Cancer

1997 Recommendations by World Cancer Research Fund
and American Research Institute for Cancer Research

Lung cancer: Leading cause of death in the world and smoking is mostly responsible. Convincing evidence that diets high in vegetables and fruits are protective and that carotenoids found in these are probably responsible for some of the protective effect. Use of antioxidant supplements (b-carotene, vitamin E) is not protective. 

Breast cancer: Most common type of cancer in women world-wide. Increased risk with rapid early growth, greater adult height, and weight gain in adulthood. Diets high in fruit, vegetables and monounsaturated fat reduce risk and small quantities of alcohol increase risk. 

Prostate cancer: Third most common cause of death in men in Australia. Vegetables may decrease risk and animal fat, saturated fat, red meat, dairy products may increase risk. 

Bowel cancer: Fourth most common cancer in world. Up to 70% can be prevented by healthy lifestyle. Physical activity and vegetable intake (and to a lesser extent fruit) are protective while a high red meat intake and alcohol probably increase risk. A study published in the December 2003 issue of Cancer Causes and Control on 133,000 US adults reported that men with the lowest intake of vegetables had a 79% increase in colon cancer incidence in the 5 years after diet was assessed. However, men eating the most vegetables had only a 31% reduced risk of colon cancer which was not statistically significant. Similarly, women with very low intakes of fruit were also at increased risk. This study suggests that low intakes of plant foods may increase risk of colon cancer.
The effect of alcohol is greater in the rectum than in the colon and beer consumption appears to exert a more profound effect than other types of alcohol. The omega 3 fatty acids found in fish appear to be a promising preventive agent for colorectal cancer. Although the epidemiological data are few, they are convincing. Animal studies are also supportive. Because of other beneficial effects on health, increased consumption of fatty fish can be recommended. Several case-control studies and animal studies are supportive of a beneficial role of folate – however more studies are needed (Kim & Mason, Nutr Rev 1996; 54: 259-79).
Cereal fibre has been shown by several studied to protect against colon cancer. In the Australian Polyp Prevention Project a combination of low fat and wheat bran supplemented diets (providing 11.5 g fibre/day) was associated with fewer new large adenomas over the 4 years of study (MacLennan et al. J Nat Cancer Inst 1995; 87: 1760-6). A study from the Arizona Cancer Centre involving 1429 men and women aged 40-80 who had recently removed an adenoma from the bowel was unable to show that taking a fibre supplement (13.5g fibre/day) would prevent the recurrence of an adenoma. In fact, multiple adenomas were more common in the high fibre group (Alberts et al. NEJM 2000; 342 (15). The different results obtained in these two studies may be explained by the types of fibre supplements used. In the Australian study an unrefined wheat bran was used which was probably higher in protective phytochemicals (phytoestrogens), vitamin E, B6 and folate. The American study used a more processed/refined fibre supplement. 

What should we eat to prevent cancer?

Focus on plant foods: choose mainly a plant based diet which is rich in fruits, vegetables, legumes and minimally processed starchy foods 

Maintain a healthy weight. Avoid getting too skinny or too fat. Avoid gaining more than 5 kg in adulthood

Keep physically active- if you have sedentary job, include 1 hour brisk walking each day and a total of 1 hour of vigorous exercise for the week. Convincing evidence can prevent bowel cancer and may keep breast and lung cancer at bay. 

Eat more vegetables and fruits; eat 5 or more serves of a variety of vegetables and fruits each day. At this point in time, the evidence is strongest for vegetables, especially for raw vegetables (or salads), green vegetables, onion family, carrots, tomatoes and citrus fruits, but these should not be eaten to the exclusion of other vegetables and fruits. Eating a variety will provide the greatest number of protective factors, some of which are yet to be discovered. Convincing evidence of links between diet and colorectal cancer to be restricted to the protective effect of vegetables. Evidence for protective effect of vegetables is also strong for cancers of mouth, pharynx, oesophagus, lung and stomach and moderately strong for the larynx, pancreas, breast and bladder. Fruits are also strongly protective. The report states that consumption of 400g/day or more of a variety of fruit and vegetables, could by itself, decrease overall cancer incidence by at least 20%. This is a large slice of the estimated 30-40% of cancers which are thought to be preventable by diet, increased physical activity and body weight maintenance. 

