If you believe that the key to controlling your weight is diet and exercise, you may be only half right. Or such are the findings from a new study led by Loyola University Chicago. Their evidence suggests that neither how much you exercise or how much you sit around has any bearing on whether you gain weight.

Crazy, no?

After all, countless experts have pinned our country's current obesity epidemic on our decline in physical activity, most notably in the workplace. We sit at desks and type into computers while our much fitter ancestors hauled rocks and built pyramids and the trade-off for our relative leisure is that roll of fat around our mid-section that's eating into our longevity.

Those countless experts had it wrong, according to the new study's lead author Lara R. Dugas, PhD, MPH.

"Our study results indicate that physical activity may not protect you from gaining weight," she writes. Dugas is an assistant professor in the Department of Public Health Sciences of Loyola University Chicago Stritch School of Medicine.

The Loyola researchers examined data from Modeling the Epidemiologic Transition Study (METS). In METS, researchers followed young adults from the United States, Ghana, South Africa, Jamaica and Seychelles (an island country east of Africa). The study subjects all wore accelerometers which tracked their energy expenditure for a week. Researchers measured subjects' weight, height and body fat at three points over a two-year period.

At the initial visit, Ghana participants had the lowest average weights, and Americans the highest. Seventy-six of Ghanaian men and 44 percent of Ghanaian women met the US Surgeon General physical activity guidelines, while only 44 percent of American men and 20 percent of American women complied. These guidelines recommend Americans engage in at least two and a half hours of moderate-intensity aerobic exercise per week.

What surprised the researchers was that the total weight gain across all the international sampling was greater among participants who met the physical activity guidelines. American men were regularly engaging in the proscribed minimum of exercise gained a half pound per year, while American men who fell short of the guidelines lost 0.6 pounds.

Furthermore, the scientists could not find any meaningful statisticalrelationships between sedentary time at the initial visit and subsequent weight gain or weight loss. The only factors that were significantly associated with weight gain were weight at the initial visit, age and gender.

To be sure, the Loyola team is not advocating a sedentary lifestyle,  as the proven health benefits of exercise – including reducing the risk of heart disease, diabetes, and cancer to improving mental health and mood – are legion. The theory they have lined up behind to support the science behind their results is that, while physical activity burns calories, it also increases appetite, and people may compensate by eating more or by being less active the rest of the day.

The study has been published on PeerJ.