Ok sorry to rant but the HN community lectures about processed food are misguided. As always, people trot out the "just eat less, its simple calories" and "stop eating junk food stupid Americans". This rests on the critical fallacy that those who do not have a weight problem are smarter, more active, or somehow make better choices. Do you really believe its that simple? This is a bit like the software devs who always believe "we'll write it better from scratch, its an _easy_ problem to solve", not realizing the people who wrote it the way it is probably had legitimate reasons to do so.
The truth is complex and no single factor can explain it. I've seen plenty of people with terrible diets eating the same or worse than others and not gaining weight -- even with little physical activity (just due to genetics), and I've seen metabolic issues make it nearly impossible for someone to lose weight even doing things "right". If you want to prove how "simple" weight loss and eating healthy is, then by all means take a thyroid blocker for a few months and get back to me.
As for blaming stupid people for just consuming too much bad food: I can tell you that this is 100% an environment / market force just like every other behavior you and I have (such as language we speak, recipes we know, and clothes we wear). Like all other animals, we have a finely tuned feeding system that is highly tuned and can be influenced by stimuli. Put junk food in the cage of some mice for a few years and see how it ends up. Without clear evidence that anyone is actively deciding to make choices they know are bad, we can only conclude these are the forces driving the decisions. In fact most "cheating" behavior is because people's judgment faculties are being outweighed by more primal hunger drives that overwhelm higher cognition.
As a kid in the USA you primarily feed on sodas, candy, cookies, corn dogs, puffs, hamburgers, french fries and other junk food. This is what your parents give you, what school serves you in the cafeteria, and what your friends eat. This is encouraged by all media (such as TV which markets directly to you), and by the powers-that-be who put soda machines and candy machines in the hallways at school and even hand out candy as treats and snacks daily.
So please try to understand that this is no more mysterious than the reason Einstein smoked: not because he was a moron with poor willpower and low self-control, but because he was a product of his time, environment, developmental influences, and available information. Its no more mysterious than the reason he spoke German, or that Romans went insane drinking from lead containers.
As for cleaning up your diet. Once I learned about these issues and started trying to eat better, it became clear just how hard it would be. If you live in a rural area, finding _any_ food that isn't processed with a multitude of sweeteners, flavor enhancers, etc is near impossible. Your only option is raw food prepared yourself at home; even spices and seasoning can be laden with additives. Without a lot of patience and examination, you _will_ be consuming these products even if you intend to avoid them. For example, virtually everything at restaurants includes a multitude of these additives.
Sorry for the rant, but I think people need to see the perspective of people who are trying to do the right thing, but up against a really oppressive system of influences, marketing, economics, and daily realities in the US.