Weight loss
Weight loss happens if you use more energy than you take in through food, drink and supplements. People often do this deliberately because they want to lose weight. But if you’re losing weight without trying to, it could be a sign of an underlying condition.
Summary
- Many people deliberately lose weight through changes in diet and activity levels.
- But losing weight without trying to can be a symptom of an underlying condition, including leukaemia or other types of blood cancer.
- If you’ve lost a lot of weight quickly without intending to, contact your GP.
About weight loss
Weight loss happens if you use more energy than you take in through food, drink and supplements.
Being a healthy weight is important and good for you. Many people deliberately lose weight through changes in diet and activity levels. But, sometimes, you may lose weight without trying to. This is called unintentional weight loss. It can be a symptom of leukaemia and other types of blood cancer. Children may lose weight, or may not grow or gain weight as quickly as they should.
Like all symptoms of leukaemia, losing weight without intending to does not mean you definitely have leukaemia. But it is often a sign of an underlying condition. If you’ve lost a lot of weight quickly without trying to, contact your GP.
Weight changes and age
- Children and young people naturally gain weight as they grow to their adult size. Health professionals record this on growth charts to check they’re gaining weight as expected for their age and height. If they’re not, it could be a sign of an underlying condition. You might hear health professionals call this ‘faltering growth’.
- Throughout adult life, weight varies a lot Typically, you tend to gain weight from your 20s to your 50s due to natural changes in your body. Usually, weight then stays fairly stable until your mid 60s, when people often start to lose weight slowly. This is usually less than 0.5 pounds (0.1kg) per year. This level of weight loss is normal in older people. But losing weight faster than this can be a sign of an underlying condition.
Overall, fewer than 4 in 10 people with unintentional weight loss have cancer. More than 6 in 10 do not have cancer. These numbers vary depending on your age. But the important thing to remember is that a lot of people with unintentional weight loss do not have cancer.
Why do people with blood cancer lose weight?
Weight loss happens when:
- The amount of energy your body needs goes up
- The amount of energy you get through food, drinks or supplements goes down
- Or both
Leukaemia, and other types of cancer, can cause both of these things.
Increased energy needs
- Cancer cells use energy to multiply. So your body uses more.
- Cancer can activate an inflammatory response in your body. This helps your immune system fight the cancer, but it also uses energy.
- You might have other symptoms of blood cancer too, like infections or fever. These also increase the energy your body uses.
Reduced energy intake
- Some of the inflammatory proteins cancer cells make can reduce your appetite. So you might eat less and get less energy.
Inflammation can also lead to muscle and fat breakdown, and make it harder for your body to make more. This also contributes to weight loss.
What else can cause unintentional weight loss?
Unintentional weight loss can be caused by lots of things. Many people who have it do not have leukaemia.
Other things that can cause unintentional weight loss include:
- Problems that make it difficult to buy or prepare food, like loneliness, physical health problems, or not having enough time or money
- Tooth, mouth or throat problems that make it hard to eat or swallow
- Gut problems, like ulcers, inflammatory bowel disease or coeliac disease
- Depression
- Eating disorders
- Dementia or Parkinson’s disease
- Overactive thyroid
- Diabetes
- Some long-term infections
- Chronic heart, lung or kidney problems
- Some medicines and recreational drugs
- Alcohol dependence
- Other types of cancer
When to seek help
Make an appointment with your GP if you’ve lost a lot of weight in a short time without intending to.
Nearly 4 in 10 people with leukaemia wait 3 months or more before contacting a GP about their symptoms.
Some signs that you should contact your GP about weight loss:
- You’re losing weight without trying to
- You haven’t changed your diet or activity levels
- You’ve lost more than 5 percent of your body weight in less than 6 months
- You have other symptoms of blood cancer
If you’ve lost weight without trying to and your GP can’t identify a cause, they should offer you urgent tests or an urgent referral. Ask them for a blood test if they don’t offer you one.
If you are struggling to get help
Nearly 3 in 10 people with leukaemia have to speak to their GP three or more times before getting a diagnosis.
There may be many possible explanations for your symptoms for a GP to consider.
