nope; it's genetic too. Everyone knows someone who can eat everything in sight without putting on an ounce - or someone who diets all the time and yet never looks like Kate Moss. Just to rehash something I've said before: my parents were the same size and shape when they married, had exactly the same diet, and got the same amount of exercise (not much). One got fat, the other didn't. Neither was lazy, or energetic; neither was an overeater.
I'm not saying eating or working out won't have some effect, just that they're by no means the only factors. There's more to life than rocket science.