So I was reading this book called Food Rules by Michael Pollan, which, by the way, is an interesting book that you can read cover to cover in under an hour and should definitely read, especially if you eat at all in the States.
This guy talks about highly processed and preservative added foods like breakfast cereal and snack bars, which are alarmingly popular in this part of the world. These foods never go bad, even after their suggested "Best Before" date. They can sit on shelves for years and years and not rot. Pollan suggests that you should only eat food that will eventually go bad.
In a different context, he talks about why food goes bad. He puts it differently from what I've usually read or heard. He says that we are in competition with the fungi and bacteria and what not around us for nutrition. When these creatures get to the food before we do, we say that the food has gone bad.
When you put these two things together, which he doesn't do in his book, you see that single celled bacteria know that processed food items do not deliver real nutrition, but we, the ones with the more highly developed brains, eat that "food" anyway. Something to think about.