I've always been a 'big girl', even when I've been correct weight for height. When your family are all between five-eight and six-foot and skinniness doesn't run in the genes, you're going to be 'of a robust build', as people used to say. That's fine, and I know of lots of people of similar build. Not fat, just 'robust' (or big, if you want to be blunt about it).
There is a difference between that and 'fat' though. And I am talking 'fat' here as opposed to 'chubby', and as opposed to the poor souls who have metabolic disorders and various other medical conditions that lead to obesity. Kids who are fat because their parents over-feed them can't help it. If your parents are obese, if their answer to feeling down, celebrating or just passing the time is to eat, then that's all the child's going to learn. And those parents are unlikely to be of help to their kids if they put the kid on a diet/lifestyle change and then don't look at themselves.
"Oh, 'ee's too fat for is 'ealth. 'Ee's allus eatin' chocolate and crisps," we hear them say about their beloved offspring, as they are in the process of lovingly frying up yet another pan of chips for the family tea.
We used to moan at my mum, because when she went on a diet, we all had to, like it or not. But she had a point.