Most nutritional research has focused on what and how much to eat, but few studies have examined the timing of when to eat. In line with the concept of chronotherapy/pharmacology, the research field of chrono-nutrition was born. In this symposium, we will review the basic research on chrono-nutrition (animal and cell experiments), including the results of our own research to date. Diet has long been known as a regulator of the circadian clock. By changing the feeding timing of mice, not only their behavioral rhythms but also the clocks of their peripheral organs are synchronized in accordance with the time of their meals. Insulin and IGF-1 are pathways through which meals regulate the circadian clock. In addition, several functional food ingredients have been reported to affect clock gene expression in peripheral organs, either directly or indirectly. Caffeine, in particular, strongly affects not only the peripheral clock but also the central clock, altering the period, amplitude, and phase of clock gene expression and behavioral rhythms. Recently, diurnal rhythms have also been reported in oral and intestinal bacteria, and their rhythmic nature is mainly driven by feeding rhythms. The diurnal rhythm of the gut microbiota has also been found to provide diurnal rhythms to physiological functions on the host, such as intestinal epithelial cells, intestinal immunity, and even the liver. The world is now talking about "time-restricted eating" (TRE), which limits meal times to 8-12 hours each day; TRE provides a regular eating habit, fasting at night, and increases the amplitude of the circadian clock, which has an anti-obesity effect, prevents type 2 diabetes, and suppresses appetite. In animal studies, it has also been reported to inhibit the speed of transplant cancer growth, have an effect on the prevention of dementia, and prevent the decline of cardiac function due to aging. On the other hand, as chrono-nutrition, it is necessary to consider how to eat in accordance with the diurnal rhythm of physiological functions. Metabolism and absorption of food and nutrients vary with time. The applications of chrono-nutrition are diverse, such as how to efficiently take in nutrients, how to efficiently lose weight, how to efficiently prevent sarcopenia, and so on. As time permits, I will also present these data, with an emphasis on animal studies.