It is getting frustrating how many times I hear friends, family, peers, doctors, the media, health professionals, bloggers and vegetarians/vegans having a go at poor old red meat. Saying things like, “red meat causes cancer,” or “red meat causes heart disease.” It is not their fault; they just hear what is perpetuated throughout the media and are following conventional wisdom. It is natural for us to follow popular belief because if the majority believe something, then it must be true.
As I get older, I have come to realize that most of the time, you are better off observing what everyone else is doing and then proceeding to do the exact opposite. This normally rings very true with topics relating to nutrition and health. The popularity of a belief does not increase the validity of it. There are many diet and health myths that I address on this blog, however today, I will be focusing on red meat. Is it really as bad as people say it is?
Most of the myths that surround the unhealthy nature of red meat are due to the media misinterpreting research and then spreading it throughout society like wildfire. This is usually due to invested interests and headlines that will sell. This post will outline the inherent problems with a lot of research studies on meat and how they do not prove that red meat is actually bad for you.
Let’s dive in.
Correlation does not mean causation.
Firstly, the studies done on meat consumption and its links to certain diseases and health issues are epidemiological or observational studies. This means that they basically take a group of participants and observe their meat intake over a number of years and then see if they develop any diseases or die. Epidemiological and observational studies can only show correlations between variables. And as you might know, correlation DOES NOT mean causation. Take this for an example. In Florida, when ice cream sales increased, shark attacks also increased. Does this mean that because more people decided to buy ice cream it therefore directly caused more sharks attacks? No. These two variables are correlated because as one increases the other also increases. However, one cannot draw direct causation between these two variables.
Similarly, observational studies of meat consumption have drawn conclusions that red meat causes certain health issues because these two variables show a correlation in their studies. Firstly, this is not ethical and it is an abuse of science. Secondly, the reason why meat consumption is correlated with health issues is due to the influence of poor information gathering and other variables that are not controlled in observational studies. This is the nature of these types of studies, they can only show correlations, but no direct conclusions can be drawn because they do not control other variables that may affect the outcome of the research. Observational and epidemiological studies are a good starting place to help generate hypotheses that can further be investigated through controlled clinical trials, however they are not the final step in the process.
As you can see there, are inherent limitations of observational and epidemiological studies in that they cannot prove causation between two variables. Now lets examine the limitations of the data gathering techniques of these studies and its impact on the results.
Can you remember what you ate for dinner last week?
Researchers in these studies normally gather participant’s information about their meat consumption through food frequency questionnaires, 24 hour and seven day dietary recall questionnaires.
Food frequency questionnaires are usually used in retrospective correlational studies, which observe the present health of a group of people and relate it to records of what they ate in the past.
This is compared to 24 hour and seven day dietary recall questionnaires, which are usually utilised in cross sectional studies and prospective studies. Cross-sectional studies look at the present health of people and relate it to their current eating habits. Where as prospective studies choose a group of people in the present and track their food exposures, as well as health outcomes over a period of time.
In short, researchers observe what people eat/ate and relate it to what diseases or health issues they get/have.
Keeping track of or recalling what you eat can be inconvenient and imprecise. Can you remember how many times this past month you consumed a serving of green vegetables or red meat? I think you see my point. Herein lies the biggest limitation of observational nutrition studies: the inaccuracy of diet reporting. People underreport, exaggerate, forget, and even consciously omit what they eat.
Research has identified common reasons why food diaries and recalls can be so inaccurate:
- People overreport foods socially considered “good,” such as vegetables and fruits
- People may not know all the ingredients in restaurant or prepared foods
- People don’t weigh or otherwise measure portion sizes
- People find tracking every bite and meal inconvenient
- People are human and just can’t remember every little thing they eat
- People tend to underreport foods socially considered (due to the media) “bad,” like red meat and alcohol. What is interesting is that people who do this tend to be more unhealthy and are the ones more at risk of disease. This ultimately leads to false conclusions.
Numerous studies have in fact shown that obese individuals tend to underreport more than non-obese. In the OPEN study, researchers compared 24-hour recalls (24HR) and food-frequency questionnaires (FFQ) to doubly labeled water and urinary nitrogen, biomarkers for energy and protein intake, respectively. Both FFQ and 24HR were underreported compared to the biomarkers, with FFQ even lower than 24HR. Obese individuals tended to underreport more than non-obese.
Despite the shortcomings of the data, dietary advice and public policy rely almost solely on what people say they eat! As a result, nutritional studies have been met with heavy criticism. A recent article from the Mayo Clinic Proceedings claims that because nutrition studies “cannot be reliably, accurately, and independently observed, quantified, and confirmed or refuted,” they do not follow the scientific method and should be regarded as “pseudoscience” at best. I would have to agree. If these studies are to continue and hold more credibility, new ways of tracking food intake need to be done such as thermodynamic models, remote swallowing sensing devices, remote food photography devices and electronic devices to easily enter food intake.
Confounding variables of meat studies.
