Nearly 14% of Americans experience chronic circadian disruption due to shift work, increasing their risk of obesity, diabetes, and other cardiometabolic disorders. These disorders are also exacerbated by modern eating habits such as frequent snacking and consumption of high-fat foods.
We investigated the effects of recurrent circadian disruption (RCD) on glucose metabolism in C57BL/6 mice and in human subjects exposed to non-24-h light-dark (LD) schedules vs. those on standard 24-h LD schedules. These LD schedules were designed to cause circadian misalignment between behaviors including rest/activity and fasting/feeding with the output of the near-24-h circadian system, while minimizing sleep loss, and were maintained for 12 weeks in mice and 3 weeks in humans. We examined interactions of these circadian-disrupted schedules compared to control 24-h schedules with a lower-fat diet (LFD, 13% in mouse and 25–27% in humans) and high-fat diet (HFD, 45% in mouse and 45–50% in humans). We also used young vs. old mice to determine whether they would respond differently to RCD.
When combined with a HFD, we found that RCD caused significant weight gain in mice and significantly impaired glucose tolerance and insulin sensitivity in both mice and humans, but this did not occur when RCD was combined with a LFD. This effect was similar in both young and older mice.
These results suggest that reducing dietary fat may protect against the metabolic consequences of a lifestyle (such as shift work) that involves chronic circadian disruption.