I actually remember a bigger Italian guy from the gym that used to bust his ass.  Of course, his diet still outpaced any calories that he burned and he never made any progress.  It's like an alcoholic continually getting loaded between meetings.  His food addiction was just out of control.  He's probably the only one that I've seen.  Other fatties just sweat a lot which makes it look like they're working hard.  Most don't even work enough to sweat (more than usual).