General
Unintentional weight loss
Losing weight without trying should always be assessed by a doctor, as it can be caused by a range of conditions including thyroid, digestive, mental health and, occasionally, serious illnesses.
Education and reference only. This explains the common causes of unintentional weight loss and the warning signs that need urgent help, in plain language — it is not a diagnosis or a substitute for advice from a clinician. If you feel very unwell or are worried, seek medical help.
Quick answer
What is unintentional weight loss?
Unintentional weight loss means losing a noticeable amount of weight without dieting or increasing your exercise. As a rough guide, losing more than about five per cent of your body weight over six to twelve months without trying is worth taking seriously.
- Get urgent help: Weight loss with coughing up blood, severe breathlessness, or chest pain needs urgent assessment. Unexplained weight loss with a new lump anywhere on the body should be checked promptly.
- Self-care: Because unintentional weight loss needs a cause to be found, the main step is to arrange to see a doctor rather than to manage it alone.
About unintentional weight loss
Unintentional weight loss means losing a noticeable amount of weight without dieting or increasing your exercise. As a rough guide, losing more than about five per cent of your body weight over six to twelve months without trying is worth taking seriously. There are many possible causes, ranging from an overactive thyroid or undiagnosed diabetes to digestive conditions, infections, depression and other long-term illnesses. Occasionally, unexplained weight loss can be one of the first signs of cancer, which is why it should always be assessed rather than ignored. Because the causes are so varied, a doctor will usually want to ask about your appetite, mood, bowel habits, and any other symptoms, and may arrange tests. Noticing weight loss early and getting it checked gives the best chance of identifying and treating whatever lies behind it.
When to get help
Call 999 or go to A&E if unintentional weight loss comes with any of these warning signs:
- Weight loss with coughing up blood, severe breathlessness, or chest pain needs urgent assessment.
- Unexplained weight loss with a new lump anywhere on the body should be checked promptly.
- Weight loss alongside blood in the stool or urine, or persistent changes in bowel habit, needs prompt medical assessment.
- Weight loss with drenching night sweats, persistent fever, or feeling very unwell warrants prompt review.
- Any unexplained weight loss should be assessed by a doctor, as it can occasionally be an early sign of cancer or other serious illness.
When to see a doctor
See a doctor if you have lost weight without intending to, particularly if it is more than a few pounds over a few months, or if it is continuing. Seek advice sooner if the weight loss comes with other symptoms such as tiredness, a change in bowel habit, a persistent cough, difficulty swallowing, a lump, or feeling generally unwell. Older adults and people with long-term conditions should have unexplained weight loss assessed promptly. Even if you feel otherwise well, it is worth getting checked, because identifying the cause early often makes treatment more straightforward.
Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.
What can cause it
Common causes of unintentional weight loss
Unintentional weight loss has many possible causes. Each links to a full, plain-language guide to that condition — what it is, how it's treated and when to seek help.
What helps
Self-care and what you can do
Because unintentional weight loss needs a cause to be found, the main step is to arrange to see a doctor rather than to manage it alone. While you wait, it can help to keep a simple record of your weight, your appetite, and any other symptoms such as changes in bowel habit, mood, or energy levels, as this information assists the doctor. If your appetite is poor, eating small, regular and nourishing meals may help maintain your weight in the meantime. Try not to put off seeking advice in the hope that the weight will come back on its own. If your weight loss is linked to stress or low mood, talking to someone you trust and seeking support can be valuable alongside medical assessment.
Answers
Unintentional weight loss: frequently asked questions
How much unintentional weight loss is concerning?
As a general guide, losing more than about five per cent of your body weight over six to twelve months without trying is worth getting checked. Any unexplained, ongoing weight loss should be discussed with a doctor.
Does weight loss always mean something serious?
No. Many causes, such as an overactive thyroid, diabetes, digestive conditions or low mood, are treatable. However, because weight loss can occasionally signal a serious illness, it should always be assessed rather than ignored.
Can stress or low mood cause weight loss?
Yes. Depression and significant stress can reduce appetite and lead to weight loss. If your weight loss is linked to your mood, mention this to your doctor, as support and treatment can help both.
What might the doctor do to find the cause?
A doctor will usually ask detailed questions about your symptoms and may arrange blood tests, examine you, and request scans or other investigations depending on what they find. The aim is to identify and treat whatever is responsible.
Sources
Where this is drawn from
- NICE CKS: Suspected cancer — recognition and referral.
- Macmillan Cancer Support
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