I gotta wonder about the first person who thought of/tried DE as a "food"....
"Hmmm... diggin' this dirt here. It's good as a pesticide, fertilizer, metal polish, and makes a dandy cat litter too. Think I'll scarf some down! Blech! Tastes like chalk, only grittier. Think I'll snack on a tablespoonful of this stuff every day from here on!"
Doc