Wood says more than half of large employers are doing some sort of program to reduce obesity and smoking. A number of employer programs offer small amounts of cash, gift cards, and other incentives. Self-insured plans also can vary their premiums 20 percent based on getting health screenings or taking steps to improve health. An amendment to a health reform bill in the Senate would allow employers to vary that up to 50 percent.

Tests for body fat, cholesterol levels, and blood pressure can be used to determine premiums, Wood says. Quest Diagnostics doesn't require employees to meet such requirements. The discount is given for taking the risk assessment, which includes a battery of other tests administered in Quest's own labs or at work.

One of the biggest initiatives at the Madison, New Jersey-based company is weight-loss programs. Almost a third of Quest's workers are obese.

After Quest salesman Bill Germanakos won NBC's The Biggest Loser in 2007, he became a full-time wellness ambassador for the company. "He's a rock star," says Williams.

But even with the push to get employees signed up for weight-loss programs and Germanakos' inspiration, the overall rate of obesity at Quest rose to 32 percent of all workers in 2008 from 31 percent the previous year. "It's definitely a journey," Williams says.

Companies share responsibility for making people fat, says Tim Crimmins, vice president of health, safety, and environment for General Mills. Working lunches with fattening choices or afternoon seminars that feature giant cookies create fat workers, he says.

"If you offer cookies and coffee, also offer fruit—and don't offer cookies the size of a football," Crimmins says. "If you put food in front of people, they will eat it."

The company also sponsors bike teams, walking clubs, an on-site fitness center, and yoga. But at headquarters in Minneapolis, there is a recognition that wherever food is offered to employees—cafeteria, vending machines, meetings—there has to be healthy choices. General Mills says its benefit-cost trends are "enviable" but won't disclose specific figures. Company officials also say they get better productivity from healthier workers, and wellness programs help attract and retain employees.

Crimmins says he believes this focus helped General Mills reduce the number of heart disease cases over the last several years at headquarters, though he didn't provide figures. Heart disease moved from the No. 2 most-common health claim to third or fourth, he says.

Seattle-based Alaska Air has refused to hire smokers since 1985 (except in a few states that prohibit the policy). Now the company is preparing to offer a new smoking-cessation program to help spouses and other employee dependents, says Tom Richards, managing director of employee benefits at Alaska Air.

Richards says his company started free health screenings last year and is looking at other preventative health care programs. Aside from the smoking ban, Alaska Air doesn't believe in the stick approach, Richards says. Preventative health care, he says, "is the right thing to do."