Diet and food supplements
Cancer and your diet
After a cancer diagnosis, many people think about making changes to their diet to help them stay as healthy as possible. Eating a healthy balanced diet is the best way to do this.
Some people believe that specific diets can treat or cure cancer. But there is no diet or food supplement that can be used instead of conventional cancer treatment.
Some people may need to change their diet due to cancer symptoms or treatment side-effects. For example, some people may need to:
- have less fibre following surgery
- eat more calories if they have lost weight
- change their diet if they have unwanted side effects affecting their digestive system.
There is no specific diet that everyone with cancer should follow. Your healthcare team will be able to advise you if you should follow a certain diet. Most people can follow a healthy balanced diet. This will give them all the nutrients they need.
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 and how to help with eating problems.
Booklets and resources
Dietary supplements
If you cannot get all the nutrients you need through your diet, you may need supplements. These are available as milkshakes, yoghurts, juices, powders and soups.
Your cancer doctor or a dietitian may prescribe these if you need extra carbohydrates, protein or fat. The supplements sometimes have extra vitamins and minerals added to them. These supplements are sometimes called oral nutritional supplements or sip-feeds.
Vitamin and mineral supplements
Vitamins and minerals are substances we all need in small amounts to help our bodies work properly.
Antioxidants help protect your cells from damage. They are made in the body and are found in many foods, especially vegetables and fruit.
Antioxidants include:
- vitamins A, C and E
- coenzyme Q10
- selenium
- some plant extracts.
You may be at risk of not getting enough vitamins and minerals if you:
- are not eating well and have not eaten well for a long time
- have had surgery to your digestive system.
Your cancer doctor or a dietitian may prescribe vitamins and minerals if you need them. This will make sure you get the full amount of the nutrients you need.
Do you need food supplements?
Some people think that if something is good for you in small amounts, it will be even better in larger amounts. But this is not always true. Nutrients are essential for our health in small amounts. But they may be harmful and cause unpleasant side effects when taken in large amounts. Some may affect cancer treatments or make them less effective.
Are food supplements safe?
If you are thinking of taking any food supplements, it is important to talk to your cancer doctor, specialist nurse, pharmacist or dietitian first.
There is no evidence to suggest that taking supplements can prevent cancer, help treat cancer or stop it from coming back. Research has found that taking some supplements may make some cancer treatments less effective. Also, some supplements may increase the risk of some cancers developing.
There is some 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.
Probiotics
If you are taking or thinking of taking probiotics, it is important to talk to your cancer doctor, specialist nurse, pharmacist or dietitian first.
Probiotic supplements contain live bacteria and yeasts which are promoted as having various health benefits. They are often said to contain ‘good bacteria’. They are usually added to yoghurts or taken as food supplements.
Some research suggests that certain probiotics are useful in treating side effects caused by some cancer treatments.
Are probiotics safe?
There is a small 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 the Macmillan Support Line on 0808 808 00 00.
Choosing a nutrition professional
Choosing a nutrition professional can be difficult. Many people claim to be experts in nutrition but have only limited knowledge or training. Unless they are on a professional register, there is no way to know what standards they follow. If you are choosing a therapist for nutrition information or advice, the information below may help.
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Registered dietitians
A registered dietitian (RD) is the only qualified health professional who can assess, diagnose and treat dietary and nutritional problems. They work with both healthy and sick people in hospital, other healthcare settings and the community.
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).
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Nutritionists
Nutritionists use their knowledge of the science of food to help people make the right choices about what they eat. They cannot join the Health and Care Professions Council (HCPC). But they can volunteer to register with the Association for Nutrition (AfN) if they meet the AfN requirements. This organisation is recognised by the NHS. Some dietitians may also call themselves nutritionists, as people understand this job title better.
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Nutritional therapists
Nutritional therapists are recognised by the Complementary and Natural Healthcare Council (CNHC) as complementary therapists. They work with people to identify and address any nutritional imbalances in the body. They are not regulated by law and cannot join the Health and Care Professions Council (HCPC). Some nutritional therapists may try to help you 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
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.
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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 informationproductionteam@macmillan.org.uk
Balneaves LG, Watling CZ, Hayward EN, Ross B, Taylor-Brown J, Porcino A, Truant TLO. Addressing Complementary and Alternative Medicine Use Among Individuals With Cancer: An Integrative Review and Clinical Practice Guideline. J Natl Cancer Inst. 2022 Jan 11;114(1):25-37. Available from: doi: 10.1093/jnci/djab048. PMID: 33769512; PMCID: PMC8755493. [Accessed September 2023].
Integrative Medicine [Internet]. Memorial Sloan Kettering Cancer Center. 2020. Available from: www.mskcc.org/cancer-care/diagnosis-treatment/symptom-management/integrative-medicine [accessed September 2023].
NICE. Guidance on Cancer Services Improving Supportive and Palliative Care for Adults with Cancer. The Manual National Institute for Clinical Excellence [Internet]. 2019. Available from: www.nice.org.uk/guidance/csg4/resources/improving-supportive-and-palliative-care-for-adults-with-cancer-pdf-773375005 [accessed September 2023].
Overview of complementary, alternative, and integrative medicine practices in oncology care, and potential risks and harm. UpToDate. Available from: www.uptodate.com/contents/overview-of-complementary-alternative-and-integrative-medicine-practices-in-oncology-care-and-potential-risks-and-harm?source=mostViewed_widget [accessed September 2023].
Date reviewed
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.
The language we use
We want everyone affected by cancer to feel our information is written for them.
We want our information to be as clear as possible. To do this, we try to:
- use plain English
- explain medical words
- use short sentences
- use illustrations to explain text
- structure the information clearly
- make sure important points are clear.
We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.
You can read more about how we produce our information here.
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