased body weight gain and higher cardiometabolic risk were observed when sweet treat was administered at the beginning of the resting period. Moreover, central clock and food intake signaling genes varied depending on snack time. Specifically, the hypothalamic expression of Nampt, Bmal1, Rev-erbα, and Cart showed prominent changes in their diurnal expression pattern, highlighting that sweet treat before bedtime disrupts hypothalamic control of energy homeostasis. Conclusions: These results show that central clock genes and metabolic effects following a low dose of sugar are strongly time-dependent, causing higher circadian metabolic disruption when it is consumed at the beginning of the resting period, that is, with the late-night snack.