Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. A fast may be total or partial concerning that from which one fasts, and may be prolonged or intermittent as to the period of fasting. Fasting practices may preclude sexual activity as well as food, in addition to refraining from eating certain types or groups of foods; for example, one might refrain from eating meat. A complete fast in its traditional definition is abstinence of all food and liquids.
In a medical context fasting may refer to (1) the metabolic status of a person who has not eaten overnight, (2) to the metabolic state achieved after complete digestion and absorption of a meal, or (3) an unusually extended period of starvation. Several metabolic adjustments occur during fasting, and many medical diagnostic tests are standardized for fasting conditions. For most ordinary diagnostic purposes a person is assumed to be fasting after 8–12 hours. Many of the metabolic shifts of fasting begin as absorption of a meal is complete (typically 3–5 hours after a meal); "post-absorptive state" is synonymous with this usage, in contrast to the "post-prandial" state of ongoing digestion. A diagnostic fast refers to prolonged fasting (from 8–72 hours depending on age) conducted under medical observation for investigation of a problem, usually hypoglycemia. Finally, extended fasting has been recommended as therapy for various conditions by physicians of most cultures, throughout history, from ancient to modern.
Health effects
See also: Famine responseGlucose is the body's primary fuel source and is essential for the brain's functioning. When denied glucose for more than 4–8 hours, the body will turn to the liver for glycogen, a storage form of glucose, to be used for fuel. A process called glycogenolysis converts glycogen into a usable form of fuel. At this point, the body will also use small amounts of protein to supplement this fuel. This fuel will last for up to 12 hours before the body needs to turn to muscle stores of glycogen, lasting for a few more days. If glucose is still denied at this point, muscle wasting is prevented by temporarily switching to fat as the fuel source, meaning fat is converted into ketone through catabolism. Ketones, while not sugars, are able to be used by the brain as a fuel source as long as glucose is denied.
Such changes in blood chemistry during fasting may have dangerous effects. The body will continue to use fat for as long as there is fat to consume. The body will generally indicate to the faster when fat levels are running extremely low (less than 7% and 10% of body weight for males and females, respectively) with an increased urge for food. Fasts are usually broken long before this point. If the fast is not broken, starvation will begin to occur, as the body begins to use protein for fuel. Death can occur if fasting is pursued to the point of complete starvation.
Research suggests there are major health benefits to caloric restriction. Benefits include a reduced risk of cancer, cardiovascular diseases, diabetes, insulin resistance, immune disorders, and more generally, the slowing of the aging process and the potential to increase maximum life span. According to Dr. Mark P. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging, fasting every other day (intermittent fasting) shows beneficial effects as strong as those of caloric-restriction diets in mice, and a small study conducted on humans at the University of Illinois indicates the same results
According to The National Academy of Sciences, other health benefits include stress resistance, increased insulin sensitivity, reduced morbidity, and increased life span . Long-term studies in humans have not been conducted. However, short-term human trials showed benefits in weight loss. The side effect was the participants felt cranky during the three week trial. According to the study conducted by Dr. Eric Ravussin, "Alternate-day fasting may be an alternative to prolonged diet restriction for increasing the life span".
Adherence to Greek Orthodox fasting periods contributes to an improvement in the blood lipid profile, including a decrease in total and LDL cholesterol, and a decrease in the LDL to HDL cholesterol ratio. A statistically insignificant reduction in HDL cholesterol was also observed. These results suggest a possible positive impact on the obesity levels of individuals who adhere to these fasting periods.
Prolonged fasting, generally more than 30 days, can result in serious health problems. It is strongly advised that those thinking of fasting as a "diet" consult a physician or dietitian before they start.
Fasting leads to lowered blood sugar and blood pressure which can lead to dizziness and blackouts. People who had low blood pressure before the fast can have these problems even on a one-day fast. For most, these problems begin five or more days into a water fast. One way to avoid blackouts is to breathe deeply before standing up, and rise slowly.
Religious fasting
Bahá'í Faith
Main article: Nineteen Day FastIn the Bahá'í Faith, fasting is observed from sunrise to sunset during the Bahá'í month of `Ala' (March 2-March 20). Bahá'u'lláh established the guidelines in the Kitáb-i-Aqdas. It is the complete abstaining from both food and drink (including abstaining from smoking). Consumption of prescribed medications is not restricted. Observing the fast is an individual obligation and is binding on Bahá'ís between 15 years (considered the age of maturity) and 70 years old. Exceptions to fasting include individuals younger than 15 or older than 70; those suffering illness; women who are pregnant, nursing, or menstruating; travellers who meet specific criteria; and individuals whose profession involves heavy labor and those who are very sick where fasting would be considered dangerous. For those involved in heavy labor, they are advised to eat in private and generally to have simpler and/or smaller meals than are normal.
Along with obligatory prayer, it is one of the greatest obligations of a Bahá'í. The Guardian of the Bahá'í Faith, Shoghi Effendi, explains: "It is essentially a period of meditation and prayer, of spiritual recuperation, during which the believer must strive to make the necessary readjustments in his inner life, and to refresh and reinvigorate the spiritual forces latent in his soul. Its significance and purpose are, therefore, fundamentally spiritual in character. Fasting is symbolic, and a reminder of abstinence from selfish and carnal desires."
Buddhism
Buddhist monks and nuns following the Vinaya rules commonly do not eat each day after the noon meal . This is not considered a fast but rather a disciplined regimen aiding in meditation and good health.
"Once when the Buddha was touring in the region of Kasi together with a large Sangha of monks he addressed them saying: 'I, monks, do not eat a meal in the evening. Not eating a meal in the evening I, monks, am aware of good health and of being without illness and of buoyancy and strength and living in comfort. Come, do you too, monks, not eat a meal in the evening. Not eating a meal in the evening you too, monks, will be aware of good health and..... and living in comfort.' " (Kitagiri Sutta-Majjhima Nikaya)
Fasting is not practiced by lay Buddhists because it is seen as a deviation from the Middle Path. This is because prior to attaining Buddhahood, prince Siddhartha practiced a regime of six years of strict austerity during which he consumed very little food. Henceforth, prince Siddhartha practiced moderation in eating which he later advocated for his disciples. However, on Uposatha days (roughly once a week) lay Buddhists are instructed to observe the eight precepts which includes refraining from eating after noon till the following morning.
The Vajrayana practice of Nyung Ne is based on the tantric practice of Chenrezig. It is said that Chenrezig appeared to Gelongma Palmo, an Indian nun who had contracted leprosy and was on the verge of death. Chenrezig taught her the method of Nyung Ne in which one keeps the eight precepts on the first day, then refrains from both food and water on the second. Although seemingly against the Middle Way, this practice is to experience the negative karma of both oneself and all other sentient beings and, as such is seen to be of benefit. Other self-inflicted harm is discouraged.
Perhaps because of sectarian differences, some lineages of Buddhism consider taking the eight precepts, even for a limited period of time, to be a fast. In fact, they are occasionally referred to as "fasting precepts." The eight precepts closely resemble the ten vinaya precepts for novice monks and nuns. The novice precepts are the same with the prohibition against handling money.
Christianity
The "acceptable fast" is discussed in the biblical Book of Isaiah, chapter 58:3-7. In essence, it means afflict the soul through abstaining from fulfilling the needs or wants of the flesh. The opening chapter of the Book of Daniel, vv. 8-16, describes a partial fast and its effects on the health of its observers.
Fasting is a practice in several Christian denominations or other churches. Some denominations do not practice it, considering it an external observance, but many individual believers choose to observe fasts at various times at their own behest. The Lenten fast observed in the Cat
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