Intermittent fasting – periods of eating little or nothing interspersed with normal food consumption – isn't an effective way to lose weight, according to a review of 22 randomized controlled trials. It seems that assurances from celebrity weight-loss gurus and appeals to historical precedent aren’t enough make a practice work.

Religions have encouraged or directed their adherents to refrain from eating, and in some cases even drinking water, to mark holy days or show penitence for thousands of years. In recent times, social media has been filled with those who advocate engaging in fasts for weight loss instead. The fact the practice has been so widespread for so long has been touted as evidence of its effectiveness. Until recently, however, most fasts were conducted in a world where calories were harder to come by the rest of the time, and whatever people's reasons for fasting, shedding fat wasn't high among them.