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Diet problems caused by cancer

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This page is about how cancer affects the way your body digests food and uses nutrients, and how cancer can affect your appetite. There is information about how cancer and symptoms affect your body and can make it hard to eat


Digestion and cancer

Many of the symptoms described on this page can happen together. One symptom can cause another and can have a kind of knock on effect. For example, if you are in a lot of pain, you are more likely to feel worn out (fatigued) and this could make you feel depressed. 

If you have any of these symptoms it is very important that you discuss them with your doctor. Most of them can be treated which will help prevent problems with your eating and drinking.


Chemical changes caused by the cancer

Cancer can cause chemical changes that make it very difficult for you to gain weight even if you are eating a high calorie diet. These chemicals are probably the cause of cachexia - the severe weight loss that some people have with advanced cancer.

Chemicals that the cancer produces may make your body work at a faster rate than normal, even when you are resting. So you have a higher than normal metabolic rate.

A cancer can produce chemicals that affect the way your normal cells work. Some of these chemicals are called cytokines. These are made normally by your immune system and released into your body when you get an infection. Cytokines help your body fight infection but they are also responsible for how you feel when you get an infection. High cytokine levels make you feel as if you have a cold or flu.

A cancer can make cytokines in larger than normal amounts. These can cause weight loss and muscle wasting by making your body break down fat and protein faster than normal. They may also affect the centre in the brain that controls hunger.

Another chemical cancers can produce is ‘proteolysis-inducing factor’ (PIF). It seems to have something to do with weight loss and muscle wasting in people with cancer. PIF is only found in the blood and urine of people with cancer who are losing weight. You don't find it in people who don't have cancer or in people who do have cancer, but are not losing weight. 

Scientists have also found that a growth factor protein called MIC-1 is produced by some cancer cells and seems to cause weight loss. Scientists may be able to produce targeted medicines in the future that can block the effects of PIF and MIC-1. This will help reduce weight loss in people with cancer and other medical conditions.


Inflammation due to cancer

Some types of cancer make the tissue around them become inflamed. The inflammation makes your body release more cytokines into your bloodstream. So the levels of these chemicals will be even higher. Because of this theory, doctors are investigating using anti-inflammatory drugs to treat cachexia.


Sickness due to cancer

The chemicals the cancer makes can also cause sickness. This also affects your appetite and weight.


Blockage in your digestive system

A cancer may block, or partly block, your digestive system just by growing in size. This can be a relatively early symptom of cancer in the foodpipe (oesophageal cancer). But it is more often a symptom of an advanced cancer, for example in stomach cancer or bowel cancer. 

A tumour in the throat and mouth can make eating or swallowing very difficult and painful.



You don’t usually feel like eating much if you are in pain. If you are in a lot of pain you may not feel like eating at all. People with chronic pain quite often lose weight because they don't feel like eating much. So the key to regaining your appetite is to try to get good pain control, which is usually possible.



Being very breathless is not usually dangerous or harmful but it can make you feel very frightened. Breathlessness can also make daily living very difficult. You use energy to prepare meals and eat. This can make you more breathless. Read about hints to help with eating, drinking and food preparation.



Tiredness that is extreme is called fatigue. It can affect you mentally, physically, emotionally and spiritually. Everyday life becomes hard work and you may find yourself not having enough energy to cook, eat, clean, bath, go shopping or even talk to your friends and family. Many people with cancer suffer from this symptom.



About 25 out of every 100 people with cancer get depressed. One of the symptoms of depression is loss of appetite and sometimes weight loss.



If you have an infection with a fever

  • You may not want to eat 
  • You may burn up calories faster 
  • You may sweat more

This can cause weight loss and dehydration.


Not enough fluid in your body (dehydration)

Severe vomiting, diarrhoea, sweating or loss of appetite can cause dehydration. The symptoms of dehydration can include

  • Feeling very tired
  • Muscle weakness and cramps
  • Headaches
  • Dizziness
  • Feeling sick
  • Dry mouth, skin and eyes
  • Sunken eyes
  • Low urine output
  • In severe cases you will become confused and can go into a coma

Increasing your fluid intake by drinking more, or having fluids through a drip into your bloodstream (intravenously), usually corrects dehydration. If you have advanced cancer, this can be more difficult. Any fluid counts, not just water. So you can drink - tea, squash, juices, soup and milky drinks.


Find out more information 

Find out about

Cause of cachexia 

Cancer and sickness

Diet and advanced cancer

Pain and pain control

Fatigue and cancer


About infection

For general information and support

Contact the Cancer Research UK nurses on freephone 0808 800 4040 (Open 9am - 5pm, Monday to Friday)

Share experiences on our online forum with Cancer Chat

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Updated: 24 February 2014