I think really the problem is many fold, it's not the "evil food companies" or anything of that nature. Now hear me out and then call me a conservative racist.
1) Breakdown of the family. No more mom making good home cooked meals keeping her family's nutrition and nourishment in mind providing a well balanced diet of things on the table because she had time to do so. No mom and dad in the home = no nice home cooked meals as one parent shoulders everything. Hell, Mom/Dad can't even pack a lunch for the kids as school won't allow it in the compound.
2) Kids not outside playing - already mentioned, sedentary lifestyle, all part of the bigger picture, that lifestyle carries over into adulthood
3) Basic nutrition not being taught in school (screw what they serve, teach them about what is good food and balance, which was the parents job in the first place and now you have removed that from the household, good job).
4) A basic lack of know how in taking care of oneself is rooted for a generation or two now because of #1.
Add it all up, and no wonder people are eating crap and not exercising. They know no other way because of #1 - nobody to teach them how to live well, only rely on others for basic calories because tummy grumbles.
Like fucking cattle.