Preservation and processing exposures reportWe analyse global research on how methods of preservation and processing of foods affect the risk of developing cancer.

Salting and other methods

Foods can be preserved and processed in a number of ways prior to consumption. These different methods affect the chemical composition of foods as well as their nutritional value and carcinogenic potential.

Processed meat generally refers to meats (usually red meats) that have been preserved by salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation. Examples of processed meat include ham, salami, bacon, pastrami and some sausages. These include sausages, bratwursts, chorizo, frankfurters and ‘hot dogs’ to which nitrites or nitrates or other preservatives are added.

Salting is a traditional method of preserving raw fish throughout much of the world. Depending on the precise conditions, salt-preserved fish may also undergo fermentation.

Cantonese-style salted fish is characterised by using less salt and a higher degree of fermentation during the drying process than fish preserved (or salted) by other means, because of the relatively high outdoor temperature and moisture levels.

Although the use of salt as a preservative has generally decreased as industrial and domestic use of refrigeration has increased, some traditional diets still include substantial amounts of salt-preserved foods, including salted meat, fish, vegetables and sometimes also fruit. The requirement for salt for human health has been estimated to be much lower than amounts currently consumed. World Health Organization pragmatically recommends restricting average salt consumption for populations to less than 5 grams per day (equivalent to less than 2 grams of sodium per day).

Our major findings on this exposure

There is strong evidence that consuming:

Preservation and processing of foods and cancer risk - evidence matrix

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“For processed meat, Cantonese-style salted fish and foods preserved by salting, the evidence shows that, in general, the more people consume, the higher the risk of some cancers.”

– This is the opinion of the Expert Panel and forms the basis of our Recommendation on processed meat

A global recommendation about consumption of Cantonese-style salted fish has not been made as this type of fish is consumed only in specific parts of the world. Nevertheless, the Panel advises that it’s best not to consume Cantonese-style salted fish.

A global recommendation about consumption of foods preserved by salting has not been made as these types of food are mostly consumed only in Asia. Nevertheless, the Panel advises that it’s best not to consume foods preserved by salting.

There is also other evidence on preservation and processing of foods that is limited (either in amount or by methodological flaws), but is suggestive of an increased risk of some cancers. Further research is required, and the Panel has not used this evidence to make recommendations. For more information download the full report.

Mechanisms

Processed meat and colorectal cancer

Overall it is likely that a combination of mechanisms contribute to higher risk of colorectal cancer among individuals consuming high quantities of processed meat. Similar to red meat, processed meat is rich in fat, protein and haem iron, which can promote tumorigenesis. Processed meats are often cooked at high temperatures, which can lead to increased exposure to heterocyclic amines and polycyclic aromatic hydrocarbons. Processed meat is invariably higher in fat content than red meat, which may promote carcinogenesis through synthesis of secondary bile acids; however, human data supporting this hypothesis are weak. Processed meat is also a source of exogenously derived N-nitroso compounds, which may have carcinogenic potential.

Cantonese-style salted fish and nasopharyngeal cancer

Cantonese-style salted fish contains nitrosamines and nitrosamine precursors. High levels of one such nitrosamine, N-nitrosodimethylamine, found in some samples of Cantonese-style salted fish, has been shown to induce cancer development in experimental models in animals.

Foods preserved by salting and stomach cancer

Animal models have shown that high salt levels alter the viscosity of the mucous protecting the stomach and enhance the formation of N-nitroso compounds. In addition, high salt intake may stimulate the colonization of H. pylori, the strongest known risk factor for stomach cancer. Finally, in animal models, high salt levels have been shown to be responsible for the primary cellular damage which results in the promotion of stomach cancer development.

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