According to Clive Thompson in Wired, Weight Watchers is an RPG.

Think about it. As with an RPG, you roll a virtual character, manage your inventory and resources, and try to achieve a goal. Weight Watchers’ points function precisely like hit points; each bite of food does damage until you’ve used up your daily amount, so you sleep and start all over again. Play well and you level up — by losing weight! And the more you play it, the more you discover interesting combinations of the rules that aren’t apparent at first. Hey, if I eat a fruit-granola breakfast and an egg-and-romaine lunch, I’ll have enough points to survive a greasy hamburger dinner for a treat!

I think WW is more of a character generation system (BURPS). Which is something of an apt metaphor.

For weight loss games, you could try the board games The Fitness Challenge or Fat Chance, or tune into the reality game show The Biggest Loser, which has it’s own board game.