Relaxation of social time pressure reveals tight coupling between daily sleep and eating behavior and extends the interval between last and first meal

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. During the COVID-19 pandemic, prolonged social restrictions (SR) 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. Using data from a global survey of 5,747 adults (mean age 37.2±13.7, 67.1% females, 100% worked/studied), we show that relaxation of the social time pressure during social restrictions 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 pre-sleep 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. We conclude that relaxed social time pressure extends habitual fasting duration and promotes co-alignment of daily fasting and sleeping. Given the finding that the sleep-fasting phase relationship during social restrictions 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.