Both plumeting savings rates and obesity are caused by the same thing--paying for convenience.

You can eat healthy on less than what you would spend on fast food if you're willing to put some effort into it. I did it in college while working and studying 60-80 hours a week. But most people aren't willing and able to do this and end up spending $300+ per person per month on high calorie food.

Doing your own yardwork, keeping a clean house, and cooking from scratch will keep you off the couch and save money. But they take discipline, something most Americans lack.