Fasting

Fasting

Fasting is primarily an act of willing abstinence or reduction from certain or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day (24 hours), or several days. Other fasts may be only partially restrictive, limiting particular foods or substances. The fast may also be intermittent in nature. Fasting practices may preclude sexual intercourse and other activities as well as food.

In a physiological context, fasting may refer to (1) the metabolic status of a person who has not eaten overnight, and (2) to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting, and some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting after 8–12 hours from their last meal. Metabolic changes toward the fasting state begin after absorption of a meal (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 observation for investigation of a problem, usually hypoglycemia. Finally, extended fasting has been recommended as therapy for various conditions by health professionals of many cultures, throughout history, from ancient to modern. Fasting is also a part of many religious observances.

Health effects

Complications

Health complications associated with fast-induced starvation include electrolyte imbalances, thinning hair, lanugo, potentially fatal cardiac arrhythmias and renal failure. Death occurs if fasting is pursued to the point of complete starvation.

Changes in blood chemistry during fasting, in combination with certain medications, may have dangerous effects, such as increased chance of acetaminophen poisoning. Excessive fasting for calorie restrictive purposes, accompanied by intense fears of becoming overweight, are associated with mental disturbances, including anorexia nervosa. See also: Starvation response

Benefits

According to Dr. Mark P. Mattson, chief of the laboratory of neurosciences at the US National Institute on Aging, fasting every other day (intermittent fasting) shows beneficial effects in mice as strong as those of caloric-restriction diets,^[3] and a small study conducted on humans at the University of Illinois at Chicago indicates the same results.^[4] According to the US 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 weight loss. The side effect was that 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".

A team of cardiologists in the UAE found that people observing Ramadan, the Islamic 30-days of fasting through the daylight hours (with meals after sunset and before sunrise) do not lose weight, yet enjoy a positive effect on their lipid profile, which means there is a reduction of LDL cholesterol in the blood. Also adherence to Eastern 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. These results suggest a possible positive impact on the obesity levels of individuals who adhere to these fasting periods.

In terms of cancer risk, there is no human evidence to date of the effects of fasting. However, animal studies found decreases in lymphoma incidence, longer survival after tumor inoculation, and lower rates of proliferation of several cell types.

Research by Valter Longo and others suggests a potential link between fasting and improved efficacy of chemotherapy.