Decorative image

Diet problems caused by cancer

Information on how cancer can affect your appetite and make it hard to eat - and how it affects the way your body digests food and uses nutrients.

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 that can cause eating problems

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.

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.

Proteolysis-inducing factor (PIF)

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.

Other causes of diet problems and weight loss

Below is a list of other ways you might experience weight loss because of your 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.

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.

Cancer treatments such as chemotherapy or radiotherapy can make your mouth very sore, which can make it very difficult to eat.

You don’t usually feel like eating much, or at all, if you are in pain.

People with chronic pain quite often lose weight. 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 be very frightening.

Breathlessness can also make daily living very difficult. You use energy to prepare meals and eat. This can make you more breathless.

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.

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.

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

Last reviewed: 
24 Feb 2014
  • Cancer and its management (7th edition)
    Tobias J and Hochhauser D
    Wiley-Blackwell, 2015

  • Symptom management in advanced cancer (4th edition)
    Twycross R, Wilcock A and Toller S
    Radcliffe Medical Press Ltd, 2009

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

Information and help

Dangoor sponsorship

About Cancer generously supported by Dangoor Education since 2010.