Balance other plant foods; eat 7 or more serves of a variety of grains, grain products, legumes, roots and tubers. Prefer minimally processed foods. Limit sugar consumption. Diets high in unrefined starch and fibre may reduce the risk of bowel, pancreatic and breast cancer. Diets high in refined starch and refined sugar may increase the risk of stomach cancer and bowel cancer respectively. Some studies have found that a high intake of sugar (as opposed to moderate) have a lower intake of micronutrients, especially if they are small eaters or their diet is limited in calories. There is no difference in cancer risk between the different types of refined sugars. 

Avoid alcohol: Alcohol is not recommended. If consumed at all, men should drink less than 2 drinks per day and women less than 1 drink per day. There is now convincing evidence that alcohol increases the risk of cancers of the mouth, pharynx, larynx, oesophagus and liver. May also increase risk of colon, breast and rectal cancer. The risk further increases in people who smoke. For these reasons alcohol is not recommended. Advice is provided for a limited amount – which takes into account the protective effect of a modest alcohol intake on heart disease risk and balances this against the general ill-effects of alcohol.

If eating meat, use as a condiment. If eaten at all, red meat should be limited to less than 80g per day. It is preferable to choose fish, poultry or meat from non-domesticated animals in place of red meat. Diets high in red meat (beef, pork, lamb) may increase the risk of bowel cancer and possibly breast, pancreas, prostate and kidney. While the fat, protein and iron content of meat – as well as the method used to cook it – have all been considered for possible explanations, it is not exactly known why a high meat diet is linked with an increased risk of cancer. It may be that meat does not cause cancer per se, but that meat rich diets simply don’t provide as much protective plant foods. As there is only so much room on your plate, be sure you maximise your protection from cancer by filling it first with a variety of plant foods, and if desired, using a small amount of meat for flavouring. In Britain, red meat intakes have been dropping while colon cancer rates have been going up. Mediterranean people today have high meat intakes, but have less colon cancer than Brits - presumably because they eat more protective plant foods.

Avoid animal fat - limit fatty foods, particularly of animal origin, use vegetable oils in moderation and choose monounsaturated types such as olive or canola oil. Plant oils are preferable in their natural liquid form and not hydrogenated so as to harden them. Monounsaturated fats may protect against breast cancer.

Slow down on salt. Limit salty foods, especially foods preserved in salt. May increase risk of stomach cancer.

Use healthy cooking methods – do not eat charred food, avoid overcooking meat, burning of meat juices if you eat fish or meat (e.g. as a result of barbecuing). Meats which are either charred or exposed to combustion products during cooking may contain cancer causing polyaromatic hydrocarbons. However, these substances are ubiquitous in our diet with considerable amounts being found in cereals and vegetables. Use only occasionally fish or meats which have been grilled in direct flame or cured and smoked meats. High temperature cooking methods such as frying, grilling and possibly roasting of meat, fish, and chicken transforms the protein into weak carcinogenic heterocyclic amines which have been shown in animals to induce cancer. About 40% of Australians have a metabolism that make the chemicals stronger, increasing the risk of developing bowel cancer. These people would have to eat charred meat regularly before putting themselves at risk. Cured and smoked meats, have other compounds incorporated into them during their processing, which have also been shown to cause cancer in animals. When cooking, wherever possible, use relatively low temperature methods, such as steaming, boiling, poaching, stewing, casseroling, curried meat, braising, baking, stir-frying and microwaving. Limit the use of grilling, pan frying and barbequing, especially for the preparation of meats. 

Supplements are not necessary: results of studies which show a protective effect of foods containing certain nutrients should not be taken to mean that these nutrients, when isolated and taken as supplements, will provide the same benefits for cancer prevention. In some cases there has been an increased risk of cancer in those taking supplements.

In summary, a lifestyle which includes a diet which is predominantly plant-based and varied, regular exercise, healthy body weight and avoidance of smoking and alcohol is the best health insurance policy you can provide for you and your family’s future protection against most diseases of affluence.

View a table of possible dietary contributors to some cancers.

Last Updated: August 2005