Você pode doar, contanto que não esteja em jejum.

Contanto que means provided that, as long as, or on the condition that.

So:

Você pode doar, contanto que não esteja em jejum.
= You can donate, as long as you are not fasting.

It introduces a condition that must be met.

In Brazilian Portuguese, contanto que is understandable and correct, but it can sound a bit more formal than some alternatives, such as desde que.

Because contanto que normally requires the subjunctive.

Portuguese uses the subjunctive after expressions that introduce:

• conditions
• uncertainty
• wishes
• requirements

Here, contanto que sets a condition, so estar becomes esteja, which is the present subjunctive form.

Compare:

• Você está em jejum. = You are fasting.
  → statement of fact, so indicative
• contanto que não esteja em jejum = provided that you are not fasting
  → condition, so subjunctive

Esteja is the present subjunctive form of estar for:

• eu
• você / ele / ela
• o senhor / a senhora

In this sentence, it matches você:

• que eu esteja
• que você esteja
• que ele/ela esteja

So não esteja means that you are not / that you not be, depending on how naturally you translate it.

Em jejum means fasting or having an empty stomach, usually because you have not eaten for some time.

It is a very common expression in medical and health contexts, for example:

• Fazer exame em jejum = to do a test while fasting
• Estar em jejum = to be fasting

In your sentence, it means the person must not be fasting.

Because estar em jejum is the usual idiomatic expression.

Portuguese often uses a structure like:

• estar em jejum = to be fasting

Even though the verb jejuar exists (to fast), the expression with em jejum is extremely common, especially in everyday and medical language.

So:

• não esteja em jejum sounds very natural
• não esteja jejuando is possible in some contexts, but less idiomatic here

Because em jejum is a fixed expression.

Portuguese often has set phrases where no article is used, and this is one of them. So you say:

• estar em jejum
• not usually estar no jejum in this meaning

Learners often want to translate word-for-word from English, but here it is best to learn em jejum as one chunk.

Doar means to donate.

Yes, something is probably being left out because the context already makes it clear. For example, in a blood donation context:

• doar sangue = to donate blood

So Você pode doar may really mean:

• You can donate blood

Portuguese often omits the object when it is obvious from the situation.

Yes. Portuguese often drops the subject pronoun when the meaning is clear from context.

So these are both possible:

• Você pode doar, contanto que não esteja em jejum.
• Pode doar, contanto que não esteja em jejum.

Including você can make the sentence:

• clearer
• more direct
• slightly more explicit

Since pode could also refer to ele/ela/você, the pronoun helps remove ambiguity.

It can suggest either one, depending on context.

Poder can express:

• ability
• permission
• possibility

In this sentence, pode most naturally means something like:

• you may donate
• you can donate

In English, both are possible, but in everyday translation, can is often the most natural choice.

Yes, normally contanto que is followed by the subjunctive because it introduces a condition.

Examples:

• Contanto que ele venha... = Provided that he comes...
• Contanto que você estude... = As long as you study...
• Contanto que não esteja em jejum... = As long as you are not fasting...

This is a good pattern to memorize:

contanto que + subjunctive

Yes. Desde que is a very common alternative and often sounds a bit more natural in everyday Brazilian Portuguese.

So this sentence could also be:

Você pode doar, desde que não esteja em jejum.

That means essentially the same thing:

• You can donate, as long as you are not fasting.

Both are correct.

Because the second part is a subordinate clause adding a condition to the main statement.

Main clause:

• Você pode doar

Conditional clause:

• contanto que não esteja em jejum

Using a comma here is standard and helps readability. In this kind of sentence, the comma is very natural.

A rough pronunciation guide would be:

vo-SEH POH-jee doh-AR, con-TAHN-too kee nown es-TEH-zhah eeng zheh-ZHOONG

A few helpful notes:

• você sounds like vo-SEH
• pode in Brazil is often close to POH-jee
• doar has two vowel sounds: do-ar
• que here sounds like kee
• jejum begins with the Portuguese j sound, like the s in measure

Pronunciation varies a bit by region, but this will get you close.

Yes, it is natural and correct, especially in an informative or slightly formal context.

It sounds like something you might see:

• in instructions
• on a medical form
• in health guidance
• in blood donation information

If the context is specifically blood donation, many speakers might also say the fuller version:

Você pode doar sangue, contanto que não esteja em jejum.

That just makes the object explicit.