Updated 14 August 2014

Can diet prevent cancer?

In South Africa one in six men and one in seven women will get cancer during their lives. Could dietary changes help prevent cancer?

Many people want to know if they can make dietary changes to either prevent cancer if they have a family history of this dreaded disease or if diet can help to cure cancer when they suffer from various types of cancer.

This is a very difficult question to answer directly because there are so many different types of cancer which can affect men and women, children and adults at various stages of their life.

Diet always makes a difference because we ingest food every day from birth to death, but how specific foods may or may not have positive or negative effects on a patient’s chances to develop cancer, is a very complex subject which has not as yet been fully clarified.


The prevalence of cancer is high in developed countries. A report from the US lists cancer as the second most deadly disease in America, which was responsible for the death of 1 500 people per day in 2012 (1 out of 4 deaths) (American Cancer Society, 2012).

In South Africa one in six men and one in seven women will get cancer during their lives. According to the SA Hospice (2013) deaths due to cancer are increasing steadily in our country, which may well be due to the changes in diet, physical activity, stress, environment, exposure to industrial pollutants, cigarette smoke, alcohol and other factors that impact on our population that is rapidly undergoing urbanisation and westernisation.

Many contributing factors

A recent article published in the Pretoria News (Sapa-AFP, 2013), reported that research stretching over more than a decade has indicated that the increasingly early onset of puberty in girls (which may or may not be driven by changes in diet, obesity and hormone or endocrine disruptors including phthalates, BPA, and pesticides), may be one of the most powerful predictors of future cancer in women. Researchers found that 40% of 1200 girls aged 6 to 8 years, who were enrolled in the study in 2004, were already in puberty at the age of 8 years.

This is a startling finding as early onset of puberty has been found to be a strong predictor of breast cancer in adulthood. From a dietary point of view, the problematic link between early onset of puberty and obesity, is something that must be addressed as soon as possible. If 70% of the women in South Africa are either overweight or obese, we are not only sitting on a ‘diabetes time bomb’, but also on a potential "cancer time bomb".

Dietary factors that play a role

Michael Donaldson in his extensive review article on "Nutrition and cancer" which was published as early as 2004, states that between 30 and 40% of all cancers can be prevented by lifestyle and dietary measures alone.

The author singles out the following nutrients or nutrient-related factors as having a role in the development of cancer:

 - Over-consumption of energy - ingestion of too much food or caloric beverages is a major risk factor for cancer. In keeping with the obesity epidemic in countries such as the USA, it has been estimated that 14% of all cancer deaths in men and 20% in women can be attributed to overweight and obesity.
 - Eating too much highly refined sugar and starch particularly sweets, cakes, and other foods that contain very high concentrations of refined sugar and flour (i.e. high or very high glycaemic index (GI) foods). Studies to test the theory that high-GI foods and diets are linked to an increased risk of cancer have shown that there is a consistent increased risk of gastric, digestive tract, endometrial, ovarian, colon and colorectal cancers as the GI of the diet increases. Being sedentary and overweight and eating high-GI diets rich in refined sugar and flour, increased the risk even further.

 - Low-fibre diets are linked to an increased risk of cancer, which may be due to the absence of the actual fibre in the diet (i.e. colorectal cancers) or the whole range of nutrients that are absent when dietary fibre from unprocessed grains and cereals, fruits and vegetables is low in the diet (i.e. vitamins, minerals, phytonutrients, etc).

 - High intakes of red meat were found to increase the risk of cancers of the colon and rectum and heterocyclic amines produced during the meat cooking process were linked to breast cancer in a study conducted in Uruguay.

 - An imbalance in the omega-6 to omega-3 ratio. Omega-6 and omega-3 are so-called essential fatty acids which are implicated in practically every body function and immune response. Ideally our diets should provide us with 1 unit of omega-3 fatty acids for every 5 units of omega-6 fatty acids. Modern western diets which are lacking in whole grains and ample amounts of fish, particularly fatty fish, have a badly skewed omega-6:omega-3 ratio as high as 50:1. In view of the finding that omega-3 fatty acids protect us against certain cancers, it is vital that this imbalance in the proportions of these different types of omega fatty acids should be redressed in the modern diet.

 - Lack of trace elements in the modern diet may also contribute to the increase in cancer prevalence. For example selenium, a trace element that protects us against a variety of cancers, is nowadays often lacking in the soils which are used to grow our staple foods. Large areas of agricultural land in many parts of the world including the USA, China, and South Africa, are deficient in selenium and it has been suggested that selenium-deficient staple foods (wheat, maize, rice) grown on such land, are contributing to a decrease in immunity and an increase in cancer.

 - Reduced intakes of protective nutrients such as vitamins, including vitamin B12, folic acid and vitamin D, as well as of alpha- and beta-carotene and other carotenoids, lycopene, vitamin C and other antioxidants, have also been implicated in the increase in cancer.

 -  The role of probiotics (“beneficial microorganisms”) in the human gut which promote immunity and produce B vitamins and what can be regarded as ‘natural antibiotics’, is still being investigated, but it is already evident that eating the correct diet that is rich in dietary fibre and protective nutrients and taking the correct type of probiotics may help the human organism to avoid a variety of life-threatening diseases.

Because we do not eat foods in isolation, the whole diet and each nutrient in the diet, therefore, can play an essential role in maintaining our health and preventing cancer.

Next week we will consider what foods should be included in our diets and which ones need to be avoided if we are to stand a chance of preventing cancer from developing or help our bodies to fight an existing cancer.

References: American Cancer Society (2012). Cancer facts and figures 2012. Atlanta: American Cancer Society, 2012; ; Donaldson MS (2004). Nutrition and cancer: A review of the evidence for an anti-cancer diet. Nutrition Journal, 3:19; SA Hospice (2013). Statistics on cancer in South Africa.; Sapa-AFP, (2013). Habitat linked to cancer. Pretoria News, Wednesday, 13 November 2013, page: 9.)

(Photo of woman with vegetables from Shutterstock)

Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Read more of her articles.


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