@jamiemccarthy @debcha That was a trope among Analog-SF writers in the 60s and early 70s, I think? Anyway, it's bullshit. While CHON are the commonest elements in stuff we eat, we need traces of a bunch more stuff—phosphorus, sulfur, selenium, iron, and so on—often bonded in unusual polycyclic aromatic organic molecules. "Food" isn't a single thing.