Would you be willing to share with your employer how much you eat, drink, smoke or exercise? Would you be willing to make lifestyle changes in return for a break on the cost of your health insurance? Many companies offer such discounts to workers in return for actions such as completing a health questionnaire or setting personal fitness goals.

But do such programs produce healthier employees and lower health-care costs?

Perhaps the most widely recognized wellness program is Safeway's voluntary Healthy Measures program, which evaluates tobacco use, weight, blood pressure and cholesterol levels. If employees "pass" all the tests, annual health insurance premiums are reduced by up to $780 for individuals and $1,560 for families.

Writing in the Wall Street Journal in 2009, the company's chief executive, Steven A. Burd, claimed the program helped Safeway keep health care costs stable during a period when costs to other companies rose by 40 percent. Among those who noticed Safeway's success was President Obama, which led to the addition of "the Safeway amendment" to his health reform law. The amendment will allow employers to tie 30 percent of an employee's health-care costs to wellness programs beginning next year.

While Safeway's program remains voluntary, others take a harder stances. CVS recently required all employees to submit to a medical exam or pay a $600 fine. Scotts Miracle-Gro bans smoking, during both work and off hours.

A 2010 analysis of 36 studies of corporate wellness programs suggested they can be effective. Researchers calculated that employers saved $6 for every $1 spent: $3.27 saved in medical costs and an additional $2.73 gained due to reduced absenteeism. An earlier analysis found that such programs reduced sick leave, health plan costs, worker compensation and disability costs by about 25 percent.

But not every study has reached the same conclusion. A series of studies published recently in the influential journal Health Affairs looked broadly at the efficacy of employer wellness programs. One study concluded that employers might save money on one aspect of health care but spend it on another. The researchers looked at one company's wellness program and found that while fewer employees were hospitalized, those savings were offset by higher amounts spent on outpatient doctor visits and prescription drugs.

A second study questions some basic assumptions of wellness programs. The authors discovered that "a majority of studies showed no significant spending differences between people who used tobacco, had high blood pressure or cholesterol levels, or got inadequate amounts of exercise, compared with other people."

The authors also suggest that while incentives may help get employees off to a good start, sustaining changes is more challenging. Incentives may help participants lose weight, but in the long run, they regained it.

For employees, perhaps the most telling red flag is that their employers may be saving money not by making them healthy but rather by shifting health-care costs onto them. "Our evidence suggests that savings to employers may come from cost shifting, with the most vulnerable employees - those from lower socioeconomic strata with the most health risks - bearing higher costs that in effect subsidize their healthier colleagues," wrote the authors.

Despite these new findings, many employers remain committed to wellness programs. Writing in April for the Hill, a representative from the U.S. Chamber of Commerce was enthusiastic, suggesting that "wellness programs continue to offer an effective way for employers to encourage healthy behavior without having to decrease benefits, reduce wages or close their doors altogether."

Those are worthy goals, but so far they remain goals. There may be benefits of workplace wellness initiatives that we haven't yet measured, such as improved morale and workplace camaraderie. But it's clear from the mixed bag of evidence so far that we need to keep studying what works and what doesn't in order to design programs that will fulfill the hope that they can save money and make people healthier.

Rahul K. Parikh is a physician and writer in the San Francisco Bay area. He wrote this for The Los Angeles Times.

Distributed by MCT Information Services.