Science Media Centre

Science Media Centre

Posted in Science Alert: Experts Respond

Get RSS of
Science Alert: Experts Respond

WHO report: Red meat linked to cancer – Expert reaction

Posted in Science Alert: Experts Respond on October 27th, 2015.

The International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organization, has evaluated the links between the consumption of red and processed meat, and cancer.

Screen Shot 2015-10-27 at 8.25.22 AMThe group has classified the consumption of red meat as probably carcinogenic to humans (Group 2A). This association was observed mainly for colorectal cancer, but associations were also seen for pancreatic cancer and prostate cancer.

The group classified processed meat as carcinogenic to humans (Group 1), based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.

For those journalists with a login, the press release, report and any associated materials are available on Scimex.

Cancer Research UK has provided a good summary of the classifications, placing the current IARC review in  context.

Feel free to use these quotes in your stories.  Any further comments will be posted on the SMC website and on Scimex. We will be gathering reaction from New Zealand-based experts today. Contact the SMC to speak to an expert.

Dr Barbara Thomson, independent consultant and registered nutritionist, comments:

“It was a “majority”conclusion, not a consensus so there was some disagreement between the experts at the IARC meeting.

“Half of the studies assessed showed a positive association between red meat consumption and CRC. Therefore half did NOT show an association. Two thirds of the studies assessed showed a positive association between processed meat consumption and CRC. Therefore one third did not.

“We do not eat single foods in isolation. How well did the authors of this evidence allow for potential confounding factors (fruit and vegetable, poultry, fish and alcohol consumption, cooking methods, obesity and exercise?)

“Increased cancer risk is low (17 and 18%). Therefore other lifestyle factors (above) are likely to be as, if not more, important for reducing cancer risk. The benefits of red meat consumption (protein and micronutrients) need to be considered alongside this small increased cancer risk.

“The potential cancer mechanisms [suggested in the review] are not compelling: cooking methods apply also to poultry and fish; we get more nitrite from vegetables than from processed meat (and vegetables are good for us); poultry and fish also contain haem, albeit at lower levels than red meat – if haem is implicated, does this cancer mechanism apply also to fish and poultry?”

Declared interests: Dr Thomson has been contracted by Beef + Lamb NZ as an independent expert.

Prof Thomas Lumley, Professor of Biostatistics, University of Auckland, comments:

“The International Agency for Research on Cancer (IARC) has declared processed meat a Group 1 carcinogen and red meat (their definition includes pork) as a Group 2A carcinogen. These are not based on new evidence and are not surprising findings; scientists have believed for a long time that some smoked, salted, or cured meats increase the risk of colorectal cancer and that higher meat consumption probably increases risk to some extent.

“IARC’s press release confirms that the risk increase (about 1.2 times higher for one daily portion of processed meat) is small from an individual point of view, but that the large number of people who eat meat means that it has a noticeable public health impact. Cancer Research UK estimates that 21% of bowel cancers and 3% of all cancers could be prevented if no-one ate any red meat or processed meat.

“Some of the publicity for the new classification has tried to link the risk of cancer from processed meat to the risk of cancer from other Group 1 carcinogens.  There is no justification for this. IARC classifications are based only on the strength of evidence for an effect at some (not necessarily realistic) dose; they do not consider the size of effect.

“Group 1 carcinogens are those where IARC believes the cancer hazard is well-established, regardless of its strength. Group 1 includes asbestos, tobacco, and plutonium, but it also includes sunlight, oral contraceptives, and alcohol.

“The only mention of other Group 1 carcinogens in the new IARC announcement is an explicit disclaimer in their Q&A, saying the classification does NOT mean that they are all equally dangerous. Bringing up other Group 1 carcinogens when explaining the cancer risks of meat consumption does not seem helpful for public understanding.”

Prof Lynnette Ferguson, Professor of Nutrition, Auckland Cancer Society Research Centre, University of Auckland, comments:

“In terms of New Zealand, the evidence is that bowel cancer is more common among people who eat a large amount of red and processed meat. It is also true that bowel cancer is common in New Zealand. Whether or not it’s the meat that is causing the cancer or if it is happening in the context of something thing else – we can’t judge

“The point about meat and the evidence they have built up is that really it is very much a matter of balance. Yes, if you eat nothing but a plate of red or processed meat regularly with very little fruits vegetables etc., then yes there is no question that there is a high risk.

“But in terms of perspective, I think the evidence is there that meat provides an important part of the diet – it’s really important to think about the whole diet and not just one part of it.

“It is not like cigarette smoking where there is no question that taking up cigarette smoking is dangerous. There is no question that eating a solidly red and processed meat diet is dangerous – but that’s not the way people eat. It isn’t really in the same category and I think that is one of the misunderstandings that is coming out.

