According to the recent editorial published in British Journal of Sports Medicine/BMJ:
A. Malhotra, T. Noakes, S. Phinney, "It is time to bust the myth of physical inactivity and obesity: you cannot outrun a bad diet", Br J Sports Med doi:10.1136/bjsports-2015-094911
According to the Lancet global burden of disease reports, poor diet now generates more disease than physical inactivity, alcohol and smoking combined.
Instead, members of the public are drowned by an unhelpful message about maintaining a ‘healthy weight’ through calorie counting, and many still wrongly believe that obesity is entirely due to lack of exercise. This false perception is rooted in the Food Industry's Public Relations machinery, which uses tactics chillingly similar to those of big tobacco. The tobacco industry successfully stalled government intervention for 50 years starting from when the first links between smoking and lung cancer were published. This sabotage was achieved using a ‘corporate playbook’ of denial, doubt, confusing the public and even buying the loyalty of bent scientists, at the cost of millions of lives. [4,5]
Coca Cola, who spent $3.3 billion on advertising in 2013, pushes a message that ‘all calories count’; they associate their products with sport, suggesting it is ok to consume their drinks as long as you exercise. However science tells us this is misleading and wrong. It is where the calories come from that is crucial. Sugar calories promote fat storage and hunger. Fat calories induce fullness or ‘satiation’.
A large econometric analysis of worldwide sugar availability, revealed that for every excess 150 calories of sugar (say, one can of cola), there was an 11-fold increase in the prevalence of type 2 diabetes, in comparison to an identical 150 calories obtained from fat or protein.
And this was independent of the person's weight and physical activity level; this study fulfils the Bradford Hill Criteria for causation.
A recently published critical review in nutrition concluded that dietary carbohydrate restriction is the single most effective intervention for reducing all the features of the metabolic syndrome and should be the first approach in diabetes management, with benefits occurring even without weight loss.
 Brownell KD, Warner KE . "The perils of ignoring history: big tobacco played dirty and millions died. How similar is big food?" Milbank Q 2009;87: 259–94. doi:10.1111/j.1468-0009.2009.00555.x
 Gornall J. "Sugar: spinning a web of influence." BMJ 2015;350:h231. doi:10.1136/bmj.h231
 Basu S, Yoffe P, Hills N, et al . "The relationship of sugar to population-level diabetes prevalence: an econometric analysis of repeated cross-sectional data." PLoS ONE 2013;8:e57873.
 Richard D. Feinman et al., "Dietary carbohydrate restriction as the first approach in diabetes
management: Critical review and evidence base", Nutrition 31 (2015) 1–13
"Exercise 'not key to obesity fight'" By Nick Triggle, BBC Health, 23 April 2015
(Note: highlights are mine)