Quiere adelgazar de forma lenta y moderada, sin dietas muy estrictas.

The form quiere is 3rd person singular of querer in the present tense. On its own, it can mean:

• he wants – él quiere
• she wants – ella quiere
• you (formal) want – usted quiere

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...

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.

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.

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.

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)

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.

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.

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.

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.

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

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.

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.

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...

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.