I think the real problem is capitalism. It makes good economic sense to sell your customers too much food. Consider Starbucks. Your parents' coffee and a donut was a 250-300 calorie breakfast. Today's latte and a scone is double that and yields a much nicer profit margin.
It's not so much processed foods - obviously you can have processed foods which are healthy too. But if people with very unhealthy diets cut out the kinds of processed foods they eat it would probably go a long way towards making them healthier.
And you're right that capitalism is the root cause - the incentives are skewed towards making foods more addictive and moreish, to help with sales, which leads to making them worse for us. Big food companies even have labs to help them optimise this: http://www.nytimes.com/2013/02/24/magazine/the-extraordinary...
The result of eating these foods are very high glucose levels in the blood + insulin levels which interferes with metabolic signaling. Insulin tells your body to store glucose as fat. Insulin inhibits leptin receptor signalling which means your brain loses the ability to sense how much fat your body is carrying around.
Fructose in large amounts is hepatotoxic, just like alcohol. In fact for the same metabolic reason as alcohol.
"Food science" has advanced to the point where companies explicitly try to hack tastebuds and desire receptors (dorritos optimizing for salty+sweet to induce more hunger while you eat) thereby increasing desire for their product and, they hope, reducing self-action of restraint towards their product.
The old time coke bottles where 8 fl oz (.23 liters). Then cans at 12 oz. Now the single serve bottles are typically 20 oz (.6 liter)
I was in NYC which labels calories in restaurants. Was a little bit of an eye opener. oversize bagels and muffins making breakfast approach half your daily caloric intake.