Somebody better put out an APB on Jared Fogle, the Subway spokesmodel for fast-food dieting. Yum! Brands' (NYSE:YUM) Taco Bell wants to replace him.

Christine Dougherty says in new TV ads and at this website that she lost 54 pounds eating Taco Bell tacos and burritos. Taco Bell calls it the Drive-Thru Diet menu, and it features seven a la carte items, each bearing less than 9 grams of fat and ready-made for the drive-thru diner.

"I reduced my daily calorie and fat intake by 500 calories, to 1250 calories a day," Christine says at the site, which includes pictures of her showing off her bikini body.

It's an interesting pitch, but investors needn't get too excited. Yum! isn't about to set off a fast-food feeding frenzy, nor will binging dieters balloon Yum!'s earnings. That job's been left to hungry folks in developing nations, who only recently enjoyed their first tastes of Yum!'s KFC, Pizza Hut, and of course Taco Bell.

We've also seen stunts like this before. Anyone else remember McDonald's (NYSE:MCD) killing its Supersize portions as it rolled out "Real Life Choices" for dieters wanting to cut fat, carbs, or calories? Or how about the "Go Active" campaign, during which Ronald subbed pedometers for toys in adult-sized, salad-stocked Happy Meals?

Stunts are par for the fast-food course. Witness Burger King (NYSE:BKC), which offered free grub to the multitudes willing to axe Facebook friends in exchange for a burger injection.

Let's be honest here, OK? For fast-food joints, healthy eating is a sideshow, a one-off benefit that's a distant third place to consumers' true interest in low cost and convenience. Busy Americans count grease as the price of handling a compressed schedule. Taco Bell and Christine won't do any better than Jared has at changing that, because they're merely marketing tools.

Sure, Christine might help Yum! coin a little extra cash, but probably not enough for it to matter to your returns as an investor.

If you really hope to profit from the dieting and exercise trends, try investing in businesses whose profits are actually tied to healthier choices -- Weight Watchers (NYSE:WTW) and Whole Foods (NASDAQ:WFMI), for example. Or perhaps, as my Fool colleague Mike Pienciak suggested, a generous spread of Smart Balance (NASDAQ:SMBL) could be the best stock choice of 2010.

That's my take. Now it's your turn to (ahem) weigh in. Do you like the new Taco Bell campaign? Does Christine inspire you? Are you more or less likely to invest in Yum! Brands? Make your voice heard using the comments box below.

Smart Balance is a Motley Fool Rule Breakers selection. Whole Foods is a Stock Advisor selection. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Tim Beyers salutes you, Mr. Giant Taco Salad Inventor. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. The Fool's disclosure policy doesn't see any lettuce.