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Unintentional weight loss means losing weight without changing your diet or exercise routine. It has many causes, most of them not cancer. But in people aged 55 and over, weight loss recorded by a GP is on its own enough to cross the risk threshold at which national guidance recommends investigating for cancer. That is why it is worth checking.
The word doing the work is unintentional. If you have been dieting, training harder or eating less because life has been busy, the weight loss has an explanation. It counts as unexplained when nothing about your eating or your activity has changed and the weight keeps coming off anyway.
There is no set number of pounds or kilograms in the NHS's own wording. The trigger is the pattern rather than the amount: you keep losing weight without changing your diet or exercise routine [1]. Most people notice it indirectly - a belt moving in a notch, clothes hanging differently, or someone else commenting before they had thought about it themselves.
NHS describes it plainly: unintentional weight loss over 5% can be a sign of stress or of a serious illness, and it is worth seeing a GP just in case [1].
See a GP if you keep losing weight without changing your diet or exercise routine [1]. That is the whole of the NHS's advice for weight loss on its own - it belongs in the non-urgent tier, so it is a reason to be seen rather than an emergency. NHS adds that it is important to see a GP as soon as possible if you have weight loss and other symptoms, because the earlier the cause is found, the sooner it can be treated [1].
See a GP, or book a specialist assessment, if:
Ask for an urgent GP appointment or get help from NHS 111 if:
Call 999 or go to A&E if:
LivingCare is a specialist outpatient service and is not an emergency care facility. If your symptoms are sudden or severe, call 999.
Most causes are not cancer, and many have nothing to do with digestion at all. NHS lists the common ones as [1]:
A stressful event - a divorce, losing a job, the death of someone close - can cause it on its own, and so can a combination of things [1]. NHS is also direct about the one everybody is thinking about: sometimes weight loss and loss of appetite can be caused by cancer, and it is important to get it checked if you are losing weight without trying [1].
Only one group on that list belongs to gastroenterology. A Gastroenterology assessment is the right route when the digestive causes are the ones in question, and part of its job is telling you when the answer is more likely to sit with your thyroid, your medication or your mood - and where to take it next.
Unexplained weight loss rarely turns up entirely on its own. Our pages on Blood in Stool and Difficulty Swallowing cover those symptoms in their own right.
A visit to your GP or gastroenterology consultation is the starting point - the specialist reviews your symptoms and arranges only the tests they call for. Your symptoms, your medical history and any previous test results are reviewed before a clinical assessment, and what happens next follows from that rather than from a standard menu. Where further investigation is needed it may include an Endoscopy, colonoscopy, blood tests, or imaging such as ultrasound, CT or MRI.
Weight loss is also one of the symptoms national guidance uses to decide who is investigated for cancer, almost always in combination with another symptom and above a stated age. NICE's suspected cancer guidance sets out, among others [3]:
NICE defines that referral by its outcome: a diagnosis or ruling out of cancer within 28 days of being referred urgently by a GP for suspected cancer [3]. The threshold the guideline uses to decide a symptom warrants investigating is a 3% positive predictive value, and a review of 25 UK primary care studies found that unexplained weight loss recorded by a GP in patients aged 60 and over passes it [2][3]. That is a rule about when clinicians investigate, not a statement about any individual's odds - but it is the reason weight loss gets taken seriously rather than watched.
If you would rather not wait to find out which kind you have, you can book a Gastroenterology Consultation directly. Self-pay, with no GP referral needed. If you are using medical insurance, your insurer may ask for a GP referral letter.
Medically reviewed by: Dr N. Chandra, Consultant Endoscopist. Last reviewed: 09/10/26
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