Common questions about diet and cancer

People often have different questions or worries about diet and cancer. Not all claims about diet and cancer are backed up by scientific evidence. The questions and answers below may help you  make more informed decisions about your  diet.

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 needed or recommended.

It is better to get your nutrients from food instead of taking a supplement. But if you find it difficult to eat a balanced diet, it might help to take an A-Z multivitamin 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. For example, supplements may be suitable for people who have had surgery for stomach cancer if they now cannot absorb all the nutrients they need.

People at increased risk of bone loss may also benefit from taking calcium and vitamin D supplements. Bone loss is called osteoporosis. Supplements can help to strengthen bones. Your healthcare team can tell you if you need to take a supplement. They can prescribe any you need.

Studies currently show 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 in some people, or may have a harmful effect on people who have had cancer.

It is also possible that some supplements may interfere with how cancer treatments work. This may make cancer 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. You can also talk to a pharmacist about any possible interactions.

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

Many research studies have looked for a link between cancer and diets with a lot of dairy products. 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 plant-based milk made from soya, rice, almonds or oats.

All cells in our bodies need glucose (sugar). Glucose gives all cells the energy to function and 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 glucose for energy, like all cells. It was thought that cutting sugar from our diet would starve the cancer or even stop it developing. But all carbohydrates break down into a form of glucose and provide energy for all of the cells in our body. So, this idea is too simple for the complex biology involved.

There is no evidence that sugar directly increases the risk of cancer or encourages it to grow. But too much sugar, or sugary foods and drinks in our diet, can cause weight gain. And 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. Sugar is found in our diet in a variety of foods. Our bodies get glucose and energy from starchy foods such as bread, breakfast cereals, rice and pasta. These are called carbohydrates. Sugar is also found naturally in some fruit, vegetables and dairy products.

Sugar can also be added to foods when they are be prepared or processed. It is also in foods like in honey, syrups, fruit juices and fruit concentrates. 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 from sugary food and drinks 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.

Artificial sweeteners are chemical substances used in many foods and drinks instead of sugar. They include aspartame, saccharin, sorbitol and xylitol.

Research continues to look into whether there is a link between artificial sweeteners and certain types of cancer. Where possible, try to have foods with naturally occurring sugars instead of foods with artificial sweeteners. This includes fruit, or unsweetened food and drinks.

Using artificial sweeteners can be an alternative to adding sugar to food or drink. This could be to help keep to a healthy weight, or if you have diabetes. If you are using them to help with weight loss, there are also other ways to manage weight without artificial sweeteners.

There have been a lot of claims made about alternative diets for treating cancer over the past few years. There have also been claims made about possible cures. It is understandable that people want to know about diets that seem to offer the hope of a cure. But there is currently no evidence that these diets can shrink or cure cancer, or increase someone’s chance of survival. The recommendation is to follow a healthy, balanced diet for your overall general health.

Some people get satisfaction from following these types of diet. But others find them expensive, unpleasant to eat and take a lot of time to follow. Some diets may lack important nutrients or be unbalanced in other ways. They may even be harmful. This may lead to unplanned weight loss during treatment and make side effects worse. They can also be hard to follow, which can take the enjoyment out of eating and make you unhappy.

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.