1. What you should do now
Quick help with unintentional weight loss
- Document your weight: weigh yourself once a week at the same time of day and note the trend.
- Record accompanying symptoms: appetite, bowel habits, pain, sleep, night sweats, mood – write everything down.
- Check medications: are you taking GLP-1 receptor agonists (e.g. semaglutide), SGLT2 inhibitors, stimulants or levothyroxine? These can trigger weight loss.
- Get a medical assessment early: do not wait – the earlier the cause is found, the better the treatment.
- With warning signs: bloody stool, coughing up blood, persistent pain, B symptoms (night sweats + fever) – prompt medical help.
Warning symptom: B symptoms!
The combination of weight loss, night sweats and fever is referred to in medicine as "B symptoms" and is typical of lymphomas and some other cancers. With this triad, seek a prompt haematological assessment – do not wait.
2. Understanding weight loss – what happens in the body?
We speak of unintentional weight loss when body weight falls markedly without a conscious diet, a change in exercise or deliberate weight reduction. Clinically relevant is usually a loss of more than five to ten per cent of body weight within six to twelve months.
In contrast to unintentional weight gain, unintentional weight loss is almost always a warning sign: in a considerable proportion of those affected a serious illness lies behind it – from cancer through chronic inflammatory diseases to hormonal disorders. Even if the weight loss is subjectively perceived "as positive" – a loss without a recognisable cause must always be assessed by a doctor.
A simple self-test: the 5-per-cent rule
Calculate how much 5% of your starting weight is. Example: at 80 kg that is 4 kg. If you lose more than these 4 kg over the last six months without changing anything about diet or exercise, a medical assessment is sensible. With more than 10% in 12 months there is definitely a clinically relevant weight loss.
3. Common causes of unintentional weight loss
3.1 Cancers
In a relevant proportion of those affected by unintentional weight loss, a cancer lies behind it – which is why the work-up is so important. Common are gastrointestinal tumours (stomach, bowel, pancreas, oesophagus, liver), lung cancer (often with a cough, shortness of breath, coughing up blood), lymphomas (Hodgkin lymphoma, non-Hodgkin lymphoma – with typical B symptoms), haematological diseases (leukaemias, multiple myeloma), kidney, bladder and prostate cancers as well as gynaecological tumours. Cancer is not the most common cause, but the most important one to rule out.
3.2 Gastrointestinal diseases
Coeliac disease: gluten intolerance with malabsorption – weight loss despite normal eating, diarrhoea, bloating.
Inflammatory bowel disease: Crohn's disease and ulcerative colitis – with bloody diarrhoea, abdominal pain and weight loss.
Pancreatic insufficiency: the pancreas does not produce enough digestive enzymes – fatty stools, weight loss despite hunger. Common with cystic fibrosis or chronic pancreatitis.
Difficulty swallowing: with dysphagia, food intake is made harder. Causes: reflux oesophagitis, tumours of the oesophagus, neurological diseases.
3.3 Hormonal and metabolic causes
Overactive thyroid: an accelerated metabolism – weight loss despite cravings, palpitations, tremor, hot flushes, diarrhoea.
Diabetes mellitus (type 1, decompensated type 2): with insufficient insulin action the body loses energy via the urine (glucosuria). Accompanying symptoms: strong thirst, frequent urination, tiredness.
Adrenal insufficiency (Addison's disease): rare, but important to rule out – with weight loss, weakness, low blood pressure and dark skin pigmentation.
3.4 Psychological causes
Depression: one of the most common psychological causes of weight loss – loss of appetite, lack of drive, no enjoyment of food. Important: depression can equally lead to weight gain – the individual pattern differs.
Eating disorders: anorexia nervosa, bulimia, ARFID. Particularly important to rule out in adolescents and young adults. Treatment should take place early in specialised centres.
Dementia: in the course of a dementia, malnutrition and weight loss often occur – through forgetting meals, swallowing difficulties or a changed sense of taste.
3.5 Chronic diseases
Chronic infections: tuberculosis, HIV, chronic hepatitis, endocarditis.
Chronic kidney disease and liver diseases: in the advanced stage with loss of appetite, nausea, muscle loss.
Heart failure: in the advanced stage cardiac cachexia – weight loss through a catabolic metabolism.
COPD in the advanced stage: increased energy expenditure from laboured breathing leads to weight loss.
4. Weight loss in older people
In older people, unintentional weight loss is to be taken particularly seriously – it is associated with increased mortality, falls, fractures and a poorer quality of life. Common causes are chronic diseases, cancer, dementia, depression, swallowing difficulties, dental problems, malnutrition and loneliness. Sarcopenia (age-related muscle loss) is accelerated by weight loss.
Polypharmacy can additionally impair appetite and the sense of taste. A structured work-up is important – including a nutritional history, the social situation, oral health and cognitive function. Points of contact are the GP practice, geriatric clinics, nutritional counselling and, if needed, outpatient care services.
Preventing sarcopenia
Strength training (effective even at an advanced age) and enough protein in the diet counteract muscle loss. At least 1.0–1.2 g of protein per kg of body weight per day is recommended in older people.
5. What you can do yourself
Document weight and symptoms
Weighing yourself regularly at the same time of day (ideally once a week) is the most important self-measure. Additionally note appetite, bowel habits, pain, sleep quality and your mental state. This documentation helps the practice to reach an assessment faster.
Optimise nutrition
With proven malnutrition, nutritional counselling can help – a high-calorie plan with enough protein can stop the loss. Several small meals a day are often easier to manage than three large ones. Use energy-rich foods (nuts, avocado, olive oil, full-fat dairy products) deliberately.
Early medical assessment
The longer the weight loss goes unnoticed, the harder the treatment of the cause becomes. Even if the symptoms seem non-specific: with a loss of more than 5% in six months, arrange an appointment at the GP practice promptly.
Unintentional weight loss is a warning symptom. More than 5% in 6 months without a diet? Have it assessed by a doctor promptly.
