Questions about diet and cancer

People often have different questions or worries about diet and cancer. The questions and answers below may help you understand more and make decisions about your own diet. 

Can diet reduce the risk of cancer coming back?

After cancer treatment, some people change how they eat because they hope it will reduce the risk of cancer coming back. There is some evidence from breast and bowel cancer studies that diet may make a difference to the chances of cancer coming back. But there is not enough clear information to give advice about what someone with a particular type of cancer should eat.

Cancer experts recommend that people who have had cancer continue to follow the same healthy, balanced diet that is recommended for cancer prevention. It is thought the same factors that can increase the risk of developing cancer might also increase the risk of it coming back after treatment.

For most people, the factors that are most likely to improve their health after cancer treatment are:

The biggest benefits will probably be from a combination of these, rather than from one change.

Your GP, dietitian, doctors and nurses can advise you if there are any lifestyle changes you can make.

What foods should I avoid when I have low immunity?

Your medical team may tell you that your immunity might be low during treatment. You can ask them whether there is any special dietary advice you should follow.

For most people, low immunity will not last long, so there is no need to follow a special diet. If you are having high-dose chemotherapy, or a stem cell or bone marrow transplant, there will be foods you cannot have. Your cancer doctor or nurse will explain more about foods to avoid.

We have more information about food safety and cancer.

Should I take dietary supplements?

For most people, a healthy, balanced diet that contains a range of fruit and vegetables will provide all the nutrients they need. Large doses of vitamins, minerals and other dietary supplements are not usually recommended.

If you find it difficult to eat a balanced diet, it might help to take multivitamins or a mineral supplement. Supplements can contain up to 100% of the recommended daily allowance. Talk to your doctor, nurse or dietitian before taking supplements or multivitamins.

Supplements may help in some situations, such as for people who cannot absorb all the nutrients they need after surgery for stomach cancer. People at increased risk of bone thinning (osteoporosis) may also benefit from taking calcium and vitamin D supplements. These can help to strengthen their bones.

Studies looking at whether taking supplements can reduce the risk of developing certain cancers have been disappointing. The evidence shows that taking supplements does not reduce the risk of cancer. There is even evidence that taking high doses of some supplements can be harmful. It can increase the risk of cancer developing in some people or may have a harmful effect on people who have had cancer.

It is possible that some supplements may interfere with how cancer treatments work. This may make these treatments less effective. If you are having cancer treatment, it is important to get advice from your cancer doctor before taking any supplements. They can advise you about:

  • any supplements you should take
  • the doses of any supplements that may be suitable for you
  • how often you should take the supplements.

They can also tell you about any possible side effects of supplements and how they might interact with other medicines.

Should I eat more ‘superfoods’?

‘Superfoods’ are foods that are believed to have special health-related powers. They are thought to be able to prevent or even cure many diseases, including cancer. Popular ‘superfoods’ include blueberries, broccoli, kale, raspberries, green tea and turmeric.

But the term ‘superfood’ is just a marketing term used to try to sell these foods. There is no scientific evidence for any type of food being a ‘superfood’. It is much better to eat a balanced diet that includes a wide range of foods.

You should aim to eat a diet that includes lots of different types of fruit, vegetables and wholegrain foods. This will help you make sure you are getting the widest possible range of nutrients. It may make your diet more enjoyable and interesting. It will probably cost less too.

Should I follow a dairy-free diet?

Dairy products, such as milk, cheese and yoghurt, are an important source of protein, calcium and some vitamins. Calcium is needed for strong bones and teeth.

Many research studies have looked for a link between diets that have a lot of dairy products and cancer. But these studies have not found a clear link. There is some evidence that dairy products may help reduce the risk of bowel cancer. But no links have been found for any other types of cancer.

Cancer experts do not recommend following a dairy-free diet to reduce the risk of cancer. If you prefer to follow a dairy-free diet, you need to make sure you get enough calcium from other foods, such as:

  • tinned sardines and tinned salmon (with bones)
  • dark green, leafy vegetables, such as spinach
  • kidney beans
  • dried figs
  • foods fortified with calcium, such as some types of soya, rice, almond or oat milk.

Does sugar feed cancer?

