5 myths on cancer and nutrition

Leah Mayes, a specialist dietitian based in the oncology suite at Nuffield Health Cambridge Hospital, is frequently asked about how diet and nutrition can influence our health by reducing our cancer risk and improving health outcomes.

Below Leah debunks some common misconceptions about the effect certain diets may have on cancer by using evidence and scientific data, and establishes how a varied and balanced diet will help patients during their cancer journey and beyond.

Myth 1: Following a ketogenic diet will reduce cancer cells

A ketogenic (or keto) diet involves consuming a low amount of carbohydrates (including cutting out sugar). There has been some research into the energy pathway of tumour cells where scientists hypothesised that cancer cells favourably metabolise sugar (Warburg effect), and if you reduce your intake of carbohydrates you may reduce cancer growth. This evidence is based mainly from animal studies and in brain tumours, with no strong evidence or numbers to support this hypothesis.

Therefore, it's not recommended from a dietetic point of view to follow a ketogenic diet. Not only is it difficult to follow, but a low-carbohydrate diet reduces the variety and balance of the foods eaten and can exacerbate some of the associated side effects of cancer treatment including constipation, diarrhoea and fatigue.

Myth 2: Cutting dairy reduces the risk of cancer

There's no data to suggest that the hormones present in milk or dairy products can cause cancer. It's important to ensure that you have enough calcium and protein in your diet as well as other vitamins and minerals.

If you are following a plant-based diet, a dietician would assess calcium intake from other non-dairy sources and it is important to remember that daily recommendations for calcium intake vary with age and gender.

Myth 3: Intermittent fasting helps treat cancer

While experimental lab and animal studies indicate short-term fasting could have a protective effect on healthy cells and leave cancer cells exposed to the toxic effects of chemotherapy, there isn't enough research.

In particular, the risks related to prolonged fasting in people undergoing cancer treatment who may be underweight and suffering from malnutrition. Current clinical guidelines don't recommend fasting before or during chemotherapy.

Myth 4: Supplements and “immune boosters” can help treat cancer

High doses of antioxidants, vitamins and minerals can interfere with how well cancer drugs work. Additionally, there are toxic side effects of high-dose vitamins and minerals.

If your diet is varied and balanced, there should be no need to take supplements. Your dietician may recommend a multivitamin and mineral supplement if your oral intake is inadequate, and it's important to check with your pharmacist to make sure there are no contraindications with your medications or therapy.

Myth 5: Isoflavones can stimulate hormone-related cancer growth

Isoflavones are a type of phytoestrogen, a plant compound that mimics the hormone estrogen. Typically found in legumes, such as soybeans and chickpeas, there is increasing evidence to suggest that isoflavones have anti-inflammatory, antioxidant and antimicrobial properties to help reduce the damage to cells.

Research further suggests that naturally occurring isoflavones eaten as part of a healthy balanced diet are safe, as well as being a good plant-based source of protein and can provide additional fibre.

Last updated Wednesday 15 February 2023

First published on Monday 13 February 2023