Learn Hardcore Spanish (Latin America): Mi tía estaba muy delgada, pero engordó un poco después de dejar el gimnasio. - My aunt was very thin, but she gained some weight after quitting the gym.

Estaba muy delgada → focuses on a temporary state or condition at that time. It suggests her thinness is seen as something that could change (and in fact, it does change in the sentence).
Era muy delgada → would describe thinness as a more permanent or characteristic trait of hers in that past period.

In this sentence, using estaba fits well because we’re contrasting that past condition (thin) with a later change (she gained weight). The imperfect (estaba) also sets a background state in the past, against which a later action (engordó) happens.

Why is “engordó” in the preterite and not “engordaba” in the imperfect?

Engordó (preterite) presents the weight gain as a completed event or change: she did gain weight, and that change is viewed as a single, finished event in the past.
Engordaba (imperfect) would emphasize an ongoing or repeated process: “she was putting on weight” or “she used to put on weight.”

In this context, the speaker is contrasting a past state (estaba muy delgada) with a specific change that happened after she quit the gym, so the preterite (engordó) is the natural choice.

What does “engordar” mean exactly, and who is the subject of “engordó”?

Engordar means “to gain weight” or “to get fat(ter)”.
It is a regular -ar verb.

In the sentence:

engordó is the third-person singular preterite of engordar.
The subject is mi tía (my aunt). Spanish omits the subject pronoun because it’s clear from context and the verb form.

So: Mi tía engordó un poco = “My aunt gained a bit of weight.”

What’s the nuance of “delgada”? How is it different from “flaca”?

Delgada = slim / thin in a neutral or slightly positive way. This is the most standard/neutral word in many contexts.
Flaca also means thin but in much of Latin America it can:
- sound more informal or colloquial,
- sometimes imply too thin or skinny,
- and can be affectionate (e.g. calling a partner flaca).

In this sentence, delgada sounds neutral and descriptive: estaba muy delgada = “she was very thin/slim.”

Why is it “muy delgada” and not “delgada muy”?

In Spanish, adverbs that modify adjectives usually come before the adjective:

muy delgada (very thin)
bastante alto (quite tall)
demasiado caro (too expensive)

Putting muy after the adjective (delgada muy) is ungrammatical. The pattern is:

[verb] + [adverb] + [adjective]
estaba muy delgada

What exactly does “dejar el gimnasio” mean here? Is it “leave the gym building” or “quit going to the gym”?

In context, dejar el gimnasio most naturally means:

to quit the gym / to cancel her gym membership / to stop going to the gym.

If you wanted to emphasize the idea of stopping attendance more clearly, a very common alternative is:

dejar de ir al gimnasio = to stop going to the gym.

Literally “to leave the gym building” would more commonly be:

salir del gimnasio = to go out/leave (physically) the gym.

Why is it “después de dejar el gimnasio” and not just “después dejar el gimnasio”?

When después is followed directly by a verb in the infinitive, you must include de:

después de
- infinitive
  - después de comer (after eating)
  - después de estudiar (after studying)
  - después de dejar el gimnasio (after quitting the gym)

Without de, it’s incorrect in this structure.

Compare:

después de dejar el gimnasio, engordó (after quitting the gym, she gained weight)
después que dejó el gimnasio, engordó / después de que dejó el gimnasio, engordó (after she quit the gym, she gained weight – using a full clause instead of an infinitive)

What’s the difference between “después de” + infinitive and “después de que” + verb?

Both can express “after …”, but:

después de + infinitive
- Used when both actions have the same subject.
- More compact:
  - Después de dejar el gimnasio, engordó un poco.
    (Subject “she” does both: quitting and gaining weight.)
después (de) que + conjugated verb
- Used with a full clause, and the subject can be the same or different.
- Example:
  - Después de que mi tía dejó el gimnasio, engordó un poco.
  - Después de que dejaron el gimnasio, mi tía engordó un poco. (They left, and then she gained weight.)

In Latin American everyday speech, “después de que + indicative” is very common for past events. Subjunctive may appear in other time frames or more formal registers, but that’s beyond this sentence.

Why is it “pero” and not “sino”?

Pero = “but” in the sense of contrast / opposition.
Sino is used mainly to mean “but rather” / “but instead” and usually corrects or replaces something negative said before.

Examples:

Uso gafas, pero no lentes de contacto.
I wear glasses, but not contacts. (contrast)
No uso lentes de contacto, sino gafas.
I don’t wear contacts, but rather glasses. (correction after no)

In your sentence there is no negation being corrected. We’re just contrasting two situations:

Mi tía estaba muy delgada, pero engordó un poco…
My aunt was very thin, but she gained a bit of weight…

So pero is the right conjunction.

Why is it “delgada” and not “delgado”? How does agreement work here?

In Spanish, adjectives agree in gender and number with the noun they describe:

Mi tía is feminine singular.
So the adjective must also be feminine singular → delgada.
If it were mi tío (my uncle), you’d say delgado.
For plural:
- Mis tías estaban muy delgadas.
- Mis tíos estaban muy delgados.

The same rule applies to gorda/gordo, alta/alto, etc.

Why is there no subject pronoun like “ella” before “estaba” or “engordó”?

Spanish is a pro-drop language: it often omits subject pronouns because the verb endings already show who the subject is.

Estaba and engordó are both third person singular forms, and the subject mi tía is mentioned at the start. So repeating ella is unnecessary.

You could say:

Mi tía estaba muy delgada, pero ella engordó un poco…

This is grammatically correct but sounds a bit redundant unless you really want to emphasize she (not someone else) gained weight.

What is the role of “un poco” in “engordó un poco”, and can it go somewhere else in the sentence?

Un poco is an adverbial phrase that means “a little / a bit”, and here it modifies the verb engordó:

engordó un poco = “she gained a little (weight).”

Natural positions:

Mi tía estaba muy delgada, pero engordó un poco después de dejar el gimnasio.
Mi tía estaba muy delgada, pero después de dejar el gimnasio engordó un poco.

You generally keep un poco close to the verb it modifies. Moving it far away (e.g. to the very beginning) would sound odd or unclear.

Does “gimnasio” in Latin America mean a fitness gym like in English, or could it mean something else?

In Latin American Spanish, gimnasio very commonly means:

a gym / fitness center where you work out, lift weights, do classes, etc.

Other uses:

In a school context, el gimnasio can be the gymnasium (the physical space/building).
In some countries, gimnasio can also be part of the name of a private school (e.g. Gimnasio Moderno), but that’s more about proper names.

In this sentence, dejar el gimnasio will normally be understood as quitting the fitness gym, not leaving a P.E. class.