Of course there is a direct relationship between calories consumed and body composition. That is why most weight loss surgery works. However, care has to be taken that hunger is controlled otherwise patients can regain the weight if they are hungry most of the time.
A concern I have noticed on very heavy people is that many have joint problems especially with the knees and back. If the knees are chronically sore then exercise would be limited because you can't train legs effectively and they are some of the largest muscles in the body. Imagine carrying around a pack weighing over 200 pounds. That would soon defeat even the strongest among us. Well, some fat people have to do that on a daily basis.
What can not be denied is that we have little clue about what it is like to carry around a huge body and be unable to do much about it. The comments, stares and so on would severely affect everyone who is supersized.