It is true that obesity is inversely correlated with level of income. As you noted, Mike, part of the problem is that the cost/calorie of foods like Mac-n-cheese or Lunchables is far lower than the cost/calorie of fresh friuts and veggies. So for less money you get more fat and fewer nutrients. And that's all supported by government subsidies of the additives (corn syrup leading among them) that go into fast and processed foods. Your typical chicken Mc Nugget is chicken (raised on corn), processed with corn syrup added, breaded in corn meal, and fried in corn oil. As long as trans fats (which don't occur in nature) are subsidized, food manufacturers will have an added incentive to put them in our food, and because it will be cheap (and tasty) we will have incentive to buy it and eat it. And we'll get fatter and fatter. Right now 2/3 of Americans are overweight or obese, and preventable, lifestyle related disease (cholesterol, diabetes, etc) account for 3/4 of our astoundingly high health care costs. Many people are literally eating them selves to death.
It's hard to be brave when you're a chicken.