At the biological level, eating schedules are predominantly dictated by endogenous timing mechanisms in multiple cells, tissues and organs. At the behavioural level, when feeding occurs at regular, anticipated times, the circadian clock initiates nutrient-sensing pathways to act synergistically to maintain nutrient homeostasis. Molecular clocks allow for temporal coordination between environmental, metabolic and behavioural cues that are caused by, or are a response to the daily perturbations in substrate availability.  When feeding occurs at random times, however, these same nutrient-responsive pathways provide feedback to the circadian clocks to ‘phase shift’ so that on subsequent days food is anticipated at the new feeding time. Such circadian 'misalignment' acutely impacts glycaemic control through impairments to beta cell function and insulin sensitivity, predisposing to an increased risk of developing obesity and type 2 diabetes. 

Periodic fasting and restricting the daily duration over which food is consumed can delay and often reverse the symptoms associated with several metabolic disorders. While the permutations in the pattern of daily food consumption are numerous, they broadly encompass three approaches: 1) sustained periods of chronic energy restriction; 2) intermittent fasting, and 3) time-restricted eating. A feature common to these dietary interventions is that perturbing feeding–fasting cycles drive robust oscillations in metabolism and circadian rhythms that confer health benefits. Indeed, a basic paradigm of circadian regulation of metabolism is that such oscillations of gene expression generate daily rhythms in cellular and whole-body metabolism. 

While almost the entire body of dietary literature to date, along with the profession of nutrition science, has focused on what we eat, recent and emerging knowledge from studies that have manipulated the feeding-fasting cycle are shifting that narrative so that now it is vital that we also consider that the timing of meals plays an important role in determining metabolic health outcomes. Without consideration of both what and when is eaten, we cannot unravel the potential synergies between these two variables and their potential impact on reducing the burden of chronic metabolic diseases at the population level.