Your explanation makes good sense to me. I understand how there must be sufficient fat reserves to sustain a faster through the various stages to completion. Is not the converse also true? By that I mean an excess of fat reserves will mean the fast will also have to be broken before completion is reached? (I assume from the little I know that hunger would in that event be triggered by the accumalative loss of muscle tissue triggering the body's natural hunger response to end the fast.)
Taken together, doesn't this mean there is an optimum starting weight or fat reserve ratio (which would vary according to one's body-type) for a fast, and also explain why more than one fast will be necessary to reach completion? The reason I ask is that in knowing this, maybe would-be fasters like myself would be better placed to know when to begin fasting, since it does seem to be an issue contributing to the likely success of a fast.