Personal Vice, Public War
[...] There are many reasons we’ve gotten fatter, but I can’t help wonder how much of the rise in eating corresponds to the drop in smoking. This article notes that smokers are less obese than non-smokers, but ex-smokers are more obese than non-smokers. Is it possible that our aggressive efforts to stomp out the “evil” cigarettes has merely skewed our vices without making us healthier or “better”?
I don't know if it's the biggest reason why obesity is increasing, but it must be a large contributing factor at the very least.