Causes of weight loss

There are a great many reasons why losing weight may happen but as a general rule, if you have lost weight and do not know why - especially if you lose as much as 4.5 kilograms or 5% of your weight within six to 12 months, then always see a doctor since a medical assessment and tests will usually be able to find the cause. Because unexplained weight loss can sometimes be a sign of a serious disease, it should never be ignored although other problems such as stress, anxiety, and a poor diet can all be a common cause. Here are some other causes of weight loss not linked to dieting and exercise;


In most cases of cancer, other symptoms occur before weight loss starts but occasionally, weight loss is the first symptom that is noticed. The weight loss is partly due to the increased activity of cancer cells in the body, and sometimes due to a lack of appetite.

Type 2 diabetes

Type 2 diabetes occurs mainly in overweight people aged 40 and over. The four common symptoms are weight loss, being thirsty a lot of the time, passing large amounts of urine, and significant tiredness. Many people pass their tiredness off as a sign of getting older and only see a doctor when they start to lose weight. The weight loss is partly due to glucose (sugar) being passed out with the urine.


Depression can have many symptoms and weight loss may develop due to someone suffering with depression not eating enough. It is sometimes the case that other causes are considered and a range of physical tests are done before the diagnosis of depression is made.

Alcohol abuse

Heavy drinkers often do not look after their general health, and this can include having a poor diet which in turn causes weight loss. They may deny having a problem with alcohol and it is their friends or family who notice they have lost weight, often without being aware the person has an alcohol problem.

Hyperthyroidism (overactive thyroid gland)

In hyperthyroidism, the body makes too much of a hormone called thyroxine, found in  the thyroid gland in the neck. This extra thyroxine causes the body's functions to speed up and so possible symptoms include restlessness, nervousness, being anxious and irritable, sleeping poorly, tremor, sweating, diarrhoea and always being active. However, another very common symptom is losing weight despite often having an increased appetite. In the early stages of hyperthyroidism some people actually feel well and full of energy and don't realise they have a problem, but continue to lose weight.

Persistent infection or inflammation

With conditions that cause chronic (persistent) inflammation in the body, weight loss can be one of the first symptoms that is noticed. Examples of these infections include tuberculosis, hookworm and HIV. Also, chronic inflammatory conditions such as polymyalgia rheumatica can also cause weight loss before any other symptoms develop.

Malabsorption syndromes

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. A common example of this is coeliac disease where there is a significant allergy to gluten in the diet, causing the small bowel to become affected.

If you have lost weight for no obvious reason then see your doctor because if you are unfortunate enough to have a serious problem then the earlier it is diagnosed, the better the long-term outlook. Following your doctor's assessment, the likely cause may be clear and your doctor will advise on what to do next, or tests may be needed to try to track down the reason. If treatment is needed, this will depend on the reason for the weight loss.