What 6 Australian scientists say about 'processed meat causes cancer' claims

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The World Health Organisation’s International Agency for Research on Cancer (IARC) has released the findings of a major review of previous studies into the links between red and processed meats and cancer, concluding that processed meats are carcinogenic, and the alarming headlines have a lot of people freaking out.

Even Australia’s incoming chief scientist has been talking about it.

To get more of an understanding on the matter, here’s what six Australian nutrition and health experts think about the WHO’s latest report.

1. Dr Trevor Lockett, research scientist at CSIRO’s food and nutrition flagship.

Bowel cancer is a complex disease. In Australia, the risk of being diagnosed with bowel cancer by the age of 85 is around 1 in 10 for males and 1 in 15 for females. As people age their risk of developing bowel cancer increases rapidly after age 50 years. Diet and lifestyle factors also impact on bowel cancer risk: Obesity and sedentary lifestyles are significant risk factors.

Numerous epidemiological studies have investigated the impact of dietary factors on risk of colorectal cancer. A summary of a new meta-analysis, published yesterday in the Lancet, suggested that consumption of high levels of red meat probably causes bowel cancer, really meaning that a positive association has been observed between high level consumption of red meat and cancer but that other explanations for the observations could not be ruled out but there was convincing mechanistic research to support the claim, while for processed meat (meat that has been treated to enhance flavour or preservation by salting, curing, fermenting and smoking, e.g. hot dogs (frankfurters), ham, sausages, corned beef, and biltong or beef jerky as well as canned meat), there was sufficient evidence in humans to conclude that the consumption of processed meat causes colorectal cancer.

A proper commentary will only be possible once the full paper detailing the study has been published, but assuming the results are correct what might this mean for us?

For processed meat it has been estimated that for every 50 g portion of processed meat one ate every day of one’s life, one’s risk of developing bowel cancer at some stage in one’s life would increase by about 18% for every 50 gram portion of processed meat consumed daily. For red meat the numbers are estimated to be 17% per 100g serving of red meat consumed daily throughout life.

At the level of the individual, these effects are quite small but they can have significant impact at a whole of population level where a high proportion of people are consuming high levels of these products daily.

But red meat is a valuable source, not only of protein but also micronutrients such as iron, zinc and vitamin B12 so how do we balance the risks against the benefits? The most recent Dietary Guidelines for Australians recommend that, over a week, no more than 7 serves (1 serve = 65g cooked or 100g raw weight) of lean red meat should be consumed.

Within this envelope the benefits of red meat should balance the risks. Further while large daily intakes of processed meats may not be recommended their occasional consumption should probably also be acceptable but the results of this study will help us reassess our current national recommendations

The devil, however, will be in the detail and we still await the publication of the full study. Key will be understanding the extent to which bowel cancer risk-reducing dietary components such as dietary fibre content of the diets and potential cofounding cancer risk factors such as overweight, obesity, alcohol consumption and sedentary lifestyle have been accommodated in the analyses.”

Conflicts of Interest: CSIRO has the total wellbeing diet series of books. We have research suggesting that dietary fibre can reduce DNA damage induced in the colons of animals and humans associated with high dietary intakes of red meat.

2. Kathy Chapman, chair of the Nutrition and Physical Activity Committee at Cancer Council Australia.

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.

3. Professor Bernard Stewart, conjoint professor with the School of Women’s and Children’s Health at the University of New South Wales and chief scientific advisor for the Cancer Council Australia. He also chaired the committee which conducted the review for WHO’s International Agency for Research on Cancer, and was the single Australian involved in the review.

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.

4. Dr Rosemary Stanton OAM, nutritionist and visiting fellow at the School of Medical Sciences, University of New South Wales.

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 recommended 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 extensive analysis from WHO’s expert group confirms the message of the Australian guidelines – to limit consumption of red meat.

The guidelines also moved processed meats out of the basic food groups to the list of ‘discretionary’ foods. These foods are not essential 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.

5. Dr Christina Pollard, nutrition policy advisor at Curtin University and a fellow of the World Cancer Research Fund International.

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.

*Equivalents the minimum number of serves of lean meats, poultry, fish, eggs, tofu, nuts and seeds and legumes per day.

6. Professor Mark L Wahlqvist, visiting professor at the National Health Research Institute in Taiwan and Zhejiang University in China and emeritus professor at Monash University.

As important as the IARC findings are, we must now be more prudent, sparing and equitable in the use of meat and meat products to be consistent with the new UN Global Goals and the increasing need for food security with climate change.

This list of opinions was compiled by The Australian Science Media Centre.

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