Learn Hardcore Spanish (Latin America): Aunque mi abuelo sea gordito, su corazón está fuerte porque camina todos los días. - Although my grandfather is chubby, his heart is strong because he walks every day.

“Sea” is the present subjunctive of “ser.”
With aunque, Spanish can use either indicative or subjunctive, and the meaning changes slightly:

Aunque + indicative → a simple, known fact
- Aunque mi abuelo es gordito…
  = Although my grandfather is chubby… (this is just presented as a fact)
Aunque + subjunctive → concession, possibility, or “even if” idea
- Aunque mi abuelo sea gordito…
  ≈ Even though / Even if my grandfather is chubby…
  It feels a bit more like: “Regardless of him being chubby…”

So “sea gordito” sounds a bit more concessive / hypothetical / less focused on the fact itself than “es gordito.” Both are grammatically possible; the choice is about nuance and style.

What exactly does “gordito” mean compared to “gordo”? Is it rude?

“Gordo” literally means “fat.”
“Gordito” is the diminutive (adding -ito) and usually softens the tone:

Meaning: physically, it still means “a bit fat / chubby.”
Tone: often more affectionate or playful:
- With family and friends in Latin America, you might hear gordito/gordita used as nicknames, even lovingly:
  - “Mi gordito”, “hola, gordita”.
It can still be offensive if said to someone who doesn’t like it or in a mocking tone.

In this sentence about a grandfather, “gordito” sounds affectionate and gentle, more like “a bit chubby” than bluntly “fat.”

Why is it “mi abuelo sea gordito” and not “mi abuelo está gordito”?

The difference is ser vs. estar with physical description:

Ser gordito → a more permanent characteristic, part of what he’s like:
- Mi abuelo es gordito. = My grandfather is (by nature) chubby.
Estar gordito → a temporary or current state (e.g., he has put on weight recently):
- Mi abuelo está gordito. = My grandfather is chubby right now / has gotten chubby.

In the sentence with “sea gordito,” we’re using ser in the subjunctive (sea), treating “being chubby” as more of a general physical trait. If you said:

Aunque mi abuelo esté gordito…

that would suggest he currently happens to be chubby (more temporary nuance).

Why is it “su corazón está fuerte” and not “su corazón es fuerte”?

Both ser and estar can go with “fuerte”, but the meaning changes:

Estar fuerte → current condition / state (often physical health or strength at this time)
- Su corazón está fuerte.
  = His heart is strong (right now / in terms of medical condition).
Ser fuerte → inherent quality, more permanent or defining, often metaphorical (courage, character):
- Su corazón es fuerte.
  = His heart is strong (could sound more like “he is strong-hearted / emotionally strong”).

Since we are talking about heart health because he walks every day, “está fuerte” fits: it’s about his current good physical condition.

Why is it “porque” as one word and not “por qué” or “porqué”?

Spanish has four different forms:

porque (one word, no accent)
→ because (introduces a reason)
- Su corazón está fuerte porque camina todos los días.
  = His heart is strong because he walks every day.
por qué (two words, with accent on qué)
→ why (in questions)
- ¿Por qué camina todos los días?
  = Why does he walk every day?
porqué (one word, with accent)
→ a noun: the reason
- No entiendo el porqué.
  = I don’t understand the reason.
por que (two words, no accent)
→ less common; appears in certain fixed constructions or after prepositions + que (e.g. luchó por que…).

In your sentence, we’re simply giving the reason, so we need “porque” = because.

Why is the verb “camina” (simple present) used to mean “walks every day,” and not something like “está caminando”?

Spanish simple present (camina) is regularly used for:

habitual actions (things you do regularly),
general truths.

So:

Camina todos los días.
= He walks every day. (habit)

If you say:

Está caminando.

that is present progressive, used for an action happening right now:

Está caminando. = He is walking (right now).

Since the idea is a daily habit, the correct form is “camina todos los días.”

Could I say “todos los días camina” instead of “camina todos los días”? Does the word order matter?

Both word orders are grammatically correct:

Camina todos los días.
Todos los días camina.

Differences:

“Camina todos los días” is the most neutral and common order.
“Todos los días camina” puts a bit more emphasis on the frequency (“Every single day he walks”).

In everyday speech, you’ll hear both, but the original order is slightly more natural and neutral.

Why is it “mi abuelo” and not “el abuelo” or just “abuelo”?

In Spanish, when you talk about your own family members, you normally use a possessive adjective:

mi abuelo = my grandfather
tu abuelo = your grandfather
su abuelo = his/her/their/your (formal) grandfather

Using “el abuelo” would usually refer to some grandfather in general, or “the grandfather” as a role, not specifically “my grandfather.”

You can drop the possessive in direct address:

¡Abuelo! = Grandpa!

but in a normal descriptive sentence like this, you say “mi abuelo.”

Why is it “gordito” and not “gordita”? How does gender agreement work here?

Adjectives in Spanish must agree in gender and number with the noun they describe:

Mi abuelo (masculine, singular) → gordito (masculine, singular)
Mi abuela (feminine, singular) → gordita (feminine, singular)

So:

Aunque mi abuelo sea gordito…
Aunque mi abuela sea gordita…

Changing abuelo → abuela would force gordito → gordita.

Can “aunque” also mean “even if” here, or is it only “although / even though”? How strong is that contrast?

“Aunque” is flexible. Depending on context and verb mood, it can be:

although / even though (contrast with a real fact),
even if (concession with something possible or not so important).

In your sentence with subjunctive:

Aunque mi abuelo sea gordito, su corazón está fuerte…

you can naturally understand it as:

Even though my grandfather is chubby, his heart is strong…
or
Even if my grandfather is chubby, his heart is strong…

The core idea is concession / contrast:
being chubby is one idea; having a strong heart is the unexpected, contrasting result.