Doktor kaže da moramo smanjiti količinu šećera u čaju.

Croatian has no articles, so there is no separate word for the or a/an.

So:

• Doktor can mean doctor, the doctor, or sometimes a doctor
• the exact meaning depends on context

In this sentence, Doktor kaže... is naturally understood as The doctor says...

Kaže means says, and da means that when it introduces a clause.

So:

• Doktor kaže = The doctor says
• da moramo smanjiti... = that we must reduce...

This is a very common pattern in Croatian:

• Mislim da... = I think that...
• Znam da... = I know that...
• Kaže da... = He/She says that...

Unlike English, Croatian often keeps da where English might sometimes omit that.

Moramo is the 1st person plural present tense of morati = must / have to.

So:

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must
• morate = you all / you formal must
• moraju = they must

In this sentence, moramo means we must.

Croatian usually does not need the pronoun mi for we, because the verb ending already shows the person.

After modal verbs like morati (must / have to), Croatian normally uses the infinitive.

So:

• moramo smanjiti = we must reduce
• literally: we-must reduce

This is similar to English:

• We must reduce
• not We must reducing

Here, smanjiti is the infinitive form of the verb.

This is about aspect, which is very important in Croatian.

• smanjiti = perfective: to reduce, to make smaller, viewed as a completed result
• smanjivati = imperfective: to be reducing, to reduce repeatedly or over time

In this sentence, the doctor is giving advice about achieving a result: reduce the amount of sugar. That is why smanjiti sounds natural.

Very roughly:

• moramo smanjiti količinu šećera = we need to reduce the amount of sugar
• moramo smanjivati količinu šećera would suggest a more ongoing or repeated process

Količinu is the accusative singular of količina (quantity / amount).

It is in the accusative because it is the direct object of smanjiti:

• smanjiti što? = reduce what?
• količinu = the amount

So:

• nominative: količina
• accusative: količinu

This is a very common feminine noun pattern in Croatian.

Because after a noun like količina (amount / quantity), Croatian normally uses the genitive for the thing being measured.

So:

• količina šećera = amount of sugar
• čaša vode = glass of water
• komad kruha = piece of bread

Here:

• količinu = amount (accusative, because it is the object)
• šećera = of sugar (genitive, because it depends on količina)

This is a very common structure and worth learning early.

Šećera is the genitive singular of šećer (sugar).

Why genitive?

Because it follows količina:

• količina šećera = amount of sugar

So even though the whole phrase količinu šećera is the object, only količinu is accusative. The noun after it, šećera, stays genitive because it means of sugar.

Because u can take different cases depending on meaning.

Here it means in the tea, referring to a location or state, so it takes the locative:

• u čaju = in the tea

The noun čaj changes like this:

• nominative: čaj
• locative: čaju

Compare:

• šećer je u čaju = the sugar is in the tea → location → locative
• staviti šećer u čaj = put sugar into the tea → motion/direction → accusative

So in your sentence, u čaju is locative because it means where the sugar is.

Yes. Croatian word order is more flexible than English word order, because case endings show grammatical relationships.

The neutral order here is:

• Doktor kaže da moramo smanjiti količinu šećera u čaju.

But other orders are possible for emphasis, for example:

• Doktor kaže da u čaju moramo smanjiti količinu šećera.
• Kaže doktor da moramo smanjiti količinu šećera u čaju.

These may sound more marked or context-dependent, but they are possible.

English relies much more on word order. Croatian relies more on endings + context.

Yes, in many contexts liječnik and doktor can both mean doctor.

However, there is a small difference in feel:

• liječnik = the standard word for a medical doctor/physician
• doktor = very common in everyday speech, and can also mean someone with a doctorate

In this sentence, Doktor kaže... sounds completely natural in everyday Croatian.

If you wanted a slightly more formal or strictly medical word, you could say:

• Liječnik kaže da moramo smanjiti količinu šećera u čaju.

Because Croatian is a language where the verb ending usually shows the subject clearly.

• moramo already means we must

So adding mi is usually unnecessary:

• moramo smanjiti... = we must reduce...

You can include mi for emphasis:

• Mi moramo smanjiti količinu šećera u čaju.
• This can sound like We must reduce the amount of sugar.

So the pronoun is optional unless you want contrast or emphasis.

A few letters here may be new to English speakers:

• š as in šećera: like sh in shoe
• ž as in kaže: like the s in measure
• č as in čaju: like ch in church
• j as in čaju: like English y in yes

A rough pronunciation guide:

• Doktor ≈ DOHK-tor
• kaže ≈ KAH-zheh
• moramo ≈ moh-RAH-moh
• smanjiti ≈ SMAHN-yee-tee
• količinu ≈ koh-lee-CHEE-noo
• šećera ≈ SHEH-cheh-rah
• u čaju ≈ oo CHAH-yoo

The exact stress can vary by dialect and standard pronunciation rules are a bit more complex, but this is a good practical start.

In meaning, it most naturally goes with the whole idea of the sugar amount: the amount of sugar in the tea.

So the sentence is understood as:

• We must reduce the amount of sugar that is in the tea

In practice, Croatian often leaves this kind of relationship to context, and the phrase u čaju works naturally here.

If needed, Croatian could make the relationship more explicit in other ways, but the original sentence is normal and clear.

Yes, in normal usage that is a very natural interpretation.

Literally, the sentence says:

• The doctor says that we must reduce the amount of sugar in tea

In real life, this often implies:

• use less sugar when making tea
• drink tea with less sugar
• cut down on sugar in tea

So even if the wording focuses on reducing the amount, the practical meaning is often put less sugar in the tea or drink tea with less sugar.