Red meat increases your risk of dying, red meat is as bad as smoking, red meat causes heart disease, red meat causes cancer. These are the type of headlines that get all the attention over the years for reasons I cannot understand other than the fact that controversy generates views. Other reasons seem to fall to factors like biased scientific funding, political motives, corporate motives, and many other things that I am not an expert in. Regardless, the result is that the science and media coverage of this topic makes things very confusing for the general public. Whether or not someone eats meat is an individual choice that I support either way. However, we all have a right to accurate and complete information so we can make properly informed choices. That is what this series of articles is about.
 
There are many people out there who are vegetarian or vegan for no other reason than the fact that they believe it is their healthiest option because that is the message they get from the media, friends, and many healthcare professionals. Regrettably, most people do not have the time to do the research necessary to find out that this belief is not true. The information on this topic can be complicated but the bottom line is the science is far from conclusive.
 
In this article, I will try to unpack the different lines of evidence used to demonize red meat and make it as simple and understandable as possible. I will not be discussing the ethical or environmental considerations of meat consumption; there are many more qualified people out there to do that.
 
Red Meat and the World Health Organization
 
Around 2015, the World Health Organisation’s International Agency for Research on Cancer classified red meat as group 2A, meaning they believe it is probably carcinogenic to humans. However, the report specifically states that “There is limited evidence in humans for the carcinogenicity of the consumption of red meat” but then goes on to say “Positive associations have been observed between consumption of red meat and cancers of the colorectum, pancreas, and prostate.” Given that the report admits there is limited evidence that red meat causes cancer in humans, why is it classified as “probably carcinogenic” and why does the media so often say it “is” carcinogenic? The scientists labeling red meat as probably carcinogenic aren’t even convinced; no wonder the general public is confused.
 
Now let’s have a look at some of the current science and dive into why many scientists don’t agree with the belief that red meat is bad for our health.
 
Understanding Relative Risk
 
Before going any further, understanding how risk is reported is very important. I am not a statistician, but here is my best explanation of relative and absolute risk. When you see headlines like “an extra serving of meat increases the risk of cancer by 18 percent” (otherwise written as 1.18) it is an example of relative risk. Obviously, 18 percent doesn’t sound unimportant when you see it; however, reporting findings in this way appears to enhance the impact. Hypothetically, let say the risk of cancer in a vegetarian population is 2 out of 100 people. Next, let’s say the risk of cancer in those who eat meat is 18 percent (1.18) higher than the vegetarian population. Although the relative increase in risk is 18 percent, the absolute increase is 2 x 1.18 = 2.36. An 18 percent increased risk sounds much worse than an increase from 2 in 100 people to 2.36 in 100 people.
 
Another consideration is that in other areas of epidemiology, for a relationship to be considered possibly causal (one thing causes the other), the relative risk must be at least 100 percent, more commonly 300 percent or higher. Going back to the above example, instead of 1.18, we would be looking at somewhere between 2 and 3. However, for some reason, in nutritional epidemiology, articles that report relative risks of much less than 100 percent are taken to support a causal relationship even though with relative risks that low, the results cannot truly be separated from chance.
 
Epidemiological Studies on Red Meat
 
Although many epidemiological studies report an increased risk of cancer/disease with increased meat consumption, the results are not without significant criticism. The relative cancer risk reported in most studies is well below the 100 percent requirement for a causal relationship and many studies have methodology issues including small sample size, not separating fresh red meat from processed meat, and not controlling for sufficient variables.
 
Meta-analysis studies are studies that take the results of multiple individual studies on the same topic and combine the data into a single study, creating a larger sample size. A more recent meta-analysis looked at 27 individual studies since 1994 and determined that the relative risk of colon cancer equated to only 11 percent (remember we need at least 100 percent to even think about considering a causal relationship). Furthermore, when this study only included individual studies that specified fresh red meat, the relative risk dropped to only 5 percent.
 
Additionally, study quality is consistently brought into question with epidemiological studies on red meat. Study quality can be impacted by controllable and uncontrollable factors. Earlier studies appear to show a higher relative risk of cancer than more recent studies and this is thought to be due to better study design in more current research. This would include more comprehensive food questionnaires, properly controlling for processed versus fresh red meat, and including controls for other confounding lifestyle factors.
 
Another issue is researcher bias and conflicts of interest. Because the results of these studies are based on calculations from the data in the food questionnaires, it is quite easy for bias and conflict of interest to influence how the questionnaires are interpreted.
 
Finally, because there are so many diet and lifestyle factors that can impact our health, it is near impossible for a study to control for every factor aside from red meat intake. In health studies, this problem goes by the name of the healthy user bias. Since not eating meat is considered healthy, vegetarians and vegans are much more likely to be otherwise health-conscious while those who eat meat are much less likely to be health-conscious.
 
A few studies have tried to address the healthy user bias by isolating health-conscious omnivores and comparing them to vegetarians, the results of which show no difference between the two groups and both groups are healthier than the general population. Ultimately, because of the high probability of confounding factors and the low relative risks that are consistently reported, it should be considered quite an embellishment to conclude that red meat causes cancer.
 
The above is just the criticisms regarding red meat and cancer, but the connection between red meat and heart disease is just as controversial and criticized for the same reasons. Such factors include low to nonexistent relative risks, lack of food questionnaire detail, food questionnaire inconsistency, food questionnaire interpretation, and inability to control for all health-related variables making the healthy user bias a major limiting factor.
 
Mechanistic Evidence
 
Now that we have discussed the issues with epidemiological studies and that relative risk reports do not really indicate red meat is a cause for concern, let’s look and what’s called mechanistic evidence. Typically, when it is determined via epidemiological studies that factor A is a likely cause of factor B, studies begin to look at possible mechanisms for how A might cause B. Since the epidemiological evidence on red meat is far from conclusive, you would think that there would be limited to no investigation into mechanisms for why red meat may be detrimental to our health; however, this is not the case. There are several suggested mechanisms for why red meat might cause cancer and be otherwise detrimental to our health including saturated fat content, polycyclic aromatic hydrocarbons, heterocyclic amines, TMAO, mTOR activation, and heme iron content.
 
The second article in this series will focus on revealing why the above mechanistic lines of evidence against red meat are also far from conclusive and discuss the nutrients meat provides that are either impossible or difficult to get from other foods.