Learn Hardcore Croatian: Doktor kaže da je pretjerivati sa solju štetno i da bismo trebali smanjiti koliko je jedemo. - The doctor says that overdoing it with salt is harmful and that we should reduce how much of it we eat.

je is the 3rd person singular of biti (to be).
Croatian likes to keep je early in the clause (it’s a clitic), so it appears right after da:
- da je pretjerivati sa solju štetno
- literally: that is overdoing with salt harmful

The underlying structure is:

[Pretjerivati sa solju] je štetno. – Overdoing it with salt is harmful.

When you put it after da, the verb je moves to its clitic position (second place in the clause):

da je [pretjerivati sa solju] štetno

So je is just the verb to be, linking the “subject” (pretjerivati sa solju) with the adjective štetno.

Can I change the word order to da je štetno pretjerivati sa solju? Is that better or worse?

Yes, that word order is perfectly correct and very natural:

Doktor kaže da je štetno pretjerivati sa solju.

Both versions work:

da je pretjerivati sa solju štetno
da je štetno pretjerivati sa solju

The difference is only in emphasis and rhythm. Native speakers probably slightly prefer:

da je štetno pretjerivati sa solju

because it mirrors English more closely: that it is harmful to overdo it with salt.

Why is pretjerivati (infinitive) used here instead of a noun like pretjerivanje?

Croatian can use both an infinitive and a verbal noun as the “subject” of a sentence like this.

With infinitive (as in your sentence):
- Pretjerivati sa solju je štetno.
- To overdo it with salt is harmful.
With verbal noun:
- Pretjerivanje sa solju je štetno.
- Overdoing it with salt is harmful.

Both are grammatically correct. The differences:

Infinitive (pretjerivati) often sounds a bit more neutral and “verbal”.
Verbal noun (pretjerivanje) sounds slightly more “thing-like” and sometimes a bit more formal or abstract.

In everyday speech, both are used. Many speakers would probably say:

da je štetno pretjerivati sa solju
or
da je štetno pretjerivanje sa solju

What exactly does pretjerivati sa solju mean? Why sa?

Pretjerivati normally means to exaggerate, to overdo.

With sa + instrumental, it often means to overdo something / to use too much of something:

pretjerivati sa solju – to overdo it with salt (use too much salt)
pretjerivati s alkoholom – to overdo it with alcohol
pretjerivati s vježbanjem – to overdo it with exercise

So sa here is the preposition with, and it takes the instrumental case.

Why is it sa solju, not s solju or sa soli?

Three points here:

Preposition form: s vs. sa
- The basic form is s.
- sa is used:
  - before words beginning with s, z, š, ž (to avoid awkward clusters),
  - and in some other cases for easier pronunciation.
Since solju starts with s, sa solju is more natural than s solju.
Case: solju
- After s/sa meaning with, you need instrumental case.
- sol in the instrumental singular is solju.
- So sa solju literally means with salt (in the sense “in terms of salt use”).
What about sa soli?
- sa can also mean from (a surface) and then takes genitive:
  - sa stola – from the table
  - sa soli could mean from the salt in a very specific context.
- For with salt / in terms of salt, sa solju (instrumental) is the form you want.

What is the difference between kaže and govori here? Could I say Doktor govori da…?

You can say both Doktor kaže da… and Doktor govori da…, but they feel slightly different:

kaže (from kazati) – a single act of saying or stating something.
- Doktor kaže da… – The doctor says that… (he states it).
govori (from govoriti) – to speak, to talk, often suggesting ongoing or repeated speech.
- Doktor govori da… – The doctor says / is saying / keeps saying that…, or the doctor talks about how…

In a sentence reporting one specific statement, Doktor kaže da… is the most natural choice.

Why is it da bismo trebali and not just da trebamo? What’s the difference?

Both are grammatical, but they differ in tone:

da trebamo smanjiti…
- more direct: that we need to / must reduce…
- sounds like obligation or clear necessity.
da bismo trebali smanjiti…
- bismo… trebali is the conditional of trebati.
- corresponds closely to English we should:
  - that we should reduce…
- softer, more advisory, less strict.