“Meat consumption is predominantly associated with bowel cancer but there is also some evidence for stomach and pancreatic cancers – however this is less clear than the link to bowel cancer.

“Given the high incidence of bowel cancer in New Zealand, this is something of which we need to be conscious.”

Statement from Fiona Grieg, on behalf of both the NZ Meat Processors Association and Beef + Lamb New Zealand:

“We acknowledge the announcement of IARC classification, but this needs to be put into perspective and context for New Zealanders.

“Firstly, the classifications are consensus statements based on existing published research, not new evidence, which we understand the association between both red and processed meat to be weak and inconsistent, without a causal relationship.

“In addition, the evaluation was a hazard analysis, therefore the numerous nutritional benefits of eating meat have not been factored in. These include quality protein and highly bioavailable iron and zinc, all essential throughout 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.

“IARC’s findings suggest that eating 50g/day of processed meat results in a small increase in cancer risk, however New Zealanders are eating under half of this at 22g/day.

“In regards to red meat consumption, the findings suggested a 17% increased risk with every 100g/day eaten. According to national nutrition survey data, we eat an average 41g/day beef and 9g/day lamb, therefore people would have to eat over double their current levels to increase cancer risk.

“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. These factors include maintaining a healthy body weight, regular physical activity, not smoking and avoiding high consumption of alcohol.

“Therefore, as part of an active, healthy lifestyle, moderate amounts of lean red meat and processed meat can be continued 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 dietitian or registered nutritionist.”

From the Australian Science Media Centre:

Kathy Chapman, Chair in Nutrition and Physical Activity Committee, Cancer Council Australia, comments:

“The new WHO analysis on red and processed meat and cancer risk is consistent with research commissioned by Cancer Council Australia that was released earlier this month. The study found that 2600 bowel cancer cases each year could be attributed to excess red and processed meat consumption.

“The National Health and Medical Research Council’s current dietary guidelines recommends consuming no more than 65 to 100 grams of cooked red meat, three-to-four times a week. Cancer Council recommends staying within this guideline but we don’t encourage avoiding red meat altogether – lean red meat is a good source of iron, zinc, vitamin B12 and protein.”

“Processed meats, however, are nutrient poor by comparison and more likely to be high in fat, salt and nitrates. This is why we recommend reducing or limiting processed meat intake.

“It’s also important to put the cancer risks associated with red and processed meat into context in terms of other preventable cancer causes. While Cancer Council’s recent research found that red and processed meat accounted for around 2600 cancer cases each year, 11,500 cancer cases each year are caused by tobacco, 3,900 cancer cases are attributable to obesity and overweight and 3,200 are attributable to alcohol. An overall healthy lifestyle, including diet, is important to reduce your cancer risk.”

Professor Bernard Stewart is Conjoint Professor with the School of Women’s & Children’s Health at the University of New South Wales and Chief Scientific Advisor for the Cancer Council Australia. He chaired the committee which conducted the review for WHO’s International Agency for Research on Cancer. He was the single Australian involved in the review. He comments:

“No-one’s proposing that we ban bacon, put warnings on hot dogs or take beef off the barbie. But this WHO review provides compelling evidence that the long-term consumption of red meat and/or processed meat increases your risk of cancer.

“This report is based on the evidence contained within 1,000 previous studies looking at this topic. So it is one of the most complex assessments of the medical and scientific literature ever undertaken concerning a particular cancer risk.

“The findings provide a new degree of certainty for health authorities who produce evidence-based dietary guidelines.”

Dr Rosemary Stanton OAM is a Nutritionist and Visiting Fellow at the School of Medical Sciences, University of New South Wales. She was a member of the NHMRC’s Dietary Guidelines Working Committee. She comments:

“No one doubts that red meat is a nutritious food. Nor is there any nutritional reason to remove it from the diet. However, in view of the World Cancer Research Fund’s evidence of a convincing relationship between red and processed meat and colorectal cancer, and the results of studies on red meat and cardiovascular disease, the Australian Dietary Guidelines recommend limiting fresh red meat to approximately 450g a week. This is well below the average consumption of 700g of red meat* reported recently by Australian men. (*This figure does not include poultry or fish)

“The guidelines also moved processed meats moved out of the basic food groups to the list of ‘discretionary’ foods. These foods that have no essential role in a healthy diet and should either be omitted or consumed only occasionally or in small quantities. Those who are overweight and those who are small and inactive have no room for discretionary foods.”

