What triggers the high rate of obesity?

As our unit consists of food politics, it has come to my attention on how obesity ties into food politics because food is everywhere we go in the U.S  you simply can't go a mere 5 blocks without running into a fast food restaurant. I believe that the main source of obesity in the U.S is the amount of fast food people eat simply due to the fact that it's convenient and very economically cheap. But the type of fast foods served upon these restaurants have such a high concentration of fats, sugars, and carbohydrates it no wonder how people can have obesity and other types of medical conditions due to obesity such as diabetes, high blood pressure, heart disease, gallstones, and other chronic illnesses. Surprisingly obesity has become such an epidemic that over 2/3's of adults are either overweight or obese and 1in 3 Americans is obese, same with children, obesity upon children has steadily increased. Obesity can be caused through various ways but the most common seems to be people consuming a higher calorie intake than what they're able to burn off and simply not burning the excess calories leads to weight gain. But some different ways of gaining weight can be caused through genetics, metabolism, your environment that you live in, the type of culture you may have and maybe even your type of behavior   

http://www.medicinenet.com/obesity_weight_loss/page3.htm