The impact of religious fasting on human health

Fasting is defined as a partial or total abstention from all foods, or a select abstention from prohibited foods. As a potential non-pharmacological intervention for improving health and increasing longevity, fasting has been the subject of numerous scientific investigations. The three most commonly studied fasts are caloric restriction (CR), alternate-day fasting (ADF), and dietary restriction (DR). A summary of the main findings is presented below.CR is the reduction of kilocalorie (kcal) intake by a certain percentage (typically 20 - 40%) of ad libitum consumption. CR has been demonstrated to improve health and increase longevity in a diverse group of species, including: dog, fruit fly, nematode, rodent, rotifer, spider, non-human primate, and zebrafish [1]. Additionally, CR appears to delay the onset of the following diseases: autoimmune diseases, atherosclerosis, cardiomyopathies, cancer, diabetes, renal diseases, neurodegenerative diseases, and respiratory diseases [2,3]. Regarding cardiovascular health, the following changes have been noted following a CR regimen: decreases in resting heart rate (HR) and blood pressure (BP); increases in HR variability; and improvements in left ventricular function, post-exercise recovery of both HR and BP, and flow-mediated vasodilation [4]. Regarding glucoregulatory health, CR has been shown to decrease fasting glucose and insulin levels, increase insulin sensitivity, decrease body fat percentage, and lower the incidence of diabetes [5,6].ADF consists of alternating 24-hour periods: during the "feast period," fasters may consume food ad libitum; during the "fast period," food consumption is restricted or halted altogether. Water is allowed ad libitum during all times. Animal ADF trials have reported extended lifespan [1] as well as the retardation or altogether prevention of the development of many morbidities, including: cardiovascular disease, kidney disease, cancers, and diabetes [4,7]. ADF has been noted to elicit the f