I wouldn't say it's the primary driver, but it does contribute to obesity. I find peoples its the modern lifestyle that is probably the biggest factor to consider. I've struggled with my weight, because I tend to turn to junk food when I am at my most stressed. I can go from being lean to packing on 10-15kg in a short amount of time. In saying that, I have known people who are real fitness enthusiasts, who regularly run marathons and the amount of sugar they get away with eating always blows my mind.