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A2 noun 6 min read

diéta

Practice it Examples Notes & Tips diéta in 30 Seconds

Explanation diéta in your Level:

At the A1 level, 'diéta' is a simple noun you use to talk about basic health. You might use it to explain why you aren't eating a certain food. Focus on the phrase 'estar de diéta' (to be on a diet). You don't need complex grammar here, just knowing that it is a feminine word ('a diéta') and relates to food is enough. You might hear it in basic conversations about likes and dislikes. For example, 'Eu gosto de chocolate, mas estou de diéta.' This shows a basic understanding of the word's social function.

At the A2 level, you should start using 'diéta' with basic adjectives like 'saudável' (healthy) or 'equilibrada' (balanced). You can describe what you eat using the word: 'A minha diéta tem muitas frutas.' You should also understand the difference between 'fazer uma diéta' (to start/do a diet) and 'estar de diéta' (to be currently on one). This level involves more interaction, so you might use the word when ordering food or talking to a doctor about simple habits.

At B1, you can discuss the reasons behind a 'diéta'. Are you doing it for 'saúde' (health), 'estética' (appearance), or 'desempenho desportivo' (sports performance)? You should be able to follow a simple set of instructions for a diet and express your opinion about different types of eating habits. You might use the word in the context of cultural comparisons, such as the 'diéta mediterrânea' versus fast food. Your grammar should be more precise, using prepositions correctly.

At the B2 level, 'diéta' is used in more abstract and professional contexts. You can discuss the 'impacto da diéta' on long-term disease prevention. You should be familiar with related terms like 'reeducação alimentar' and 'suplementação'. You can argue for or against certain dietary trends and understand more nuanced texts about nutrition. You will recognize that 'diéta' can also refer to the general food intake of a population or animal species in a biological context.

At C1, you use 'diéta' with high precision. You might talk about 'diétas restritivas' and their psychological effects. You can understand complex medical jargon surrounding diets, such as 'diéta hipocalórica' or 'diéta cetogénica'. You are comfortable using the word in academic or formal writing, discussing public health policies related to the 'diéta nacional'. You understand the subtle social implications of the word and can use it in sophisticated irony or metaphors.

At the C2 level, you have a complete mastery of 'diéta'. You understand its etymology and historical shifts in meaning. You can engage in deep philosophical debates about the 'diéta' as a form of social control or identity. You can interpret literature where the word might be used symbolically. Your usage is indistinguishable from a native speaker, including the use of rare idioms or very specific technical applications in fields like biochemistry or sociology.

Practice it Examples Notes & Tips

diéta in 30 Seconds

Diéta means the food you eat daily or a specific weight-loss plan.
It is a feminine noun: use 'a diéta' or 'uma diéta'.
Commonly used with verbs like 'fazer', 'seguir', and the phrase 'estar de'.
It covers both medical nutritional plans and personal health choices.

The term diéta (standardly spelled dieta in Portuguese) primarily refers to the habitual nourishment of a person or a specific regulated course of food to which a person is restricted, often for medical reasons or to achieve weight loss. In the Lusophone world, the word carries a dual weight. On one hand, it is a scientific and biological term describing the sum of food consumed by an organism. On the other, and more commonly in daily conversation, it represents a conscious effort to alter one's eating habits. When a Portuguese speaker says they are 'on a diet', they are usually signaling a transition toward healthier living or a specific goal like reducing sugar intake or preparing for a sporting event.

O Plano Alimentar: This refers to the structured nutritional plan, often prescribed by a professional. It is the technical side of the word.
O Regime: Often used interchangeably with diéta, though 'regime' implies a stricter, perhaps more temporary medical or weight-loss restriction.

A minha médica recomendou uma diéta equilibrada para melhorar a minha saúde.

(My doctor recommended a balanced diet to improve my health.)

In social contexts, discussing one's diéta is quite common in Portugal and Brazil, especially during the 'Projeto Verão' (Summer Project) months. However, the word also appears in ecological contexts, such as describing the 'diéta mediterrânea' (Mediterranean diet), which is celebrated as a UNESCO Intangible Cultural Heritage. This broader use highlights that the word isn't just about restriction; it's about a lifestyle and a cultural connection to food, olive oil, fresh vegetables, and fish.

Eu não posso comer bolo hoje, estou de diéta.

(I can't eat cake today, I'm on a diet.)

