Periods of voluntary abstinence from food and drink (i.e., intermittent fasting) has been practiced since earliest antiquity by peoples around the globe. Books on ethnology and religion describe a remarkable variety of fasting forms and practices.Renewed interest in fasting regimens is evidenced by a plethora of popular press publications and diet recommendations. For example, in 2013, Mosley and Spencer published a best-selling book titled “The Fast Diet,” which touts the benefits of restricting energy intake severely for two days a week while eating normally the rest of the week.Dozens of books promote various fasting dietary patterns and the web offers hundreds of fasting-related sites. However, scientific evidence for the health benefits of intermittent fasting in humans is often extrapolated from animal studies, based on observational data on religious fasting (particularly Ramadan), or derived from experimental studies with modest sample sizes.