Nader Lessan

Every year, healthy adult Muslims practice dawn to sunset fasting for a whole lunar month. No food or fluid is allowed for the fasting time window. After sunset, eating is allowed. The dramatic change in the timing of meals is accompanied by changes in sleeping hours and thus alterations in circadian rhythms. Hormonal mechanisms mainly determined by the latter also change. These include shifts in cortisol and melatonin. Food‐dependent hormones such as Ghrelin and leptin also show changes. A well‐established principle of chrononutrition is that the timing of eating may be as or more important than the content of food. Ramadan fasting (RF) is distinct from other forms of intermittent fasting, although there are also some similarities with time restricted eating (TRE). Both have been shown to have health benefits. Here, we examine existing literature to understand and learn from this very commonly practiced form of fasting and its relationships to circadian rhythms and homoeostatic mechanisms.