With the advent of technology and the availability of resources, a steady rise in chronic metabolic diseases such as diabetes and obesity has been observed in parallel to changes in behaviors such as sleep (timing and duration of sleep) and activity (frequency of exercise). The impact of milder circadian desynchronization that occurs in daytime workers who have irregular sleeping and eating behaviors on diabetes risk is not entirely understood. Whether these perturbations due to mistiming of circadian and social behavior in otherwise healthy people increases disease risk remains unclear. In this study, we demonstrated that early chronotype and larger percentage of daily calories consumed before noon were both associated with insulin sensitivity in people without type 2 diabetes. Moreover, nocturnal melatonin secretion was also associated with diabetes risk, with lower nocturnal secretion associated with increased insulin resistance. These results support a role of circadian regulation in glucose metabolism in healthy free-living individuals. It is necessary to analyze the timing of sleep and dietary behaviors on diabetes risk under natural environmental conditions, to better understand the effect of our daily behavior on health. Additionally, this study will contribute to the development of future, more effective lifestyle interventions for high-risk individuals.