My experience of long distance hikes is limited to one. But on that journey of 1000miles I carried 2.5lbs/day. In the beginning I was stuffing myself and burying extra; at the end, I was still hungry. We all have our own personal relationship to hunger, but for me, I would hate to jeopardize my hiking enjoyment by being hungry or listless, or whatever it is you become when your body is anxious for food. Whatever you start with, plan on increasing your rations gradually after about a week, or ten days.
If you're quite extreme (as some contributors, or even founders, of this website), you could try to put on 10-15 lbs beforehand, planning to burn it off. Probably against doctor's orders, but its also surely what our species did as a matter of course before agriculture; why not put those vestigial storage genes to good use!