Learn Hardcore Spanish (Latin America): Quiere adelgazar de forma lenta y moderada, sin dietas muy estrictas. - She wants to lose weight slowly and moderately, without very strict diets.

Spanish often omits the subject pronoun because the verb ending already shows the person and number. Context tells you whether the speaker means he, she, or you (formal).

If you want to make it explicit, you can say:

Él quiere adelgazar...
Ella quiere adelgazar...
Usted quiere adelgazar...

Why is adelgazar in the infinitive form after quiere?

The verb querer often takes another verb in the infinitive to express want to do something.

Pattern: querer + infinitive

Some examples:

Quiero comer. = I want to eat.
Queremos viajar. = We want to travel.
Quiere adelgazar. = He/She/You (formal) wants to lose weight.

So adelgazar stays in the infinitive because it’s the action that is wanted.

What is the difference between adelgazar, bajar de peso, and perder peso?

All three can translate as to lose weight, but there are slight nuances:

adelgazar – literally to become thin/slimmer. Very common and natural in all contexts.
bajar de peso – literally to go down in weight. Very common in Latin America, especially in everyday speech.
perder peso – literally to lose weight. Also common and clear.

In your sentence, you could say:

Quiere adelgazar...
Quiere bajar de peso...
Quiere perder peso...

All would be understood. Adelgazar is a bit more compact and sounds very natural.

What does de forma lenta y moderada mean grammatically? Why use de forma?

De forma lenta y moderada literally means in a slow and moderate way and works as an adverbial phrase (it tells us how the person wants to lose weight).

Structure:

de (preposition)
forma (noun: form, way, manner)
lenta y moderada (adjectives describing forma)

Spanish often uses de forma or de manera + adjective to express in a ... way:

de forma rápida = in a fast way / quickly
de forma responsable = in a responsible way

So de forma lenta y moderada = slowly and in a moderate way.

Why are lenta and moderada feminine and singular?

They agree with forma, which is:

feminine: la forma
singular: forma (not formas here)

So the adjectives must match:

forma lenta (slow way)
forma moderada (moderate way)

If you changed the noun, the adjectives would change:

de modo lento y moderado (because modo is masculine singular)
de formas lentas y moderadas (if you made formas plural)

Could I say de forma lenta y moderado instead?

No. That would be incorrect agreement.

forma is feminine singular, so both adjectives must also be feminine singular:
- lenta
- moderada

Correct:

de forma lenta y moderada

Incorrect:

de forma lenta y moderado
de forma lento y moderado, etc.

Can I just say lentamente instead of de forma lenta?

Yes, you can. Both are grammatically correct, but they sound slightly different:

lentamente = slowly (adverb)
de forma lenta = in a slow way (more literally)

Possible versions:

Quiere adelgazar lentamente y de forma moderada.
Quiere adelgazar lenta y moderadamente.
Quiere adelgazar lentamente y moderadamente.

De forma + adjective is very common and a bit more neutral/formal; -mente adverbs like lentamente are also completely standard.

What exactly does moderada add here? Is it like “moderate” in English?

Yes, moderada (from moderado, -a) is very close to English moderate.

In this context, de forma lenta y moderada suggests:

not too fast (lenta)
not extreme or drastic (moderada)

So the idea is slow and not extreme / not drastic weight loss.

What does sin dietas muy estrictas mean grammatically?

Sin means without. The structure is:

sin + noun phrase

Here:

sin dietas muy estrictas = without very strict diets

Breakdown:

dietas – plural noun (diets)
muy – very
estrictas – strict, feminine plural, agreeing with dietas

So the phrase means the person wants to lose weight without following very strict diets.

Why are estrictas and dietas plural and feminine?

Dieta is a feminine noun:

singular: la dieta
plural: las dietas

So:

dietas is feminine plural.
The adjective estrictas must match in gender and number:
- estricta (feminine singular)
- estrictas (feminine plural)

You say:

una dieta estricta – a strict diet
dos dietas estrictas – two strict diets
sin dietas muy estrictas – without very strict diets

Could I say sin una dieta muy estricta instead of sin dietas muy estrictas?

Yes, but there is a nuance:

sin dietas muy estrictas – in general, without following very strict diets (plural, more general).
sin una dieta muy estricta – without a very strict diet (singular, more like one strict regime).

Both are correct. The original sentence sounds more general: the person doesn’t want strict dieting as a concept.

Why is it muy estrictas and not mucho estrictas?

In Spanish:

muy = very (used with adjectives and adverbs)
- muy estrictas, muy rápido, muy grande
mucho / mucha / muchos / muchas = a lot (of) (used with verbs or nouns)
- trabaja mucho – he works a lot
- mucha comida – a lot of food

Since estrictas is an adjective, you must use muy:

dietas muy estrictas = very strict diets
Not: dietas mucho estrictas.

Could the sentence be talking to tú instead of usted or él/ella? What would change?

To talk directly to tú (informal you), you’d change quiere to quieres:

Quieres adelgazar de forma lenta y moderada, sin dietas muy estrictas.
- You (informal) want to lose weight slowly and moderately, without very strict diets.

For usted (formal you), él, or ella, you keep quiere and rely on context:

(Usted) quiere adelgazar...
(Él) quiere adelgazar...
(Ella) quiere adelgazar...

Can I replace de forma lenta y moderada with something more colloquial?

Yes. Some natural alternatives in Latin American Spanish:

poco a poco – little by little
- Quiere adelgazar poco a poco, sin dietas muy estrictas.
despacio – slowly
- Quiere adelgazar despacio, sin dietas muy estrictas.
sin apuro / sin prisa – without rush
- Quiere adelgazar sin apuro, sin dietas muy estrictas.

All keep the same basic idea: gradual, non-extreme weight loss.