Processed meat carcinogenic to humans

The International Agency for Research on Cancer (IARC), an agency of the World Health Organization (WHO), has stated in a study that consumption of processed meat is carcinogenic to humans and can cause colorectal cancer. IARC evaluated the carcinogenicity of consumption of red meat and processed meat.

A working group of 22 experts from 10 countries convened by the IARC Monographs Programme thoroughly reviewed the scientific literature. The experts concluded that each 50-gram portion of processed meat eaten daily increased the risk of colorectal cancer by 18 per cent. The group also classified the consumption of red meat as probably carcinogenic to humans.

The classification is based on “limited evidence” from epidemiological studies showing positive associations between eating red meat and developing colorectal cancer as well as strong mechanistic evidence, IARC said. Limited evidence means that a positive association has been observed between exposure to the agent and cancer, but that other explanations for the observations (technically termed “chance”, “bias”, or “confounding”) could not be ruled out.

The Monographs Programme identifies and evaluates environmental causes of cancer including chemicals, complex mixtures, occupational exposures, physical agents, biological agents and personal habits in humans. This association between cancer and red meat was observed mainly for colorectal cancer, but associations were also seen with pancreatic cancer and prostate cancer. “For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed,” said Kurt Straif, head of the IARC Monographs Programme.

“Given a large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”

The working group of the IARC considered more than 800 studies that investigated associations of more than a dozen types of cancer with the consumption of red meat or processed meat in many countries and populations with diverse diets. The most influential evidence came from large prospective cohort studies conducted over the past 20 years.

“These findings further support current public health recommendations to limit the intake of meat,” says Christopher Wild, director of IARC.

“At the same time, red meat has nutritional value. Therefore, these results are important in enabling governments and international regulatory agencies to conduct risk assessments, to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations.”

Red meat refers to all types of mammalian muscle meat, such as beef, veal, pork, lamb, mutton, horse, and goat.

Processed meat refers to meat that has been transformed by salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation. Most processed meats contain pork or beef, but processed meats may also contain other red meats, poultry, offal, or meat by-products such as blood. 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.

High-temperature cooking methods generate compounds that may contribute to carcinogenic risk, but their role is not yet fully understood. Cooking at high temperatures or with the food in direct contact with a flame or a hot surface, as in barbecuing or pan-frying, produces more of certain types of carcinogenic chemicals (such as polycyclic aromatic hydrocarbons and heterocyclic aromatic amines). However, there were not enough data for the working group of the IARC to reach a conclusion about whether the way meat is cooked affects the risk of cancer.

Meat consists of multiple components, such as haem iron. Meat can also contain chemicals that form during meat processing or cooking. For instance, carcinogenic chemicals that form during meat processing include N-nitroso compounds and polycyclic aromatic hydrocarbons. Cooking of red meat or processed meat also produces heterocyclic aromatic amines as well as other chemicals including polycyclic aromatic hydrocarbons, which are also found in other foods and air pollution. Some of these chemicals are known or suspected carcinogens. But despite this knowledge, it is not yet fully understood how cancer risk is increased by red meat or processed meat.

Different preservation methods could result in the formation of carcinogens (e.g. N-nitroso compounds), but whether and how much this contributes to the cancer risk is unknown.

There were no data to address this question about cancer risk, said IARC. However, the separate question of risk of infection from consumption of raw meat needs to be kept in mind.

The strongest, but still limited, evidence for an association with eating red meat is for colorectal cancer. There is also evidence of links between pancreatic cancer and prostate cancer.

The IARC Working Group concluded that eating processed meat causes colorectal cancer. An association with stomach cancer was also seen, but the evidence is not conclusive.

Eating meat has known health benefits. Many national health recommendations advise people to limit intake of processed meat and red meat, which are linked to increased risks of death from heart disease, diabetes, and other illnesses.