Medical implications of controlled fasting

The custom of fasting is common to most Eastern and Western cultures and is widely practised. The reasons for fasting include health, protest and religious expressions of devotion, aestheticism and purification. Fasts can last from hours to months and can range from restricting certain foods to complete abstinence from all food and drink. Here I review the medical implications of controlled fasting in which food and drink is completely restricted from sunrise to sunset for consecutive days. This regimen has also been described as Ramadan-type fasting, partial fasting, restricted fasting, fasting-refeeding, periodic food and water deprivation, and daily starvation-feeding. The Muslim fast of Ramadan, undertaken by about a billion people annually, is the most widely observed controlled fast today and has provided the setting for most of the research conducted.