In the broad sense of the word, most meat is processed-cooking is a process. But as commonly used, the term ‘processed meat’ refers to meats (usually red meats) preserved by smoking, curing or salting, or by the addition of preservatives. Meats preserved only by refrigeration, however they are cooked, are usually not classified as ‘processed meat’.

Ham, bacon, pastrami, and salami are processed meats. So are sausages, bratwursts, frankfurters, and ‘hot dogs’ to which nitrites or nitrates or other preservatives are added. Minced meats sometimes fall inside this definition, often if they are preserved chemically, but not always. The same point applies to ‘ham burgers’. Given the importance of this issue, transnational burger caterers should specify the methods they use to process their products.

Nitrite or nitrate is used to preserve processed meats (it is extremely toxic to bacteria) and gives cured meats their recognizable colors and flavors. The addition of nitrite or nitrate to meat is regulated and monitored in most countries. Dietary nitrites and nitrates are probable human carcinogens because they are converted in the body to N-nitroso compounds which are known carcinogens and they have positive association with colon and pancreas cancer.

Freezing and cooling by use of natural ice and snow is a method of food preservation traditionally available only in cold climates or in winter in temperate climates. Natural ice refrigeration on an industrial scale first developed in the late 19^th century, when refrigerated containers used in trains, ships, and then later trucks, greatly increased the production and consumption of red meat. Domestic freezing, chilling, and refrigeration on a mass scale is a phenomenon mostly of the second half of the 20^th century.

Today, much perishable food is solid frozen or chilled. Together with the growth of industrial refrigeration, domestic refrigerators began to be used in the USA, Australia, and New Zealand on the scale in the 1920s, and the Europe and Japan mostly since the 1950s. In Japan, for example, household processing refrigerators increased from 9 per cent in 1960 to 91 per cent in 1970, and 99 per cent in 2004. Supermarkets with freezers, chill cabinets, and domestic refrigerators are now commonable in the cities and towns of tropical countries; poorer rural communities still rely on drying, fermenting, salting, bottling, tinning, and other methods of food preservation, as well as their own gardens and farms. It is unlikely that refrigeration itself has any direct effect on the risk of cancer. Their effects are indirect.

• Refrigeration enables consumption of fresh perishable foods including seasonal vegetables and fruits all year round, as well as of fresh meat.
• Refrigeration reduces microbial and fungal contamination of perishable foods, notably cereals (grains) and pulses (legumes).
• Refrigeration reduces the need for and use of salting, smoking, curing, and pickling as methods of preserving vegetables, fruits and meat.

It can therefore be said that refrigeration (including freezing and chilling) indirectly influences risk of those cancers, the risk of which is affected by the above factors.

Evidence mounting to a judgement of ‘convincing’ or ‘probable’ for such factors relates to cancers of the mouth, pharynx, larynx, masopharynx, oesophagus, lung, stomach, pancreas, liver, and colon.

Reference: Reports from World Cancer Research Fund and American Institute for Cancer Research