Let me comment very briefly, and put forward a controversial additional explanation for the growth in obesity. I do believe that more is spent on advertising of goods than of political candidates, but I do not believe goods advertising is at a lower level than political advertising. Just the opposite in many cases!
Farm subsidies are not the main cause of the decline in the price of fat. These subsidies were generally just as high, if not higher, in the '50s and '60s as during the '80s and '90s. However, the total cost of food declined during the past couple of decades, but it did not before that.
One reasons seldom mentioned as a general factor partly behind the rise in obesity is the expectation that new drugs will greatly reduce the adverse consequences of being obese. I am not claiming that many teenagers are conscious of this consideration. However, any one who has observed the development of blood pressure and cholesterol lowering drugs during the past few decades can rationally believe that in twenty years or so still newer drugs that control diabetes and other diseases will be developed. Then for anyone who likes to eat sugary and fat foods, it does not seem so irrational to do so when the consequences will be much less harmful to health than they are at present.
To be sure, if the government will pay for the use of such drugs, obesity imposes costs on others. So becoming obese may not be socially "rational" or efficient, but there seems to be an important element of individual rationality, given the trend in drug development. That conflict between private and social behavior is worth investigating further, although I have seen very little discussion of it.