Now lets examine the significant confounding variables in these studies that are not accounted for, which in turn have a profound impact on the results of these studies, which is why they should be interpreted with caution.
Observational meat studies measure meat consumption as one variable and risk of disease and mortality as another variable. As mentioned before, many of these studies have shown a correlation between these two variables and there is a clear explanation for why. Let me explain…
Because these are observational studies, they do not control confounding variables. Red meat is commonly blamed for contributing to cancer (especially colon cancer) and heart disease, which are multifaceted, complex health issues that have many risk factors and contributing factors. However, these meat studies do not take these risk factors (variables) into consideration. Research shows that people who eat a lot of meat are more likely to smoke, exercise less, eat less fresh produce and generally have lifestyle habits that are all risk factors for developing heart disease and cancer, but the observational research does not control these confounding variables and are purely only looking at meat consumption. Also, these studies do not control stress of the participants and chronic stress has been linked to many health issues. Without controlling these variables there is no way to make a direct connection between meat consumption and these diseases.
Furthermore, some of the meat studies that usually look at meat consumption and risk of certain diseases, do not account for a confounding variable called the ‘healthy user bias.’ These observational studies usually compare meat eaters to vegetarians. The meat eaters end up showing higher rates of disease compared to the vegetarians, however this is due to the healthy user bias. Which means, due to their chosen lifestyle choices, vegetarians are probably more likely to engage in other healthy behaviours, which puts them at a lower risk for disease. As opposed to the meat eaters who were more likely to engage in other unhealthy behaviours which are risk factors for disease. This also provides fuel for vegetarians and vegans to claim that a diet free of dead flesh is healthier than one with. This is another topic for another post, which will definitely be on the way!
Now, this does not mean that we discredit all of epidemiological research because the confounding variables are hard to control. Like I said, it is a starting place to look deeper into a particular correlation and a correlation is then strengthened when potential mechanisms behind the correlation can be explained. As you can see in the case of red meat though, there are too many explainable variables that can skew the strength of the relationship between red meat and cancer. It is necessary to always have our critical thinking caps on when reviewing health claims. We must think about how the claims were reached.
What types of meat are the participants consuming?
Another variable that is not accounted for in these studies is that they normally do not take into consideration the quality of meat being eaten. When people report their red meat intake within these studies, the researchers do not differentiate between red meat on a pizza or in a pie, and grass fed steak. Meat consumed with refined carbohydrates and sauces, is very different to a good quality steak.
Furthermore, there are much bigger concerns to your health than red meat, such as smoking and alcohol. Red meat is a nutrient dense food that should be incorporated into a healthy diet. It is a good source of protein, healthy fats, along with vitamins and minerals such as B12, zinc and iron.
We treat individuals not populations.
While these studies do not provide conclusive evidence against red meat consumption, it is important to note that these studies are based on populations, and as a practitioner, I am treating individuals, not populations. Therefore, because these studies are based on averages, I know that for the majority of the population red meat is completely fine and beneficial for health. However, it is also important for me to remember that there may be certain minority groups that will not do well with a high red meat intake. For example, those who have a genetic condition called hemochromatosis, where they absorb excessive amounts of iron from the diet, causing high levels in the body, which can increase their risk of many diseases, including cancer.
Wrapping it up.
As you can see, there are some extreme limitations of these meat studies, which actually prove nothing. It is scary how shoddy research can be perpetuated by the media to society. This is not a joke, peoples health is at stake here and it really irks me how hard it is for the general person to find out what is actually good for them and what is actually not so good. I hope after reading this you may be more skeptical about conventional claims about red meat.
There has never been any research, which can draw a causative link between red meat and cancer. Nor has there ever been a study that has shown red meat causes heart disease, or increases your chances of mortality from all causes. This is because they are ALL epidemiological studies. It is simply not possible to find a causative link by performing Randomized Controlled Trials (RCT). It would be unethical and way to expensive. Think about it….
Researchers would have to lock up a group of people in a hospital who are similar in physical characteristics. The group would then be split into two and the only difference between them would have to be their red meat consumption. This means that whatever they eat, how much they eat, how much they exercise etc. would all have to be the same. It would also be necessary to control their stress levels, which would be very hard. Then you would observe them for 25 years, because that’s how long it takes for cancer to develop. As you can see that is not possible.
Therefore, we can only go on observational studies and as you would know, humans do not live in a vacuum. There are so many things in our world today that increase our risk of disease such as cancer. Because these variables cannot be controlled for, it is simply not possible to say that red meat causes such and such. And to reiterate, there have been numerous studies that show people who eat red meat tend to engage in lifestyle behaviours, which increase their risk of disease and death.
To wrap up, here is a meta analysis of 35 epidemiological studies that looked at the association of red meat to various health issues. The researchers of this meta analysis found that the associations drawn between red meat and various health issues like colon cancer were very weak. Furthermore, most of the studies results were not statistically significant, meaning that we cannot be sure if the results were due to chance or not.