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Perda de peso não intencional

A perda de peso é muitas vezes uma questão de escolha - escolhemos mudar nossa dieta e hábitos de exercício para nos tornarmos mais saudáveis. Se houver uma razão clara e saudável, então a perda de peso é normal. A perda de peso não intencional é diferente. Isso ocorre quando uma pessoa perde peso sem tentar. É importante relatar isso a um médico para que uma causa possa ser identificada. Este folheto lista algumas das causas mais comuns de perda de peso não intencional.

Em resumo

  • Unintentional weight loss is typically a loss of more than 5% of body weight.

  • Many health conditions can cause unintentional weight loss, including cancer, diabetes, and thyroid problems.

  • Mental health conditions like anxiety and depression can also lead to weight loss.

  • Social factors such as financial difficulties or problems accessing food may also cause weight loss.

  • If you are losing weight for no clear reason, you should see a doctor.

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Some causes of unintentional weight loss

Weight loss is sometimes the first symptom noticed by the person, relative or friend. However, when carefully questioned by a medical professional, people may realise they have more symptoms in addition to their unintentional weight loss. Weight loss is usually defined as a loss of more than 5% of the person's body weight.

Common causes of unintentional weight loss are listed below. The list is not exhaustive.

Câncer

In the vast majority of cases of cancer, other symptoms will develop before any weight loss occurs. The first signs of cancer depend on the type and site of the cancer. However, occasionally, weight loss is the first symptom that is noticed. Common cancers that cause weight loss include those affecting the pancreas, the oesophagus, the stomach, the bowel e the lung. The blood cancer lymphoma, of which there are several types, can cause unintentional weight loss among other symptoms.

Diabetes

Ambos Tipo 1 e Diabetes tipo 2 can cause unintentional weight loss. As with all causes of unintentional weight loss, it is important to report this to your doctor, as early diagnosis is important.

Anxiety and depression

Ansiedade e depressão have many symptoms and unintentional weight loss can occur for multiple different reasons. People suffering with these symptoms may experience weight loss or weight gain, for example, some people may respond by comfort eating, whilst others may experience a reduced appetite. Fumantes may find they respond by smoking more; nicotine can reduce your appetite, causing weight loss. Some people may resort to alcohol to combat anxiety and this may also be associated with weight loss. Loneliness is a common experience for older adults and can affect a person's mood. Weight loss affecting someone whose mental health is suffering may be the most obvious symptom to family and friends.

Dependência de álcool

Some people who drink a lot of alcohol may struggle to look after themselves well, which can cause them to lose weight. Family and friends may show concern about weight loss and not be aware that the person has an alcohol problem.

Hipertireoidismo

Hipertireoidismo occurs when the thyroid gland produces too much of a hormone called thyroxine. This condition is also known as an overactive thyroid. The extra thyroxine causes many of your body's functions to speed up. This often causes many symptoms affecting different parts of the body. In the early stages of hyperthyroidism some people actually feel well and full of energy and don't realise they have a problem despite their weight loss.

Persistent (chronic) infection or inflammation

It would be unusual not to have other symptoms with a chronic infection. But, occasionally, the first symptom that is noticed with infections such as tuberculose ou teste de HIV is weight loss. Hookworm infection of the gut is another example where weight loss may be the first indication of disease. Hookworm is a very common problem worldwide (but rare in the UK). Likewise, there are various conditions that cause persistent inflammation of a part or parts of the body. Again, other symptoms would be usual. However, sometimes an inflammatory condition such as polymyalgia rheumatica may make you feel vaguely unwell and lose weight prior to other symptoms developing.

Síndromes de má absorção

There are various diseases that can affect the way food is absorbed and taken into the body from the gut. These would normally cause gut symptoms such as diarrhoea and abdominal pain. However, weight loss may be the first symptom noticed. Examples include doença celíaca, Doença de Crohn e colite ulcerativa.

Demência

People with demência may struggle to look after themselves well and lose weight as a result. There can be many reasons for this. In older adults, weight loss may sometimes be the first symptom friends or family notice.

Transtornos alimentares

In conditions such as anorexia, a person usually knows they are tightly controlling their diet and exercise and are actively trying to lose weight. However, this may be very carefully hidden from friends and family and may not be divulged even to the doctor.

