Carcinogenicity of red and processed meat

Red meat refers to all mammalian muscle meat, including beef, veal, pork, lamb, mutton, horse and goat.

Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking or other processes to enhance flavour or improve preservation.

Examples of processed meat include hot dogs (frankfurters), ham, sausages, corned beef and biltong or beef jerky, as well as canned meat and meat-based preparations and sauces.

The categories of the classification indicate the strength of the evidence as to whether a substance is capable of causing cancer (technically called “hazard assessment”), but it does not measure the likelihood that cancer will occur (technically called “risk characterization”) at a particular level of exposure to the substance. Group 2A is the second highest hazard classification, meaning there is evidence of carcinogenicity but that it is not definitive.

In the case of red meat, the classification is based on limited evidence from observational studies showing positive associations between eating red meat and developing colorectal cancer as well as strong mechanistic evidence (evidence showing how it could cause cancer).

Group 1 is used when there is sufficient evidence of carcinogenicity in humans. In other words, there is convincing evidence that the substance causes cancer. The evaluation is usually based on epidemiological studies showing the development of cancer in exposed humans.

The strongest evidence suggests that eating red meat is linked to colorectal cancer, although the evidence is still limited. There is also some evidence that it may be linked to pancreatic and prostate cancers.

The evidence shows that eating processed meat causes colorectal cancer. It also suggests a link with stomach cancer, but there is not enough evidence to draw a firm conclusion.

Meat can be part of a healthy diet and provides nutrients that are important for good health. However, many national dietary guidelines recommend limiting processed meat and red meat because higher intakes are linked to an increased risk of heart disease, type 2 diabetes and some cancers.

The risk increases with the amount of red or processed meat consumed, but the data available for evaluation did not permit a conclusion at the time of the original assessment about whether a safe level exists. WHO is currently developing a guideline on the optimal intake of animal-source foods, which will include recommendations on the amount of red and processed meat to consume.

This category is used when there is sufficient evidence of carcinogenicity in humans. In other words, there is convincing evidence that the agent causes cancer. The evaluation is usually based on epidemiological studies showing the development of cancer in exposed humans.

In the case of processed meat, this classification is based on sufficient evidence from epidemiological studies that eating processed meat causes colorectal cancer.

WHO is currently developing a guideline on the optimal intake of animal-source foods, which will include recommendations on red and processed meat.  As part of this work, several systematic reviews of the scientific literature are being undertaken that will inform the recommendations, including those covering red and processed meat consumption and cancer risk, among many other relevant health outcomes.

The consumption of processed meat was associated with small increases in the risk of cancer in the studies reviewed. In those studies, the risk generally increased with the amount of meat consumed. An analysis of data from 10 studies estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%.

The cancer risk related to the consumption of red meat is more difficult to estimate because the evidence that red meat causes cancer is not as strong. However, if the association of red meat and colorectal cancer were proven to be causal, data from the same studies suggest that the risk of colorectal cancer could increase by 17% for every 100 gram portion of red meat eaten daily.

The IARC Working Group consisted of 22 experts from 10 countries.

IARC is a research organization that evaluates the evidence on the causes of cancer but does not make health recommendations as such. The IARC Monographs are, however, often used as a basis for making national and international policies, guidelines and recommendations to minimize cancer risks. Governments may decide to include this new information on the cancer hazards of processed meat in the context of other health risks and benefits in updating dietary recommendations.