"An egg is a food."
You would never use a with food. "A food" is a terrible translation. It should be an egg is food. Never a food.
Agreed. As a US English speaker, "X is a food" sounds just fine to me. Or at least I'm sure I've heard it before...
But maybe it's incomplete. How about, "an egg is a food that has many uses in cooking." Does that sound more natural?
It would actually sound weird to me to say "a type of food" in that sentence, because it would sound like eggs are a whole category of food, like fruits or vegetables, but really when I say "an egg", I'm referring to only one kind of egg (chicken), and probably so are you.
Personally, I think either "egg is a food" or "eggs are food" or "an egg is food" are fine but "an egg is a food" sounds wrong. A food means a type of food which requires a more general form of the subject.
Wow. Surprising number of comments about this one, just came through to flag that no kanji (beyond 食) is being accepted (1.31.18). 卵は食べ物です.
Not going to lie, i guessed which word was egg thanks to a certain handheld game.