Side-effects from medication

Sometimes medication may cause side-effects resulting in weight loss. For example, some medicines may cause a loss of appetite, or a boca seca. Some cause azia or give a mild tummy discomfort. Others may affect the sense of taste or smell, or make people feel sick. Any of these side-effects could affect eating habits and result in weight loss.

Other common causes

There are many reasons a person can lose weight unintentionally, and they are not all because of specific health conditions. Common issues such as lack of money, lack of access to food, difficulty buying and cooking food or difficulty eating can all cause unintentional weight loss. At each of these stages there are many, wide ranging causes which can result in unintentional weight loss. For example difficulty eating can be due to having a problem in your mouth or any condition affecting your ability to accurately place food in your mouth.

If you keep losing weight for no reason, see a doctor. This is because, as a general rule, the earlier a serious problem is diagnosed, the better the chance that treatment may improve the outlook (prognosis).

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Your doctor is likely to ask various questions. He or she may actually uncover other symptoms that you were either unaware of or did not think were significant. He or she may also examine you. Tests, such as exames de sangue, may or may not be appropriate. Following a doctor's assessment, the likely cause may be clear or you may require more investigations. Your doctor will advise on what is needed depending on what they think is causing the weight loss.

The treatment depends on the cause. See individual leaflets on the various diseases that can cause weight loss. The conditions above are not an exhaustive list.

Perguntas frequentes

What is considered a significant amount of unintentional weight loss?

Unintentional weight loss is typically defined as losing more than 5% of your body weight without actively trying to do so. This can be a noticeable amount and might be the first symptom that you or others observe.

Can certain medications cause unintentional weight loss?

Yes, some medications can lead to weight loss as a side-effect. This can happen if the medicine causes a loss of appetite, a dry mouth, heartburn, mild stomach discomfort, or affects your sense of taste or smell. Any of these effects can change your eating habits and result in weight loss.

Are there non-medical reasons why someone might lose weight unintentionally?

Yes, there are many reasons for unintentional weight loss that aren't directly related to a health condition. These can include practical issues such as not having enough money for food, difficulty accessing food, problems with buying or cooking meals, or even difficulties with the act of eating itself, such as mouth problems or issues with placing food in your mouth accurately.

Can weight loss be an early sign of dementia?

In older adults, weight loss can sometimes be an early sign of dementia. People with dementia might find it hard to look after themselves properly, and this can lead to them losing weight. This is often one of the first symptoms that family or friends might notice.

Can an overactive thyroid cause weight loss even if I feel well?

Yes, hyperthyroidism, or an overactive thyroid, can cause weight loss. In the early stages, some people might actually feel energetic and well, and may not realise they have a problem despite losing weight. This is because the extra thyroxine hormone speeds up many of the body's functions.

If I suspect my weight loss is due to mental health issues like anxiety or depression, how can that cause it?

Anxiety and depression can lead to weight loss in several ways. Some people might experience a reduced appetite due to their mental state. Others might respond by smoking more, as nicotine can suppress appetite. Loneliness, especially common in older adults, can also affect mood and contribute to weight loss. Someone's mental health suffering might present with weight loss as the most obvious symptom to those around them.

Leitura adicional e referências

  • Câncer suspeito: reconhecimento e encaminhamento; Diretriz NICE (2015 - última atualização em abril de 2026)
  • Cao Y, Hardy R, Wulaningsih W; Associations of medical conditions, lifestyle and unintentional weight loss in early old age: The 1946 British Birth Cohort. PLoS One. 2019 Apr 9;14(4):e0211952. doi: 10.1371/journal.pone.0211952. eCollection 2019.
  • CKS Malnutrition. February 2024 (UK Access only)

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Dr Caroline Wiggins, MRCGP

Médico Generalista, Autor Médico

MBBS Honras (com Distinção), MRCGP (2016), MSc.SEM (com Distinção), BSc (Hons)

A Dra. Caroline Wiggins é uma médica substituta atualmente no sudoeste da Inglaterra. 

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Dra. Toni Hazell, MRCGP

MBBS, BSc, MRCGP, DFSRH, Dip GU med, DRCOG, DCH (London, UK, 2000)

A Dra. Toni Hazell se formou na Escola de Medicina do Hospital St. Mary e fez seu VTS no Hospital Northwick Park.

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