So:

da bismo trebali smanjiti koliko je jedemo ≈ that we should reduce how much of it we eat (recommendation, advice).
da trebamo smanjiti koliko je jedemo ≈ that we need to / must reduce how much of it we eat (stronger necessity).

What exactly is bismo trebali grammatically, and why is bismo in that position?

bismo trebali is the 1st person plural conditional of trebati.

Form:

conditional auxiliary bismo (from biti, would be)
past participle trebali (plural, because mi = we)

Together: (mi) bismo trebali – we should / we would need to.

Position:

bismo is a clitic, and Croatian clitics usually stand in second position in their clause.
In da bismo trebali smanjiti…:
- the first word of the clause is da,
- so the clitic bismo comes right after it: da bismo trebali…

You cannot write da trebali bismo smanjiti…; that would sound wrong.

In koliko je jedemo, what is je? Is it again the verb to be?

In koliko je jedemo, je is not the verb to be.

Here, je is the clitic object pronoun:

je = her / it (3rd person singular feminine, accusative)

It refers back to sol (salt), which is feminine in Croatian.

So:

jedemo je – we eat it (salt).
koliko je jedemo – how much of it we eat.

Again, je is a clitic, so it must be in second position in that clause:

koliko je jedemo (correct)
koliko jedemo je (incorrect)

Why koliko je jedemo and not something like koliku je jedemo?

Because koliko here is an adverb of quantity, not an adjective.

koliko – how much / how many (adverb, does not change form for gender/case here)
kolika/koliki/koliko (adjectival forms) would agree with a noun: koliku sol etc.

In koliko je jedemo:

koliko modifies the amount of the action (how much we do it), not a noun directly.
The noun sol is only implicit; it’s represented by the pronoun je.

You could say more explicitly:

da bismo trebali smanjiti koliko soli jedemo – …reduce how much salt we eat.

But with the pronoun:

koliko je jedemo = how much of it we eat (adverb koliko
- clitic object je).

Could I say koliko soli jedemo instead of koliko je jedemo? Is there any difference?

Yes, koliko soli jedemo is perfectly correct and very common:

…da bismo trebali smanjiti koliko soli jedemo.

Difference:

koliko soli jedemo – explicit noun soli (how much salt we eat).
koliko je jedemo – uses pronoun je referring back to sol; stylistically a bit lighter, avoids repeating the noun.

Both are fine; which you choose is mostly a matter of style and avoiding repetition.

Why is štetno in neuter form? Shouldn’t it agree with sol somehow?

Štetno is neuter singular because it agrees with an entire clause / infinitive phrase, not with sol.

The logical “subject” is:

pretjerivati sa solju – to overdo it with salt

When the subject is:

an infinitive (pretjerivati),
or a whole clause (da + clause),

Croatian normally uses a neuter singular adjective:

Pretjerivati sa solju je štetno.
Da pušimo je štetno.
Pušiti je nezdravo.

So štetno is neuter because it’s describing the idea “overdoing it with salt”, not the noun sol itself.

Why is the aspect pretjerivati (imperfective) and smanjiti (perfective) used here?

Aspect matches what is being talked about:

pretjerivati – imperfective
- expresses a general, repeated or habitual action.
- pretjerivati sa solju je štetno = Habitually overdoing it with salt is harmful (in general).
smanjiti – perfective
- expresses a complete, one-time change or result.
- trebali smanjiti = we should reduce (bring it down) – a concrete action leading to a new state.

If you said smanjivati, it would sound more like describing an ongoing, repeated process (we should be constantly in the process of reducing), which doesn’t fit as well as a clear recommendation to lower consumption.

Why is da repeated: …štetno i da bismo trebali…? Could I drop the second da?

In this sentence you normally repeat da:

Doktor kaže da je pretjerivati sa solju štetno i da bismo trebali smanjiti…

You have two separate subordinate clauses, both depending on kaže:

da je pretjerivati sa solju štetno
(da) bismo trebali smanjiti koliko je jedemo

They are coordinated by i (and). In careful, standard speech and writing, you keep da with each clause.

In very informal speech, someone might drop the second da, but that is less standard and can sometimes sound sloppy or ambiguous. The safe, correct version is with da repeated.