Translation:You can't eat cabbage at every meal.
Thanks for your comment, otherwise there is no way to know that "à tous les repas" doesn't mean "(only) for every meal". - How would you say that in French?
Although you wouldn't say "at every meal" but "with every meal" to express that it is eaten as a part of every meal.
I think you are right here. This sentence is a regular negation! "You cannot eat cabbage at every meal!" It DOES NOT necessarily mean the person is eating ONLY cabbage. It is like telling a kid they cannot have chocolate milk at(with) every meal. There is a negation to say you cannot have ONLY cabbage or telling the kid they cannot have ONLY chocolate. NE....QUE!!! Tu ne peux manger que du chou à tous les repas"== You cannot eat (notice no pas here) QUE(ONLY) du chou à tous les repas.