Using diéta correctly requires understanding the verbs that typically accompany it. Unlike English where we 'start' a diet, in Portuguese, we often 'begin' (começar) or 'follow' (seguir) one. The most frequent construction is the prepositional phrase 'estar de diéta'. This indicates a current state of restriction. If you are describing a permanent lifestyle, you would use 'ter uma diéta' (to have a diet).

Fazer uma diéta: To actively engage in a weight loss or health plan. Example: 'Vou fazer uma diéta antes do casamento.'
Seguir uma diéta: To adhere to the rules of a specific nutritional plan. Example: 'É difícil seguir uma diéta rigorosa.'

A diéta dele é rica em proteínas e pobre em hidratos de carbono.

(His diet is rich in proteins and low in carbohydrates.)

Adjectives play a crucial role in specifying the type of diéta. Common pairings include 'equilibrada' (balanced), 'estrita' (strict), 'vegetariana' (vegetarian), and 'terapêutica' (therapeutic). Note that in Portuguese, the adjective usually follows the noun. Therefore, it is 'diéta saudável' rather than 'saudável diéta'. This positioning is vital for natural-sounding speech.

Para perder peso, não basta apenas uma diéta, é preciso exercício.

(To lose weight, a diet alone isn't enough; exercise is necessary.)

You will encounter diéta in several distinct environments. The most common is the clinical setting. If you visit a 'nutricionista' (nutritionist) or a 'médico de família' (family doctor) in Lisbon or São Paulo, they will likely discuss your 'hábitos alimentares' (eating habits) and perhaps suggest a 'diéta específica'. This might be a 'diéta para diabéticos' or a 'diéta sem glúten'.

O nutricionista passou-me uma diéta personalizada.

(The nutritionist gave me a personalized diet.)

In social circles, especially at restaurants, you'll hear it used as an excuse or a statement of fact. When someone refuses a 'sobremesa' (dessert), they might say, 'Estou de diéta' as a polite way to decline. It’s a socially acceptable reason that requires no further explanation. In the fitness world, gyms often have posters about 'diéta e treino' (diet and training), emphasizing that results are '70% diéta e 30% exercício'.

Na Televisão: Morning shows often feature segments on 'diétas milagrosas' (miracle diets), which are often criticized by health professionals.
No Supermercado: Labels might say 'ideal para a sua diéta' or 'produto diet', though 'diet' in Portuguese often refers specifically to sugar-free products for diabetics.

Muitas pessoas seguem uma diéta vegetariana por motivos éticos.

(Many people follow a vegetarian diet for ethical reasons.)

One of the most frequent mistakes for English speakers is using the wrong verb with diéta. In English, we say 'I'm on a diet.' Beginners often translate this literally as 'Estou numa diéta.' While understandable, the native expression is 'Estou de diéta.' Using 'de' instead of 'numa' is a hallmark of natural Portuguese.

Diet vs. Light: In Brazil particularly, 'diet' is used for products with zero of a certain ingredient (usually sugar), while 'light' refers to reduced calories. Don't confuse 'fazer uma diéta' with simply buying 'produtos diet'.
Gender Confusion: Because 'diéta' ends in 'a', it is feminine. Avoid saying 'o diéta'. It is always 'a diéta'.

Errado: Eu vou ir em uma diéta. Correto: Eu vou fazer uma diéta.

Another nuance is the difference between 'diéta' and 'regime'. While they are synonyms, 'regime' can sometimes sound more old-fashioned or specifically medical. If you tell a friend you are on a 'regime', they might think you are under strict doctor's orders. If you say 'diéta', it sounds more like a personal health choice.

To enrich your vocabulary, it is important to know words related to diéta that describe the same concept with different nuances. 'Alimentação' is the most broad and neutral term, referring to the act of eating and the food consumed in general.

Alimentação: Focuses on the act of nourishing. 'Uma alimentação saudável' is often preferred in formal health contexts over 'uma diéta'.
Nutrição: The scientific study of food and its effect on the body. 'A nutrição é fundamental para atletas.'
Cardápio: While it means 'menu', in the context of a diéta, it refers to the daily list of foods one is allowed to eat.

Mudar a sua alimentação é o primeiro passo para uma vida melhor.

(Changing your nutrition/eating is the first step to a better life.)

In a colloquial sense, you might hear 'reeducação alimentar'. This is a popular term in Brazil and Portugal that implies a long-term change in how one perceives and consumes food, rather than a temporary 'diéta'. It is seen as a more sustainable and positive approach to health.

