How cancer causes diet problems

Cancer can cause changes to your body, making it hard to eat or digest food and use its nutrients.


Many of the symptoms of cancer can happen together.

One symptom can cause another and have a knock on effect. For example, if you are in a lot of pain, you are more likely to feel worn out (fatigued). This can make you feel depressed and less motivated to eat. Over time you can lose weight.

Talk to your doctor if you have any of these symptoms. They can treat most of them. Treatment will improve problems with your eating, drinking and digestion.

Causes of diet problems

Cancer can cause diet problems in the following ways:

Cancer may block, or partly block, your digestive system by growing in size. But it is more often a symptom of advanced cancer, such as in stomach cancer or bowel cancer.

A blocked bowel can cause you to feel and be sick, have pain and stomach cramps or constipation. You may not feel like eating because it can make your symptoms worse. This can cause you to lose weight.

A blockage can also be an early symptom of cancer in the food pipe (oesophageal cancer). Eating and drinking might be difficult or painful, causing you to eat less and lose weight.

Some head and neck cancers, such as mouth or throat cancers, can make eating or swallowing difficult and painful. People with head and neck cancers often lose weight.

It is quite common not to feel like eating much, or at all if you are in pain. People with chronic pain often lose weight. Chronic pain means having pain for more than three months. Your appetite might get better if your pain is under control. This is usually possible.

When the level of red cells in your blood is low, you might feel breathless. Breathlessness can also be a symptom of advanced cancer.

Being breathless is not usually dangerous or harmful, but it can be very frightening. You may feel anxious, which in turn can make you feel sick and stop you from eating.

Breathlessness can also make daily living very difficult. Preparing meals and eating can be a struggle if you are out of breath.

Tiredness when having cancer is also called fatigue. Many people with cancer say it goes on for most of the time. And it does not get better from resting. Tiredness can affect you mentally, physically, emotionally and spiritually.

Some cancers make substances called cytokines. Cytokines are a group of proteins in the body that play an important part in boosting the immune system. These can cause tiredness.

You may find yourself not having enough energy to cook, eat, clean, bath or go shopping. Even talking to your friends and family might be hard. All this may cause you not to enjoy eating on your own or with family or friends.

About 20 out of every 100 people (20%) with cancer get depressed. There are many causes of depression in people with cancer. But doctors think that one reason is certain chemicals made by some cancers. These chemicals can cause changes to your mood.

A low mood and depression can cause a loss of appetite and sometimes weight loss.

Cancer can cause sickness (vomiting) or a feeling of wanting to be sick (nausea) in many different ways. Some of these are:

  • changes to the levels of chemicals in the blood
  • a slow gut
  • a cancer that blocks the digestive system
  • a cancer growing in the brain causing increased pressure in the head

Feeling and being sick can affect your appetite, causing you to eat less and lose weight.


Your immune system releases several types of chemicals into your body during inflammation or infection. These chemicals are called cytokines. The cytokines help your body to deal with inflammation or infection.

Cytokines are also responsible for how you feel when having inflammation or an infection. High levels can feel as if you're having a cold or flu.

Your immune system also releases cytokines into the bloodstream when it tries to fight cancer cells. And so do some cancer cells.

Cytokines change the way your body uses carbohydrates, fat and protein. This can cause weight loss, including fat and muscle wasting. Other chemicals released by cancer cells can also cause weight loss and muscle wasting.

The cytokines may speed up your metabolism so that you use calories faster. As a result, your body will use up energy faster than it is getting it. And you can have severe weight loss even if you are eating normally. This is called cachexia (kak-ex-ee-a).

Last reviewed: 
28 Feb 2020
Next review due: 
24 Feb 2023
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  • 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 with details of the particular issue you are interested in.

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