Going without food. The metabolic fasting state begins some 4 hours after a meal, when the digestion and absorption of food is complete and body reserves of fat and glycogen begin to be mobilized.
Choosing not to eat anything or a particular food item for a specified period of time. Frequently associated with religious observances or political protests. Unsupervised fasting to reduce weight can result in death.
Fasting simply means abstaining from consumption of food for a period of time such as during sleep. A typical period of time for a fast for assessing nutritional status is 12 hours; however, fasts can be established for longer or shorter periods.
Not eating or eating fewer calories than the body needs at rest. During fasting, the body compensates by slowing the metabolic rate (a measurement of the body’s need for calories to sustain basic functions while at rest). Prolonged or severe fasting can slow the metabolic rate and reduce maintenance requirements to as low as 500 calories a day. When the metabolism slows this much, the body is not burning sufficient calories to warm itself (even in summer). Fatigue, depression, constipation, and dry skin and hair are consequences of a severely reduced metabolic rate. Doctors caution that fasting should never be used to lose weight. A drop in the metabolic rate eventually produces a frustrating plateau in weight loss, since energy requirements become lower. When a normal diet is resumed, the reduced metabolism results in a more rapid weight gain than before fasting. Very low-calorie diets are associated with health hazards including an increased risk for sudden death. People who need to fast for religious reasons and have diabetes mellitus or a history of heart problems should talk to their doctors about fasting.
Abstention from, or deprivation of, food and drink. It may result from a genuine desire to lose weight in an attempt to improve health and/or appearance or from a mental illness such as depression, or from an eating disorder. Certain religious customs and practices may demand periods of fasting.
Going without food or other nutritional support. This forces the body to catabolize its own glycogen, fat, and protein reserves in order to produce glucose. The products of incomplete fat metabolism (fatty acids, diacetic acid and acetic acid) produce ketosis and mild acidosis. Since glycogen reserves are depleted quickly in children, fasting can be especially hazardous to their health.
Fasting is the intentional avoidance of nourishment for a deliberate duration, with the goal of facilitating the expulsion of harmful substances from the body and fostering physical well-being.
Depriving a test vector of food for short periods. The term is inappropriate because fasting normally implies a voluntary abstinence from food by the subject, rather than an enforced deprivation, but its use in vector studies is now so common that a contra-recommendation is not justified.
Refraining from all types of food and consuming only water is referred to as fasting. Under moderate physical activity and temperate conditions, a person can survive on just water for over two months. However, if one abstains from both food and drink, it typically results in death within approximately ten days.
When there is no intake of food, the body derives the necessary energy to sustain critical bodily processes from substances stored in body tissues. Roughly six hours post the last meal, the body begins utilizing glycogen, a carbohydrate stored in the liver and muscles. This process lasts for around 24 hours, after which the body derives energy from stored fat and by degrading protein in the muscles. If the fasting persists, the body’s metabolism decelerates in an effort to conserve energy, resulting in a slower consumption of fat and protein reserves.
During the early phases of fasting, weight loss occurs swiftly. However, it subsequently slows down, partly due to the reduction in metabolism, but also because the body starts conserving its salt reserves, leading to water retention in the tissues. This build-up of fluid results in edema, or swelling, primarily impacting the legs and abdomen.
During extended periods of fasting, the capability to digest food may be compromised as the stomach ceases to produce digestive juices. Extended fasting can also put a halt to the creation of sex hormones, resulting in amenorrhea, or the lack of menstruation, in women.