I did some more research because I wasn't clear about autophagy, if that can remove senescent cells, meaning cells that have stopped dividing and are poisoning the surrounding healthy cells. And I now learned that eating up the senescent cells is called autolysis:
"The physiology of fasting favors healthy cells. Another definition of fasting includes any process that initiates autolysis, during which poorly functioning cells are destroyed, first in the process of fasting, and then the cellular components are broken down and remetabolized. This usually begins after three days of juice or water fasting, ..." - http://treeoflifecenterus.com/fasting-t ... xpression/
So autophagy seems to be for cleaning cells internally, while autolysis is for consuming whole cells, such as damaged cells and senescent cells.
And notice that autolysis according to the article begins AFTER three days of water fasting. Dry fasting some say is three times faster, but does that hold even for autolysis? I doubt that there yet is much scientific research about that. But 3 days of soft dry fasting definitely should be enough, at least with an additional initial night.