Excess sugar and carbs, not physical inactivity, are behind the surge in obesity, say experts in an editorial in the British Journal of Sports Medicine published online today.

It's time to bust the myth that anyone--and that includes athletes--can outrun a bad diet, they say.

Regular exercise is key to staving off serious disease, such as diabetes, heart disease, and dementia, write the authors, but our calorie laden diets now generate more ill health than physical inactivity, alcohol, and smoking combined.

The evidence now suggests that up to 40% of those within a normal weight (BMI) range will none the less harbour harmful metabolic abnormalities typically associated with obesity.

But few people realise this, and many wrongly believe that obesity is entirely due to lack of exercise, a perception that is firmly rooted in corporate marketing, say the authors.

They describe the public relations tactics of the food industry as "chillingly similar to those of Big Tobacco," which deployed denial, doubt, confusion and "bent scientists" to convince the public that smoking was not linked to lung cancer.

"Celebrity endorsements of sugary drinks and the association of junk food and sport must end," they declare, adding that health clubs and gyms need to set an example by removing the sale of these products from their premises. "The 'health halo' legitimisation of nutritionally deficient products is misleading and unscientific," they write.

Public health messaging has unhelpfully focused on maintaining a 'healthy weight' through calorie counting, but it's the source of the calories that matters, they point out. "Sugar calories promote fat storage and hunger. Fat calories induce fullness or satiation," they write.

The prevalence of diabetes increases 11-fold for every 150 additional sugar calories consumed daily, compared with the equivalent amount of calories consumed as fat, they say.

And the evidence now suggests that carbs are no better, they add. Recent research indicates that cutting down on dietary carbohydrate is the single most effective approach for reducing all of the features of the metabolic syndrome and should be the primary strategy for treating diabetes, with benefits occurring even in the absence of weight loss.

Furthermore, other research suggests that rather than carbohydrate loading ahead of intense exercise, athletes would be better off adopting a high fat low carb diet, particularly those who are already insulin resistant.

The food environment needs to be changed so that people automatically make healthy choices, suggest the authors. This "will have far greater impact on population health than counselling or education. Healthy choice must become the easy choice," they say.

"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. You can't outrun a bad diet," they conclude.