WHO: Processed meat is carcinogenic to humans; red meat probably carcinogenic

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The WHO’s International Agency for Research on Cancer (IARC) has classified processed meat as carcinogenic to humans and red meat as probably carcinogenic to humans.

The classification comes after thorough review of the accumulated scientific literature by a Working Group of 22 experts from 10 countries convened by the IARC Monographs Programme. The decision for red meat has been taken based on limited evidence that the consumption of red meat causes cancer in humans and strong mechanistic evidence supporting a carcinogenic effect, while that was processed meat was based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.

The IARC Working Group 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.

Experts concluded that each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18 per cent while risk of colorectal cancer could increase by 17 per cent for every 100 gram portion of red meat eaten daily.

“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,” says Dr Kurt Straif, Head of the IARC Monographs Programme. “In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”

IARC notes that in the case of red meat, 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. 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.

In case of processed meant, 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.

While processed meat has been classified as carcinogenic to humans under Group 1 – the same group wherein tobacco
smoking and asbestos are also both present – IARC notes that this does NOT mean that they are all equally dangerous. The IARC classifications describe the strength of the scientific evidence about an agent being a cause of cancer, rather than assessing the level of risk.

As far as the types of cancers are concerned, red meat has been associated with colorectal cancer as well as pancreatic cancer and prostate cancer, based on the strongest, but still limited, evidence. 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.

The IARC cites the most recent estimates by the Global Burden of Disease Project, an independent academic research organization, and note that about 34,000 cancer deaths per year worldwide are attributable to diets high in processed meat. Eating red meat has not yet been established as a cause of cancer. However, if the reported associations were proven to be causal, the Global Burden of Disease Project has estimated that diets high in red meat could be responsible for 50 000 cancer deaths per year worldwide. These numbers contrast with about 1 million cancer deaths per year globally due to tobacco smoking, 600,000 per year due to alcohol consumption, and more than 200,000 per year due to air pollution.

The IARC, citing health benefits listed by 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. The risk increases with the amount of meat consumed, but the data available for evaluation
did not permit a conclusion about whether a safe level exists.