Abstaining from all food and drinking only water. In temperate conditions and at moderate levels of physical activity, a person can survive on water alone for more than 2 months; however, without food or drink, death usually occurs within about 10 days. About 6 hours after the last meal, the body starts to use glycogen (a carbohydrate stored in the liver and muscles). This continues for about 24 hours, after which the body obtains energy from stored fat and by breaking down protein in the muscles. If fasting continues, the body’s metabolism slows down to conserve energy, and the fat and protein stores are consumed more slowly. In the initial stages of fasting, weight loss is rapid. Later it slows down, because metabolism slows down and the body starts to conserve its salt supply, which causes water retention. In prolonged fasting, the ability to digest food may be impaired because the stomach stops secreting digestive juices. Prolonged fasting also halts production of sex hormones, causing amenorrhoea (absence of menstruation) in women.


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