In the same way, our bodies presume we will have periods of famine or at least food shortages. Judging by the records of human tooth fossils, and from studies of hunter-gatherer societies, humans and protohumans experienced regular periods of food shortages, probably because of seasonal changes in food availability.
So the body apparently waits until those shortages come before doing certain kinds of maintenance, like removing the plaque from the inside of arteries, or the lysis of unneeded cells. As soon as you fast, these processes begin.
While food is coming in, the body seems to say, "We'll create growth now and we'll do the cleanup when food stops coming in."
Also, the human body seems to "try" to put on a little extra weight. It is preparing for the inevitable food shortages.
The problem with all of this is with the advent of agriculture, those food shortages stopped. So now damage accumulates and weight accumulates and the expected food shortages never come, so the important maintenance doesn't happen.
This is one way of looking at fasting that fits the research.