My twitter feed went insane this morning following a news release from The Lancet about an article titled Carcinogenicity of consumption of red and processed meat. For anyone interested in toxicology, human health risk assessment or simply regular readers of the academic literature the Lancet article was nothing particularly new. Unfortunately, that group does not typically include the news media. For the news media the article appear to be ground-breaking news worthy of front pages and blaring headlines. Even some scientific news outlets got into the swing of things with Scientific American going farthest off the deep end with an initial headline that pronounced: Processed Meat Poses Same Cancer Risk as Smoking, Asbestos...apparently someone with half a lick of sense read the article and they quickly changed the headline to read: “Processed Meats Cause Cancer, World Health Organization Says”. As a blogger on topics of science communication, this is the sort of thing I write about all the time and so thought I could do a quick take to add some clarity to the mix.
Let’s start with the basics. It has been known for a long time that both the grilling of meat and the processing of meat increases its risk for human consumption. Reports to this effect have been coming out for years in general interest journals like PLOS (Public Library of Science) A Prospective Study of Red and Processed Meat Intake in Relation to Cancer Risk, to cancer journals like the International Journal of Cancer Meat consumption and risk of colorectal cancer: A meta-analysis of prospective studies to specialty journals like Meat Science: Red meat consumption: An overview of the risks and benefits.
To explain the toxicology, the grilling of meat has long been known to produce polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines both of which are associated with cancers. Similarly the processing of meat and the use of preservatives have been linked to human health risks for a very long time. Moreover, meat can be relatively challenging to digest so even non-grilled meat poses a challenge to the human gut. Vegans and vegetarians have been using this line of argument as a reason to stop eating meat for years as well as anyone who has ever visited a PETA web page knows.
So I suppose the question being asked today is: what is so new about this report? The answer is that after all this time the International Agency for Research on Cancer (IARC) finally decided to get into the mix. As I have discussed previously in a post titled On Wi-Fi in Schools and the Precautionary Principle the IARC has the job of assessing what is a carcinogen and what is a possible carcinogen. The thing to understand is that the IARC is only looking at carcinogenicity, it doesn’t ask the obvious next question which is whether the risk meets the standard of being really important. You will notice I did not use the word “significant”. The word significant is an often misused one in the scientific community and will be avoided in this discussion. The IARC is tasked with producing monographs evaluating carcinogenic risks to humans. Based on the Lancet summary (the IARC report is not out yet) the following conclusions were made:
Overall, the Working Group classified consumption of processed meat as “carcinogenic to humans” (Group 1) on the basis of sufficient evidence for colorectal cancer. Additionally, a positive association with the consumption of processed meat was found for stomach cancer. The Working Group classified consumption of red meat as “probably carcinogenic to humans” (Group 2A). In making this evaluation, the Working Group took into consideration all the relevant data, including the substantial epidemiological data showing a positive association between consumption of red meat and colorectal cancer and the strong mechanistic evidence.
The IARC the Group 2A designation (assigned to red meat) is often misunderstood. A Group 2A carcinogen means a compound that is “probably carcinogenic to humans”. This is a compound where but where “there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals”.
What the Lancet report also points out is that the increase in incidence of cancers is around 17% per 100 g a day of red meat. What it fails to tell you is what that means in the real world. Based on the Canada food guide 75 g of meat is a serving. In restaurants the serving size for a steak is typically in the 6 ounce range which is about 170 grams. So 100 ounces doesn’t seem like a lot, but put into a different perspective I do not know many people who eat 100 g of red meat a day 365 days a year. If you are like me you likely eat red meat once or twice a week as part of a healthy, varied diet.
That being said, colorectal cancer is the 3rd most commonly diagnosed cancer in Canada with a 5 year survival rate of around 64% -65%. The incidence of colorectal cancer is about 35.2 cases per 100,000 population. So 17% turns out to be about 6 cases per 100,000 so an increase by 17% is a non-trivial number.
What all these numbers fail to discuss is whether red meat has positive effects that could counter-weigh the negative. This is an important point that is very often missed in the rush to judgement after the publishing of a report of this kind. The Canadian food guide recommends red meat as part of a healthy diet because red meat provides a number of critical components for a healthy diet. Even the Canadian Cancer Society points out that red meat is a valuable source of several nutrients, in particular protein, iron, zinc and vitamin B12. Vegetarians are often warned of the importance of getting enough of these nutrients as well as critical fatty acids that are plentiful in red meat but are more difficult to obtain via a vegetarian diet.
The question not asked, nor answered by the IARC is how the typical person should read this report. As I note above, except for the true heavy duty carnivores the results of this study are not really that problematic. I think the best conclusion was presented by the authors of one of the peer-reviewed scientific article above:
moderate consumption of lean red meat as part of a balanced diet is unlikely to increase risk for CVD or colon cancer, but may positively influence nutrient intakes and fatty acid profiles, thereby impacting positively on long-term health.
Put more completely, meat, and red meat can be part of a good diet and the exclusion of meat from your diet should not be done without careful thought about how you will replace the essential nutrients you currently get from meat. You can live a healthy life eating meat and you can also live a healthy life while eating meat-free in moderation is the key. The other conclusion of this report is well-known to mothers across Canada, excess consumption of red meat, especially grilled red meat, is not good for you...but then we all knew that before the Lancet broadcast it to the world didn’t we?
Note for readers:
I have written a lot in the last year about how risk is communicated to the public. Unfortunately, due to the nature of my blogging platform (read free and simple since I am a chemist and not a web designer) it is not terribly easy to figure out what I have written in the past so I will summarize here. I prepared a series of posts to help me out in situations like this. The posts started with “How Big and Small Numbers Influence Science Communication Part 2: Understanding de minimis risk” which explained how the science of risk assessment establishes whether a compound is “toxic” and explained the importance of understanding dose/response relationships. It explained the concept of a de minimis risk. That is a risk that is negligible and too small to be of societal concern (ref). The series continued with “How Big and Small Numbers Influence Science Communication Part 3: Understanding "Acceptable" Risk” which, as the title suggests, explained how to determine whether a risk is “acceptable”. I then went on to explain how a risk assessment is actually carried out in “Big and Small Numbers in Science Communication Part 4: the Risk Assessment Process. I finished off the series by pointing out the danger of relying on anecdotes in a post titled: Risk Assessment Epilogue: Have a bad case of Anecdotes? Better call an Epidemiologist.