I know I’m not the first one to touch on this, but I see this still being an issue with the rise of vegetarian and vegan diets. Not to say I have a beef (ha) with people who eat this way, but the claim that red or processed meat causes cancer is one rooted in poor reporting of data.
Here’s the story: In 2015, the World Health Organization (WHO) published a report on meat and its links to causing cancer. They categorized red meat as “probably carcinogenic to humans” and processed meat as “definitely carcinogenic to humans”¹. Sounds scary, right? Here’s the issue with this: the WHO doesn’t measure how dangerous something is or the level of risk the item in question has; it measures the strength of the evidence to indicate that it’s carcinogenic (cancer-causing). While that sounds like the same thing, it’s not. If the studies aren’t well-conducted or not measuring what you’re looking for, then the evidence may be strong, but it’s not accurate.
Before we go further, I want to clarify the difference between “red meat” and “processed meat”. The WHO defines red meat as “all mammalian muscle meat, including, beef, veal, pork, lamb, mutton, horse, and goat”¹. Basically, any meat you see in clear packages that looks fresh from the animal. Processed meat is “meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation”¹. Think of hot dogs or turkey and pastrami slices.
Study Designs and Confounding Variables
The issue with the body of evidence about meat and cancer is that a lot of it is from what are known as epidemiological studies. This study design attempts to find the source of a disease by following a specific population over a long period of time (years, decades, lifetime, etc.) and see what happens to them. Through this, they attempt to find trends or common habits and behaviors that a lot of the population does as a potential explanation for a disease or condition.
For example, epidemiological studies have found a strong correlation between smoking and lung cancer formation. Through a different type of study called mechanistic studies, they have discovered the chemicals in tobacco that lead to the lung cancer over time from consistent inhalation of cigarettes. Of course, not everyone who smokes will develop cancer though, so we cannot say with 100% certainty that smoking causes cancer. Epidemiological studies cannot prove anything, just find associations.
Back to meat, the problem with these types of studies and meat consumption is that there are so many other areas and functions of a person’s life that could contribute to cancer formation that these external factors could be driving the cancer formation instead of the meat itself. For example, wealthier countries typically consume more meat than poorer countries. Wealthier countries and individuals can also afford more cigarettes; what if someone was smoking and eating meat but the study only was measuring for meat consumption. Was it the cigarettes or the red meat? This is known as a confounding variable. It’s something that cannot be accounted for in a study that may influence the result.
My personal opinion is that there are many confounding variables that are likely contributing to cancer formation in people who eat meat than the actual consumption of meat itself (meat eaters may be more stressed, unhealthier, sedentary, etc.). So while there is a correlation between processed meat and cancer, there are still so many things that could contribute to it, it probably would serve you better to move around more and eat better than to cut out your occasional deli sandwich or sausage.
On the other hand, there have been some chemicals found in cooked meat that are carcinogenic, should we be concerned? Probably not and here’s why.
While the risk of red or processed meat and cancer risk has been quantified, the number is very misleading. On the Q&A page of the WHO website and in news outlets, you will see that you have an 18% risk of developing cancer if you eat processed (not red) meat daily. The nuance here is that 18% is a relative risk, not an absolute risk. What this means is that if your current risk of cancer without eating red or processed meat is 3%, then your risk of getting cancer moves up to 3.5% if you choose to eat red or processed meat daily. Why 3.5? Relative risk factors in the risk you already have and then multiplies that by the percentage of the new risk factor (18%). Here’s the actual math:
3% (expressed as a decimal is 0.03) x 18% (1.18 as a decimal because you’re adding the risk of 18% from the 3%, hence the 1 in front of the decimal)=3.5%. Try putting in your calculator 0.03 x 1.18.
So in theory, the risk of developing cancer from red or processed meat is very, very small. Almost insignificant. For that individual, the absolute risk of developing cancer from processed or red meat is 0.5% because their total risk of cancer increased by 0.5% after including the relative risk of 18%.
To clarify, the body of evidence for processed (not red meat) shows a strong link between daily consumption of processed meat and cancer risk, meaning that cancer-causing chemicals are most likely in these processed meat, but the risk of actually getting cancer from these chemicals is so small that there are many other things to worry about than the meat you’re eating. As for red meat, the evidence is not as clear as it is for processed meat. They think there could be a link, but confounding variables are still clouding the final decision. The following is a short concise list of a few more points I want to really hammer home quickly.
- People say processed meat is in the same category as smoking, so it should be just as bad. Again, this list only measures the strength of the evidence, not the magnitude of risk for the specific item. Smoking is very much more likely to lead to cancer than a hot dog is.
- The 18% risk that is so popular to throw around is accounting for processed meat consumption on a daily basis. Chances are you’re probably not eating processed meat every single day.
- There are may things in our lives that come with some sort of risk. And many things can cause cancer. What’s life without the things you enjoy? If you enjoy eating red or processed meat every now and then, freaking have it. If you’re afraid of getting cancer because you ate a slice of deli meat, your priorities are out of whack. My point here is there are many things that will kill you, cause cancer, etc. If you spend your whole life trying to avoid them, what kind of life are you living?
Should you cut out red and processed meat? Probably not, as you read, the risk of getting cancer from these foods is very slim (even more slim from unprocessed red meat). Conversely, could you benefit from reducing your intake? Yeah, most likely! There are plenty of sources of animal protein that are not red meats which are still tasty and nutritious along with plant-based protein sources that can be often even more nutrient-dense. Many people could probably live healthier lives if they lowered their meat consumption (but not completely eliminated it).
It just simply does not make sense to completely cut out red or processed meat from your diet if you’re worried about cancer; because chances are, you’re probably doing something else in your life that is contributing more to your cancer risk than some meat. Just enjoy your damn food and don’t eat too much of any one thing. Drop a line in the comments about your thoughts or favorite meat-based recipes! Below you can find some other resources if you want to do more reading for yourself.