It is not exactly surprising that reducing time spent in front of the television helps burn more calories. But for the first time, a study has measured the benefits, and it turns out that a little less channel surfing could leave us all trimmer.

In Archives of Internal Medicine, researchers report that cutting daily television viewing time by half would help the average adult burn 119 more calories – about what it takes to walk one mile.

“If they continued this calorie burn every day, it would amount to about 12 pounds a year,” says lead researcher Jennifer J. Otten, PhD, a postdoctoral research fellow at Stanford University School of Medicine in Palo Alto California.

Most adults watch almost five hours of television a day. And while experts say diet and exercise are frequently mentioned ways to prevent obesity, there’s a growing recognition that reducing sedentary behaviors is just as important.

“One of the points I want to make is, no one really knew if [turning off the TV] was meaningful,” says Otten. “Yeah if you turned off your TV you’d probably do something better, but there was no research as to what that would be and if it would be meaningful and 120 calories a day is pretty meaningful,” she adds.

Otten and her colleagues gathered this data by doing a randomized, controlled trial of 36 adults who had a body mass index between 25 and 50 and who said they watched at least three hours of TV a day.

Between January and July 2008, participants were observed for a three-week period and their TV time was assessed.

Twenty people were then randomly assigned to use an electronic device that shut off their TV after they had reached a weekly limit of 50 percent of their previously measured TV viewing time. Sixteen other participants were the control group and their TV time was not limited.

Participants wore an armband to measure their physical activity and those with the lock-out systems burned 119 calories more a day, while the control group burned 95 fewer per day.

“We don’t know exactly what they were doing,” says Otten. “When we asked anecdotally, a lot of them reported they read more. One woman organized her photos. A few people told me they took their dogs out for walks more. Some of them did a yoga class and one group said they played more with their kids doing active things,” she adds.

Researchers say reducing TV time and being more active may also help alleviate chronic sleep deprivation. Lack of sleep is also thought to contribute to obesity.

Susan Sewell, is the director of the Weight Management Center at The Jewish Hospital in Cincinnati, Ohio. She says the study is interesting because it proves that people didn’t just trade in one sedentary activity for another.

“I did find it interesting because they made a point that said people could have just turned off the TV and moved to the computer or doing other sedentary activities and they didn’t,” Sewell says. “From that perspective it was nice to see if adults are encouraged to turn off the TV, they will be more active.”