Why is Junk Food so addictive?

Why is it that even though we all know that carbs, grease and salt are not good for you, they are so irresistable?  Why do some junk foods (Cheetos, I'm talking to you) just beg you to eat more of them?  Why do others seem perfectly designed to make you feel okay about eating them (pita chips, ahem)?

It turns out this is not coincidental, but rather the result of decades of research on the science of producing foods with these characteristics and on the marketing of them to consumers.

This article looks at the history since the early 1990's when it was starting to be recognized that obesity was becoming pandemic of the food industry's efforts to head off possible lawsuits or governmental regulations.  To their credit, there was serious discussion and effort at producing healthier snack foods.  In many cases these failed compared to less healthier options.  At the same time, the snack food makers were pouring millions of dollars into devising ways to make their products literally irresistible.

Interviews with some of the people involved over the years are also revealing of motivations and conflicts both at the corporate and personal levels. The last interview about the successful marketing of plain baby carrots by selling them like junk food (but not as junk food) is worth the read.