If you think spending more time at the gym can compensate for that extra slice of bread or cake, think again. New research shows that sugar and carbs — not a lack of exercise — are the chief cause of obesity.

Even the strenuous types of exercise done by athletes cannot counter a bad diet packed with excess sugar and carbohydrates, say the researchers, Medical News Today reports. The findings, published in the British Journal of Sports Medicine, suggest the global epidemic of obesity "cannot be outrun by exercise."

They cite evidence that while obesity has rocketed in the past 30 years, "there has been little change in physical activity levels in the western population."

The researchers — Aseem Malhotra, M.D., a U.K. cardiologist; Tim Noakes of the Sports Science Institute of South Africa in Cape Town; and Stephen Phinney, M.D., professor emeritus of medicine at the University of California-Davis — do not dismiss the benefits of regular exercise.

But they argue it "does not promote weight loss" as effectively as dietary changes, although there is a great deal of evidence showing that moderate physical activity "reduces the risk of developing cardiovascular disease, Type 2 diabetes, dementia, and some cancers by at least 30 percent."

Poor diet, they say, is a bigger risk and it "generates more disease than physical inactivity, alcohol, and smoking combined."

The authors’ conclusions are based on a review of the medical literature and studies examining diet, fitness, and obesity. They argue that the food industry has created a false public perception that "obesity is entirely due to lack of exercise."

They argue: "It is time to wind back the harms caused by the junk food industry's public relations machinery."