The key to losing weight? "You can't outrun a bad diet"

If you're hitting the gym every day but don't see the numbers going down on the scale, you might be going about weight loss all wrong. New research says focusing solely on exercise is not the answer to losing weight.

In an editorial published in the British Journal of Sports Medicine, researchers say excess sugar and carbs -- not physical inactivity -- are primarily to blame for the growing obesity epidemic.

Researchers write that although regular exercise has many health benefits -- reducing the risk of developing cardiovascular disease, type 2 diabetes and some forms of cancer by 30 percent -- it is our high caloric diets that lead to obesity.

"In the past 30 years, as obesity has rocketed, there has been little change in physical activity levels in the Western population," they write. "This places the blame for our expanding waist lines directly on the type and amount of calories consumed."

However, another study published last summer reached different conclusions, pinning more of the blame on our couch-potato ways. Focusing on the U.S. -- where a third of the population is obese -- it found that the number of American women who reported no physical activity in their free time increased from about 19 percent in 1994 to nearly 52 percent in 2010. In men, the number rose from about 11 percent in 1994 to 44 percent in 2010.

Still, there can be no doubt that dietary excess leads to trouble. The British researchers estimate that up to 40 percent of people in the normal weight range still harbor some harmful metabolic abnormalities typically associated with obesity, which raises the risk of diabetes, heart disease and other conditions. "Our calorie laden diets now generate more ill health than physical inactivity, alcohol, and smoking combined," they write.

But calorie counting alone isn't the answer -- the source of the calories matters too. For every additional 150 calories of sugar (say, one can of cola), there was an 11-fold increase in the prevalence of type 2 diabetes, compared to 150 calories obtained from fat or protein. These results were independent of the person's weight and physical activity level.

"Sugar calories promote fat storage and hunger," the write. "Fat calories induce fullness or satiation." They say food marketers mislead the public with the message that all calories count equally.

Lisa Sasson, a registered dietician and clinical associate professor of nutrition at New York University, gave an example. Energy and protein bars are nothing more than "glorified candy bars," she told CBS News, and people are mistaken if they believe they need to consume them in order to lose weight or gain muscle. "Most people who want to lose weight should not be taking in extra calories," she said.

The researchers conclude that changing the food environment and our understanding of what it takes to reach a healthy weight is key to fighting the obesity epidemic.

"It's time to wind back the harms caused by the junk food industry's public relations machinery. Let's bust the myth of physical inactivity and obesity," they write. "You can't outrun a bad diet."