Dr Christina Pollard, Nutrition Policy Advisor at Curtin University and a Fellow of the World Cancer Research Fund International, comments:

“The IARC assessment are a hazard analysis, answering the question “is there evidence that substance(agent), in this case meat, is carcinogenic (capable of causing) cancer in humans?” ranking from Group 1 “carcinogenic to humans” to Group 5 “probably not carcinogenic to humans”.

“Group 1 means convincing evidence that the agent causes cancer in humans.  Evidence shows development of cancer in exposed humans and also strong evidence in experimental animal research.

“Group 2 agents have varying evidence of carcinogenicity in humans and experimental animals.

“Group 2A means the agent is probably carcinogenic to humans (limited evidence of carcinogenicity in humans (positive association, but cannot rule out confounders) and sufficient in experimental animals.)

“You cannot compare agents in the same group because the risk associated with exposure is not part of the assessment.

“Group 1 agents are all hazards, they are capable of causing cancer, but the risk may be different due to different levels of exposure across the population.

“What do cancer findings mean for Australian population health dietary recommendations?

“The risk associated with meat (red meat and processed meat) consumption in the Australian diet was reviewed for the 2013 Australian Dietary Guidelines.

“The risk of cancer and other chronic disease as well as beneficial contributions of foods in the overall diet was considered (for meat protein-rich and an important source of iron, zinc).

“Due to risk of colorectal cancer,  Australian guidelines do not recommend processed and cured meats and recommendation to limit intake of lean meat or equivalents *to a maximum of 455grams per week of per week (one serve of 65grams of cooked lean red meat a day) for adults.

“Mean daily intake of meat was greater than recommended for men, and the guidelines suggested eating 20% less on average.”

From the UK Science Media Centre:

Prof Kevin McConway, Professor of Applied Statistics, The Open University, comments:

“The key thing about this 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. 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 non-smokers in the UK, around 1 will get lung cancer. For 100 smokers of a pack a day, more than 20 will get lung cancer. That’s a huge increase in risk. Again in the UK, about 6 people in every 100 will get bowel cancer in their lives. According to the IARC data, if these 100 people in the UK start eating an extra 50g of processed meat a day, then 7 of them will get bowel cancer.

“OK, an increase, but only one more death and that’s nothing like the effect of cigarette smoking. So why are smoking and processed meat eating both in the same IARC group? Just because in both cases IARC is convinced that the evidence of some kind of effect, big or small, is quite strong. There are plenty of other agents in IARC Group 1 besides smoking and processed meat eating. Many of them are chemicals that most people (including me) won’t have heard of, but others are more familiar, such as burning coal at home, or working as a painter. Some of these have a big effect on risk, others don’t.

“Likewise, IARC have put eating non-processed red meat into their Group 2A, which means that they are considered “Probably carcinogenic to humans”. But all that means is that the evidence they cause cancer is a bit weaker than for the things in Group 1. Again Group 2A contains a huge range of things, for which, if they do actually cause cancer, the increased risk might be big or it might be quite small. The group contains some scary-sounding things like glyphosate weedkiller, but plenty of others, including some kinds of shiftworking, or working as a hairdresser or barber, are familiar. Again you have to remember that the increased risk may be small, and in fact IARC do not consider that there is decisive evidence that there is an increased risk at all (or they’d have put it in Group 1).

“In an important sense there’s really nothing new in this announcement. No new evidence has been collected – instead IARC have collated existing evidence and come to a decision on how strong that evidence is. And they have not yet published the detailed monograph that describes their findings, just a set of summaries. IARC make it explicitly clear anyway that they are not making recommendations on what we should eat. Others have already made such recommendations, based on the evidence that IARC have reviewed. This latest news has not, in itself, changed anything.”

Dr Gunter Kuhnle, a food nutrition scientist at the University of Reading, comments:

“The WHO’s decision means that there is sufficient evidence that processed meat consumption causes cancer – it does not mean, as purported by many stories 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 per day increases the risk of lung cancer six-fold (600%) – eating 50g of processed meat increases the risk of colorectal cancer by 20%. This is still very 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.

“The evidence is overwhelming: data from a wide range of studies, both observational and experimental, show that processed meat intake increases risk markers and risk of colorectal cancer. The criticism that correlation does not imply causation, and therefore the conclusions by IARC are flawed, overlooks that the classification is not merely based on observational but also experimental data. The evidence is less clear for red meat and therefore it is considered to be only probably carcinogenic to humans.

“So how does processed meat cause cancer? Most processed meat is cured with curing salt, and the nitrite in curing salt can cause the formation of nitrosamines in the intestinal tracts. Many nitrosamines are carcinogenic compounds as they can react with DNA and eventually cause tumours to form. The evidence available shows that this happens: nitrosamines are found in the intestinal tract. Moreover, nitrosamines induce a specific mutation pattern which is found in many colorectal tumours.

