Marcy McCall MacBain
The World Health Organization (WHO) and its International Agency for Research on Cancer (IARC) have issued evidence to categorise two types of meat as probably carcinogenic in humans. The full article appears in an online edition of The Lancet Oncology medical journal. For a brief Q&A on the topic, you can link here.
The media attention abounds, so let us take a closer look.
This report is a meta-analysis of prospective, cohort studies. This type of study, if designed and implemented to perfection, will provide us with correlational data. Causal interactions (statements such as X causes Y) would usually be the result of randomized controlled trial (RCT), or a meta-analysis of results from such studies. This is an important distinction for the reader of this, and other health reports. Important because while cancer may be associated with a high consumption of certain meats, the actual attribution of the human consumption of that meat is nearly impossible to extrapolate in these study conditions. Confounding factors, risk of bias and lack of controlled variables prohibit any certainty of causation in this case.
In dietary data collection, there is an added complication in using survey techniques. Consider this: do you always tell the truth when a health official asks you about what you had to eat the past few days? Or can you even remember what you ate, and how many grams of it you ate for dinner last night? The conduct of nutritional-related studies using participant recall surveys have been criticised for their invalid data collection methods. Read more here about why some people feel these kinds of studies are an entire waste of time and resources.
The WHO/IARC working group reviewed 800 prospective, cohort studies to determine their results. Thirty-three of these 800 studies were used to determine the risk of colon cancer attributed to dietary intake of processed meat or red meat. The report states:
Of the 15 informative case-control studies considered, seven reported positive associations of colorectal cancer with high versus low consumption of red meat. Positive associations of colorectal cancer with consumption of processed meat were reported in 12 of the 18 cohort studies that provided relevant data (Bouvard et al., 2015).
The most curious incident in the paper, the authors then proceed to report quantitative data from a meta-analysis of ten cohort studies, but provide only one academic reference. In taking a look at that one academic reference, it is verbatim the results form an earlier study conducted in 2011 by Chan and colleagues from the United Kingdom. Turns out the relative risks reported in this ‘new’ study are not really all that new. T
In spite of some obvious shortcomings to the data collection and analysis, thank you, IARC and WHO – for putting our dietary choices back on the health agenda!
What is particularly interesting from a public health perspective, the report reminds us there could be a sizable reduction in cancer incidence if all of us eliminated processed meat. On a population level, this is an important result that warrants the press it has received.
My personal disclaimer before you read on: I’m a farmer’s daughter, raised most of my life on beef, pork, poultry and all sorts. Off the farm, I have experimented with periods of my life as a vegan, vegetarian, pescatarian and raw-foodist. At one time, I worked with as a food policy analyst the WHO to curb the obesity epidemic. Today, as a health care researcher interested in chronic disease prevention, I do advocate for healthy lifestyle choices. I especially wish we could all choose more fresh and organic vegetables, more of the time. And consume less sugar.
Now let’s get back to the WHO report.
Basically, the evidence suggests your individual risk of contracting colon cancer because you eat a lot of processed meat (i.e. 50g a day) is higher than your twin who does not eat it (assuming all other risk factors between you remains equal).
If you decide to drop processed meat from your diet, you will have less chance of contracting colon cancer in your lifetime – unless, of course, you replace your bacon with a cigarette. That would be an exponentially worse choice for your health.
So from the evidence-based playbook, you are called to assess your individual risk. What difference would the elimination of processed meat from your diet mean for your health? You will want to consider your own risk profile (i.e. genetics, other lifestyle factors) along with how much you value your meat versus a potential increase in cancer.
As for red meat, it has been classified as a 2a, with limited evidence to rule out confounding, bias or random effects in the research findings. Conclusions from this report suggest there is a positive correlation of red meat and cancer incidence, but there is too little evidence to quantify or confirm an additive risk.
Beyond the health care researcher’s perspective, let us take one brief moment to look from the eco-centric perspective.
In 2013, a landmark study by the National Academy of the United States of America exposed an over-dependency on animal products in the western diet. In particular, cows. Their results suggested our meat-oriented food choices were perhaps the greatest contributor to green house gas emissions and effectively, responsible for climate change. On balance, the less-red-meat argument might weigh more in a battle to preserve the health of our natural environment, rather than a direct link to human cancer rates.
In any case, it might be time to re-think your meat.