The word derives from the Greek auto (self) and phagein (to eat). So the word literally means to eat oneself. Essentially, this is the body’s mechanism of getting rid of all the broken down, old cell machinery (organelles, proteins and cell membranes) when there’s no longer enough energy to sustain it. It is a regulated, orderly process to degrade and recycle cellular components.

https://idmprogram.com/fasting-and-autophagy-fasting-25/