Never mind all the fuss about sugary snacks and oversize meal portions.

A group of researchers, including one from the University of South Carolina, have concluded that the nation’s obesity epidemic has been largely caused by a decline in jobs requiring physical activity.

“The vast majority of the words devoted to (the nation’s obesity problem) talk about diet — sugary foods and so on,” said Steven Blair, a researcher with USC’s Arnold School of Public Health. “What people don’t realize is that caloric intake has really not changed over the years.

“So where does the obesity epidemic come from if we’re not eating more?” he said. “It has to be that the energy expenditure side of the equation must be going down.”

It’s a straightforward law of thermodynamics. Eat more calories than you burn, and you gain weight. Burn more than you eat, and you lose weight.

Blair said the study, “Trends Over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations With Obesity,” delved into statistics and studies about the calories people consume and how much they exercise outside of work, and found that neither has changed very much.

“Americans are consuming more high-fructose corn syrup, but that doesn’t mean they are consuming more calories,” Blair said. “Americans are eating more outside the home, and portion sizes are larger, but that does not mean people are eating more calories.”

What the researchers found to explain the caloric imbalance is this:

“In the early 1960s almost half the jobs in private industry in the U.S. required at least moderate intensity physical activity whereas now less than 20 percent demand this level of energy expenditure. Since 1960 the estimated mean daily energy expenditure due to work related physical activity has dropped by more than 100 calories in both women and men.”

For men, it was a difference of 142 calories every workday, which the researchers said would explain the weight gain seen in men over that period. Results were similar for women.

The decline in physical activity at work is a consequence of the decline in goods-producing jobs, such as manufacturing and farming, Blair said.

“What’s gone up is service jobs, and that’s often sitting at a computer all day,” he said.

The study did not address childhood obesity, which also has been described as a national epidemic, but Blair said that children are far less likely to walk or ride bikes to school than they were years ago.

“I’m not saying ignore the dietary components, but if we’re right, then all the ranting and raving about sugarysnacks is not going to make a difference,” he said.

“I don’t think we’re too far away from being able to tell schools and employers to build in a (exercise) break.”

Some employers are already doing just that, regardless of what’s causing their employees to be overweight and unhealthy.

“I think the employers are well-aware of it, and they’re beginning to see that if their folks are unhealthy, they’re paying more than they need to for health care,” said Deb Campeau, who leads a 6-year-old regional workplace wellness program for Trident Health System.

“We see, at our roundtable meetings, that we’ll have 30 companies in the room trading ideas with each other,” she said.

The Well Workplace Roundtable is a quarterly forum where area employers who are actively engaged in workplace wellness efforts meet and share ideas, many of which are aimed at increasing employees’ physical activity.

The city of Charleston has been working on this issue for several years as well.

“We see the effects of obesity on our employees, in diagnoses like diabetes and heart problems,” said Jan Park, the city’s wellness manager. “We do have several wellness programs, and pushing physical activity is a priority.”

In addition to basics, such as offering employees a

reimbursement program for gym memberships, the city initiative organizes exercise programs and contests where departments compete for prizes.

“We encourage people to get away from their desks every hour, even if it’s for two minutes, and take a walk or do some stairs,” Park said.

In one initiative, 90 city employees participated in a 10-week “Biggest Loser” contest and collectively lost 910 pounds, she said.

Park said it makes sense that jobs requiring little physical activity would contribute to obesity.

“I think it’s a factor, for sure,” she said. “Also, it’s what we eat.”