MORE: Kick it Up
Today's workers are burning an average of 120 to 140 fewer calories a day at their jobs than workers in the 1960s, finds a new study by top national physical activity experts.
Men burn an average 142 fewer calories a day at work; women, 124.
The lower activity level is due to a dramatic drop in the number of active jobs in manufacturing and farming and an increase in office jobs that are mostly sedentary, the study says.
"The jobs requiring moderate physical activity have all but disappeared," says Timothy Church, the study's lead author. He is director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge .
"We have transitioned from jobs that primarily involved doing physical activity on our feet to ones where most of us make our living while sitting," he says.
Church and colleagues analyzed data from the U.S. Bureau of Labor Statistics from the 1960s to 2008. They assigned metabolic equivalent values, a measure of intensity of physical activity, to different jobs, and from there calculated how many calories people used in those occupations.
Researchers also studied government obesity data, and with computer modeling found that a significant portion of the increase in obesity could be accounted for by the decrease in physical activity at work.
About a third of adults in the USA are obese, defined as 30 or more pounds over a healthy weight. That's up from roughly 13% in the early 1960s.
"I don't want to say that we've completely explained the obesity epidemic," Church says. "This is a crude analysis, but clearly work-related physical activity has decreased dramatically, and it appears to have impacted obesity in this country."
Barbara Rolls, professor of nutritional sciences at Pennsylvania State University, says the research "confirms what most of us knew was happening. We know that people are sitting at their desks for long hours and not out working at highly physically active jobs."
But the obesity epidemic is not due to that alone, she says. Many people are eating too much.
Adult calorie requirements vary depending on gender, age, height, weight, activity level and other factors, but typically a small sedentary woman needs about 1,400 to 1,600 calories a day, and a sedentary man about 2,000 to 2,200 a day. Most surveys indicate an increase in calorie intake over the last few decades, Rolls says.
"Our eating habits have changed. Portion sizes are huge, we're eating more food away from home, high-calorie foods are everywhere. We have opportunities to eat all day, and we're doing it."
The study's findings appear online in PLoS (Public Library of Science) ONE.