“When to eat” is important for our health as well as “What to eat,” because it has been revealed that the circadian clock in our bodies plays a key role in our health. The study on feeding timing and our health is called “chrononutrition.” The master clock is located in the suprachiasmatic nucleus of the brain and is synchronized by light stimuli. Peripheral tissue clocks, such as the liver clock, are regulated by feeding timing. Indeed, shift work, which is impossible to avoid an irregular lifestyle, is a known risk factor for many metabolic disorders. Previously, we found that some irregular feeding timing model animals showed abnormal circadian oscillation of hepatic clock genes and lipid metabolism-related genes, suggesting that regular feeding timing is required for our health. The macronutrients, such as carbohydrate and protein, are thought to be synchronizers for circadian clock. In addition, we previously reported that insulin is a key synchronizer for circadian clock. Furthermore, some food factors, such as caffeine, catechin, curcumin, and resveratrol, have shown not only health benefits but also the potential to synchronize the circadian clock. In this chapter, we introduce the progressive in chrononutrition and which nutrients and food factors regulate circadian clocks.