Calorie restriction is probably the most important aspect of short term fasting of the sort achieved by eating only in some parts of the day. Animal studies sh

Calorie restriction is probably the most important aspect of short term fasting of the sort achieved by eating only in some parts of the day. Animal studies show that isocaloric intermittent fasting, altering eating schedules, to e.g. alternate day, while still ingesting the same amount of calories, do have benefits. Those benefits hit many of the same areas of metabolism as calorie restriction, but are still significantly different in their overall operation. They are also not as effective at extending life. Time spent being hungry might be a good metric, but even that is overly simplistic. Grehlin has all sorts of regulatory connections throughout metabolism, but you can't point to any one thing. All of these dietary changes, less calories or more hunger, cause sweeping changes throughout metabolism that are not well understood as a whole. Cause and effect and which parts are important versus not is very much open for debate for any part of this system. Further, fasting (or fasting mimicking) for longer periods is clearly a different beast from just rescheduling a few meals. In humans fasting for 72 hours or more results in very different outcomes for immune health than anything less than 72 hours. The longer fast kills up to a third of the immune system, which then repopulates when the individual starts eating again, and thus has very beneficial effects in people whose immune system is damaged or dysfunctional in some way (e.g. as the results of chemotherapy). Similarly these longer fasts produce changes to insulin metabolism that last for months after the fasting is done, which is not the case for fasting in the rearranging a few meals sense.