All cells in our bodies need glucose (sugar). Glucose gives cells energy to survive. Cancer cells, like all other cells, also need glucose.

The idea that sugar feeds cancer developed because cancer cells grow and multiply quickly, and need a lot of glucose. It was thought that cutting sugar from our diet would starve the cancer or even stop it developing. But this is a very simple idea of the biology involved. There is no evidence that sugar directly increases the risk of cancer or encourages it to grow.

Too much sugar in our diet can cause weight gain. Being overweight or obese can increase the risk of some cancers.

It is important for the healthy cells in our body to get enough energy from our diet. This is especially true during cancer treatment. As well as from sugar, our bodies get glucose and energy from starchy foods (carbohydrates). These include bread, breakfast cereals, rice and pasta. There are also sugars in some fruit, vegetables and dairy products. Sugar itself contains no useful nutrients, apart from energy. It is possible to get all the energy you need from healthier foods.

It is best to limit the amount of sugar in your diet, unless you have received specialist advice from a dietitian. Foods high in sugar include:

  • biscuits and cakes
  • chocolate and sweets
  • syrups
  • fruit juice
  • fizzy drinks.

What about artificial sweeteners?

Artificial sweeteners are used in many foods and drinks. Large studies in humans have provided strong evidence that artificial sweeteners do not increase the risk of cancer.

Should I only eat organic food?

Many people wonder whether they should follow an organic diet to prevent cancer or reduce the risk of it coming back. So far, no research has proven that eating organic food will reduce the risk of cancer. Some studies claim that organic fruit and vegetables have better flavour and stay fresh for longer. But others find them expensive compared to non-organic products.

Some people worry that pesticides used in non-organic farming may cause cancer. In the UK, a pesticide can only be used once its safety has been tested. Laws ensure that all agricultural pesticides are used within a safe level.

It is your choice whether you buy organic or non-organic food. Current advice is to thoroughly wash all fruit and vegetables before you eat them, whether they are non-organic or organic. This removes pesticides and harmful bacteria.

What about GM foods?

Genetically modified (GM) foods have not been around for very long. They are not common in the UK. So far there is no research to show that they cause cancer. Because GM foods have not been available for long, their long-term effects are unknown and more research is needed. Because of this, some people choose not to eat them.

Do anti-cancer diets work?

There have been a lot of stories about alternative diets for treating cancer over the past few years. Many dramatic claims about cures have been made. It is understandable that people want to know about diets that seem to offer the hope of a cure. But there is no evidence that these diets can shrink or cure cancer, or increase someone’s chance of survival.

Some people get satisfaction from following these types of diet. But others find them expensive, unpleasant to eat, time-consuming and hard to follow. Some diets may lack important nutrients or be unbalanced in other ways and may even be harmful.

It can be confusing to have different advice about what to eat. Dietitians, doctors and specialist nurses recommend a well-balanced and enjoyable diet as the best way to keep healthy. If you choose to follow a specific diet, speak to a dietitian to check if you are missing any important nutrients.

Can I have soya if I have had breast cancer?

There have been some concerns about soya and its effect on breast cancer. There is currently no evidence to suggest that a moderate amount of soya is harmful. Recommendations say it is safe to have 1 to 2 servings a day of whole soya foods.

Whole soya foods are unprocessed soya foods, for example miso, tempeh, tofu, soya beans (edamame), soya nuts and soya milk.

These are examples of 1 serving of soya:

  • 1 large glass of soya milk
  • 50g of tofu
  • 100g of soya mince
  • 28g of soya nuts or edamame beans.

If you have questions about soya, talk to your doctor, dietitian or specialist nurse.

About our information

  • References

    Below is a sample of the sources used in our healthy eating information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    Fang X et al. Quantitative association between body mass index and the risk of cancer: A global Meta-analysis of prospective cohort studies. International Journal of Cancer. 2018 Oct 1;143(7):1595-1603.

    British Nutrition Foundation website www.nutrition.org.uk (accessed December 2019).

    Bhaskaran K et al. Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5·24 million UK adults. The Lancet, August 2014..

    The Eatwell Guide: Helping you eat a healthy, balanced diet, Food Standard Scotland, October 2019.



  • 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 Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    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.