A friend of mine recently slimmed down on Weight Watchers. She joined two months ago, and in just a couple of weeks, she’d shed 10 pounds. She’d been trying for a year to lose weight, but nothing worked– until now.

Why did Weight Watchers work so well? For a really fascinating reason: because it isn’t a normal diet. It’s something more.

It’s an RPG.

The Weight Watchers program is designed precisely like a role-playing dungeon crawler. That’s why people love it, stick to it and have success with it. And it points to the way that we could use game design to make life’s drudgery more bearable.

When I asked my friend to see how Weight Watchers works, she showed me the ingenious system. “The best part is the web tool,” she said, pulling it up on her laptop. When you first log in to Weight Watchers, it determines how much food you’ll be allowed to eat that day, expressed as a number of “points.” My friend gets 23 points per day. Each time she eats a piece of food, she enters it into the online database, and it calculates how many points she’s used. A small apple is one point; a piece of fried chicken is seven points.

When she first started the program, she was stunned at how quickly she burned through her daily points. A single bagel was six points– more than 25 percent of her daily quota.

But pretty soon she learned to hack her daily eating to suit the system. She snacked on vegetables that took zero points– like bell peppers– or only one or two points, like a tasty brand of microwave popcorn. Then she’d save up the big points for a really decent dinner.

IF I EAT AN EGG-AND-ROMAINE LUNCH, I’LL HAVE ENOUGH POINTS TO SURVIVE A GREASY HAMBURGER DINNER.

What makes this point-counting possible is Weight Watchers’ elegant online tool. Type in any food you can think of– including brand-name snacks or boxed meals– and Weight Watchers has already calculated the points for you. If she makes a special sandwich at home, she can calculate the ingredients, save it with a custom name, and then drag and drop it into her day every time she eats one.

As I watched her poke around on the screen, managing inventory, calculating points, staying within her range, it hit me:

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!

Even the Weight Watchers web tool is amazingly gamelike. It has the poke-around-and-see-what-happens elegance you see in really good RPG game screens. Accidentally snack on a candy bar and ruin your meal plan? No worries: Just go into the database and see what spells– whoops, I mean foods– you can eat with your remaining points.

And those 35 extra points you get every week? They’re like a special buff or potion– a last-ditch save when you’re on the ropes.

Indeed, I’m in awe of the sheer brilliance of Weight Watchers in adopting the word “points” as its metric for measuring food. It immediately shoves the user into the semantics– and fun– of gameplay. You regard losing weight as an intriguing challenge, as opposed to a grind.

This puts me in mind of the talk that Jane McGonigal– a brilliant and pioneering alternative-reality game designer – gave at this year’s South by Southwest conference. She argued that game designers ought to put their skills to use in the real world by reshaping dull, everyday activities into fun challenges. Why not a game that gives you points for walking your dog or jogging?

“Games are an incredible language and system. They should be everywhere,” she said. Why aren’t we doing that to help people navigate and understand the world around us?

As McGonigal points out, there are already some witty attempts– like Chore Wars, Wii Fit or Seriosity’s system, which tries to limit corporate e-mail overload by forcing people to “spend” virtual totems to send a message. I can think of tons of things I’d love to see turned into a game: doing my taxes, dealing with my inbox, being stuck in traffic.

And this stuff is clearly possible, because if Weight Watchers can turn something as unpleasant as dieting into a playful activity, the sky’s the limit.

Just ask my friend.

Clive Thompson is a contributing writer at The New York Times Magazine.