Almost all organisms are subjected to daily changes in their environment with light-dark cycles that are caused by the Earth’s rotation around its own axis. To anticipate these changes, organisms possess an evolutionary conserved endogenous oscillator, the circadian clock, that drives daily rhythms in behavior and physiology with a 24 h period. In mammals, these pacemakers regulate most physiological processes such as sleep-wake cycles, body temperature, heartbeat, and many other aspects of the physiology. Consequently, the mammalian circadian clock plays a fundamental role in the orchestration of metabolism and allows a timely controlled regulation of fatty acid, glucose and drug metabolisms in an anticipated manner. While mechanisms allowing these controls by the molecular oscillator and feeding rhythms are not completely understood, it is accepted that they involved rhythmic transcriptional and posttranscriptional regulation of genes encoding enzymes implicated in different aspects of animal physiology. However, perturbation of the natural environment is a hallmark of our modern society. For example, approximately 600 million people are exposed to shift work around the world, the main cause of circadian disruption in the population. Because of the central role of the circadian clock in the regulation of physiology, its disruption is associated with a wide range of physiological and pathological conditions including obesity and type 2 diabetes, Alzheimer’s disease and cancer. In this context, it is essential to understand the causal relationship between altered circadian rhythms and pathological conditions.