If you have to go back to your GP three or more times about the same symptom, remind them about Jess’ rule. This encourages GPs to ‘reflect, review and rethink’, particularly if:
- You still have the symptoms
- They have got worse
- They are unexplained
Take a look at our Spot Leukaemia campaign to find out what we’re doing to help the public and GPs spot the signs of leukaemia sooner.
Sources
We used an AI tool to help identify relevant evidence sources for this webpage, such as scientific journals and clinical guidelines. A human checked the reliability of these sources.
Sources we used to develop this information
Black GB, Boswell L, Harris J, Whitaker KL. What causes delays in diagnosing blood cancers? A rapid review of the evidence. Primary Health Care Research & Development. 2023 Jan;24:e26. DOI: https://doi.org/10.1017/S1463423623000129
Clarke RT, Jones CH, Mitchell CD, Thompson MJ. ‘Shouting from the roof tops’: a qualitative study of how children with leukaemia are diagnosed in primary care. BMJ Open. 2014 Feb;4(2):e004640. DOI: https://doi.org/10.1136/bmjopen-2013-004640
Clarke RT, Van den Bruel A, Bankhead C, Mitchell CD, Phillips B, Thompson MJ. Clinical presentation of childhood leukaemia: a systematic review and meta-analysis. Archives of Disease in Childhood. 2016 Oct 1;101(10):894-901. DOI: https://doi.org/10.1136/archdischild-2016-311251
Hariyanto TI, Kurniawan A. Cachexia in cancer patients: systematic literature review. Asian J Oncol. 2020 Oct 15;6(03):107-5. DOI: https://doi.org/10.1055/s-0040-1713701
Howell DA, Smith AG, Jack A, Patmore R, Macleod U, Mironska E, Roman E. Time-to-diagnosis and symptoms of myeloma, lymphomas and leukaemias: a report from the Haematological Malignancy Research Network. BMC Blood Disorders. 2013 Oct 31;13(1):9. DOI https://doi.org/10.1186/2052-1839-13-9
National Institute for Health and Care Excellence (NICE). Clinical Knowledge Summary: Faltering growth. Revised September 2023. Available at: https://cks.nice.org.uk/topics/faltering-growth/ [Accessed Sept 2026]
National Institute for Health and Care Excellence (NICE). Suspected cancer: recognition and referral. NICE guideline NG12. 23 June 2015; updated 25 April 2026. Available at: https://www.nice.org.uk/guidance/ng12 [Accessed May 2026]
Neshan M, Tsilimigras DI, Han X, Zhu H, Pawlik TM. Molecular mechanisms of cachexia: a review. Cells. 2024 Jan 29;13(3):252. DOI: https://doi.org/10.3390/cells13030252
NHS cancer programme: faster diagnosis framework. November 2022. Available at: https://www.england.nhs.uk/publication/cancer-programme-faster-diagnosis-framework/ [Accessed May 2026]
NHS England. National Cancer Patient Experience Survey 2024. Available at: https://www.ncpes.co.uk/latest-national-results/ [Accessed May 2026]
NHS Scotland. Scottish referral guidelines (SRGs) for suspected cancer: Haematological cancers. Available at: https://www.rightdecisions.scot.nhs.uk/scottish-referral-guidelines-srgs-for-suspected-cancer/haematological-cancers/ [Accessed May 2026]
Perera LA, Chopra A, Shaw AL. Approach to patients with unintentional weight loss. Medical Clinics. 2021 Jan 1;105(1):175-86. DOI: https://doi.org/10.1016/j.mcna.2020.08.019
Smith AE, Shah M, Badireddy M. Failure to thrive. In: StatPearls 2026 Jan. StatPearls Publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK459287/ [Accessed Sept 2026]
Soo MR, Khor JH, Cheah MH, Nashi NB. Approach to weight loss in adults. Singapore Medical Journal. 2024 May 1;65(5):291-4. DOI: https://doi.org/10.4103/singaporemedj.SMJ-2021-223
Yeom E, Yu K. Understanding the molecular basis of anorexia and tissue wasting in cancer cachexia. Experimental & Molecular Medicine. 2022 Apr;54(4):426-32. DOI: https://doi.org/10.1038/s12276-022-00752-w
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Page last reviewed: 10 September 2026
Updated September 2026
Next review due: 30 September 2029
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