Statistics show that an average of 35 percent of all cancers are related to the food we eat. Thus a good portion of all human cancers may be potentially preventable. While no single food can prevent cancer, making better food choices can certainly reduce your risk for certain types of cancer.

The types of cancers that seem to be especially diet-related are cancer of the digestive tract (oesophagus, stomach, liver, colon and pancreas), lung, breast and prostate. Let’s take a look at the specific constituents of diet that have been associated with either the cause or prevention of cancer.

Overweight
 Unfortunately, being overweight is often seen as more of a social or cosmetic problem than a medical one. This leads to a severe lapse in regard to its significance as a chief contributor to lifestyle diseases, including cancer. Excess weight is associated with increased cancer mortality in both men and women. Focusing on weight reduction is therefore an important preventative measure in the fight against cancer.

Dietary fats
Of all the nutrients, an excess intake of fat is probably the most plainly established dietary promoter of cancer. It is fairly well established that cancer is more common in countries where people have a high average intake of total fat. This is particularly relevant with regards to breast cancer: when calorie intake exceeds calories burned, body fat grows. As body fat increases, oestrogen levels in the tissue increase, and studies have implicated oestrogen in the promotion of breast lesion growth.

In addition to the quantity of dietary fat, the type of fat consumed may be an important risk factor for cancer, saturated (animal) fats, tend to increase cancer risk, as opposed to polyunsaturated omega-3 fats (found in fish and certain seed oils), which may decrease the risk.

Fibre
 In recent years, there have been numerous investigations into the possible protective role of fibre in the prevention of cancer of the colon and rectum. Possible mechanisms by which risk may be reduced are:

  • Fibre decreases transit time of waste products through the digestive tract, thus reducing exposure time to potential carcinogens (substances that induce cancer).

  • Because of fibre’s water-holding ability, it increases faecal bulk thus diluting potential carcinogens.

  • Fibre by nature is not digested and absorbed — by binding to some potentially harmful substances in the gut, fibre thus prevents them from being absorbed.

  • Fibre is fermented by bacteria in the colon to produce substances called short chain fatty acids — these acids not only support growth of the gut, but may have a role in cancer prevention.

    Foods high in fibre include whole grain cereals, breads, rice, fruits, vegetables, nuts, beans and seeds. We should all be including at least six servings of whole grain breads, cereals and rice, two to three servings of fruit (a serving is one piece or one half a cup) and three to five servings of vegetables (a serving is one half cup cooked or one cup raw) in our daily routines.

    Antioxidants
     Free radicals are molecules that are all around us. They are produced both as a natural product of living (through metabolism) and by external sources such as sunlight, cigarette smoke and general pollution. Free radicals are used by the immune system to fight off invading bacteria and viruses. However, when produced in excess, they damage human cells and tissues too.

    Our natural defence mechanisms — antioxidants — are usually able to neutralise the majority of these destructive molecules, but there are times when there may not be enough to counteract them and tissue damage occurs. In fact, free radicals have been implicated as causal factors in cancer development.

    The most potent antioxidant nutrients are vitamins A, C, E, beta-carotene and selenium. Studies of the effects of supplemental antioxidant nutrients on the prognosis of patients with existing cancers have yielded conflicting results — more research is necessary in this area before any conclusions can be drawn.

    Alcohol
     Alcohol is not a carcinogen but may play a causative role in cancer promotion, by acting as a cell toxin, depressing the immune response or by altering the metabolic actions of vitamins. The malnutrition associated with alcoholism is also likely to be important in the increased risk for certain cancers in alcoholic individuals.

    Calcium and vitamin D
     Evidence suggests that calcium may decrease the risk of cancer. This is because calcium in the intestine binds with fats and bile acids to form calcium soaps, which may reduce the exposure of the gut to potential toxic substances. Dietary vitamin D intake has also been associated with a lowered risk of colon cancer — whether this is part of its role in the transport of calcium or an independent effect, is unknown.

    Artificial sweeteners
    Artificial sweeteners — namely saccharine, cyclamate and aspartame — have been linked to bladder cancer in animal studies. However, there is no scientific evidence of this in human studies, especially where moderate amounts are consumed.

    Other factors

  • Compounds known as indoles, flavonoids and phenols found in cruciferous vegetables (cabbage, broccoli, Brussels sprouts and cauliflower) are thought to protect against cancer of the stomach and colon.

  • Although coffee intake has long been investigated as a possible risk factor for various cancers, the majority of evidence suggests that there is no real relationship.

  • Polycyclic hydrocarbons are toxic substances formed during combustion of carbon fuel, which commonly occurs during the frying and smoking of meats or a charcoal barbecue (braai). Evidence suggests an increased risk of stomach and oesophageal cancers with the frequent intake of smoked and fried foods.

  • There may be a relationship between intake of sodium and potassium nitrates (used in the process of salting, pickling and curing foods) and cancer risk.

  • Recent studies suggest that folic acid may protect against cancer. Folic acid is found in dark green veggies, lentils, oat bran and other fortified cereals, and orange juice.

  • Studies indicate that high consumption of tomatoes and tomato products is strongly linked to a reduced risk of certain cancers. This is due to the antioxidant lycopene.

  • Regular physical activity may help reduce the risk for several cancers.

    Unfortunately, the role of diet in cancer prevention and control is not well understood. Although diet is not the be-all and end-all cure for cancer, it is one step that we can all take against cancer.

    All these indications just reinforce what dieticians have been saying all along — eat low-fat, high-fibre foods, increase your intake of fruit and vegetables, and get active!


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