Nu trition & Cancer

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
In the past two decades, the clearest research finding to emerge from studies on how the things we eat affect our risk of cancer, has been that there are protective effects associated with eating plenty of fruit and vegetables. Just which chemical ingredients in plant foods are mainly responsible for these effects is still the subject of intensive research. Well known substances like vitamin C, betacarotene (from which vitamin A can be formed), vitamin E and fibre have proved to be effective in reducing the risk of cancer in laboratory animals. Many other compounds are currently being investigated and it is likely that several, and possibly many of these will ultimately prove to be of benefit. How much of these substances we need to consume in order to make a significant impact is still unresolved.

With few exceptions, cancer is much more common in countries where people eat diets high in fat. A large number of studies with laboratory animals have also demonstrated ways in which fat may be involved in the development and growth of cancer.

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
Plant foods contain material which we cannot digest in the upper intestine/small bowel, but which can be fermented by bacteria in the large bowel. This somewhat indigestible component of the food we eat is called DIETARY FIBRE.

Dietary fibre may reduce the risk of bowel cancer because it:

  • lessens the time partially digested food (and toxic wastes) reside in the gut;
  • removes potentially harmful digestive by products;

  • can be fermented by bacteria living in the
    bowel of all healthy people to provide
    substances called volatile fatty acids that
    improve the health of the bowel lining;
  • changes the types of bacteria living in the
    gut and gives a healthier balance.

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.

People who drink heavily have a much greater risk of developing cancer of the mouth, throat and oesophagus. This risk is especially high if they smoke as well. Small amounts of alcohol have also been shown to increase the risk of breast cancer and the higher the consumption, the greater the risk. High beer consumption has been associated with bowel cancer.

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
There is considerable evidence suggesting that people who eat large amounts of food (more than is needed to maintain normal body function and weight) are more at risk of cancer than those who eat more modestly. While our understanding of how excess food intake may increase cancer risk is still incomplete, most doctors would agree that moderating food intake sufficient to maintain weight that is acceptable for height, is likely to be beneficial.

Vitamin and Mineral Supplements
As mentioned in the section on fruit and vegetables, the vitamins from plant sources have been found to have protective effects in many different experimental situations.

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
There has been a lot of publicity (much of it bad) over the use of food preservatives and additives. However, there has been a massive decrease in the occurrence of stomach cancer this century which can probably be explained by better methods of food handling. This includes refrigeration and the use of preservatives that prevent growth of microorganisms capable of producing some extremely harmful substances.

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 highly reactive chemical compounds which usually exist for short periods of time before they encounter another chemical substance with which they can react.

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.

In recent times, much research has focussed on the role of phytoestrogens in the prevention of hormone related cancers. It would seem that Asian countries have a much lower incidence of breast and prostate cancer than Western countries and it is thought that a higher consumption of soy foods - which are a rich source of phytoestrogens - may contribute to this.

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.

Cooking Methods
The ways in which we prepare our food may also affect its safety. Avoid high temperature, prolonged browning of all foods, especially meats. It is wise to use lean meat and remove all fat before cooking. Avoid frying in fat or oil, and take care when barbecuing not to allow fat to drip onto the flames or carcinogens (substances which initiate cancer) can be reabsorbed into the meat.

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.

Dietary Guidelines
Eat plenty of Fruit and Vegetables
Aim for 3 pieces of fruit and 4 servings of vegetables each day. Leafy green and yellow vegetables such as spinach, carrot, pumpkin and sweet potato are excellent choices as they contain betacarotene and vitamin C. The cabbage family (cruciferous vegetables) such as broccoli, cauliflower, cabbage and Brussels sprouts contain cancer protective factors and folate. All vegetables contain complex carbohydrates and a range of vitamins, minerals and fibre.

Eat plenty of Breads and Cereals
Five serves a day is the very minimum to aim for. A serve is equal to a slice of bread, a cup of cooked pasta, half a cup of cooked rice, 4-5 crispbreads or 1 cup of breakfast cereal flakes. Most breads and cereals provide dietary fibre and a wide range of vitamins and minerals, but wholegrain and wholemeal varieties provide the most.

Eat small amounts of Fat
Buy lean cuts of meat and grill, steam, boil or dryroast meats instead of frying. Brush the pan with a little vegetable oil if frying food, and use a nonstick pan. Try using low-fat dairy products such as yoghurt, milk and cheeses. Children under 5 years old need regular rather than reduced fat dairy products because of their high growth needs.

Limit alcohol intake
Too much of anything is harmful for you, and alcohol is no exception. Try not to have more than two drinks a day. This will help control your weight too. Drink more water - aim for 6 to 8 glasses a day. Try to have at least one alcohol free day each week.

Use cured foods in moderation
Smoked, salt-cured or pickled foods such as bacon, hams, sausages, cured fish or corned beef may be a problem only if eaten in large amounts. Aim for moderation.

Control your weight
Obesity (30%-40% or more over normal weight) may be linked to some forms of cancer. Avoid overeating and be as physically active as possible. Try to eat less fatty foods and more cereal foods, fruits and vegetables.

Eat a wide variety of foods
A wide range of nutritious foods is important for your body's health. Choose foods from all the following food groups each day, and enjoy the variety! The food groups are: breads and
cereals, vegetables, fruits, milk and milk products and meats and meat alternatives.