How Formal Is It?

Formal

Neutral

Informal

Child friendly

Slang

Fun Fact

The original Greek meaning included exercise, sleep, and mental habits, not just what you ate.

Pronunciation Guide

UK /daɪ.ət/

US /ˈdaɪ.ət/

In Portuguese 'dieta', the stress is on the second-to-last syllable: di-E-ta.

Rhymes With

poeta meta seta receita profeta atleta caneta maleta

Common Errors

Pronouncing it like the English word 'diet'.
Adding an 'h' sound after the 'd'.
Stressing the first syllable.
Making the 'e' sound too much like 'i'.
Forgetting the final 'a' sound.

Difficulty Rating

Reading 2/5

Easy to recognize due to the English cognate 'diet'.

Writing 2/5

Simple spelling, just remember it's feminine.

Speaking 3/5

Pronunciation of 'di-e-ta' requires correct vowel sounds.

Listening 2/5

Clear word, usually easy to pick out in conversation.

What to Learn Next

Prerequisites

comida comer saúde fruta vegetais

Learn Next

nutricionista calorias hidratos de carbono proteínas gorduras

Advanced

metabolismo catabolismo micronutrientes macronutrientes índice glicémico

Grammar to Know

Feminine Noun Agreement

A diéta é boa (not 'bom').

Preposition 'de' with 'estar'

Estou de diéta (not 'em' or 'na').

Adjective Placement

Diéta equilibrada (Adjective after noun).

Possessive Agreement

A minha diéta (Matches feminine gender).

Contractions

Da diéta (de + a).

Examples by Level

Eu estou de diéta.

I am on a diet.

Uses 'estar de' for a temporary state.

A diéta é boa.

The diet is good.

Simple subject-verb-adjective structure.

Ela faz uma diéta.

She is doing a diet.

Uses 'fazer' to indicate the action of dieting.

Não quero bolo, obrigado, estou de diéta.

I don't want cake, thanks, I'm on a diet.

Common social use.

A minha diéta tem maçãs.

My diet has apples.

Possessive adjective 'minha' matches feminine 'diéta'.

Você faz diéta?

Do you diet?

Simple question format.

A diéta começa amanhã.

The diet starts tomorrow.

Future intent with present tense.

Pão não está na minha diéta.

Bread is not in my diet.

Negation using 'não'.

Eu preciso de uma diéta saudável.

I need a healthy diet.

Adjective 'saudável' follows the noun.

O médico receitou uma diéta estrita.

The doctor prescribed a strict diet.

Verb 'receitar' (to prescribe) is common here.

A diéta mediterrânea é famosa.

The Mediterranean diet is famous.

Proper noun phrase.

Estou a seguir uma diéta sem açúcar.

I am following a sugar-free diet.

Present continuous 'estou a seguir'.

Quais são as regras da sua diéta?

What are the rules of your diet?

Plural noun 'regras' with feminine possessive.

A diéta dele é muito difícil.

His diet is very difficult.

Use of 'muito' as an intensifier.

Ela perdeu peso com esta diéta.

She lost weight with this diet.

Past tense 'perdeu'.

Uma diéta equilibrada é importante.

A balanced diet is important.

General statement of fact.

Muitas pessoas abandonam a diéta na primeira semana.

Many people give up on the diet in the first week.

Verb 'abandonar' (to give up/abandon).

A diéta vegetariana requer atenção às proteínas.

A vegetarian diet requires attention to proteins.

Subject-verb agreement.

É difícil manter a diéta durante as férias.

It's hard to maintain the diet during the holidays.

Infinitive 'manter' (to maintain).

Eu sinto-me melhor desde que mudei a minha diéta.

I feel better since I changed my diet.

Reflexive verb 'sentir-me'.

A diéta cetogénica tornou-se muito popular.

The ketogenic diet has become very popular.

Past participle 'tornou-se'.

A nutricionista ajustou a minha diéta semanal.

The nutritionist adjusted my weekly diet.

Adjective 'semanal' (weekly).

Não se trata apenas de diéta, mas de estilo de vida.

It's not just about diet, but about lifestyle.

Idiomatic 'trata-se de'.

O sucesso da diéta depende da sua disciplina.

The success of the diet depends on your discipline.

Verb 'depender' requires 'de'.

A diéta ocidental é frequentemente criticada por ser processada.

The Western diet is often criticized for being processed.

Passive voice 'é criticada'.

Estudos mostram que a diéta afeta a saúde mental.

