Fasting is the voluntary abstinence of all food and drink. Lasting from 12 hours – 90 days, usually due to religious or therapeutic reasons. An absolute fast or dry fasting is normally defined as abstinence from all food and liquid for a defined period, usually a period of 24 hours, or a number of days. Water fasting allows drinking water but nothing else. Other fasts may be partially restrictive, limiting only particular foods or substances.