That little voice nagging you to put down the cake and lace up the running shoes is increasingly coming from your employer, and is likely to grow louder with a looming change under the federal health care overhaul.

More companies are starting or expanding wellness programs that aim to reduce their medical costs by improving their employees' health. They're asking workers to take physical exams, complete detailed health assessments and focus on controlling conditions such as diabetes. Also, some companies are dangling the threat of higher monthly insurance premiums to prod workers into action.

The Affordable Care Act is one reason the programs are spreading. The federal law calls for a 40 percent tax on expensive benefit plans starting in 2018, and many companies that offer employer-based coverage already have begun looking for ways to lower costs and avoid that tax.

"It is a very powerful ... visible wake-up call to all employers," said Helen Darling, chief executive of the National Business Group on Health, a nonprofit that represents large employers on health care issues.

Businesses see wellness programs as a win for themselves and their workers. But studies have shown that the programs have a limited ability to reduce costs. They also raise concerns about privacy and discrimination against older workers or those who are more likely to have chronic conditions.

Penalties can hit lower-wage workers harder than they would executives because premiums already consume a larger portion of those workers' paychecks.

"The top-line concern is that it has a huge potential to be discriminatory," said Lydia Mitts, with nonprofit Families USA.

Benefits consultants say federal regulations help guard against that. Companies can be penalized under the overhaul for offering coverage that is considered unaffordable.

Businesses also are required to offer alternatives that help workers avoid penalties like a higher premium because they can't meet a wellness program goal.

Despite employee concerns, the idea of prevention as a way to reduce health care costs has been largely embraced by employers, who provide the most common form of health insurance in the U.S.

For years, they have offered rewards to employees who agree to get physical exams, fill out health assessments or take other steps to monitor their health. The goal is to at least make workers more aware of their health, and it worked for Roy Simmons, a 55-year-old nuclear power plant manager for energy provider Dominion Resources.

Dominion started offering a $400 premium credit a couple of years ago for employees who agreed to have a health assessment, so Simmons had the basics measured. He then forgot about the numbers until a reminder arrived. Another physical told him he had gained 40 pounds and his cholesterol was up.

"That was a bit of a wake-up call for me," said Simmons, who has since dropped the weight.

Benefits experts say companies haven't seen enough cases like Simmons', in which an incentive helps nudge an employee to participate in a wellness program, so some employers have started using penalties.

These penalties most often stick employees who do not participate with larger premiums or deductibles, but they also can come as a monthly surcharge, deducted from paychecks.

Companies also are moving to requiring workers to reach a health goal such as improved blood pressure, said Beth Umland of consultant Mercer.

Whether wellness programs are reducing company health costs is a matter of debate.

The average annual premium for employer-sponsored family health coverage topped $16,000 last year, says the nonprofit Kaiser Family Foundation. Employers, who pay most of that bill, have watched that figure climb faster than inflation for years, and it has more than doubled since 2002.

Researchers have said companies should not assume wellness programs will lower costs.

And the programs have generated a backlash from employees.

A CVS Caremark Corp. employee has filed suit in California, accusing the company of asking personal questions in its wellness survey, including whether its workers are sexually active. She also alleged that blood work in the exam is used to flag employees at risk for certain conditions.

A CVS spokeswoman said the company offers a lower premium for employees who complete a health assessment and screening. She said an outside company designed the questionnaire and CVS had asked it to "remove certain questions" before the complaint.

She said CVS management cannot see employee-specific information compiled in the wellness exams.