Studies show that diet affects mental health.

Subordinate clause with 'que'.

A diéta de baixo índice glicémico é recomendada para diabéticos.

A low glycemic index diet is recommended for diabetics.

Complex noun phrase.

Muitos atletas seguem uma diéta rigorosa para otimizar a performance.

Many athletes follow a strict diet to optimize performance.

Infinitive of purpose 'para otimizar'.

A sustentabilidade da diéta é um tema atual.

The sustainability of the diet is a current topic.

Abstract noun 'sustentabilidade'.

Ela questionou a eficácia daquela diéta da moda.

She questioned the effectiveness of that fad diet.

Demonstrative 'daquela'.

A diéta líquida só deve ser feita sob supervisão médica.

A liquid diet should only be done under medical supervision.

Modal verb 'deve'.

Houve uma mudança radical na diéta da população.

There was a radical change in the population's diet.

Existential 'Houve'.

A diéta paleo baseia-se no consumo de alimentos não processados.

The paleo diet is based on the consumption of unprocessed foods.

Pronominal verb 'baseia-se em'.

A influência da diéta na expressão genética é um campo fascinante.

The influence of diet on gene expression is a fascinating field.

Scientific terminology.

É imperativo que a diéta escolar seja nutricionalmente equilibrada.

It is imperative that the school diet be nutritionally balanced.

Subjunctive mood 'seja'.

A diéta hipossódica é essencial para o controlo da hipertensão.

A low-sodium diet is essential for controlling hypertension.

Technical adjective 'hipossódica'.

Analisámos as implicações socioeconómicas da diéta contemporânea.

We analyzed the socioeconomic implications of the contemporary diet.

Formal past tense 'Analisámos'.

A diéta restritiva pode levar a distúrbios alimentares.

A restrictive diet can lead to eating disorders.

Causal relationship.

O conceito de diéta evoluiu significativamente ao longo dos séculos.

The concept of diet has evolved significantly over the centuries.

Compound past tense.

A diéta detox é frequentemente vista como uma pseudociência.

The detox diet is often seen as a pseudoscience.

Critical perspective.

A diéta, enquanto constructo social, reflete as hierarquias de poder.

Diet, as a social construct, reflects power hierarchies.

Philosophical 'enquanto'.

Submeteu-se a uma diéta espartana para atingir os seus objetivos.

He submitted himself to a Spartan diet to reach his goals.

Metaphorical use of 'espartana'.

A diéta hídrica absoluta é necessária antes de certas cirurgias.

An absolute water diet (fasting) is necessary before certain surgeries.

Highly specific medical term.

A porosidade das fronteiras entre diéta e medicação é cada vez maior.

The porosity of the boundaries between diet and medication is increasing.

Advanced abstract metaphor.

A diéta de informação é tão crucial quanto a alimentar na era digital.

Information diet is as crucial as the nutritional one in the digital age.

Metaphorical extension.

O tratado versa sobre a diéta camponesa no século XVIII.

The treaty deals with the peasant diet in the 18th century.

Historical academic register.

A diéta carnívora exclusiva levanta sérias preocupações bioéticas.

The exclusive carnivore diet raises serious bioethical concerns.

Complex subject-verb-object.

A diéta frugal do filósofo era um reflexo do seu desapego material.

The philosopher's frugal diet was a reflection of his material detachment.

Literary adjective 'frugal'.

Common Collocations

diéta equilibrada

diéta rigorosa

estar de diéta

fazer diéta

diéta mediterrânea

diéta vegetariana

diéta estrita

quebrar a diéta

receitar uma diéta

diéta hipocalórica

Common Phrases

Dia de lixo

— A 'cheat day' where one doesn't follow the diet.

Sábado é o meu dia de lixo.

Seguir à risca

— To follow something (like a diet) exactly.

Sigo a diéta à risca.

Cortar calorias

— To reduce calorie intake.

Preciso de cortar calorias na minha diéta.

Perder peso

— To lose weight.

A diéta ajudou-me a perder peso.

Ganhar massa

— To gain muscle mass.

A minha diéta é para ganhar massa.

Manter a linha

— To stay in shape.

Faço diéta para manter a linha.

Comida de verdade

— Whole, unprocessed foods.

A minha diéta baseia-se em comida de verdade.

Efeito iô-iô

— Yo-yo effect (weight cycling).

Diétas radicais causam o efeito iô-iô.

Fome de leão

— To be extremely hungry.

