I could be in the minority but I just don't comment on anyone's food unless it looks or smells fantastic. I used to be chubby and I hated people doing it to me, whatever their intentions - I do find it funny that now people comment more often on my food choices than before when I wasn't fit. Maybe I'm letting the past dictate; people could just be asking out of curiosity. Though I can't imagine anyone asking "are you sure you should be eating that" to an overweight person, like that just seems so monumentally stupid. Wtf are you expecting in answer when you ask that. Apparently it happens though.
Whenever you're fat, the meal you're eating right then is the meal you eat all the time
This gets me - and when you see someone obviously fit getting a pizza I've "earned it" or it's a "cheat meal". Immediately explained away as something they deserve.