Dietary Coke

I was looking to see if ‘diet’ comes from δίαιτα — it does — and came upon a fact which ought not be surprising — but it was mildly so — that ‘diet’ the adjective, a la diet coke, is only attested from 1963. (I guess dietary previously fit the bill.) This is apples and oranges since ‘diet’ is both noun and adjective (and verb) but here is ngrams for diet, dietary.