The portuguese equivalent of “An apple a day keeps the doctor away” is pleasing because it rhymes just like the english version
Uma maçã por dia, não sabe o bem que lhe fazia
It isn’t usually used in that form though. If you look for the second part online it’s more often used with “um livro por dia”, “uma música por dia” “uma panda por dia” or any other noun you care to name
Luso 