Implementation

Three steps should be considered to implement primary prevention for diet nationally.

• Set up collaboration between the NCCP and agricultural stakeholders in both the government and industry.
• Perform a sampling survey to determine current dietary practices.
• Establish a primary prevention program for diet using the threefold strategy of education, legislation and national leadership as summarized on slide 7 and discussed in more detail below.

Dietary factors are thought to account for about one-third of cancers. It makes sense then to consider dietary modification as one way to prevent the disease. But more than for any other risk factor, there remains confusion as to what clear recommendations can be made from a high research literature where the evidence for a quantitative relationship between cancer and food or specific nutrients is not as strong as it is for tobacco and alcohol and for some chemical carcinogens. Recommendations are further complicated by the need to adjust to local cultures, customs, culinary styles, seasonality, cost and the availability of certain foods. Three categories must be considered: natural food ingredients, contaminants and additives.

Natural Food Ingredients

Dietary fat. Research data indicate a high correlation between the intake of dietary fat and the incidence of breast, prostate, uterine (body), ovarian and colonic cancers. There are parallel data from animal experiments. Studies show that dietary fats are a determinant of risk for breast cancer. There is a significant effect for total fat intake, and for saturated fat in particular. There is even greater evidence for an effect of total fat and meat consumption in increasing the risk of colon cancer. There is also some evidence that cancers of the prostate and ovary are associated with high intake of animal fat and red meat.

Nitrites and salt. There is a declining incidence of stomach cancer in most countries that is thought to be related to less salting and pickling to preserve food. The chemicals used in these processes react with protamines in the stomach to produce nitrosamines which are powerful carcinogens. Moreover, grilling or broiling meat or fish as a method of food preparation can produce carcinogenic substances for animals, but their significance in human beings is unclear.

Fruits and vegetables. Colorectal, stomach, oropharyngeal and esophageal cancers are reduced in populations that consume substantial amounts of fruit and vegetables. The protective effect for colorectal cancer can be greater than that for fibre intake. Vitamin C has been shown to have some protective effect for pharyngeal, stomach and breast cancers. Conversely, a reduced consumption of fruits and vegetables showed an increased risk of precancerous lesions of the esophagus. Protective effects have also been ascribed to beta-carotene.

Contaminants

Food may become contaminated with carcinogens. Also certain substances naturally present in food and others generated during its preparation may have carcinogenic potential. In Africa the growth of mould on nuts and other food when they are stored in a particular way can produce aflatoxin. This material is a potent carcinogen that is implicated in the high incidence of primary liver cancer seen in Africa. In general food contaminants cause only a small amount of diet-related cancer.

Additives

Substances added to food to preserve it or to enhance colour may be carcinogenic. But it is unlikely that currently used additives have any significant effect in increasing cancer risk. This is because since 1956 the Food and Agriculture Organization/World Health Organization (FAO/WHO) Food Standards Program has established maximum levels for additives, contaminants and pesticide residues that are implemented by the Codex Alimentarius Commission.

Evaluation

For dietary control, WHO (1995) recommends the following indicators as examples.

Process Measures

Over 80% of schoolchildren aged 10 years and over get education about sound dietary practices.
Over 50% of adults get a message yearly about diet and cancer.
More than one legislative measure about diet and health is implemented.

Impact Measures

Over 80% of schoolchildren aged 10 years and over are aware of sound dietary practices.
Over 50% of adults are aware of the link between diet and cancer (sampling survey).

Outcome Measures

Short term: More than a third of adults are modifying their diets.
More than a third of adults exercise at least 3.5 hours weekly.
Medium term: Reduced incidence of colon cancer and cardiovascular disease.
Long term: Reduced incidence of breast and stomach cancers.

Dietary Recommendations

A recent landmark study was published by the World Cancer Research Fund and the American Institute for Cancer Research in 1997. It should be consulted for the most recent and comprehensive research and recommendations. A summary of their advice is presented here.

