YOU SAID:
You can't eat your cake and have it too.
INTO JAPANESE
ケーキを食べながら食べることもできません。
BACK INTO ENGLISH
You can't eat while eating cake.
INTO JAPANESE
ケーキを食べながら食べることはできません。
BACK INTO ENGLISH
You can't eat while eating cake.
That didn't even make that much sense in English.