Fasting is the willing abstinence or reduction of some or all food, drink, or both, for a period of time. An absolute fast or dry fasting is normally defined as abstinence from all food and liquid for a defined period. Other fasts may be partially restrictive, limiting only particular foods or substances, or be intermittent.
In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting. Some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting once 8–12 hours have elapsed since the last meal. Metabolic changes of the fasting state begin after absorption of a meal (typically 3–5 hours after eating).
https://en.wikipedia.org/wiki/Fasting
Autophagy
Dr. Colin Champ, a board-certified radiation oncologist and assistant professor at the University of Pittsburgh Medical Center explains it thus:
“Your cells create membranes that hunt out scraps of dead, diseased, or worn-out cells; gobble them up; strip ’em for parts; and use the resulting molecules for energy or to make new cell parts.”
Autophagy is an collection of cellular maintenance processes, focused on clearing out waste and recycling damaged components. Greater autophagy taking place in tissue should mean fewer damaged and disarrayed cells at any given moment in time, which in turn should translate to a longer-lasting organism. The paper linked below is one of the more compelling of recent arguments for putting more effort into treatments based on artificially increased levels of autophagy. This has been a topic in the research community for some time, as many of the methods known to modestly slow aging in laboratory species are associated with increased levels of autophagy. https://www.fightaging.org/archives/2016/01/autophagy-key-to-restoring-function-in-old-muscle-stem-cells/