Weight loss

Losing weight when you are not trying to is a common symptom in people with cancer.

Weight loss and cancer

Weight loss is common in people with cancer. It might be one of the reasons why you first go to the doctor.

There are several causes of weight loss and your doctor can treat many of these.

Losing weight is often associated with a loss of appetite. But this is not the only cause. For people with cancer, other causes are:

  • pain
  • a swollen tummy (abdomen)
  • feeling and being sick (nausea and vomiting)
  • difficulty swallowing
  • feeling full because of a swollen (enlarged) liver
  • a blocked bowel
  • high levels of calcium in the blood
  • not being able to absorb nutrients from food (malabsorption)


Some people may lose weight despite eating normally. This is called cachexia. With cachexia, your body may not be absorbing all the fat, protein and carbohydrate from the food you eat. And you may be burning up calories faster than normal.

People with cachexia lose muscle and often fat too. Scientists think that cancer releases chemicals into the blood. The chemicals contribute to the loss of fat and muscle.

Continuous weight loss can be worrying and a constant reminder of your illness. It can affect your quality of life and how you feel about yourself.

Weight loss can depend on cancer type

Weight loss can depend on the type of cancer you have.

About 60 out of 100 people with lung cancer (60%) have a loss of appetite and significant weight loss at the time of their diagnosis. In people with upper gastrointestinal cancer, this number is 80 out of 100 people (80%). Upper gastrointestinal cancers include:

  • food pipe (oesophagus) cancer
  • stomach cancer
  • small bowel cancer
  • pancreatic cancer
  • liver cancer (including primary and secondary liver cancers, bile duct and gallbladder cancer)

When to worry about your weight

Your doctor will want to find out the cause if you lose, without dieting, more than 5% of your normal weight over 6 to 12 months.

Losing 5% of your normal weight may not seem like a lot. But if you continue to lose weight at this rate, it could become a severe problem.

Monitor your weight

You can:

  • weigh yourself once a week at the same time, wearing the same clothes
  • keep an eye on how tight or loose your clothes, watch or rings are if you don't have scales

Let your doctor or nurse know if you are worried about changes in your weight.

  • Nutrition and Cancer
    Edited by Clare Shaw
    Wiley-Blackwell, 2011

  • When should unexpected weight loss warrant further investigation to exclude cancer?

    B Nicholson and others

    British Medical Journal (BMJ) 2019; 366: l5271

  • Approach to the patient with unintentional weight loss

    R Gupta and others

    UpToDate website

    Accessed March 2020

  • Assessment of unintentional weight loss

    BMJ Best practice website

    Accessed March 2020

  • Pathogenesis, clinical features, and assessment of cancer cachexia

    A Jatoi and others

    UpToDate website

    Accessed March 2020

  • Nutrition in Cancer Patients

    P Ravasco

    Journal of clinical medicine, 2019, 8(8), 1211.

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in.

Last reviewed: 
13 Mar 2020
Next review due: 
13 Mar 2023

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