You get free food yeah but you get tired of eating the same limited menu every day. And it's simply hard to eat as much as you burn. At an 8 hour shift, I burned the equivalent calories as walking 10 miles. (Not that many steps but that many calories from adrenaline and whatever.) You'd have to basically eat an extra large meal a day on top of your normal diet to make up for it. Plus you're flat out working for those whole eight hours, so you're too tired to cook dinner when you get home.