Eating a healthy, balanced diet is important when undergoing treatment for cancer. With a lot of false information readily available online, it is advisable for individuals with cancer to seek nutritional advice from a registered dietitian to ensure that it is safe and evidence-based. 

We spoke to Dawn Wilson, Oncology Specialist Dietitian, to debunk common cancer diet myths and find out more about eating well with cancer.

What is your role at Cromwell Hospital?

I am currently working as an Oncology Specialist Dietitian at Cromwell Hospital. On a day-to-day basis, I see patients with a range of cancer diagnoses in a variety of settings, including inpatients on the oncology ward, outpatients, and patients undergoing treatment on the chemotherapy day unit or in the radiotherapy department. I have been working with cancer patients as a dietitian for over three years and I really enjoy being able to support these patients with their dietary needs and concerns at such a difficult time both physically and emotionally.

How do dietitians support individuals with cancer?

Dietitians support cancer patients by assessing their nutritional status and providing dietary advice to ensure that patients are well-nourished before, during and after their cancer treatment to minimise side effects of treatment, improve treatment outcomes, and improve quality of life.

Dietitians provide dietary advice to help patients manage possible symptoms which occur as a result of their treatment that may impact the amount and types of food people can eat, such as taste changes, mouth sores/ulceration, nausea, vomiting, and altered bowel habits. Dietary advice may include changes to the texture of foods and nutrition support advice to help patients maintain their weight during treatment.

Dietitians may provide cancer patients with oral nutritional supplement drinks if they are unable to eat enough to meet their nutritional requirements. Dietitians can also support patients with tube feeding or intravenous nutrition (referred to as parenteral nutrition) if required depending on their diagnosis and treatment.

Explore the link between bowel cancer and diet >

Can you cure cancer through diet alone?

In recent years, there has been a lot information in the media claiming that alternative diets can be used in treating cancer. It is understandable that people want to know about potential diets that offer the hope of a cure. Unfortunately, there is no evidence to suggest that a particular diet will cure cancer or increase the likelihood of survival. These diets can be confusing and difficult to follow at an already challenging time. It is recommended that cancer patients follow a healthy, balanced diet if they are able to do so throughout their treatment.

What are some myths about diet that you hear from individuals with cancer?

Myth one: Dairy causes tumour growth

Many research studies have looked for a link between diets that are high in dairy products and cancer. It is thought that hormones used in the production of milk promote hormone-related cancer growth. These studies haven’t shown a clear link and therefore cancer experts do not recommend following a diary-free diet to reduce the risk of cancer.

Dairy products are an important source of protein, calcium, and other vitamins.
If you decide to follow a dairy-free diet, it is important to get calcium from other food sources such as sardines, dark green leafy vegetables, or fortified foods such as plant milks.

There is evidence to suggest that dairy may play a protective role in the development of breast cancer.

Myth: Sugar feeds cancer cells

Sugar in the diet doesn’t directly increase the risk of cancer or encourage it to grow. Cutting out sugar from the diet does not restrict sugar (glucose) to cancer cells. It is thought that cutting out sugar will “starve” surrounding healthy cells and tissues and therefore it is not recommended to cut out sugar from the diet.

Sugars are also found in many healthy foods such as pasta, rice, fruits and vegetables, which are an important part of a healthy, balanced diet. However, it is recommended to reduce excessive “free” sugars in the diet – for example, those found in fizzy drinks.  

Myth: Soya contains isoflavones which may stimulate cancer growth

Isoflavones found in soy products have a similar chemical structure to the hormone oestrogen. Oestrogen can stimulate some cancers and therefore it was thought that foods containing isoflavones might have a similar effect. Current evidence suggests that a diet containing naturally occurring isoflavones is safe. Soya foods can be used as part of a healthy balanced diet as they are a good source of protein and fibre.

Myth: Alkaline diets promote good health

It is thought that alkaline environments are beneficial and promote good health whereas acidic environments promote ill health. It is thought that foods can affect the body’s pH and therefore individuals should aim to avoid eating acidic foods.

However, the body’s pH is regulated by the kidneys and respiratory system and is not altered by foods. The alkaline diet proposes that eating alkaline foods will create an alkaline environment which can kill cancer. Neither cancer cells nor healthy cells can survive in an alkaline environment. Therefore, there is no scientific evidence that shows the benefit of an alkaline diet for the prevention of cancer.

Is there any diet that can prevent or lower your risk of developing cancer?

