Weight loss is often a matter of choice - we choose to change our diet and exercise habits to become healthier. If there is a clear and healthy reason then weight loss is normal. However, it is also common to lose weight if you have a serious disease. An unexplained weight loss of 10 pounds or more should be investigated by a doctor. This leaflet lists some of the more common causes of unintentional weight loss.
Some causes of weight loss
Some people with unintentional weight loss as a first symptom actually have one or more symptoms if they were questioned about them. Weight loss is sometimes the first symptom noticed by the person, relative or friend.
Common causes of unintentional weight loss are listed below. The list is not exhaustive.
In the vast majority of cases of cancer, other symptoms will develop before any weight loss. The first signs of cancer depend on the type and site of the cancer. However, occasionally, weight loss is the first symptom noticed. The weight loss is partly due to the increased activity of cancer cells in the body that require nutrition. (Weight loss in more advanced cancer is due to various combined factors.) Common cancers that cause weight loss include those affecting the pancreas, the oesophagus, the stomach and the lung.
Type 2 diabetes
Type 2 diabetes occurs mainly in people aged over 40, although it can occur at younger ages. The four common symptoms are being thirsty a lot of the time, passing large amounts of urine, tiredness and weight loss. Some people pass off the first three symptoms to do with other things, or 'getting older'. So, weight loss is sometimes the first thing reported to a doctor. The weight loss is partly due to the sugar (glucose) that is passed out with the urine.
Depression has a number of symptoms. However, some people do not recognise that they have depression. They may feel low and not right but cannot say why. They may even think of it as just normal for them. Many people with depression can hide their true feelings from friends and family. Weight loss may develop due to not eating much. It is sometimes friends or family who may actually notice that a person has lost weight and it then turns out to be due to depression.
Anxiety can be associated with weight loss or weight gain. While some people react to stress by comfort eating, others may experience a reduced appetite. Anxiety and depression often occur together, and the depressive features may result in reduced food intake. Smokers may find they respond to stress by smoking more; nicotine can be a potent appetite suppressant. Some people may resort to alcohol to combat anxiety and this may also be associated with weight loss (see below).
Some people who drink a lot of alcohol do not look after themselves very well. Their diet may not be very good and they may lose weight. However, they may be in denial about an alcohol problem. It may be friends or family who actually notice that the person has lost weight. Indeed, this is a way that a hidden alcohol problem in some people comes to light. Family and friends may show concern about weight loss and not be aware that the person has an alcohol problem.
Hyperthyroidism means that you make too much of a hormone called thyroxine. The extra thyroxine causes many of your body's functions to speed up. There are lots of possible symptoms such as:
- Being restless.
- Being nervous or anxious.
- Being more emotional.
- Being irritable.
- Sleeping poorly.
- Having the sensation of a 'thumping heart' (palpitations).
- Shaking (tremor).
- Sweating more.
- Loose and/or frequent stools (diarrhoea).
- Being 'always on the go' or not able to relax.
Another typical symptom is losing weight despite an increased appetite. This may be a first symptom. However, again, some of the other symptoms that may occur, such as being restless, nervous, emotional or irritable, may just be put down to a stressful time of life or to your personality. In the early stages of hyperthyroidism some people actually feel well and full of energy and don't realise they have a problem but lose weight.
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 tuberculosis or 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 just make you feel unwell and lose weight prior to other symptoms developing.
There are various diseases that can affect the way food is absorbed and taken into the body from the gut. These would normally cause symptoms such as diarrhoea. However, weight loss may be the first symptom noticed. Examples include coeliac disease, Crohn's disease and ulcerative colitis.
People in the early stages of dementia may appear to get by reasonably well but, in fact, they are not able to look after themselves very well. They may have a poor diet but appear happy in themselves. Again, it is sometimes friends or family who may first notice that a person is not right and has lost weight and it then turns out to be the early stages of dementia.
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 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 pills may cause a loss of appetite, or a dry mouth. Some cause heartburn 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 a loss of weight.
General blood tests available now
Give yourself a check-up with a general blood profile, now available in Patient Access
When to see a doctor
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).
What assessment and tests may be done?
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 blood tests, may or may not be appropriate. Following a doctor's assessment, the likely cause may be clear and your doctor will advise on what to do next.
What is the treatment?
The treatment depends on the cause. See individual leaflets on the various diseases that can cause weight loss.
Further reading and references
Suspected cancer: recognition and referral; NICE guideline (2015 - last updated August 2023)
Diabetes - type 2; NICE CKS, April 2020 (UK access only)
De Stefani FDC, Pietraroia PS, Fernandes-Silva MM, et al; Observational Evidence for Unintentional Weight Loss in All-Cause Mortality and Major Cardiovascular Events: A Systematic Review and Meta-Analysis. Sci Rep. 2018 Oct 188(1):15447. doi: 10.1038/s41598-018-33563-z.
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 914(4):e0211952. doi: 10.1371/journal.pone.0211952. eCollection 2019.