Global health experts have found that processed meat such as hot dogs, ham and sausages can cause bowel cancer
Red meat is also “probably” carcinogenic, with associations mainly with bowel cancer, but also with pancreatic cancer and prostate cancer, according to a World Health Organisation (WHO) report. The International Agency for Research on Cancer (IARC), the cancer agency of the WHO, said: “Processed meat was classified as carcinogenic to humans, based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.”
Experts found that each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer, also known as bowel cancer, by 18%.
Processed meat refers to meat that has been transformed through 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 beef jerky as well as canned meat and meat-based preparations and sauces.
The 22 experts from 10 countries, convened by the IARC Monographs Programme, classified the consumption of red meat as “probably carcinogenic to humans”, based on limited evidence that the consumption of red meat causes cancer in humans and “strong mechanistic evidence supporting a carcinogenic effect”.
Dr Kurt Straif, head of the IARC Monographs Programme, said: “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.
“In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”
Dr Christopher Wild, director of IARC, said: “These findings further support current public health recommendations to limit intake of meat. “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, in order to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations.” The IARC 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.
Consumption rates matter
The consumption of meat varies greatly between countries, from a few per cent to up to 100% of people eating red meat, and somewhat lower proportions eating processed meat, the report said.
The classification given to processed meat – ‘’carcinogenic to humans’’ – is the highest of five possible rankings, shared with alcohol, asbestos, arsenic and cigarettes.
The World Cancer Research Fund (WCRF) has warned for several years that there is ‘’strong evidence’’ that consuming a lot of red meat can cause bowel cancer.
It also says there is “strong evidence” that processed meats – even in smaller quantities – increase cancer risk.
One possible reason is that the compound that gives red meat its colour, haem, may damage the lining of the bowel.
In addition, when meat is preserved by smoking, curing or salting, or by adding preservatives, cancer-causing substances – called carcinogens – can be formed.
Studies also show that people who eat a lot of red meat tend to eat fewer plant-based foods that protect against cancer.
The decision from the IARC, after a year of deliberations by international scientists, will be welcomed by cancer researchers but it triggered an immediate and furious response from the industry, and the scientists it funds, who rejected any comparison between cigarettes and meat.
“What we do know is that avoiding red meat in the diet is not a protective strategy against cancer,” said Robert Pickard, a member of the Meat Advisory Panel and emeritus professor of neurobiology at Cardiff University. “The top priorities for cancer prevention remain smoking cessation, maintenance of normal body weight and avoidance of high alcohol intakes.”
Prof Tim Key, Cancer Research UK’s epidemiologist at the University of Oxford, said: “Cancer Research UK supports IARC’s decision that there’s strong enough evidence to classify processed meat as a cause of cancer, and red meat as a probable cause of cancer.
“We’ve known for some time about the probable link between red and processed meat and bowel cancer, which is backed by substantial evidence. “This decision doesn’t mean you need to stop eating any red and processed meat. But if you eat lots of it you may want to think about cutting down. You could try having fish for your dinner rather than sausages, or choosing to have a bean salad for lunch over a BLT.”
Dr Elizabeth Lund – an independent consultant in nutritional and gastrointestinal health, and a former research leader at the Institute of Food Research, who acknowledges she did some work for the meat industry in 2010 – said red meat was linked to about three extra cases of bowel cancer per 100,000 adults in developed countries.
“A much bigger risk factor is obesity and lack of exercise,” she said. “Overall, I feel that eating meat once a day combined with plenty of fruit, vegetables and cereal fibre, plus exercise and weight control, will allow for a low risk of colorectal cancer and a more balanced diet.”
Prof Ian Johnson, emeritus fellow at the Institute of Food Research, also said the effect was small. “It is certainly very inappropriate to suggest that any adverse effect of bacon and sausages on the risk of bowel cancer is comparable to the dangers of tobacco smoke, which is loaded with known chemical carcinogens and increases the risk of lung cancer in cigarette smokers by around twentyfold.”
Meat industry reacts
The North American Meat Institute said defining red meat as a cancer hazard defied common sense.
“It was clear, sitting in the IARC meeting, that many of the panellists were aiming for a specific result despite old, weak, inconsistent, self-reported intake data,” said Betsy Booren, the institute’s vice-president of scientific affairs. “They tortured the data to ensure a specific outcome.
“Red and processed meat are among 940 agents reviewed by the IARC and found to pose some level of theoretical ‘hazard’. Only one substance, a chemical in yoga pants, has been declared by the IARC not to cause cancer. “The IARC says you can enjoy your yoga class, but don’t breathe air (class 1 carcinogen), sit near a sun-filled window (class 1), apply aloe vera (class 2B) if you get a sunburn, drink wine or coffee (class 1 and class 2B), or eat grilled food (class 2A). And if you are a hairdresser or do shift work (both class 2A), you should seek a new career.”