• Plant-based diet: One should choose predominant plant-based diets rich ina variety of vegetables and fruits, pulses (legumes) and starchy staple foods that have been minimally processed.
• Body weight: Maintain individual body mass index (BMI) between 18.5 and 25. Avoid being under- or overweight. Limit weight gain during adulthood to less than 5 kg (11 lb.).
• Physical activity: Throughout life maintain an active lifestyle equivalent to a physical activity level (PAL) of at least 1.75, including opportunities for vigorous physical activity. Where occupational activity is low or moderate an hour’s brisk walk or similar activity is recommended daily plus an hour’s vigorous activity a week.
• Fruit and vegetables: Consume year-round a variety of fruits and vegetables to provide 7% or more of total energy (calories). This means eating 400-800 grams (15-30 ounces) or five or more portions (servings) a day of a variety of fruits and vegetables all year round.
• Other plant foods: A variety of minimally processed starchy or protein-rich foods should provide 45-60% of total energy (calories). Limit refined sugar to less than 10% of total energy. This means eating 600-800 grams (20-30 ounces) or more than seven portions (servings) a day of a variety of minimally processed cereals (grains), pulses (legumes), roots, tubers and plantains, and limiting consumption of refined sugar.
• Alcohol: Alcohol consumption is not recommended and excessive consumption discouraged. At the very least restrict it to less than 5% of total energy for men and less than 2.5% for women, meaning less than two drinks a day for men and one for women.
• Meat: Red meat should provide less than 10% of total energy, if it is eaten at all. This means less than 80 grams (3 ounces) daily if eaten at all. Fish, poultry or meat from non-domesticated animals is preferred to red meat.
• Fats and oils: Total fats and oils should provide 15-30% of total energy. Consumption of fatty foods should be limited, especially of animal origin. Use modest amounts of appropriate vegetable oils.
• Salt and salting: Limit consumption of salted foods and the use of cooking and table salt. Salt from all sources should amount to less than 6 grams per day (0,25 ounces) for adults. Season foods with herbs and spices.
• Storage: Perishable food should be stored so as to minimize fungal contamination. Avoid food that has been stored for long times at room temperature. It may be contaminated with mycotoxins.
• Preservation: Perishable food should be consumed promptly or kept frozen or chilled. By refrigeration.
• Additives and residues: Establish safety limits for food additives, pesticides and their residues, and other chemical contaminants in the food supply, and monitor their enforcement. This is particularly important in developing countries.
• Preparation: Cook meat and fish at relatively low temperature. Avoid charred food and the burning of meat juices. Only occasionally should one consume meat and fish grilled (broiled) in direct flame, cured and smoked meats.
• Dietary supplements. This report considers dietary supplements to be unnecessary for reducing cancer risk if the above recommendations are followed. However, this is a controversial area and the recommendations could change: for example, recent data suggesting that selenium supplements lower the incidence of lung, colorectal and prostate cancers, or the Finnish study showing that vitamin E prevents prostate cancer.
• Tobacco: Neither smoke nor chew tobacco, and discourage its production, promotion and use in any form.

(Adapted from World Cancer Research Fund and American Institute for Cancer Research (1997). Food, Nutrition and the Prevention of Cancer: A Global Perspective. Washington, DC, ISBN 1-899533-05-2. Pages 522-523.)

WHO (1995) National Cancer Control Programmes: Policies and managerial guidelines. World health Organization, Geneva.
Diet, Nutrition, and the Prevention of Chronic Diseases. Report of a WHO Study Group. WHO Technical Report Series 797. World Health Organization, Geneva 1990.
Greenwald P & Clifford C (1995) Dietary prevention. In: Greenwald P, Kramer BS & Weed DL Cancer prevention and control. Marcel Dekker, Inc. New York, p303.
DeVita VT, Jr, Hellman S & Rosenberg SA (1997) (Ed). Cancer: Principles and practice of oncology. Ed 5 Lippincott-Raven, Philadelphia. See Willett WC Fat, p559; Greenwald P Dietary fiber, p566; Meyskens FL Jr Micronutrinets, p573; and Geenwald P Dietary carcinogens, p 579.

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