Both of them, actually, are on record as stating that fasts longer than three days require the supervision of a physician.
One thing we do know is that all proteins appear to have a designed lifespan, ranging from several seconds to several years (I’d love to know how they determined this), so autophagy must be going on at some level all the time. Also, damage to a protein causes that protein to be proteolysed (broken down).
As Prof. Benjamin Bikman states, the metabolism is never completely catabolic or completely anabolic, since both sets of processes are needed all the time, but the body does have states in which one set predominates, and fasting is a predominantly catabolic state.
I think this is the wisest statement in the entire thread.
And this is the second-wisest comment! and one with which I heartily agree.