STUDY OBJECTIVES: As a day-active species, humans abstain from some or all foods and beverages and rest at night. The modern social clock diverged from the natural light-dark clock with far-stretching consequences for both fasting/eating and sleep/wake daily cycles.
METHODS: During the COVID-19 pandemic, prolonged social restrictions (SRs) offered a quasi-experimental protocol to directly test the impact of the relaxed social clock on eating and sleep behaviors and the coupling between them.
RESULTS: Using data from a global survey of 5747 adults (mean age 37.2 ± 13.7, 67.1% females, 100% worked/studied), we show that relaxation of the social time pressure (STP) during SRs led, on average, to a 42 min increase in the habitual fasting duration (FD, interval between the last and the first meal) (from 12:16 ± 2:09 to 12:57 ± 2:04) and a 34 min delay in the fasting window. FD was extended by lengthening both the presleep fasting and sleep durations. Pre-SR breakfast eaters delayed sleep and fasting, while breakfast skippers delayed sleep and advanced meals. Stopping alarm use on workdays was associated with a larger increase in FD. The correlations between chronotype, FD, and the mid-fasting time became more robust during SR.
CONCLUSIONS: We conclude that relaxed STP extends habitual FD and promotes co-alignment of daily fasting and sleeping. Given the finding that the sleep-fasting phase relationship during SRs remained stable, we suggest that a "daily sleep-fasting structure" may be a novel circadian marker quantifying the coupling between daily rhythms. These results may inform strategies of public circadian health management. Statement of Significance The current study leverages the unique quasi-experimental context of COVID-19 social restrictions (SRs) to reveal a previously unexplored link between social time pressure (STP), daily fasting and sleep in a large, global adult sample from the Global Chrono Corona Survey. We demonstrate that relaxed social schedules induce spontaneous extension of fasting duration and co-alignment of fasting and sleep rhythms. During SRs, the sleep-fasting phase relationship was stable, despite substantial shifts in meal and sleep timings. These findings unveil the role of STP in shaping daily rhythms, with broad implications for metabolic and sleep health. The daily sleep-fasting structure can serve as a novel marker for future research and interventions aimed at optimizing circadian health outcomes in modern societies.
