That’s the bet entrepreneur Adam Bosworth, a veteran of Microsoft (MSFT) and Google (GOOG), is making with Keas, an online service that aims to make exercising and eating your vegetables more fun — or at least a little less painful.

San Francisco-based Keas (pronounced kee-ahs, it is named for a bird found in New Zealand) sells its web-based app to companies, which in turn push it out to their employees. Co-workers form teams of five or six and enter a competition in which members earn points by answering online quizzes about healthy foods, taking breaks at work to reduce stress, and meeting weekly goals for eating fruits and vegetables, sleeping, and, of course, exercising. All the activities are shared among participants on a Facebook-like news feed, where teammates and rivals can comment, give verbal pats on the back, or urge each other on.

Keas charges $12 per user for a year and lets companies personalize the site and choose what rewards, if any, they give to winning teams. “You can change people’s behavior a little, but you have to make it fun for them,” says Bosworth, who previously ran Google Health, the search giant’s now defunct effort to create online medical records. “People will fall off the wagon, and that’s when you need a social mechanism to help them climb back on.”

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Early results are encouraging. Bechtel, the construction giant, deployed Keas as part of a larger wellness initiative. About 8,000 employees in 44 countries signed up, and roughly half reported losing weight over an initial 12-week period. At Progress Software (PRGS), of some 600 employees who signed up, two-thirds reported losing some weight, one-third said they were less stressed, and scores said they pared down unhealthy foods. “If you are engaged with others and you have a support mechanism, it is going to have a tremendous impact,” says Joe Andrews, who heads human resources at Progress.

But experts warn that while promising, health apps like Keas should be put in perspective. “You can change behavior for a short time with just about anything,” says Toni Yancey, professor of public health at UCLA. “Where the pedal hits the metal is in getting people to change behavior for the long term.”

Despite questions about their overall efficacy, corporate wellness apps are proliferating in part because many investors are betting that the social-gaming wave popularized by Zynga (ZNGA) can be harnessed to fight obesity. Keas, which has raised $17.5 million from investors, competes with Virgin HealthMiles, part of Richard Branson’s Virgin Group, and Red-Brick Health, among others. It seems counterintuitive, but if game-based health companies succeed, they may have couch-potato favorites such as FarmVille and Mafia Wars to thank.

This article is from the March 19, 2012 issue of Fortune.