© Leonardo Franko -
For people trying to lose weight, it has been the eternal question? Is exercise more important or is reducing calories?

A group of health researchers appears to come down on the side of exercise. Their new study, published in the American Journal of Medicine, searched for the primary cause of obesity.

These Stanford University researchers started with the fact that there has been a significant increase in the average body mass index (BMI) over the last 20 years. They determined there has also been a dramatic decrease in physical exercise over that same period.

Women increasingly sedentary

But the average calorie intake has remained about the same. Therefore, they conclude that a sedentary lifestyle – more than diet – is largely responsible for people being overweight or obese.

Some of the data the researchers analyzed is alarming. The number of U.S. women who reported no physical activity surged from 11.4% in 1994 to 43.5% in 2010. Average BMI increased among all groups over those 16 years, with the biggest increase among young women ages 18-39.

"These changes have occurred in the context of substantial increases in the proportion of adults reporting no leisure-time physical activity, but in the absence of any significant population-level changes in average daily caloric intake," said lead investigator Uri Ladabaum, of the Stanford University School of Medicine. "At the population level, we found a significant association between the level of leisure-time physical activity, but not daily caloric intake, and the increases in both BMI and waist circumference."

Misplaced blame

The debate over the obesity epidemic has largely focused on the food and beverage industries, with high-calorie foods and sugary beverages getting the lion's share of the blame for America's expanding waistline. But the researchers suggest the blame is misplaced.

"Our findings do not support the popular notion that the increase of obesity in the United States can be attributed primarily to sustained increase over time in the average daily caloric intake of Americans," Ladabaum said. "Although the overall trends in obesity in the United States are well appreciated and obesity prevalence may be stabilizing, our analyses highlight troublesome trends in younger adults, in women, and in abdominal obesity prevalence, as well as persistent racial/ethnic disparities."

While a healthy, nutritious diet is important to both weight control and overall health, the exercise side of the equation continues to get more attention. The Stanford researchers aren't the only ones who want to get Americans up off the couch.

Affects cardiofitness levels

Cardiologists at UT Southwestern Medical Center in Dallas have now linked sedentary behavior with lower cardiorespiratory fitness levels. Writing in the Mayo Clinic Proceedings, they claim two hours of sitting can be just as harmful as 20 minutes of exercise is beneficial.

It's just the latest research to sound an alarm about too much sitting. A 2011 Canadian study linked prolonged sitting to an elevated cancer risk. A 2012 Australian study linked sitting with an early death.

A Kaiser Permanente study earlier this year showed prolonged sedentary behavior in men led to significantly higher risk of heart attack.

Unanswered questions

But why isn't exactly clear.

“Our data suggest that sedentary behavior may increase risk through an impact on lower fitness levels, and that avoiding sedentary behavior throughout the day may represent an important companion strategy to improve fitness and health, outside of regular exercise activity,” said Dr. Jarett Berry, senior author of the UT Southwestern Medical Center study.

For people stuck at their desks 8 hours a day, this may not sound like good news. But the research team offers some tips; shift positions frequently; get up and stretch from time to time; when on the phone, stand up and pace around.

If you get short breaks during the day, use them to walk around. Use the stairs instead of the elevator.

“We also found that when sitting for prolonged periods of time, any movement is good movement, and was also associated with better fitness,” said Dr. Jacquelyn Kulinski, one of the authors.

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