Fasting

Alternate-day fasting (alternating between a 24-hour "fast day" when the person eats less than 25% of usual energy needs, followed by a 24-hour non-fasting "feast day" period) has been shown to improve cardiovascular and metabolic biomarkers similarly to a calorie restriction diet in people who are overweight, obese or have metabolic syndrome.

[10] There is little evidence to suggest that intermittent fasting for periods shorter than 24 hours is effective for sustained weight loss in obese adults.

[14] As prolonged fasting continues, drastic decreases in sodium, potassium, magnesium, and other minerals are noted, which can lead to hyponatremia.

[14] In early fasting, during periods of high gluconeogenesis, roughly two-thirds of weight lost is lean muscle mass as opposed to fat.

When too much food or liquid nutrition supplement is eaten during the initial four to seven days following a malnutrition event, the production of glycogen, fat and protein in cells may cause low serum concentrations of potassium, magnesium and phosphate.

[18][19] The electrolyte imbalance may cause neurologic, pulmonary, cardiac, neuromuscular, and hematologic symptoms—many of which, if severe enough, may result in death.

A hunger strike is a method of non-violent resistance in which participants fast as an act of political protest, or to provoke feelings of guilt, or to achieve a goal such as a policy change.

[28] Yom Kippur and Tisha B'Av are 25-hour fasts in which observers abstain from consuming any food or liquid from sunset until nightfall the next day and include other restrictions.

The fasts of Esther, Gedalia, Tamuz, and Tevet all last from dawn until nightfall and therefore length varies depending on the time of the year.

Members of the Church of Jesus Christ of Latter-day Saints (Mormons) generally abstain from food and drink for two consecutive meals in a 24-hour period on the first Sunday of each month and use the money they save for charity.

[30] Members of the Baháʼí Faith observe a Nineteen Day Fast from sunrise to sunset during March each year.

[35] Linda Hazzard, a notable quack doctor, put her patients on such strict fasts that some of them died of starvation.