It's easy to pack on the pounds in a 9-to-5 world, but not so simple to take them off.
Obesity expert Dr. Jim Levine said that's not surprising: Many Americans sit almost all day long behind a desk. It's that sedentary environment, he says, that's making us fatter and less healthy than ever before.
When "20/20" first met Levine a few years ago, he had outfitted lean and obese people at his Mayo Clinic lab with data-logging underwear to track their every move. What he discovered astonished him.
"People with obesity have a natural tendency to be seated for two-and-a-half hours per day more [than people who are not considered obese]," he said. "It was staggering."
It was so staggering that Levine hasn't stopped walking since and even does his work while walking at a low speed on a treadmill.
"I spend my entire work day at one mile an hour," he said. "I work at my computer at one mile an hour. I have my meetings at one mile an hour."
It may sound quirky, until you find out that walking a few hours every day can cut up to 350 calories a day or add up to a weight loss of 30 to 50 pounds a year. Levine believes more movement can help combat obesity, and he's on a mission now to get people out of their chairs.
Last September, Levine literally transported his lab to SALO, a financial staffing firm in Minneapolis, Minn.
There he launched a six-month study to determine whether a moving office could actually help workers lose weight.
"The entire company spent its day on its bottom," he said. "Like nearly every company in the modern world."
Given an inside look at this ultimate office makeover with state-of-the-art treadmill desks, "20/20" tracked six of the 18 employees who volunteered to participate.
Co-owners Amy Langer and John Folkestad were the first to offer themselves up as guinea pigs. Since they started the company, Folkestad's weight has fluctuated -- he's now close to 70 pounds overweight.
"You know the thing about having a six-pack? I've got a keg," he said.
And Langer's been battling the bulge around her midsection since giving birth to three kids in four years.
"I'm working on 15 pounds," she said. "The twins gave me a lot extra to work on."
Langer took to the treadmill desk right away, calling it "simple."
"It's as easy as walking and chewing gum," she said.
Because the treadmill only goes up to two miles per hour, it is pretty simple to keep up with your work. Each employee also wore tiny devices that recorded their every step, courtesy of the Mayo Clinic.
"I got to see how active or how inactive I was," Folkestad said. "It was actually kind of a good wake-up call."
And since they knew that there would be a print-out of their activity or inactivity, it was a motivator of sorts to keep everyone up and moving.
"We don't like sitting anymore. It's funny," Folkestad said.
Surprisingly, the most popular time to use the moving desks was after lunch, when office workers are typically the most lethargic. The staff began reporting more energy both inside and outside the office.
But what if you don't have access to a treadmill desk in your office? Levine says don't worry -- just walk and talk. He says these low intensity movements can burn an extra 100 to 150 calories an hour.
The biggest complaint from the SALO employees was that four walking desks weren't enough. So they brought in 12 more, including some for the conference room for walking meetings. At around $4,000, the treadmill desk isn't cheap. The average worker can't afford them, so some people have gotten creative, designing their own walking offices at home.
Sharon Odom, who lives in Houston, says her weight skyrocketed after the birth of her triplets. Working from home on her Internet consulting business, she felt like she would never lose the weight until she made her own walking desk from a leaf from her dining room table.
"And the weight just started to just melt away because it was so easy," she said.
Odom said it was so easy that in a year and a half she has lost nearly 50 pounds.
And they've been successful at SALO too. Six months after installing the treadmill desks, the office staff has lost a total of nearly 200 pounds by walking just a few extra hours a day. Langer's down 12 pounds and three dress sizes.
Almost everyone reached his or her goal -- and then some. Folkestad is down 24 pounds and hopes to lose 50 more.
"I haven't changed my diet per se. So it's just really more activity," he said.
Levine says low-level activity is crucial to fighting chronic obesity.
"I would say for those people who do the best, it's about making a commitment to a lot of small adjustments," he said. "It's almost a matter of saying, I'm going to change my chair-based life to a dynamic and sort of more exciting life."