Five common myths around food and cancer

After a diagnosis some people turn to diet as a method of treatment. What we put in our bodies is our choice and sometimes it can feel like it’s the only thing we can control during this time. Unfortunately there are many myths around food and cancer and these can have a negative impact on treatment success or overall quality of life. The following are examples of food myths we are commonly asked about.

Myth: The alkaline diet cures cancer
Cancer cells cannot survive in an alkaline (basic) environment but neither can our healthy cells. Our bodies tightly regulate pH levels and we are not able to change it by foods we eat. This diet does not change blood pH to outside normal range and excludes important food groups. Restricting food groups and nutrients can make eating harder than it might already be. During treatment it is important to eat a balanced diet to help you get nutrients for energy and overall wellbeing.

Myth: Sugar feeds cancer
This myth leads some people to avoid all carbohydrate-containing foods. This is counter-productive for anyone struggling to maintain their weight due to side effects of cancer and treatment. All our cells, including cancer cells, use sugar for energy and depriving cancer cells of sugar doesn’t slow or alter their growth. Avoiding foods with processed sugar is a good idea for general health, but eliminating foods with natural sugar won’t stop cancer cells from dividing.

Myth:  Supplements prevent cancer
Supplements provide a large amount of a single vitamin or mineral.  Food contains other compounds which work together with vitamins and minerals for health such as antioxidants and fibre.  If you are eating a variety of food from the different food groups in most cases you don’t need supplements. Many studies have shown these high doses do not work as effectively as eating the vitamin or mineral from foods and some can adversely affect your cancer treatment. Supplements may be recommended in specific cases and you should discuss this with your doctor if you are concerned.

Myth:  Artificial sweeteners (most commonly aspartame) cause cancer
This old myth is based on animal studies that have been largely criticised by scientists for using poor methods and not being very relevant to humans. When consumed, aspartame breaks down into aspartic acid and phenylalanine (both naturally occurring amino acids) and methanol. Methanol is non-toxic in small amounts, naturally produced by the body and found in fruit, fruit juice, fermented beverages and some vegetables. The amount of methanol produced from aspartame breakdown is lower than the amount found in many common foods. Evidence concludes artificial sweeteners do not cause cancer in the small amounts we consume.


Myth: Soy causes cancer
Theory: natural soy foods contain isoflavones (similar to oestrogen) that could raise the risk of some cancers because oestrogen is linked to hormone sensitive cancers (e.g. breast cancer). However, while isoflavones may act like oestrogen, they also have anti-oestrogen properties. Some studies have even shown that people who ate soy were less likely to get breast cancer. Current evidence does not support avoiding soy foods for cancer prevention however, for women with a hormone receptor positive breast cancer it is recommended to keep their soy intake at a moderate level.

There are many nutrition related myths circulating the internet and it can be difficult to know who to trust. If you have any questions contact the Cancer Society for evidence-based, practical advice.


Anna Small, NZ Registered Dietitian and Health Promoter.

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