Common questions about diet and cancer

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:

• eating a healthy diet
• keeping to a healthy weight
• doing regular physical activity.

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.

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.

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.

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.

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.

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.