Unintentional weight loss: causes, red flags and what to expect

Weight fluctuates by a kilogram or two over days, and deliberate changes in diet and exercise are expected to lower it. The concern is weight loss that happens without a clear reason, particularly if it continues, is noticeable to others, makes clothes loose or comes with other symptoms. The NHS defines the symptom as losing weight without changing your diet or exercise routine.

The NHS page gives no fixed figure, and neither can this guide. In practice clinicians pay attention to how much has been lost over what period, how it compares with your usual weight, whether appetite is reduced or normal and whether you are eating as usual. Weighing yourself at the same time and on the same scales, and noting the dates, helps the GP judge it.

The NHS says unintentional weight loss can have many causes and sometimes a combination. It lists the following.

The NHS says sometimes weight loss and loss of appetite can be caused by cancer and that it is important to get it checked if you are losing weight without trying. Weight loss is listed among symptoms of several cancers on NHS pages: for lung cancer, alongside a cough that is not going away, shortness of breath, coughing up blood, chest or shoulder pain, repeated chest infections, not feeling hungry and feeling tired all the time; for bowel cancer, alongside changes in poo, blood in poo, tummy pain, a lump and bloating; and for pancreatic cancer, alongside jaundice, loss of appetite, tiredness and indigestion-type symptoms. Non-Hodgkin lymphoma and testicular cancer lists also include weight loss.

These pages stress that the symptoms are common and can be caused by many conditions, and that having them does not definitely mean cancer, but finding cancer early may make it easier to treat. Most people who lose weight unintentionally and are investigated turn out to have a non-cancer cause.

• Ask for an urgent GP appointment or contact NHS 111 if weight loss comes with black or dark red stool, or bloody diarrhoea, as the NHS bowel cancer page advises.

• Ask for an urgent GP appointment or contact NHS 111 if weight loss comes with yellow skin or eyes, or if you have been sick for more than 2 days or have had diarrhoea for more than 7 days, as the NHS pancreatic cancer page says.

• Ask for an urgent GP appointment or contact NHS 111 if you have coughed up blood or noticed blood on a tissue; the NHS lung cancer page says this.

• Seek early review for a persistent cough lasting more than 3 weeks, shortness of breath, swollen glands or a painless lump, drenching night sweats, new difficulty swallowing, or constant tiredness.

• Seek urgent review for weight loss with extreme thirst, passing large amounts of urine, tiredness and sickness, which can mean diabetes needing prompt treatment.

• Call 999 or go to A&E for black sticky stool or vomiting blood, severe tummy pain, chest pain, or struggling to breathe, per the NHS stomach ulcer and lung cancer pages.

• Seek help for thoughts of self-harm or if you are restricting food because of distress; the NHS page lists eating disorders among causes, and a GP can arrange support.

The GP will ask how much weight has gone and over how long, appetite, food intake, nausea, swallowing, bowel and urine changes, pain, cough, fevers, night sweats, mood, stress, alcohol, smoking, drug use, medicines and supplements, and family history. For older adults, questions cover teeth and dentures, loneliness, ability to shop and cook, and memory.

Examination includes weight and body mass index, pulse, blood pressure, temperature, thyroid, lymph node areas, the tummy, the chest and sometimes a rectal examination. The NHS says the GP will ask about your health and may arrange some tests or scans.

First-line tests are usually blood tests: full blood count, inflammatory markers, kidney, liver and bone profile, thyroid function, glucose or HbA1c and coeliac antibodies, plus a urine test. A faecal immunochemical test for blood in the stool and a chest X-ray are common additions, as the NHS bowel and lung cancer pages describe. If initial results are unrevealing and the weight loss continues, further imaging such as CT, or endoscopy, may be needed, and the NHS says the GP may refer you to a specialist.

Treatment depends on the cause: the NHS says a GP may advise on ways to reduce stress, recommend treatment for any condition causing weight loss, or refer you to a specialist. Where poor intake is the problem, dietitian support, fortification of meals and oral nutritional supplements can help restore weight while the underlying cause is addressed.