Every time I think of this I think "If my gym were smarter about game mechanics and WoWed up all their participation stats I would have +5 Abs of Steel and Epic Purple Arteries by the end of summer." (They've taken wee baby steps: at the end of the workout the screen will say "You burned 120 calories, which is an apple." and "Yay! You've completed your 17th Tokyo Marathon." That's great, but I think two guys and a couple boxes of ramen could do much better.)
The rest of the Hacker's Diet is worth reading and has an excellent analytical approach to describe the eating (inputs) and energy use / exercise (outputs) of a simple model for your body.