Food and cancer: separating fact from fiction

If you have searched for information about food and cancer, you have probably come across a lot of advice.

One article might claim a particular food can prevent cancer. Another might tell you to avoid it completely. Social media posts, celebrity stories and wellness influencers can make it even harder to know what to believe.

It is understandable to feel confused or worried by some of these claims.

At Macmillan, we know people often have questions about food, diet and cancer. Here we look at some common claims and explain what the evidence says.

Key things to know

• There is no single food, diet or supplement that can prevent, treat or cure cancer.
• No individual food has been shown to stop cancer coming back.
• During treatment, getting enough energy and nutrients is important.
• A balanced diet can support your overall health and wellbeing.
• Many food and diet claims shared online are not backed by strong evidence.
• If you are unsure what to believe, speak to your healthcare team or use trusted sources of information, such as the NHS website. You may also find it useful to read our guide to how to find reliable health information online.

You may have heard that eating sugar ‘feeds’ cancer. This idea comes from research done in the 1920s that looked at how cancer cells use glucose (sugar). Some people wrongly thought this research showed that cutting sugar from your diet could starve cancer cells or stop cancer from developing.

There is no evidence that sugar directly increases the risk of cancer or encourages it to grow.

All cells in our bodies need glucose (sugar) for energy. Our bodies get this energy from many foods, including bread, breakfast cereals, rice, pasta, fruit, vegetables and dairy foods. It is important for the healthy cells in our body to get enough energy from our diet. This is especially true during cancer treatment.

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

Reducing the amount of the amount of sugar in your diet, can help improve your general health. 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 people have found no strong evidence that artificial sweeteners increase the risk of cancer.

The health benefits of fasting often make the headlines. You may have heard of approaches such as intermittent fasting or the 5:2 diet.

Although there has been some research into fasting and cancer risk, there is no good evidence that fasting reduces overall cancer risk.

You may also have heard that fasting during chemotherapy can improve how well the treatment works or reduce the side effects. There is not enough evidence to say whether this is the case. Fasting during treatment may mean that you are not getting the nutrition your body needs. It is important to discuss fasting during treatment with your healthcare team.

You can help to reduce your risk by keeping a healthy weight and eating a balanced diet. This includes cutting down on:

• processed foods and red meat
• alcohol
• high calorie foods and sugary drinks.

You may have seen claims about dairy foods increasing the risk of cancer.

Dairy products, such as milk, cheese and yoghurt, are important sources 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.

Researchers 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 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.

Should I eat a plant-based diet?

Plant-based diets are sometimes promoted as a way to treat cancer.

There is not enough evidence that a plant-based diet will reduce the risk of cancer. But eating a diet rich in vegetables, grains and nuts can be helpful generally.

This is because reducing the amount of red meat and high-calorie processed food you eat will have other health benefits. For example, maintaining a healthy weight can help to reduce your risk of cancer.

No single food can prevent cancer.

Lemons are a source of vitamin C which is a type of antioxidant. Antioxidants help keep cells healthy by reducing the number of free radicals in the body. High levels of free radicals are linked to illnesses, including diabetes, heart disease, and cancer.

Eating a balanced diet which includes fruit and vegetables will give you a good source of antioxidants. This covers a broad range of foods, for example, peppers, tomatoes, berries and carrots.

There is no scientific evidence that lemon juice can prevent cancer.

Should I take supplements?

You may have seen claims that certain supplements can prevent cancer, improve treatment outcomes or stop cancer coming back.

There is no strong evidence that supplements can do this for most people.

Some supplements can also affect medicines and cancer treatments.

Supplements are not a substitute for cancer treatment or a balanced diet.

If you are thinking about taking vitamins, herbal remedies or other supplements, speak to your healthcare team first.

Read more in our information about diet and food supplements.

Before making changes to your diet, it can help to ask:

• Who produced this information?
• Is it based on research and evidence?
• Does it promise a cure or quick fix?
• Does it rely on personal stories rather than scientific evidence?
• Are trusted organisations saying the same thing?

Be cautious of claims that suggest a single food, supplement or diet can prevent, treat or cure cancer.

If something sounds too good to be true, it often is.

Ultimately making positive lifestyle changes such as stopping smoking, being active and eating healthily is important for everyone, especially if you have been affected by cancer.

If you are thinking about making any big changes to your diet, it is important to discuss this with your healthcare team.

Other ways to get help

If cancer is affecting your relationship with food, you are not alone.

We have information about:

• Healthy eating and cancer
• Managing eating problems

If you’d like support, you could start with:

• Talking to your healthcare team or a dietitian

Get in touch

• Contact the Macmillan Support Line for free, 7 days a week, 8am to 8pm.
• Join the Online Community to connect with others
• Find local support through Cancer Care Map 

This information has been written, revised and edited by Macmillan's Digital Content Editor team. Learn more about our Digital Content Editors and how we produce our cancer information. 

Accurate information helps you make informed choices. Look for trustworthy, reliable sources such as Macmillan Cancer Support, the NHS and your own healthcare team. 

We have more information on how to find reliable health information online and understanding cancer misinformation.