CHICAGO (AdAge.com) -- Did you hear the one about the Taco Bell diet? Better yet, did you know it wasn't a joke?

Bloggers are having a field day over Taco Bell's new ad campaign that takes a page from Subway's iconic Jared effort. The Mexican fast-food chain's push introduces Christine Dougherty, a "real-life Taco Bell customer" who lost 54 pounds over a two-year period by replacing her usual fast-food lunch or dinner with an item from Taco Bell's Fresco menu. Ms. Dougherty, who exercised and cut her daily caloric intake from 1,750 to 1,250 per day, admits in the ads that her "results aren't typical, but for me, they're fantastic!" Taco Bell's creative agency is DraftFCB, Irvine, Calif.

Taco Bell's Fresco menu consists of seven items, such as a regular bean burrito or chicken soft taco, but replaces salsa for cheese or sour cream. In a web infomercial for the "Drive-Thru Diet," Taco Bell, however, underscores that it "isn't a weight-loss program," even though the campaign has "diet" in its name.

"Over the years, we've heard stories from our customers who have lost weight by incorporating Fresco into their meal choices, and Christine had written Taco Bell a letter detailing her journey," said Taco Bell spokesman Rob Poetsch. "Her story is a great example of how making better choices can inspire many."

Much of the online chatter has been blistering. Jezebel put it this way: "It's not surprising that diet companies are pushing their products hard during New Year's resolution season, but you know things have gotten a little out of control when even Taco Bell hops on the ol' weight loss bandwagon."

According to Zeta Buzz, which mines blogs, message boards and social media postings to measure buzz about a subject, Taco Bell's buzz rating has dropped six points after launching the diet. While volume of posts increased 44%, the tone has become more negative.

Prior to launch, posts were 73% positive, putting it ahead of beloved chains like Subway, Wendy's and Domino's. Words associated with the brand online were "love," "delicious," and "favorite." Postings are now 67% positive, putting Taco Bell behind White Castle, Blimpie and Arby's, which rank among the category's lower tier. Now three of the words most closely associated with Taco Bell and its campaign have been "fat," "stop," and "joke." BrandIndex shows the chain's buzz and quality ratings falling among women aged 18-34 since the beginning of December, and particularly since Christmas.

"It seems like it's backfiring in a big way," said Al DiGuido, CEO of Zeta Interactive. "It seems like this execution has people really confused and now folks are lobbying in their own way to have it stopped."

Taco Bell is serious about the program, and has brought a registered dietician from the NBA's Portland Trail Blazers on board to lend credibility to the effort. "The reality is most Americans are on-the-go and will eat foods purchased through a drive-thru an average of 10 times a month," said Ruth Carey, the Blazers' nutritionist, whose role in the push is to offer consumers tips for healthier choices while eating at quick-service restaurants. Mr. Poetsch added, "It's our hope that people who are looking to eat fewer calories and fat will hear about our new menu and Fresco-style foods and learn how they can fit them into their lifestyles."

In the meantime, Subway got some Jared fans worried when it deepened its longstanding "Biggest Loser" sponsorship by adding season eight contestant Shay Sorrells to its roster. Ms. Sorrells lost 161 pounds during the show, and Subway is offering her a tasty incentive to keep losing: $1,000 for every pound she loses between now and "Biggest Loser's" season nine finale in May. Ms. Sorrells has already dropped from 476 to 315 pounds. But Ms. Sorrells isn't replacing Jared; she'll merely be joining him in the chain's healthy-eating marketing campaign.

Subway will let consumers watch Ms. Sorrells lose weight, with in-show and online integrations with "Biggest Loser," including periodic check-ins, a mid-season weigh-in and a follow-up package at the end. Consumers can also follow her progress at NBC.com and SubwayFreshBuzz.com. Subway's FreshFit menu offers eight sandwiches that have six grams of fat or less.