**Abstract**

Circadian rhythm is a fundamental process of sustaining metabolic homeostasis by predicting changes in the environment. This is driven by biological clocks, which operate within a 24-h period to orchestrate daily variation of metabolism and sleep. The central clock in the hypothalamus is the master keeper of the circadian rhythm and is primarily reset by light, while the feeding-fasting rhythm, that is, nutritional stimulus, entrains peripheral clocks in peripheral organs such as the intestine and liver. Nutritional stimuli are important modulators of peripheral circadian rhythms and may affect the central clock and sleep homeostasis through metabolic alterations. In this chapter, I will summarize the significance of circadian rhythm and sleep in metabolic regulation as well as discuss the impact that diet has on circadian rhythm and sleep.

**Keywords:** circadian rhythm, sleep, clock gene, intestinal microbiota, jet lag
