Nie mam apetytu, dlatego jem tylko zupę.

Because after negation, the direct object of many verbs often changes to the genitive in Polish.

• Affirmative: Mam apetyt.
• Negative: Nie mam apetytu.

Here’s what is happening:

• mam = I have
• apetyt is a masculine inanimate noun
• with mieć (to have), the object is normally in the accusative
• but in the negative, Polish commonly uses the genitive instead

So:

• apetyt = nominative / accusative form
• apetytu = genitive form

This is a very common pattern:

• Mam czas. → Nie mam czasu.
• Mam samochód. → Nie mam samochodu.

Because zupa is the direct object of jem (I eat), so it has to be in the accusative case.

• zupa = nominative form
• zupę = accusative form

For many feminine nouns ending in -a, the accusative singular ends in -ę:

• kawa → kawę
• herbata → herbatę
• zupa → zupę

So:

• Jem zupę. = I eat / am eating soup.

Because in Polish, the verb ending usually already shows who the subject is.

• mam = I have
• jem = I eat / I am eating

So ja is not necessary. Polish often leaves subject pronouns out unless you want emphasis or contrast.

Compare:

• Nie mam apetytu. = normal, neutral
• Ja nie mam apetytu. = I don’t have an appetite (maybe contrasting with someone else)

This is similar to Spanish or Italian more than English.

Dlatego means therefore, that’s why, or for that reason.

It introduces a result:

• Nie mam apetytu = cause
• dlatego jem tylko zupę = result

So the logic is:

I have no appetite, therefore I’m only eating soup.

A useful comparison:

• bo = because → introduces a reason
• dlatego = therefore / that’s why → introduces a result

Compare:

• Jem tylko zupę, bo nie mam apetytu.
  I’m only eating soup because I have no appetite.

• Nie mam apetytu, dlatego jem tylko zupę.
  I have no appetite, therefore I’m only eating soup.

Because dlatego is linking two clauses here, and in standard Polish punctuation you put a comma before it in this kind of sentence.

The two parts are:

• Nie mam apetytu
• dlatego jem tylko zupę

So the comma helps separate the cause from the result.

This is normal Polish punctuation:

• Jest zimno, dlatego zamknąłem okno.
• Nie mam czasu, dlatego nie przyjdę.

Because Nie mam apetytu means I have no appetite in a general sense.

When you want to say appetite for something specific, you usually use:

mieć apetyt na + accusative

For example:

• Mam apetyt na pizzę. = I feel like pizza / I have an appetite for pizza.
• Nie mam apetytu na mięso. = I don’t feel like eating meat.

But in your sentence, the speaker is talking about appetite in general, so just:

• Nie mam apetytu.

Because jem is the imperfective verb form, and that is the normal choice for a present action.

• jeść = imperfective = to eat
• zjeść = perfective = to eat up / finish eating

In Polish, perfective verbs do not normally have a true present meaning. A form like zjem usually means future:

• jem = I am eating / I eat
• zjem = I will eat up / I will eat

So in this sentence:

• jem tylko zupę = I’m only eating soup

That fits the present situation.

No, Polish word order is fairly flexible, but different word orders change the emphasis.

The sentence as given is natural and neutral:

• Nie mam apetytu, dlatego jem tylko zupę.

You could also hear:

• Dlatego jem tylko zupę. = That’s why I’m only eating soup.
• Nie mam apetytu, dlatego tylko zupę jem. = stronger emphasis on soup
• Tylko zupę jem. = I’m eating only soup

So the meaning stays similar, but the focus shifts depending on where words are placed.

Here, tylko most naturally modifies zupę.

So:

• jem tylko zupę = I eat only soup

In other words, soup is the only thing being eaten.

Word placement matters for emphasis:

• Jem tylko zupę. = I’m eating only soup.
• Tylko jem zupę. = less natural in this context; it could sound like I’m only eating soup with a special contrast
• Tylko zupę jem. = strong emphasis on soup

So in your sentence, the simplest reading is: I’m not eating anything else, just soup.

It can be either, depending on context.

Polish does not usually make the same strong distinction that English does between:

• I eat
• I am eating

So jem can mean:

• I eat
• I am eating

In this sentence, because it describes a current situation, English would usually translate it as:

• I’m only eating soup

But grammatically, Polish just uses the present tense jem.

The word zupę is pronounced approximately like ZOO-peh with a nasalized final vowel, though in everyday speech the final ę is often not strongly nasal.

A practical learner-friendly approximation is:

• zupa ≈ ZOO-pa
• zupę ≈ ZOO-peh

You do not need to overdo the nasal sound at the end. In normal speech, final ę is often pronounced quite lightly.

Also remember that Polish stress is usually on the second-to-last syllable, so:

• ZU-pę

Yes, but the meaning changes a little.

• Nie mam apetytu = I have no appetite
  This sounds more physical, especially about food.

• Nie mam ochoty = I don’t feel like it / I’m not in the mood
  This is broader and often needs more context.

For food, you might hear:

• Nie mam apetytu. = I’m not hungry / I have no appetite.
• Nie mam ochoty na zupę. = I don’t feel like soup.

So apetyt is the more direct choice in your sentence.