"I do not eat honey, but I eat bread."
Translation:Я не їм мед, але я їм хліб.
Because мед is masculine (ending in a consonant, тато is an exception) and молоко is neuter (ends in o) they do not change their form for the accusative case (receiving the action of the verb) the only time you change the ending to make it accusative is if the noun is feminine. For example, lets use студентка. "The student loves" would be translated as, "студентка любить" it is ending with an a because it is nominative (subject) for "we love the student" it would be "ми любимо студентку" because in this case the student is receivin the verb "to love". I do not speak ukrainian (yet) and i do not have a full understanding of cases but duolingo did do this in future lessons when going in depth on the accusative case, i hope this helped.
The question here was, whether to use Accusative (мед, молоко) or Genitive (меду, молока) and whether there is any difference in the meaning. For example, in a positive sentence only Accusative is possible: Я їм мед/молоко, meaning either "I am eating it right now" or "I eat it in general" while for a negative sentence it seems to me that the difference should be so.
I am a native speaker :D Was trying to answer the question posed by jmango2 about "мед" VS "меду". I wrote "I think" because this is my intuitive native-speaker answer and does not come from the knowledge of linguistics (since this is not my profession)
Oh, thank you. It seems I made a mistake when reading their question because I thought they were saying that masculine and neuter nouns must change their ending to become accusative. I did not realize that they were talking about the genitive case. I also did not realize you were a native speaker.