While there are many known nutritional benefits to eating red meat, there is a small increased risk linking high consumption of processed meat to bowel cancer and a probable – though not proven – lower risk from red meat, an international hazard analysis has decided.
The International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organisation, has evaluated the carcinogenicity of the consumption of red meat and processed meat.
The Working Group of 22 experts from 10 countries convened by IARC thoroughly reviewed the accumulated existing scientific literature – over 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.
In a released summary published in the Lancet medical magazine yesterday, the IARC group classified processed meat, meat that has been transformed by salting, curing, fermentation, smoking or other processes to enhance flavour or improve preservation, as carcinogenic to humans (Group 1), based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer. The experts concluded that each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18 percent.
The consumption of red meat was classified as probably carcinogenic to humans (Group 2A) based on limited evidence that the consumption of red meat causes cancer in humans and strong mechanistic evidence supporting a carcinogenic effect. The association was observed for colorectal cancer, but associations were also seen for pancreatic cancer and prostate cancer. For the purposes of the study, red meat meant all mammalian muscle meat including beef, veal, lamb, mutton, pork, horse and goat.
The consumption of meat varies greatly between countries, with from a few percent up to 100 percent of people eating red meat, depending on the country, and somewhat lower proportions eating processed meat.
“For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but the 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 in of public health importance.”
IARC director Dr Christopher Wild says the 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.”
Beef + Lamb NZ Inc nutrition manager Fiona Greig agrees, saying the valuation was a hazard analysis, so the numerous nutritional benefits have not been factored in. “These include quality protein and highly bioavailable iron and zinc, all essential through the life stages. Many New Zealanders are lacking in dietary iron, namely women and adolescent females, therefore careful consideration needs to be given with advice around nutrient-rich meat consumption.”
The key thing about the classification is that it is based solely on strength of evidence that there is some increase in risk and not on how much the risk increases, comments Professor Kevin McConway, professor of applied statistics for The Open University.
“There are well over 100 different agents in IARC’s ‘Group 1’. These are things where IARC thinks there is sufficient evidence that they really do increase cancer risk. But some may increase by a lot, some by a small amount.
“Of 100 lifetime smokers in the UK, around one will get cancer. For 100 smokers of one pack a day, more than 20 will get cancer. That’s a huge increase in risk. Again, in the UK, about six people in every 100 will get bowel cancer in their lives,” he says. “According to the IARC data, if these 100 people in the UK start eating an extra 50g of processed meats a day, then seven of them will get cancer.”
Dr Gunter Kuhnle, a food nutrition scientist at Britain’s University of Reading has also put the findings into context.
“The WHO’s decision means that there is sufficient evidence that processed meat consumption causes cancer – it does not mean, as purported by many cases in the media, that eating bacon is as bad as smoking. This is a dangerous oversimplification as processed meat can be part of a healthy lifestyle – smoking can’t.
“It is important to put these results into perspective, three cigarettes a day increases the risk of lung cancer six-fold (600 percent) – eating 50 g of processed meat increases the risk of colorectal cancer by under 20 percent. This is still relevant from a public health point of view as there are more than 30,000 new cases per year – but it should not be used for scaremongering.”
So, how much is enough?
The IARC experts suggest that eating 50 grammes per day of processed meat results in a small increase in cancer risk. However, Greig says that New Zealanders are eating under half of this at an average of 22g per day.
“In regards to red meat consumption, the findings suggest a 17 percent increased risk with every 100g per day eaten. According to national nutrition survey data, we eat an average of 41g per day beef and nine grammes per day of lamb, so people would have to eat over double their current levels to increase cancer risk,” she says.
According to Grieg, current New Zealand consumption fits within international guidelines of no more than 500g cooked (750g raw) per week. “Current Ministry of Health guidelines recommend lean red meat within one of the four food groups for good health.”
Method of cooking
There was not enough data for the IARC Working group to reach a conclusion about the way meat is cooked affects the risk of cancer. However, cooking at high temperatures or with the food in direct contact with flame or a hot surface as in barbecuing or pan-frying, has been found to produce more of certain types of carcinogenic chemicals, such as polycyclic aromatic hydrocarbons and heterocyclic aromatic amines.
Healthy lifestyle key
The causes of cancer are many and complex, with lifestyle factors playing more of an important role in reducing cancer risk than omitting single foods, comments Greig. “These factors include maintaining a healthy body weight, regular physicial activity, not smoking and avoiding high consumption of alcohol.
“Therefore as part of an active, heathy lifestyle, moderate amounts of lean red meat and processed meat can continue to be enjoyed as part of a balanced diet, with plenty of vegetables, fruits, wholegrain and other foods rich in fibre, which play a role in reducing cancer risk.
“We advise if anyone is concerned about their dietary habits and cancer risk, they should seek advice from a dietician or registered nutritionist.”
The IARC is considered the leading authority in cancer with a primary role to promote international research. Its findings will inform health guidelines around the world.
The summary of the final evaluations is available online in The Lancet Oncology and the detailed assessments will be published as Volume 114 of the IARC Monographs. See http://www.iarc.fr/index.php.