Or both.
I've seen 8 year old girls with HUGE bellies. Abdominal fat, the deadly kind. And their mothers are too busy looking at new shoes for themselves. Too many happy meals and definitely not enough exercise.
While our country has a glut of food (and fast food, which is cheaper and more readily accessible than spending an hour each day making something decent); a lot of which people don't bother to make their own informed choices about and has helped contribute to obesity, our society is also prone to being deskbound and lethargic. Sit at a desk for 8 hours, go home, sit on the couch. (assuming people have only one job.) TV, portable music, other gadgets that isolate people from each other is a possible, though usually indirect, cause for obesity.
People need to be taught, in school, to make their own conscious choices. And we all know that isn't happening today. They're being told "What's right", and such preaching is insulting, if not disingenuous in the extreme. If people aren't happy and are slowly rotting, I suppose that's their choice. But on a financial, if not social, level, we're still in this together.
--Too many happy meals and definitely not enough exercise.
My mother was nutrition-challenged and I grew up eating the worst kind of foods but I was one of the skinniest guys in school I guess because I was out running around non-stop.
Me eating 3 meals a day plus midmorning & midday snack would put my daily food budget at $15/day plus about 45-60 minutes for going to the fast food place + waiting + returning. Grocery shopping and developing an efficient way of preparing healthy food has my daily food costs at about $7/day and less than 30 minutes of prep time.
Granted, I do only have to prepare for myself, but I believe (and of course this is just my opinion), that prep and costs are lower for "do it yourself" meals.