As Americans' waistlines continue to expand, more companies are experimenting with ways to help employees win the battle of the bulge.

But while overweight workers get perks for losing pounds, critics say thin people are being discriminated against and companies are putting unfair pressure on employees to get fit.

"I am all for good nutrition and exercise. I do those things that keep me healthy, but this company is behaving in a manner that's not only discriminatory, it's both dangerous and counterproductive," Marilyn Wann, author of "Fat! So?," told Fox News' Neil Cavuto, referring to VSM Abrasives' in-house fitness program.

Brent Barton, president of the Missouri-based company, started the voluntary "Get Healthy for Life Contest" in which participants choose teams with names like "Five Fat Men" to help employees slim down together. As rewards, people get a paid day off and $25.

"What we're seeing is more and more people will get healthier, use medication less, go to their doctor less, and, therefore, we will see lower premiums in the future," Barton told Fox News.

While health experts have long encouraged Americans to lay off fatty foods and exercise more, corporate bosses are finding incentives like cash get workers onto the treadmill (search). And that's good for companies too.

The cost of obesity (search) to U.S. businesses -- for health care, sick leave and life and disability insurance -- is estimated at $12.7 billion a year, according to the American Journal of Health Promotion. And the Washington Business Group on Health (WBGH) said obesity is associated with 39 million lost workdays and 63 million doctor visits a year.

These numbers add up, especially when almost two-thirds of American adults are overweight, according to the Centers for Disease Control and Prevention (search).

Now, employees have one more reason to shed excess fat.

VSM employee Don Richards lost 37 pounds during his company's contest, and said the camaraderie helped motivate him to lower the scale's needle.

"With the teams, there's a certain esprit de corps and everybody wants to help out each other," Richards said. "I think it's definitely helped the morale of the people in the company."

Ellen Lipschitz, a scientist at Hoffmann-La Roche pharmaceutical company, dropped 93 pounds and lowered her blood pressure after participating in her office Weight Watchers (search) program.

"I'm so proud of what I've done," Lipschitz said. "If we didn't have it at work, I probably wouldn't be doing it."

But these programs are drawing fire for creating a culture of peer pressure and discrimination.

"We've got slim people that were upset that they couldn't join in," Barton said. "They do feel a little bit jokingly discriminated against, but we give them opportunities for free days off of work for other things, for attendance and things like that."

But Wann argued the programs could trigger eating disorders and cause people to yo-yo diet.

"It's just counterproductive and not really forward thinking," she said. "It's certainly not diversity minded."

Nevertheless, the corporate diet movement is gaining momentum.

Nearly one-third of U.S. businesses polled by a recent employee benefits survey said they helped pay gym membership -- up 35 percent in four years. Other companies offer cholesterol screenings and nutritional counseling on the job.

And skinnier employees can fatten a company's bottom line.

"Even though the payoff may not come for many years, employers know that healthy employees make less health care claims and are more productive," said Craig Gunsauley, managing editor of Employee Benefit News.

This summer, the WGBH's Institute on the Costs and Health Effects of Obesity was launched to help businesses fight obesity in the workforce. It informs employers about the cost tolls of weight problems and how workers can win the fight against fat by taking the stairs and picking healthier lunches.

About 200 companies, including General Mills, Fidelity Investments, Microsoft, PepsiCo., American Express and IBM, are involved in the institute.

"Research has shown that the overall impact of obesity on health and costs outweighs even that of smoking," said WBGH President Helen Darling. "No company in America can afford to ignore the problem of obese and overweight employees."

The Associated Press contributed to this report.