Clive Thompson compares Weight Watchers to video games:
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!
(Hat tip: Kottke)