Yet another thing that's making you fat: work

It's no secret that Americans have seen their waistlines expand over time. As it turns out, just showing up at work may be contributing to our collective battle of the bulge.

More than half of U.S. workers -- 55 percent -- feel they're overweight, and 44 percent say they've gained weight while at their present jobs, according to a national survey released by CareerBuilder on Thursday.

Among those who have packed on pounds while at their jobs, more than half admitted that sitting at their desks for most of the day has contributed to their weight gain. Nearly half (45 percent) reported being "too tired from work to exercise," and 36 percent blamed stress-related eating (think mid-afternoon sugar fix), according to the survey, conducted by Harris Poll, of more than 3,000 full-time workers.

Twenty-five percent reported gaining more than 10 pounds, while 17 percent of workers say they've lost weight.

The CareerBuilder survey found a strong link between on-the-job stress levels and work-related weight gain. Fewer than half of workers with very low stress levels feel they're overweight. But 77 percent with very high stress levels consider themselves, well, fat.

The survey's findings come as no surprise to Ron Goetzel, senior scientist and director of the Institute for Health and Productivity Studies, a collaboration between the Johns Hopkins Bloomberg School of Public Health and Truven Health Analytics, a health care data and analytics firm.

About two-thirds of the U.S. population is either overweight or obese, and the national rate of obesity continues to climb each year, said Goetzel. About 150 million Americans are working, and they spend most of those hours cooped up in offices, he said.

"Most people are sitting a lot, not exercising and have a lot of stress at work in terms of performance and productivity pressures. That stress is often associated with increased eating and binge eating," said Goetzel.

His research has found that the growing number of workplace wellness programs have yielded mixed results.

These programs are likely to flop, said Goetzel, if they don't have the backing of senior corporate leaders and, of course, engage most of the workers within an organization, rather than just the "health nuts."

It's not enough for companies to pay lip service to employee health by offering one-off events, such as "Biggest Loser"-themed contests or pedometer challenges. Effective wellness programs, Goetzel explained, can include simple perks, such as low-cost salad bars in company cafeterias, on-site exercise equipment or serving healthy snacks during meetings, rather than greasy pizza or other carb-loaded treats.

Some evidence even shows that well designed wellness programs may actually lead to better business performance. Earlier this year, the nonprofit Health Project, of which Goetzel is president, released a study that found a portfolio of publicly traded firms that had received its C. Everett Koop National Health Awards in recognition of their wellness programs outperformed the S&P 500 index between 1999 and 2014.

"Companies tend to understand that encouraging wellness is a good idea," said Goetzel, "but they often don't know how to do it or do it well."