The circadian clock, a highly specialized, hierarchical network of biological pacemakers, directs and maintains proper rhythms in endocrine and metabolic pathways required for organism homeostasis. The clock adapts to environmental changes, specifically daily light-dark cycles, as well as rhythmic food intake. Nutritional challenges reprogram the clock, while time-specific food intake has been shown to have profound consequences on physiology. Importantly, a critical role in the clock-nutrition interplay appears to be played by the microbiota. The circadian clock appears to operate as a critical interface between nutrition and homeostasis, calling for more attention on the beneficial effects of chrono-nutrition.

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The approach to healthful eating proposed by Maimonides (1135–1204), a medieval Jewish philosopher and doctor also known as Rambam, has garnered followers from well beyond the grave. In his writings, the Rambam gave clear instructions regarding what, when, and how much people should eat in order to lead a healthy life. One of his well-known quotes is: “Eat like a king in the morning, a prince at noon, and a peasant at dinner.”

Feeding behavior is a principal factor that plays a role in the organism’s nutritional status. Eating schedules are predominantly dictated by an inherent timing mechanism, but in addition, are affected by food availability, hunger, and satiety and also by social habits and convenience. A large body of nutritional studies has extensively examined the effect of the quantity and quality of food ingested on the organism’s well-being. Nowadays, it is widely accepted that these parameters are critical and that their alteration is associated with morbidity and mortality (e.g., high-fat diet). Evidence accumulated during recent years suggests that meal timing can affect a wide variety of physiological processes, including sleep/wake cycle, core body temperature, performance, and alertness. Moreover, it appears that feeding time has a dramatic effect on health and can be employed to prevent obesity and various other metabolic pathologies. Hence, “chrono-nutrition” refers to food administration in coordination with the body’s daily rhythms. This concept reflects the basic idea that, in addition to the amount and content of food, the time of ingestion is also critical for the well-being of an organism.

Hitherto, as detailed in this Review, the vast majority of studies have focused on the effect of scheduled meals on metabolic pathologies such as obesity and diabetes. However, one can envision that the “optimal” feeding schedule might harbor wide medical benefits beyond metabolic syndrome. Future studies are expected to shed more light on the prospects of feeding timing in preventing morbidity and reducing mortality in relation to other pathologies such as aging.

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