Why diet is important

Eating a balanced diet can help you cope with cancer and its treatments.

How eating well helps

Eating and drinking a balanced diet when having cancer is important. It helps you to cope with cancer and its treatments. A balanced diet means eating foods from all the food groups that your body needs.

But for many people with cancer, eating and drinking well can be a struggle. Up to 40 out of every 100 people (40%) have unplanned weight loss when diagnosed with cancer. Unplanned weight loss can affect your quality of life.

Eating and drinking a balanced diet can help your body to:

  • cope with treatment side effects
  • handle the best dose of certain treatments to treat your cancer
  • recover and heal faster
  • fight off infections
  • feel stronger, healthier and have more energy

So, eating and drinking well can help you to cope better and recover faster. This could improve your chance of survival.

A balanced diet, with plenty of calories, also helps your immune system to work well. A healthy immune system can help you to fight off infections and kill cancer cells.

A balanced diet

Try to eat foods from all food groups to include everything your body needs to work well. These include:

  • beans, pulses, fish, eggs, meat and other proteins
  • potatoes, bread, rice, pasta and other starchy carbohydrates
  • fruit and vegetables
  • oil and spreads (fats)
  • milk, yoghurt and cheese (dairy products)

The diagram below is of a plate of food. Each slice shows how much of that food group should be on your plate to follow a healthy balanced diet. This guidance is from Public Health England (PHE).

A balanced diet can help to reduce your risk of chronic diseases. If you have problems that are affecting your diet, your doctor or healthcare professional may suggest that you change the amounts you eat from each group. 

Your diet should be made up of mostly fruits, vegetables and wholegrain carbs, with some protein and dairy, or dairy alternatives

Vegan diet

A vegan diet excludes animal products, such as meat, fish, eggs, dairy, and honey. People often follow a vegan diet for ethical or philosophical reasons. These can be to protect animals and the environment.

A vegan diet is thought to increase the foods that protect against cancer. And to exclude those that increase the risk of cancer.  

Researchers found that a vegan diet could reduce the overall risk of cancer, but not of specific cancers. They did a systematic review  of observational studies on vegetarian and vegan diets in 2017.

Although a vegan diet contains grains, plant oils, nuts, seeds, legumes, fruit and vegetables, you might still lack certain nutrients. You may lack:

  • iron
  • calcium
  • zinc
  • vitamin B12
  • vitamin D


Malnutrition means getting too little of the types of food necessary for good health. About 3 million people in Britain have malnutrition. This affects their health and ability to work.

Some people are more at risk than others. Between 40 to 80 out of every 100 people with cancer (40 to 80%) have malnutrition. You can be malnourished or at risk of being malnourished regardless of how much you weigh. 

Not being able to eat enough protein and calories is one of the main problems for people with cancer. Extra protein helps with healing after treatments such as surgery.

The MUST screening tool for malnutrition

The British Association for Parenteral and Enteral Nutrition (BAPEN) developed a tool called the ‘Malnutrition Universal Screening Tool’ (MUST). This simple tool is available to GPs and other people working in health care.

The MUST tool helps to identify people who are:

  • at risk of malnutrition
  • already malnourished

The results from the screening tool will show if you need more support with your diet. Your doctor or another health professional can then refer you to a dietitian.

Self screening

BAPEN also has a self screening tool for malnutrition. They based it on the MUST tool. Research showed that self screening for malnutrition works well.

Talk to your doctor about the results of the self screening tool if you are worried.

For general information and support contact the Cancer Research UK nurses on freephone 0808 800 4040 Monday to Friday, 9am to 5pm.
Last reviewed: 
26 Feb 2020
Next review due: 
24 Feb 2023
  • Quality standard for nutrition support in adults (QS24)

    National Institute for Health and Care Excellence (NICE), November 2012

    Accessed February 2020

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

  • Introduction to malnutrition

    BAPEN (British Association of Parenteral and Enteral Nutrition)

    Accessed February 2020

  • Nutrition in Cancer Patients

    P Ravasco

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

  • Molecular nutritional immunology and cancer

    R Çehreli

    Journal of Oncological Sciences, Volume 4, Issue 1, April 2018, Pages 40-46

  • The role of parenteral and enteral/oral nutritional support in patients with cancer

    A Jatoi and others

    UpToDate website

    Accessed February 2020

  • 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.

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