I'm a huge advocate of knowing the source of your meat, so when the recent WHO study came out regarding the red meat cancer connection, I assumed that it only applied to unhealthy CAFO meats. Many of my patients and friends, however, took the media coverage to mean that the red meat was indeed a real threat.
In this post, Natcha Maithai – a cancer researcher and nutritionist – breaks down what this study REALLY says (not the media) so that we can make up our own minds about enjoying great steak. ~Emily
In October 2015, the World Health Organization published a report in Lancet Oncology titled “Carcinogenicity of Consumption of Red and Processed Meat.” This study took the internet by storm, and was largely misinterpreted by the media since it distilled down to, “Red Meat Causes Cancer.”
As a cancer researcher and an evidence-based holistic nutritionist, I feel compelled to clarify the WHO's actual message and recommendations, as well as discuss related scientific evidence before giving my own recommendations in a way that is as unbiased as possible. First, I’ll explain and evaluate the study. In part two of this series, I’ll write about my recommendations with respect to how to eat red meat and prevent cancer.
Red meat has been associated with cancers and several other negative health outcomes for decades.
There have been numerous studies in this topic, so this is nothing new.
This Lancet Oncology article was a meta-analysis, which took studies that have been published in the past, and re-analyzed them. They concluded by categorizing red meat and processed meats as “class 2A” and class 1 carcinogens.
What makes this red meat cancer study credible?
This study was published in Lancet Oncology, which is a very prestigious and high impact medical journal. It was written by the International Agency for Research on Cancer (IARC) committee of the World Health Organization, which is a diverse group of researchers in terms of field of interest and country of origin. Therefore, it’s considered highly credible because it’s written by a prestigious organization and published in a prestigious journal.
What did the study actually say?
First, the authors (IARC committee) stated that red meat is a nutritious food. Then, they discuss how cancer-causing chemicals arise when we cook or process meats. They claim that they examined over 800 epidemiological studies to investigate the association of cancer with consumption of red and processed meats.
While red and processed meats have been associated with several types of cancer, the evidence is strongest for colorectal cancer, with about 17% increased risk per 100 gram of red meat and 50 grams of processed meats.
Based on the data, the committee largely concluded that there is sufficient evidence to say that processed meat may cause cancer, but not for red meat as the evidence was rather mixed. Several epidemiological studies showed positive associations for red meat, but a number of them did not. The authors stated that other confounding factors like diet and lifestyle risks may result in the observed associations rather than red meat consumption itself.
Here's a direct quote from the study:
Consumption of red meat appears to increase mutations or switching off of the gene called APC, which is often found in colorectal cancers. It is also found to increase oxidative status in mice and humans. Therefore, mechanistically, they couldn't say that red meat doesn't cause cancer, either.
With all of this evidence of over 800 epidemiological studies and several other mechanistic studies, the IARC committee classified red meats as “probably carcinogenic to humans” (Group 2A), and processed meats as “carcinogenic to humans” (Group 1).
What this study did well, which made them more credible
They authors were very balanced and unbiased. They clearly wrote the article to state both sides of the evidence and not to mislead the readers. The committee declared no financial conflict of interest and appears to have no agenda.
They couldn’t be fairer with their reviews of the literature. I was surprised to find in this article that they actually did not say that red meat causes cancer (in contrary to what some media said). Instead, the article stated that due to the mixed nature of the epidemiological evidence, there is not sufficient evidence to say that red meat causes cancer.
Flaws of this study
Because it’s a meta-study, they had to rely on the previously published studies and the data that was available for them to review. There's a few problems with this. First, most of these studies were based upon epidemiological evidences – this means they studied the health of those in defined populations, along with the correlation between their consuming red meat and the incidence of disease. The problem is that simply because the correlation exists between red meat consumption and a disease does not mean that red meat consumption caused the disease.
Secondly, these studies were also based on self-reported food consumption, which is often not accurate. Not only did many of the studies rely on self-reported red meat consumption, several studies relied on self-reporting of food consumption years back into the past rather than actually analyzing food journals. These results can be influenced by personal bias, as well as other potential confounding factors, e.g. people who consume a lot of red meat often lived an overall less healthy lifestyle with less vegetables, less fiber and less exercise.
In addition, the mechanistic evidence that supports red meat consumption often comes from the evaluation of isolated chemicals or red meat on its own, rather than in a context of a healthfully diverse diet of a human. Evidence is clear that chemicals caused by overcooking or processing meats, regardless of whether the meat is conventional or organic, can and do cause cancer. However, we don’t eat red meats alone. In fact, studies show that chlorophyll in vegetables and other compounds in cruciferous vegetables can offset the cancer-causing effects of these chemicals in red meat (source and source).
In the field of epidemiology, the effects of red meat appear to be much smaller than other things that actually cause cancer. For example, when statistical associations indicate that red meat causes cancer, the risk is usually around 1.1 to 1.5 times those without red meat consumption. Whereas cigarette smoking, which has been conclusively shown to cause cancer, had risks up to 30 times those who did not smoke.
Interestingly, a member of the IARC (Klurfeld DM) claimed in another review article that confusing this small increase in statistical risks for cause and effects has previously caused the field of nutrition to make unfounded recommendations regarding low fat diets, breast cancer, and heart disease.
So should you worry about the red meat cancer connection?
Whether or not the red meat cancer connection is an issue for YOU largely depends on what you eat with your red meats as well as your surrounding lifestyle. The evidence of this particular study is rather inconclusive. Studies can be misinterpreted when one attempts to translate that into lay terms, and the general public may not be familiar with the nuances of interpreting scientific research.
We see this often as studies are misquoted in the media, which is the one issue that I am very passionate about addressing. This study on its own did not warrant the red meat cancer scare, and there are things we can do to ensure that your red meat is safely nutritious, rather than detrimental.
In the next article of this series, I’ll discuss solutions and recommendations with respect to red meat consumption for health and cancer prevention. For now, you should be able to enjoy red meats in your diet without concerns that they will cause cancer. I highly recommend choosing pasture-raised meats over conventional meats, cooking them gently – avoid charring or overcooking and including lots of greens in your diet.
Have you been worried about the red meat cancer scare?
Let us know in the comments below.
Natcha Maithai is a cancer researcher turned “health detective.” She helps investigate hormonal problems for her clients and demystify relevant biomedical research for the general public. She is passionate about helping women become masters of their bodies through fitness, nutrition, hormone balancing, functional medicine and quantified-self technologies. Find her at natchamaithai.ca.