What Is Fasting?

Answer:
Fasting is when a person willingly abstains from consuming

some or all food, drink, or both, for a period of time. Depending on what the person is fasting from, the fast may be total or partial, and the time period of the fast may be prolonged or intermittent. The fasting period may involve abstaining from sexual activity, or from certain types of food, such as meat. A complete fast is abstaining from all foods and liquids.

In medical terms, fasting can refer to one of three things: the metabolic status of a person that has not eaten overnight, the metabolic state after complete digestion and absorption of a meal, and an extended period of starvation. Many medical tests need to be performed under fasting conditions. The body makes some metabolic adjustments to itself while fasting. For most medical tests, the period of fasting is eight to twelve hours prior to the test being performed. Most of the metabolic changes occur as the meal is completely absorbed (usually 3-5 hours after a meal); this is commonly referred to as “post-absorptive state.” A diagnostic fast is a period of prolonged fasting conducted under medical supervision in order to find a problem (usually 8-72 hours depending on the patient’s age). This is usually performed in order to study hypoglycemia. Also, from ancient times to today, doctors have recommended extended fasting for treatment of various medical conditions.

The body’s primary source of fuel is glucose, which is also essential for proper brain function. When glucose is not available for four to eight hours, the body will turn to the liver, where glucose is stored as glycogen, for fuel. The process of turning glycogen into usable fuel for the body is called glycogenolysis. The body will also use small amounts of protein during this time in order to supplement the fuel. This will provide fuel to the body for up to twelve hours, at which point it will need to turn to glycogen stores in the muscles for a few more days. If there still is no glucose at this point, muscle wasting is avoided by changing to fat for a fuel source. The fat in the body will be converted into ketone through a process known as catabolism. Ketones are not sugar, but they can be used as a source of fuel for the brain until the glucose supply is restored.

Some changes in blood chemistry during prolonged fasts can have dangerous side effects. As long as there is fat to consume, the body will continue to use it for fuel. The body will warn the faster when fat levels are running low (7% for males and 10% for females) by increasing the urge for food. If the fast is not ended at this point, starvation will start to occur, as the body will begin to use protein for its fuel. Death will occur if this condition persists.

Fasting is also a part of most religions throughout the world, both as purification and as a form of worship.