There is no specific diet that individuals can follow to prevent or lower the risk of developing cancer. Following a healthy, balanced diet and participating in regular exercise helps individuals to maintain a healthy weight, which can help to reduce the risk of developing some cancers.

For most people, a healthy, balanced diet includes:

  • Plenty of fruit and vegetables (aiming for five portions of fruit and vegetables per day)
  • Plenty of carbohydrates such as bread, rice, pasta, noodles and potatoes
  • Protein-rich foods such as meat, poultry, fish, nuts, eggs and pulses
  • Some milk and dairy foods such as cheese and yoghurt
  • Small amounts of foods high in fat, sugar and salt

In the UK, a healthy, balanced diet is based on the Eatwell Guide. The Mediterranean diet may contribute to a reduced cancer incidence as it is characterised by foods that contain antioxidant and anti-inflammatory properties, which slow down the development of various forms of cancer. The Mediterranean diet is high in vegetables, fruit, nuts, beans, cereals, grains, fish and unsaturated fats such as olive oil. It also involves a low intake of saturated fats from meat and dairy foods.

In addition to the diet, it is important to think about regular exercise which also helps to reduce the risk of cancer. In the UK, adults are recommended to do 150 minutes of moderate intensity physical activity each week.

Although these recommendations are thought to help reduce the risk of cancer, there is no one diet that can guarantee that you won’t get cancer.

Why can fad diets for individuals with cancer be dangerous?

Fad diets can be extremely restrictive which can make them difficult to follow, especially at an already challenging time for those with a cancer diagnosis. They are often not sustainable and can have an impact on both physical and mental health.

Certain fad diets encourage cutting out certain food groups which can result in individuals missing certain nutrients which are important for a range of body functions. Fad diets can also often be very expensive, as they may involve buying premium foods and supplements which are not necessary. This is often at a time when finances can be difficult, perhaps due to being unable to work during cancer treatment.

The long-term effects of fad diets are not known and therefore it is unclear whether they can be dangerous for cancer patients and others.

What dietary advice would you give to individuals experiencing cancer?

The most important advice for cancer patients is to maintain their weight, strength, and muscle mass for cancer treatment. If cancer patients become weak, they may not be fit enough to continue receiving their oncology treatment.

This can be difficult due to side effects of the cancer itself and the treatment. If eating and drinking becomes difficult with cancer, dietitians would advise prioritising a high calorie, high protein diet to ensure the body has enough energy to cope with what it is going through.

Some patients struggle with their appetite and therefore it is recommended to follow a little and often approach with small meals and snacks at regular intervals during the day. This is often more manageable as large meals can be overwhelming.

If cancer patients are struggling with their and eating and drinking or are losing weight unintentionally, I would recommend asking to speak with a registered dietitian. 

What would be your advice for a cancer patient who wants to follow a specific diet?

As a healthcare professional, it is important to discuss these specific diets (such as keto or plant-based) with the patient to allow them an opportunity to discuss why they wish to follow a specific diet. It is important that these discussions are non-biased and non-judgmental whilst providing expertise and advice to allow the patient to make an informed decision.

If a particular diet has no proven benefit but will not cause any harm to the patient, then the role of the dietitian would be to support the patient to follow their wishes. This involves respecting the patient’s decision and will ensure a better working relationship for the future.

Are dietary supplements beneficial to individuals with cancer?

Many people ask about whether it is recommended to take dietary supplements. For most people, a healthy, balanced diet provides all the vitamins and minerals we need and therefore dietary supplements are not recommended for most people. 

People that find it difficult to eat a balanced diet may benefit from taking a multivitamin or mineral supplement – for example, a calcium supplement for those who do not eat sufficient dairy. It is also important not to take high doses as this may lead to toxicities.

Supplements may be beneficial in some situations – for example, those who can’t absorb all the nutrients they need as a result of gastrointestinal surgery.

It is possible that some dietary supplements may interfere with how cancer treatments work and make them less effective. Therefore, it is always recommended to seek advice from your cancer specialist.

Find out more about our cancer services >

Why choose Cromwell Hospital?

Choose us for expert oncology nutritional guidance – as part of our holistic approach to cancer care, we tailor personalised diets to support your treatment journey.

At Cromwell Hospital, we prioritise evidence-based nutrition, focusing on your unique needs. Our dietitians will empower you to make informed dietary choices and improve your overall health.

Get in touch with our team today >


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