7-Eleven is known for Big Gulps, Big Bites, decadent nachos, doughnuts, and the Slurpee -- not exactly healthy fare. But Weight Watchers (NYSE:WTW) now hopes that some of the convenience store's customers will also hanker for low-calorie options.

Reuters reported that Weight Watchers plans to distribute a line of snack cakes and muffins in 7-Eleven's U.S. stores. It's the company's latest bid to increase Weight Watchers' licensing business, as it steps up distribution of its prepared diet foods in grocery stores and other venues.

Weight Watchers has little choice but to diversify as more and more diet-plan rivals step forward. Nestle's (OTC: NSRGY.PK) Jenny Craig and NutriSystem (NASDAQ:NTRI) spring to mind. The latter is an interesting new entrant into the subscription-diet market; its recently announced NutriSystem Advanced adds new "proprietary ingredients" to its foods to support heart health, including Omega-3 fatty acids and soluble fibers.

Meanwhile, Weight Watchers' old-school brand almost seems stodgy -- a dangerous trait in a fad-sensitive market, where consumers are always looking for the next successful weight-loss strategy. Remember, the carb-counting Atkins and South Beach diets made 2003 a difficult time for Weight Watchers.

It'll likely be tough for 7-Eleven to shed its reputation for chili-laden hot dogs, but healthier options from Weight Watchers might lure new customers into the stores. Just don't forget the rivals waiting to chip away at 7-Eleven's market share. Britain's Tesco is venturing into the U.S. with small, convenience-oriented stores dubbed Fresh & Easy. And Whole Foods Market (NYSE:WFMI) is also experimenting with smaller, quicker formats, like the Whole Foods Express it mentioned in August. (Admittedly, that's probably aimed at more upscale customers than 7-Eleven and Weight Watchers generally pursue.)

Weight Watchers has the right spirit in trying to increase its distribution as competition mounts. But don't assume that 7-Eleven's move to cut calories among its food offerings will ultimately bulk up either company's business.

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Alyce Lomax owns shares of Whole Foods Market. The Fool has a disclosure policy.