Nutrition and cancer myths busted

A diagnosis of cancer can be crushing for many people and often, the only thing that family/friends feel that they can take control of to help fight against cancer, is their eating and drinking.  


Going on the internet can be overwhelming. There is so much misinformation out there in regards to diet and cancer and it can be difficult for patients and their loved ones to know what to trust. As a registered dietitian working on an oncology ward, here are the top three common myths that my patients ask me about for further clarification.

1. Sugar feeds cancer

I’ve lost count of the number of times this has been said to me. First thing first…what is sugar? Sugar is essentially a carbohydrate and comes in various forms: we have the simple ones such as sugars found in table sugar and confectionery, or more complex carbohydrates such as those in vegetables, pasta, bread etc.  

Our body will break down most carbohydrates into glucose, which is used as the primary fuel for all our cells, particularly our brain. Each and every one of our body cells need energy in the form of glucose, including cancer cells. However, this does not mean that sugar itself is the primary source of cancer.

Cancer itself leads to people needing more energy and so cutting out a whole food group can be detrimental to a person’s health. The body and the cancer will need energy one way or another - if it doesn’t get glucose from the food we eat, then your body will start breaking down your muscle and fat in order to get the substrates necessary to produce glucose and get the energy it needs. This ultimately results in weight loss, a weakened immune system and potentially making you unfit for further treatment.  

Additionally, when you cut out carbohydrates in order to avoid sugar, you will be missing out on many key phytochemicals, minerals and vitamins - all of which we know plays a vital role in a healthy diet.

2. Alkaline water/diet cures cancer

The alkaline diet has been making the rounds on social media, having first come into prominence in 2002 and subsequently attracting many celebrities. Proponents of this diet claim that by influencing the pH of our body via diet, we can maintain health and fight/cure diseases such as cancer.

The hypothesis relating to cancer is that cancerous cells produce an acidic local environment in the surrounding tissues which are out of sync with our body’s natural blood pH of 7.4. Thus, a diet that is high in alkaline foods can provide a microenvironment which is hostile to cancer cells which kills them off. Sounds like something that makes sense, right? However, our bodies do not work in such simple ways.  

Our body’s pH is tightly controlled by multiple mechanisms. When this goes wrong you can end up seriously unwell in hospital, often needing life support. When the alkaline diet proponents talk about foods having either an alkaline or acidic effect, they are talking about the breakdown of foods which produce compounds that are indeed either acidic or alkaline. However, our bodies compensate for these pH changes instantly via our kidneys and respiratory systems.  

Healthy salad

When people test their urine pH to ‘prove’ that the diet is changing their body’s pH, all they are actually ‘proving’ is that the body has managed to maintain a stable pH by excreting the small amounts of extra acid or alkaline without impacting upon our blood’s pH.

3. Dairy causes cancer

This myth first started cropping up in the early 2000s when a patient with breast cancer claimed that her breast cancer stopped progressing due to removing dairy from her diet. She associated that a lower intake of dairy in China led to lower incidences of breast cancer in Chinese women compared to western women.  

However, this association isn’t really rooted in scientific evidence and there are many other reasons to explain the lower incidence in Chinese women, not limited to: the lower level of alcohol consumption, the lower rate of obesity and the fact that Chinese women tend to get pregnant younger than western women - these are all known to reduce breast cancer risk.

So what does the evidence actually say? The majority of studies have shown that in relation to breast and colorectal cancer, dairy products likely decrease the risk of these cancers although dairy (apart from whole-fat dairy) may increase the risk of prostate cancers.

Dairy is a very good source of protein and calcium and is often tolerated well in patients with cancer, thus also being an important source of calories. Restricting dairy in the face of a lack of evidence can often be more harmful to a patient with cancer and is not recommended.

In summary, when looking up nutrition and cancer online, be wary of the avalanche of misinformation out there. If you are struggling with your eating and drinking, reach out to a registered healthcare professional who can work with you and guide you to make well-informed choices.

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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London SW14 & E18
Written by Rania Salman, Registered Dietitian, PgDip (Merit), BSc (Honours), MBDA
London SW14 & E18

Rania Salman is a trained dietitian who uses an evidence-based approach to support you in reaching your goals. Her areas of expertise include cancer care, liver disease, diabetes and weight loss/gain in addition to general health and wellbeing. She has worked in some of the most well-known NHS trusts, in addition to working for the private sector.

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