Diet and food supplements

Some people think about making changes to their diet, or about taking dietary supplements, such as anti-oxidants, after a cancer diagnosis.

Cancer and your diet

Many people make changes to their diet after a cancer diagnosis to help them stay as healthy as possible. Some people may also have to change their diet to lose or gain weight, or because of symptoms from surgery or other treatments.

There is no one diet that is suitable for everyone with cancer. It depends on whether you are below or above a healthy weight for your height and what symptoms and side effects you have.

You may be able to follow a standard healthy diet if:

  • you are not struggling with your weight
  • you do not have any unwanted symptoms or side effects in your digestive system.

We have more information about healthy eating and cancer, including a video.

Your healthcare team might refer you to a dietitian for advice. This may happen if you:

  • are underweight
  • find it difficult to maintain a healthy weight
  • have problems with symptoms and side effects when you eat or drink.

We have more information about a building-up diet.

Dietary supplements

Sometimes we need extra nutrition when we cannot get enough nutrition through our diet alone. This is called supplementary nutrition. It can come as milkshakes, yoghurts, juices, powders and soups. Your cancer doctor may prescribe these if you need extra carbohydrates, protein or fat. The supplements sometimes have extra vitamins and minerals added to them. Dietitians call these supplements oral nutrition support, or sip-feeds.

Food supplements

Food supplements come as tablets, capsules, powders and tonics. They include vitamins, minerals, fats, proteins and plant extracts.

You may be at risk of developing a lack of (deficiencies in) vitamins and minerals if you have:

  • not eaten well for a long time
  • had surgery to your digestive system.

Your cancer doctor can prescribe vitamins and minerals. If you are not able to eat a healthy balanced diet, your doctor may prescribe a multi-vitamin and multi-mineral supplement to take every day. This will give you the full amount of the nutrients you need. This is called the Nutrient Reference Value (NRV).

Nutrients are essential for our health, in small amounts. But they be can be harmful and cause unpleasant side effects when taken in large amounts. Some may affect cancer treatments or make them less effective.

Antioxidant food supplements

Antioxidants are some of the most common dietary supplements. They can help to prevent cell damage. They include:

  • vitamins A, C and E
  • coenzyme Q10
  • selenium
  • some plant extracts.


If you are thinking of taking food supplements, it is important to talk to your cancer doctor or specialist nurse first.

Despite a lot of research into cancer and food supplements, there is no good evidence to suggest that taking them can help treat cancer or stop it from coming back. But research has found that taking certain supplements could increase the risk of some cancers developing.


Probiotics are live bacteria and yeasts which are promoted as having various health benefits. They are usually added to yoghurts or taken as food supplements.

It is thought that probiotics help restore the natural balance of bacteria in your gut (including your stomach and bowel). This could be when the balance has been affected by an illness or a treatment. They are thought to be safe for people who have strong immune systems.

Some research suggests that certain probiotics are useful in treating side effects caused by some cancer treatments. But there is also a risk that probiotics could cause an infection from the yeast or bacteria in the product. This is because some cancer treatments can lower the number of white blood cells in the body, which fight infection. Because of this risk, it is important to talk to your cancer doctor before taking any probiotics or live yoghurts.

If you would like to discuss dietary supplements and get more information, call us on 0808 808 00 00.


Always tell your cancer doctor if you are thinking of taking any food supplements. Antioxidants can help prevent cell damage and help with any side effects of cancer treatment. But there is also evidence that taking high-dose antioxidant supplements during cancer treatment may make cancer treatment less effective. Until more evidence is available, your cancer doctor may recommend that you do not take antioxidant supplements during your treatment, unless it is as part of a clinical trial.

You do not need to limit antioxidants that are found naturally in food.

Choosing a nutrition professional

Choosing the right person to get help and advice from can be difficult. Many people claim to be experts in nutrition but have very limited knowledge and offer no protection to the public. 

  • Registered dieticians

    A registered dietitian (RD) is the only qualified health professional that can assess, diagnose and treat dietary and nutritional problems. They can do this at an individual and wider public health level. They work with both healthy and sick people. Dietitians use current medical evidence to give specific advice to people with eating or weight problems. They also give advice on healthy eating in general. Some dietitians specialise in helping people affected by cancer. Dietitians are regulated by law and must meet a national standard of practice from the Health and Care Professions Council (HCPC).

  • Nutritionists

    Nutritionists are only qualified to provide information about food and healthy eating. They cannot join the Health and Care Professions Council (HCPC). The job title of nutritionist is not protected by law. This means anyone can call themselves a nutritionist. Some registered dietitians may also call themselves a nutritionist, as it is a better understood job title.

  • Nutritional therapists

    Nutritional therapists are different again. Some nutritional therapists are qualified to provide information on healthy eating, but they are not regulated by law and cannot join the Health and Care Professions Council (HCPC). Some nutritional therapists may try to improve your health using methods such as detoxing, or suggesting you take high-dose vitamins. These types of diet are not recommended for people with cancer.

About our information

  • References

    Below is a sample of the sources used in our complementary therapies information. If you would like more information about the sources we use, please contact us at

    Cassilieth B. The Complete Guide to Complementary Therapies in Cancer Care: Essential Information for Patients Survivors and Health Professionals. 2011. 

    Ernst E, et al. Oxford Handbook of Complementary Medicine. 2008. 

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Dr Saul Berkovitz.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 31 October 2019
Next review: 31 October 2022

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.