this reminds me of a documentary about weight @
Starfall posted a while back, in which people consistently of healthy weight agreed to eat way more food than they need for some length of time. a couple of the people didn't actually gain all that much fat, because their bodies apparently converted some of the excess energy to muscle in order to adapt, which increased their BMR. i wonder if they were more mesomorphic in nature. so for these sorts of people, the body takes care of this on its own (there are internal processes to do that), but for more endomorphic types, you have to do work to create the process as you don't naturally build muscle, which sadly is the case for me probably.