Consumption is not the sole criteria for determing foodstuffs. Eating dirt doesn't confer nutrition on dirt, nor make it safe to consume.
Poisons are eaten; they hardly qualify as food, as they do not serve to supply nutrients, but serve to kill.
A thing, like gum, can be considered edible, but just because something's edible doesn't make it food. My definition of food includes, but is not limited to, a sustenance factor, which includes nutrients or other aspects upon which the body relies. One can't, for instance, find much nutrition in water, but we need it to live.
Which, of course, causes this post to segue into the nutrition of air, which leads to Breatharians, which naturally causes this:
