Informed

The truth about processed meat and bowel cancer risk

Recently there was global media interest in our advice to parents to avoid giving children ham in packed lunches. Here we talk about the scientific evidence behind this Recommendation, explain what processed meat is and how it raises the risk of bowel cancer

What is processed meat?

Processed meat is meat, usually pork or beef, which has been treated by various methods (excluding refrigeration), including curing (adding salt and other additives), drying and smoking to improve quality or flavour and for preservation [1]. There is a wide variety of processed meat products and there is no specific categorization. Processed meat includes bacon, ham (raw, smoked or cooked), sausages, such as hot dogs or salami, black pudding, pates and canned meat. Hamburgers are sometimes classified as processed meat. More than 70 per cent of the UK population eats bacon and ham on a regular basis [2].

Processing methods and types of processed meats

The need to preserve meat started when easy access to fresh food and refrigeration was not available. Some industrial processes were later introduced to enhance flavour and improve safety for the consumer. Two processes, curing and smoking, have become especially common.

Curing is the addition of salt, sugar and either nitrate or nitrite. Salt improves meat flavour and preserves it by reducing water activity thereby stopping bacterial growth. Nitrate and nitrite occur naturally in the environment and are also added to meat for preservation, colour enhancement and flavour. Nitrite in particular stops the germination of Clostridium botulinum spores. Dry curing is a traditional way of preserving meat, especially ham. Traditionally only salt was used but the method required a long time and low temperature [3]. Nowadays most hams also contain nitrites and other preservatives. Smoking enhances meat colour and flavour and helps its preservation [3].

The scientific evidence

As part of the WCRF/AICR Second Expert Report, for which scientists worldwide reviewed all the available evidence on diet, physical activity, weight and cancer risk, 14 large cohort studies on processed meat and cancer risk were identified [1]. The meta-analysis showed that regular consumption of an average of 50g per day of processed meat increased the risk of bowel cancer by 20 per cent. The average intake of processed meat for European men is 48g per day [4].

The review also showed a dose-response relationship where the more processed meat is consumed, the greater the risk. Since the Report was published in 2007 more evidence has become available, which confirms the WCRF/AICR findings [3, 5, 6, 7].

Recommendations for patients

The Panel of Experts could find no amount of processed meat that can be confidently shown not to increase cancer risk. That is why WCRF UK recommends people avoid processed meat to reduce their bowel cancer risk.

Mechanisms of action

Several hypotheses have been tested that may explain why processed meat consumption increases bowel cancer risk. Here we look at the main ones:

• Nitrites and N-nitroso compounds (NOCs).Nitrites are preservatives that can react with secondary amines (contained in protein-rich foods) to produce NOCs, particularly in the absence of inhibitors of nitrosation such as vitamin C and in the presence of enhancers such as red meat [3]. Many NOCs, including nitrosamines and nitrosamides, are carcinogenic. NOCs can be formed during the curing process, and are also formed in the body from ingested nitrites and nitrates in red and processed meat [1].
• Haem in red meat. Haem is an iron-containing molecule present in animal blood and meat, especially red meat. Free iron can induce the production of free radicals, which can damage cell DNA [1]. Haem can also act as a nitrosation agent and induce the formation of NOCs in the body [3].
• High-temperature cooking. Cooking meat at a high temperature, especially frying and grilling, can cause the formation of carcinogenic compounds, such as heterocyclic amines and polycyclic aromatic hydrocarbons [1, 3].

Promote informed choices

In conclusion, there is substantial epidemiological and biological evidence to advocate a diet free from processed meat. Making people aware of the link allows them to make an informed choice to avoid or cut down on processed
meat as they wish. See our Red and Processed Meat: Finding the Balance for Cancer Prevention leaflet for ideas on alternatives to processed meat for packed lunches and traditional dishes.

References

1. WCRF/AICR. Food, Nutrition, Physical Activity, and Prevention of Cancer: a Global Perspective. Washington DC: AICR, 2007
2. The National Diet and Nutrition Survey Volume 1. 2002. London: HMSO
3. Santarelli RL et al 2008 Nutr Cancer 60(2): 131–144
4. Linseisen J et al 2006 Public Health Nutr 9:449–64
5. Cross AJ et al 2007 PLoS Med 4(12):e325
6. Huxley RR et al 2009 Int J Cancer 125(1):171-80
7. Tasevska N et al 2009 Am J Clin Nutr 89(6):1884-94