Learn Hardcore Spanish (Latin America): Mi hermana está muy delgada porque adelgazó con ayuda de una nutricionista moderada, no estricta. - My sister is very thin because she lost weight with the help of a moderate nutritionist, not a strict one.

In this sentence, está is used because the speaker is presenting the sister’s thinness as a resulting or current state, not as a permanent characteristic.

Ser delgado/a = to be thin as a more or less permanent trait (the kind of person who is thin).
Estar delgado/a = to be thin right now, often because of a recent change (diet, illness, exercise, etc.).

Since the sentence explains why she’s thin (because she lost weight with a nutritionist), we’re talking about a change and a current result, which fits estar perfectly:

Mi hermana está muy delgada porque adelgazó…
= My sister is very thin (now) because she lost weight…

What’s the difference between delgada and flaca?

Both can mean “thin”, but they differ in tone and nuance:

Delgada is more neutral and polite. It’s the standard word you’d use in most contexts, including formal or medical ones.
Flaca is more informal/colloquial and can be:
- affectionate (e.g., to a partner or close friend, depending on the culture):
  - Oye, flaca, ven acá. – “Hey, skinny, come here.”
- or slightly negative, like “skinny / scrawny,” depending on tone and context.

In this sentence, talking about health and a nutritionist, delgada is the more natural and respectful choice.

Why is it adelgazó and not something like ha adelgazado?

Adelgazó is the preterite (simple past), and ha adelgazado is the present perfect.

In most of Latin America:

The preterite is used a lot more often for completed past actions, even if they are recent:
- adelgazó = she lost weight (a completed event in the past).
The present perfect (ha adelgazado) is less common in everyday speech and can sound more formal or peninsular (Spain-like) in many areas. It tends to emphasize a connection to the present, but Latin Americans often use the preterite even with that connection.

So:

Mi hermana está muy delgada porque adelgazó…
sounds completely natural in Latin American Spanish.

Ha adelgazado would be understood, but in Latin America it can sound a bit less colloquial in many regions.

What exactly does adelgazó mean, and is it reflexive?

Adelgazó comes from adelgazar, which means “to lose weight / to slim down.”

It can be:

intransitive:
- Mi hermana adelgazó. – “My sister lost weight.”
or reflexive (especially when implying intentional effort):
- Mi hermana se adelgazó. – “My sister slimmed down (she made herself lose weight).”

In everyday Latin American speech, both forms can be used, but in many places adelgazó (without se) is completely normal for “she lost weight,” especially when the context makes it clear she did it intentionally (with a nutritionist, a diet, etc.).

In this sentence, adelgazó is fine and idiomatic.

Why is it una nutricionista and not just nutricionista without an article?

Spanish generally requires an article with singular countable nouns when you introduce them, unless there’s a special reason not to.

con ayuda de una nutricionista
= “with the help of a nutritionist” (some nutritionist, not previously identified).

If you said:

con ayuda de nutricionista

that would sound incomplete or incorrect in standard Spanish, because nutricionista is a singular, countable noun and needs an article (una).

You would omit the article mainly in job titles after ser:

Ella es nutricionista. – “She is a nutritionist.”
(No article needed there.)

But after a preposition like de, you go back to normal noun rules, so you use una.

Why is nutricionista, moderada, and estricta feminine?

Because they’re all describing a female nutritionist:

una nutricionista – the article una marks feminine.
moderada and estricta agree in gender (feminine) and number (singular) with nutricionista.

Key points:

Words ending in -ista (like nutricionista, artista, pianista) are often gender-variable nouns:
- el nutricionista = male nutritionist
- la nutricionista = female nutritionist
The adjectives must match the noun:
- una nutricionista moderada, no estricta
- un nutricionista moderado, no estricto

Here, the speaker is clearly talking about a woman in that profession.

What does moderada mean here? Is it “moderate” in the sense of politics?

In this context, moderada describes the nutritionist’s style or approach, not politics.

una nutricionista moderada means:
- she is not extreme,
- she recommends balanced, reasonable diets,
- she is not too strict or harsh.

So the idea is:
The nutritionist gave a flexible, reasonable plan, instead of a super strict, punishing one.

Political “moderate” can also be moderado/a, but here it’s clearly about how strict or relaxed she is with diets and nutrition plans.

Why add no estricta after moderada instead of using pero (but)?

The structure:

una nutricionista moderada, no estricta

is a compact way of clarifying or redefining what “moderate” means in this context.

It’s like saying:

“a moderate nutritionist – not a strict one”

You could also say:

una nutricionista moderada, pero no estricta
(a moderate nutritionist, but not strict)

Both are correct.
The version without pero is slightly more concise and emphatic, directly contrasting “moderate” with “strict” as opposite qualities:

moderada, no estricta ≈ “moderate rather than strict”

Why is it con ayuda de una nutricionista and not just con una nutricionista?

Con ayuda de emphasizes the role of the nutritionist: that she helped the sister lose weight, not just that the sister was with her.

con ayuda de una nutricionista
= “with the help of a nutritionist”
(the nutritionist guided her, gave a plan, etc.)

If you said:

adelgazó con una nutricionista

it would still be understandable, but it’s slightly more ambiguous—it could be taken as “she lost weight while being with a nutritionist / under a nutritionist’s care,” without clearly stressing the idea of help.

Con ayuda de makes the cause-and-effect relationship clearer: the sister lost weight thanks to the nutritionist’s help.

Why is it porque and not ya que or como?

All three (porque, ya que, como) can introduce reasons, but they have different tendencies:

porque = the most common, neutral way to say “because”.
ya que = often a bit more formal or explanatory, like “since / given that.”
como (meaning “since/because” at the start of a sentence) tends to be more stylistic and is used mostly at the beginning:
- Como adelgazó con ayuda de una nutricionista…, está muy delgada.

In the middle of a sentence explaining a straightforward cause:

Mi hermana está muy delgada porque adelgazó…

Porque is the natural, default choice for everyday speech.

Is there any difference between adelgazó and expressions like bajó de peso?

Yes, they’re close in meaning but with a small nuance:

adelgazar = “to lose weight / to slim down”
Slightly more directly about body weight and figure.
- Mi hermana adelgazó. – “My sister lost weight.”
bajar de peso = literally “to go down in weight”
Very common, slightly more neutral/clinical:
- Mi hermana bajó de peso. – “My sister lost weight.”

In your sentence, you could say:

Mi hermana está muy delgada porque bajó de peso con ayuda de una nutricionista…

and it would still be completely correct and natural.
Adelgazó just puts a bit more focus on the change in her body figure.

Could I say Mi hermana es muy delgada here, or would that change the meaning?

You could say:

Mi hermana es muy delgada.

But that usually means:

she is naturally / characteristically thin (as a stable trait).

If you then add:

porque adelgazó con ayuda de una nutricionista…

it becomes somewhat contradictory: you’d be describing an apparently permanent trait as the result of a recent action.

So:

Mi hermana está muy delgada porque adelgazó…
= She is (now) very thin as a result of losing weight.
Mi hermana es muy delgada.
= She is a thin person (in general), without focusing on recent weight loss.

In this context, está is strongly preferred.