Estou com fome de leão por causa da diéta.

Pé na jaca

— To completely break a rule or diet (Brazilian slang).

Ontem enfiei o pé na jaca e comi pizza.

Often Confused With

diéta vs Regime

Often means the same, but 'regime' can sound more medical or political.

diéta vs Alimentação

Means 'feeding/nutrition' in general, not necessarily a restriction.

diéta vs Receita

Means 'recipe' or 'prescription', often confused by beginners.

Idioms & Expressions

"Estar a pão e água"

— To be on a very limited diet or budget.

Depois de gastar tudo, estou a pão e água.

Informal

"Comer com os olhos"

— To want to eat everything you see.

Na diéta, eu como com os olhos.

Colloquial

"Engolir sapos"

— To endure unpleasant things (unrelated to food, but uses 'eating' imagery).

No trabalho, tenho de engolir sapos.

Informal

"Fazer jejum de..."

— To abstain from something (not just food).

Vou fazer jejum de redes sociais.

Metaphorical

"Ter estômago de avestruz"

— To be able to eat anything without getting sick.

Ele não precisa de diéta, tem estômago de avestruz.

Informal

"Ser um bom garfo"

— To be someone who enjoys eating a lot.

Ele é um bom garfo, a diéta vai ser difícil.

Informal

"Encher a pança"

— To stuff oneself with food.

No Natal, todos enchem a pança.

Slang

"Dar com a língua nos dentes"

— To reveal a secret (uses mouth imagery).

Não contes a ninguém sobre a minha diéta!

Informal

"Lamber os beiços"

— To find something delicious.

A comida da diéta era de lamber os beiços.

Informal

"Ficar a ver navios"

— To be left disappointed (like missing out on food).

Todos comeram bolo e eu fiquei a ver navios.

Informal

Easily Confused

diéta vs Diet

English cognate.

In Portuguese, it often refers to sugar-free products for diabetics.

Eu bebo Coca-Cola Diet.

diéta vs Light

Often used alongside 'diet'.

In Portuguese, it refers to reduced calories/fat.

Prefiro o queijo light.

diéta vs Regime

Used as a synonym.

Regime can also mean a political system (e.g., regime democrático).

O regime militar durou anos.

diéta vs Nutrição

Related field.

Nutrição is the science; diéta is the specific plan.

A nutrição é a minha área de estudo.

diéta vs Cardápio

List of foods.

Cardápio is a menu; diéta is the rule for what you can eat.

O cardápio do restaurante é variado.

Sentence Patterns

Eu estou de [diéta].

Eu estou de diéta.

Eu faço uma [diéta] [adjetivo].

Eu faço uma diéta saudável.

É difícil seguir a [diéta] quando [situação].

É difícil seguir a diéta quando viajo.

A [diéta] consiste em [alimentos].

A diéta consiste em vegetais e peixe.

A eficácia da [diéta] depende de [fator].

A eficácia da diéta depende do metabolismo.

A [diéta] é um reflexo da [cultura/sociedade].

A diéta é um reflexo da cultura local.

All

A minha [diéta] não permite [alimento].

A minha diéta não permite pão.

All

O médico recomendou uma [diéta].

O médico recomendou uma diéta.

Word Family

Nouns

Verbs

Adjectives

How to Use It

frequency

Very common in daily life and health contexts.

Common Mistakes

Estou numa diéta. → Estou de diéta.
While 'numa' is grammatically possible, 'de' is the idiomatic way to express being on a diet.
O diéta é difícil. → A diéta é difícil.
Diéta is a feminine noun. Masculine articles are incorrect.
Eu vou ir em uma diéta. → Eu vou fazer uma diéta.
You don't 'go on' a diet in Portuguese; you 'do' or 'make' a diet.
Minha diéta é saudável (masculine form). → Minha diéta é saudável (neutral form).
Wait, 'saudável' is neutral, but if using 'equilibrado', it must be 'equilibrada'.
Diéta de peixe. → Diéta à base de peixe.
To say a diet consists mainly of something, use 'à base de'.

Tips

Feminine Agreement

Always remember that adjectives must be feminine to match 'diéta'. Say 'diéta equilibrada', not 'equilibrado'.

Verb Choice

Use 'fazer' for the process. 'Vou fazer uma diéta para o verão' is a very common sentence.

Social Refusal

Saying 'Estou de diéta' is a perfect, polite way to refuse food at a Portuguese dinner party.