“What does this mean? As with most food-related stories, there will be probably be a short term impact on consumption. In the longer term, it is important to address these findings and mitigate the risks, for example by updating dietary advice or developing new meat products. The meat processing industry is already involved in a large EU funded project to develop new meat products.”

Prof Sir David Spiegelhalter, Winton Professor of the Public Understanding of Risk, University of Cambridge, comments:

“There may be good evidence for there being an increased risk, but the magnitude needs to be put into perspective.  In the normal run of things, around 6 in every 100 people would be expected to get bowel cancer in their lifetime.  If all these 100 people ate a three-rasher (around 50g) bacon sandwich every single day of their lives, then according to this report we would expect that 18% more would get bowel cancer – which is a rise from 6 cases to 7 cases. So that’s one extra case of bowel cancer in all those 100 lifetime bacon-eaters.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, comments:

“The IARC classification seems to be falling in line with the WHO and World Cancer Research Fund on strength of evidence – that is, convincing and probable – as those on which to take action. However, these do not take into account effect size of the risk. Generally for colorectal cancer, where the data is more consistent than other sites of cancer, the relative risks are small – 1.1 to 1.3.  This is in contrast to the large variation in colorectal cancer between different countries.

“The comparison on which evidence is based is for high versus low categories of consumption. Studies of vegetarians who eat no meat do not show consistently lower incidence rates of colorectal cancer, and in the case of the UK vegetarians, a higher rate was noted in the Oxford cohort compared to meat-eaters.

“The definition of red meat generally includes beef, lamb and pork. Processed meats include burgers, sausages, salami and ham. Some of these processed meats are treated with nitrites and may contain nitrosamines, which are known carcinogens – however, nitrate/nitrite curing of meat prevents Clostridium botulinum bacterial growth in these products.

“There is no evidence to show saturated fat is linked to cancer risk. The evidence regarding salt is not so much about sodium chloride as nitrates/nitrites.

“Red meat is a good source of heme iron, which is better absorbed than plant sources.  It is also a good source of zinc and vitamin B12. Iron and zinc deficiency are major nutrient deficiencies of concern worldwide but you do not need to eat large amounts of meat to get what you need – say 30g/d would be sufficient.

“Generally dietary advice has been to reduce the intake of red meat to 1-2 times a week and to avoid fatty meat products as much as possible. Ham is not fatty but is salty.

“The problem with this issue is that food is not like tobacco – we have to eat something.”

Prof Tim Key, Cancer Research UK’s epidemiologist at the University of Oxford, comments:

“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.

“Eating a bacon bap every once in a while isn’t going to do much harm – having a healthy diet is all about moderation. Overall red and processed meat cause fewer cases of cancer in the UK than some other lifestyle factors. And by far the biggest risk to your health is smoking – causing over a quarter of cancer deaths in the UK and nearly one in five cancer cases.”

Dr Ian Johnson, nutrition researcher and Emeritus Fellow, Institute of Food Research, comments:

“IARC has concluded that the evidence in favour of an association between processed meat consumption and cancer, probably because of the ingredients used in processing, meets their criteria for placing this class of foods on the list of recognised human carcinogens. It is important to emphasise however that this classification reflects the strength of the evidence for an effect, not the actual size of the risk.

“Meat consumption is probably one of many factors contributing to the high rates of bowel cancer seen in America, Western Europe and Australia, but the mechanism is poorly understood, and the effect is much smaller than, for example, that of cigarette smoking on the risk of lung cancer.  It is also worth noting that there is little or no evidence that vegetarians in the UK have a lower risk of bowel cancer than meat-eaters.”

* http://www.iarc.fr/en/media-centre/pr/2015/pdfs/pr240_E.pdf

? ‘Carcinogenicity of consumption of red and processed meat’ by Véronique Bouvard et al. was published in the Lancet Oncologyon Monday 26 October 2015. 

Declared interests

Prof Kevin McConway: “I have no relevant interests to declare.”

Dr Gunter Kuhnle: IARC used Gunter’s research and he is a Member of Council, Nutrition Society.

Prof Sir David Spiegelhalter declares that he has no conflicts of interest.

Prof Tom Sanders: “I was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain. I have previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and I am a member of the Programme Advisory Committee of the Malaysian Palm Oil Board. In the past I have acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC. My research on fats was funded by Public Health England/Food Standards Agency.”

Dr Ian Johnson: “I have no conflicts of interest.”

None others received.

 

 

Comments from the Australian SMC:

 

 

Print Friendly
Copyright 2016 Science Media Centre (New Zealand)

Disclaimer | Privacy Policy