It is not just about calories per day. Going without food (even if only for overnight) puts the body in ketosis. If ketosis does not happen often enough, some

It is not just about calories per day. Going without food (even if only for overnight) puts the body in ketosis. If ketosis does not happen often enough, some of the body's tissues lose the ability to burn fat, which has deleterious effects (including IIRC insulin resistance). And without fasting, the removal of damaged intracellular proteins ("autophagy") won't happen or will proceed at a suboptimal rate.