in a short period of time.
(Words form Michael Pollan - The Omnivore's Dilemma)
What foods go bad? Dairy, Meat, Fruits and Vegetables, Whole Grain Bread, etc.
I made some blueberry muffins from scratch last week that were very healthy (for muffins). I used whole wheat flour, very little sugar, etc. Well the kids didn't them and I really only wanted one so they went bad - very quickly. I was a little upset that I had not thought to freeze them ahead of time but on the other hand was happy that they were moldy only after one week because that's what real food does - it goes bad!
If your food can sit on a shelf for days, months, even years- it is probably not "real" food.