Updated 14 August 2014

Foods that may help prevent cancer

When it comes to making healthy food choices, which foods should you eat, and which should you rather avoid to prevent cancer or help your body fight an existing cancer? DietDoc takes a closer look.

There are a number of dietary habits which have been linked to an increased risk of developing various types of cancer. However, when it comes to making healthy food choices, which foods should you eat, and which should you rather avoid to prevent cancer or help your body fight an existing cancer?

It is important to keep in mind that many different factors may be responsible for the cancers people develop. In addition, it is vital to remember that we do not eat foods in isolation - our whole diet and each nutrient in the diet can play an essential role in maintaining our health and preventing cancer, or conversely triggering cancer.

Avoid foods that fuel obesity

We are aware of the statistic that 70% of women in South Africa are either overweight or obese, and that there has been a global shift in the age of onset of puberty which is possibly determined by high levels of childhood overweight and obesity (Pretoria News, 2013). This early onset of puberty in girls at the average age of eight years is believed to be responsible for breast cancer when these girls grow up. It therefore stands to reason that it is imperative to prevent overweight and obesity in children, teenagers, pregnant women even before they conceive and in all females to lower the risk of developing breast cancer. A low-fat, low-GI diet rich in protective nutrients throughout life may well be the answer.

Dietary factors that play a role

Based on recommendation made by Michael Donaldson in his review article on ‘Nutrition and cancer” (2004), the following foods should be avoided:

Foods to Avoid:
 - High-energy, nutrient-poor foods - in other words foods or drinks that contribute mainly empty kilojoules to the diet in excessive amounts. Examples of such foods/drinks are:

Highly processed starches like white or sifted maize meal, white flour, and all types of foods produced from such overrefined starches including cakes, biscuits, pies, tarts, and unfortified sifted maize meal or flour (i.e. without the 8 nutrients that have been added back to maize meal by government decree).
 - High-fat, very-high-energy foods, particularly foods rich in saturated fats and trans-fats. The energy content of liquid and solid fats of all types is the highest of all the so-called macronutrients, namely 37 kJ per gram. So for every gram of fat you avoid, you ‘save’ 37 kJ and in many cases avoid exposure to trans-fats which are implicated in cancer genesis.

Such trans-fats are artificially produced when oils are converted to liquid fats through the process of hydrogenation to produce hard cooking and baking fats or when oils are heated over and over again to cook foods like chips. SA legislation has prohibited the presence of these artificially produced trans-fats in locally manufactured foods, but the labelling of many products imported ‘under the table’ from the East, does not list trans-fat content, so be careful what ‘bargains’ you buy with foreign labels.

Also beware of those vividly coloured and cheap snack foods that are sold in vast plastic bags with no label at all. If you do purchase take-aways limit them to only once or twice a month, avoid deep-fried foods (choose grilled instead) and beware of dingy shops where the oil in the deep fryer is not changed from one week to another and the entire area is permeated with a rancid odour.

 - High-sugar foods and particularly liquids that have a high sugar content can contribute to obesity especially in children and teenagers. Although sugar like all carbohydrates has a much lower energy content than fat (16 kJ/gram versus 37 kJ/gram), we tend to eat such large quantities of sweets and sugar, and consume such amazing volumes of sweetened cold drinks, squashes, and energy drinks that our energy intake from sugar can in many cases exceed that of fat.

 - It goes without saying that foods and drinks that combine refined starches with sugar and fat such as listed above, are very high in kilojoules and need to be avoided to keep weight down and prevent cancer.
 - Alcohol is the second most energy-rich macronutrient contributing 29 kJ/gram. We are all acquainted with ‘beer boeps’ in South Africa, which represent mountains of solid fat deposited in the dangerous abdominal area that owe their origins to copious intakes of alcohol of all types. Overconsumption of alcohol also depletes the body of protective nutrients and may replace healthy foods in the diet thus exacerbating vitamin and mineral deficiencies.

Adhere to the following SA Food-Based Dietary Guidelines which suggest:
 - Use fat sparingly; choose vegetable oils rather than hard fats
 - Use food and drinks containing sugar sparingly

Foods to Include liberally in the diet:
 - High-fibre foods which include all unprocessed grains and cereals, fruits and vegetables, as well as legumes (dry cooked or canned beans, peas, lentils and soya and all products made with legumes such as Soya mince, tofu, bean curd, etc). The more dietary fibre a carbohydrate contains, the lower the energy content will be. Eat 6-8 portions of these foods a day.
 - Foods rich in omega-3 fatty acids such as fatty fish, flaxseed, canola, walnut, and soy oils, or salmon oil or flaxseed oil supplements, and foods with added omega-3 fatty acids such as omega-3 eggs, milk, and bread. Eat fish 2 to 3 times a week or take an omega-3 supplement.

 - Foods rich in phytonutrients, vitamins, minerals and trace elements. Fruit and vegetables, unprocessed grains, and legumes lead the way when it comes to providing protective nutrients that can keep us healthy, boost our immune systems and potentially protect again cancer.

There are many examples, but if we select lycopene, a phytonutrient that protects against prostate cancer, then fresh tomatoes and all products made from tomatoes are rich in lycopene. In particular processed tomato products such as tomato sauce, puree and paste, have a higher lycopene content because they are much more concentrated than fresh tomatoes. Eat 5 or more servings of vegetables and fruit a day. Include legume dishes at least once a day.
 - Probiotics (“beneficial microorganisms”) which may also help us fight cancer, particularly of the bowel, are found in unprocessed yoghurt and other fermented foods such as maas. Have 3 servings of milk, yoghurt or maas a day.

In other words, honour the SA Food-Based Guidelines which state:
 - Make starchy foods part of most meals
 - Eat plenty of vegetables and fruit every day
 - Eat dry beans, split peas, lentils and soya regularly
 - Fish, chicken, lean meat or eggs can be eaten daily
 - Drink milk, maas or yoghurt every day

If we apply the above dietary changes suggested by Donaldson (2004) and our own Food-Based Dietary Guidelines and combine them with a prudent lifestyle (avoidance of smoking and environmental pollutants) and regular daily exercise, it is entirely possible that we may be able to prevent 30 to 40% of all cancers and also keep existing cancers at bay.

(References: Donaldson MS (2004). Nutrition and cancer: A review of the evidence for an anti-cancer diet. Nutrition Journal, 3:19; Pretoria News (2013). Habitat linked to cancer. Pretoria News, Wednesday, 13 November 2013, page: 9.)

(Photo of woman eating salad 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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