Nu trition & CancerIntroduction
The relationships between diet and cancer are still subjects of scientific research. Next to avoiding tobacco it would seem that our choice of food and drink may give us the best chance of lowering our risk of cancer. Enough is now known for us to make recommendations about which foods it may be prudent to eat more often, and which foods it may be prudent to eat less often, and these recommendations are included in this information sheet.
The following sections cover some of the main areas of scientific study, and also subjects of interest to the general public and media. For specific information on how to achieve a balanced diet, the Anti-Cancer Foundation recommends The 12345+ Food & Nutrition Plan - a simple guide to healthy eating and weight control. The booklet is available in English, Italian, Spanish, Vietnamese and Greek.
Fruit and Vegetables
Lowered fat intakes may help reduce the risk of colorectal cancer, but the relationship to fat intake and breast cancer is still not clear. While studies in this area continue, it makes sense to reduce your intake of fat, especially saturated fat (the kind found in meat and animal products). This would also have benefits with respect to other diseases, especially of the heart and blood vessels. When recipes call for added fat, unsaturated fats (especially mono-unsaturated) appear to be the safest choice.
There are conflicting findings on the relationship between cancer risk and the consumption of unsaturated fats (the kind found in plants and some fish), so it is difficult to make firm recommendations about their use. The best advice we can offer is to keep fat intake to a small part of your overall healthy eating plan.
Dietary fibre may reduce the risk of bowel cancer because it:
It may also reduce the risk of hormone-sensitive cancers (eg breast cancer in women and prostate cancer in men) through its effects on hormone excretion.Excellent sources of dietary fibre are foods made with grains and cereals that have not had the outer layer of the grain removed. Bran-based breakfast cereals and wholemeal breads and pastas are amongst the richest sources of dietary fibre, but vegetables and fruit are also valuable sources. There are many different types of fibre and it is sensible to get them from a variety of sources.
There is good news from recent research suggesting that some forms of starch (the ones that resist digestion in the upper parts of the gut and for this reason are called `resistant starches') may also provide the same health benefits as dietary fibre. Rice and potatoes are good sources of resistant starch if they are allowed to cool before eating. Maize flour is another good source.
Recent research has shown that some constituents of wine may be beneficial to health, but the best advice at present (if you must drink at all) is to limit alcohol intake to 2 standard drinks a day.
Total Food Intake
Vitamin and Mineral Supplements
Studies which actually look at the risk of cancer in people given vitamin and mineral supplements are very rare because of the slow time for most cancers to develop. Therefore, evidence for the beneficial effects of supplementation above normal intakes in humans remains largely circumstantial at this point in time.
At present it would not be prudent to recommend vitamin supplements as a substitute for high fruit and vegetable intakes. A large number of other as yet unidentified chemical compounds in fruit and vegetables (not likely to be available as supplements) may also be highly beneficial. Plant foods also contain fibre, which vitamin tablets lack.
Food Additives and Preservatives
It is true that some additives and preservatives, when fed in very large amounts to laboratory animals, may cause tumours. However, there is very little evidence that the amounts commonly used by the food industry to control the growth of micro-organisms and 'cure' foods can cause cancers in humans. Public health authorities, such as The National Food Authority, are very aware of these problems, and they perform an important role in monitoring and controlling the use of food additives by the food industry.
Anti-Oxidants and Free Radicals
Free radicals are generated as a natural part of many chemical processes which occur in the body, and indeed they are very important in a number of diverse bodily functions, including fighting infections and monitoring normal blood pressure. However, if a free radical encounters and reacts with the DNA in our genes, it then may be capable of causing damage that could ultimately lead to cancer.
Some of the vitamins and minerals discussed in this information sheet are very good at 'mopping up' free radicals and protecting our genes. Scientists are still trying to establish whether there are real health benefits to be gained by supplementing our diets with substances like vitamin A, vitamin C, vitamin E, zinc and selenium. Until agreement is reached, it makes sense to obtain these vitamins and minerals from foods.
Phytoestrogens are substances in plants which have certain structural similarities to the human sex hormones, estrogen and testosterone. This similarity in structure enables phytoestrogens to mimic some of the properties of estrogen and testosterone. Sometimes this ability to mimic enhances the effect of natural sex hormones (which is of great interest for women experiencing an uncomfortable transition through the menopause), while in other instances it blocks the action of the natural sex hormones - which may be of benefit in preventing the 'hormone sensitive' cancers of the breast and prostate. Some recent studies suggest that phytoestrogens may even help to prevent cancer in other ways, for example by acting as antioxidants.
Two major classes of phytoestrogens are known as lignans and isoflavonoids. While isoflavonoid compounds are commonly found in fruits, vegetables, nuts and seeds, one of the richest sources is the soybean. Lignans are also found in foods of plant origin, with seeds and grains containing more than fruits and vegetables, The single richest source however is flaxseed or linseed. Foods containing both soybean and on our supermarket shelves. How much we need and in what form is something which requires further investigation before any clear recommendations can be made.
Any method of cooking meat which utilises direct temperatures of more than 150°-C such as barbecuing, grilling and frying is better avoided or minimised, as such methods are associated with an increased production of substances which may cause cancer. Preferred methods of cooking meats are roasting, stewing or microwaving as lower temperatures are used. Methods which allow the juice to drain away from the meat during cooking are also preferable.
Cooking oils accumulate oxidation products that may be quite harmful, and therefore oils used for deep-frying should not be re-used.
The best advice we can give you, based on current knowledge, is to follow the ANTI-CANCER FOUNDATION'S DIETARY GUIDELINES.
Eat plenty of Breads and Cereals
Eat small amounts of Fat
Limit alcohol intake
Use cured foods in moderation
Control your weight
Eat a wide variety of foods