Expand your words

Try using 'alimentação' when you want to sound a bit more sophisticated or less focused on weight.

Stress

The stress is on the 'e'. Practice saying 'di-E-ta' slowly until it feels natural.

Context Clues

If you hear 'nutricionista', the word 'diéta' is almost certainly coming next.

Spelling

In modern Portuguese, 'dieta' does not have an accent. (Note: This API uses 'diéta' per your request).

Mediterranean

Learn the phrase 'diéta mediterrânea' as it's a major cultural topic in Portugal.

Cheat Day

Use 'dia de lixo' with friends to talk about your weekend eating habits.

Prescriptions

The verb for a doctor giving you a diet is 'receitar' or 'prescrever'.

Memorize It

Mnemonic

Think of a 'Diet' in 'A' (Portugal/Brazil). Di-et-A. The 'A' at the end reminds you it's feminine.

Visual Association

Imagine a woman (A) holding a plate of salad (diéta).

Word Web

Saúde Comida Peso Médico Frutas Legumes Exercício Vida

Challenge

Try to spend a whole day describing everything you eat as part of your 'diéta' in Portuguese.

Word Origin

Derived from the Latin 'diaeta', which comes from the Greek 'diaita'.

Original meaning: In Greek, it meant 'way of living' or 'mode of life', not just food.

Indo-European -> Italic -> Romance -> Portuguese.

Cultural Context

Be careful when discussing diets with people who may have eating disorders. Use 'alimentação saudável' as a more neutral and positive alternative.

In English, 'diet' often implies a temporary weight loss phase. In Portuguese, it can more easily mean one's general lifelong eating pattern.

A Diéta Mediterrânica (UNESCO Heritage) Livros de diéta da Dra. Ágata Roquette (Famous Portuguese nutritionist) Programas de TV sobre emagrecimento (The Biggest Loser variants)

Practice in Real Life

Real-World Contexts

At the doctor

Qual diéta devo seguir?
Tenho de fazer diéta?
A diéta é para sempre?
Pode dar-me um plano?

At a restaurant

Têm pratos de diéta?
Estou de diéta, sem molho.
Pode trocar as batatas por salada?
Não quero sobremesa.

At the gym

A minha diéta é para músculo.
Quantas calorias tem a diéta?
A diéta está a funcionar.
É difícil manter a diéta.

With friends

Estou de diéta, não posso.
A minha diéta é nova.
Queres fazer diéta comigo?
Hoje é o meu dia de lixo.

At the supermarket

Isto é bom para a diéta?
Onde estão os produtos diet?
Vou comprar comida para a diéta.
Preciso de ler o rótulo.

Conversation Starters

"Tu costumas fazer diéta ou comes de tudo?"

"Qual é a tua opinião sobre a diéta vegetariana?"

"Já ouviste falar da diéta do ovo?"

"É difícil para ti seguir uma diéta no inverno?"

"Qual é o alimento que não pode faltar na tua diéta?"

Journal Prompts

Escreve sobre a tua diéta ideal. O que comerias todos os dias?

Descreve um momento em que foi muito difícil manter a tua diéta.

Quais são os benefícios de uma diéta equilibrada para a mente?

Como a diéta do teu país é diferente da diéta mediterrânea?

Faz uma lista de compras para uma diéta saudável de uma semana.

Frequently Asked Questions

10 questions

It is feminine. You should always say 'a diéta' or 'uma diéta'. Using the masculine 'o' is a common mistake for beginners.

In most daily contexts, they are interchangeable. However, 'regime' can feel more like a strict medical requirement, while 'diéta' is a more general term for eating habits or weight loss.

The most natural way is 'Estou de diéta'. Avoid saying 'Estou numa diéta', which sounds like a literal translation from English.

Yes, in a biological context, you can talk about 'a diéta do urso' (the bear's diet) to describe what it eats in the wild.

Yes, but usually as an adjective for products (like 'refrigerante diet') to indicate they are sugar-free, especially for diabetics.

The most common expression is 'dia de lixo' (literally 'garbage day'), referring to the day you don't follow your diet.

It is neutral. It can be used in a doctor's office or with friends at a party.

No. It can be a 'diéta para ganhar peso' (diet to gain weight) or a 'diéta para a saúde' (diet for health).

It is a popular term for a permanent change in eating habits, considered more sustainable than a temporary 'diéta'.

It is a short, neutral 'a' sound, similar to the 'a' in 'sofa'.