As more people sit - literally - in more sedentary jobs, they're packing on the pounds, and it's this inertia that's a major contributor to the obesity epidemic, new research suggests.
Staring at the computer for hours rather than hoeing the fields means people are burning 500 to 600kJ less a day than they did 50 years ago.
So promoting any kind of physical activity needs to have an even greater emphasis in this war on weight, according to a study in the journal PLoS ONE.
"It's all about kilojoules in and kilojoules out, and we're putting more kilojoules in than we're taking out," said Dr Robert Graham, a primary care physician at Lenox Hill Hospital in New York City.
People eating more and exercising less
A tilt towards kJ in has resulted in two-thirds of US adults now being overweight or obese.
Although both eating habits and exercise have been studied in relation to the obesity epidemic, these researchers, from the Pennington Biomedical Research Center in Baton Rouge, La., said much of the blame for the extra poundage has been placed on kJ intake.
That's because the amount of leisure-time physical activity hasn't really changed over the years. But what about the physical demands of work, where so many people spend most of their waking hours?
These researchers cross-referenced US Bureau of Labor Statistics on the prevalence of different jobs with a large national database that includes information on body weight.
Exercise guidelines would keep people trim
Fifty years ago, about half of private-industry jobs in the United States involved some kind of physical activity, things such as farming, mining, construction and manufacturing. Today, that number is less than 20%, thanks to the dominance of jobs in retail, education and business.
The authors estimated that 420kJ less going out every day would result in a weight gain in line with what the US population has seen since 1960.
Yet, if Americans were following federal guidelines for physical activity (150 minutes a week of moderate-intensity exercise or 75 minutes of more vigorous activity), those extra kJ would have been evened out. Only one in four Americans is doing the recommended level of exercise, the authors stated.
"We need to encourage physical activity even more, especially given that we sit more during the day than we did 100 years ago," said Keri Gans, a spokeswoman for the American Dietetic Association and author of The Small Change Diet.
"The demands of everyday life are competing with exercise," Graham added. "We just have to make time for it."
Gans recommends that people move at work even if they have what amounts to a desk job. That could mean taking the stairs when you can, walking over to a co-worker's desk when you can and going for a walk at lunchtime. And if your company happens to have a gym or exercise programme, by all means, partake.
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