Red Meat: Healthy, Hazardous, or Harmless?

Does less red meat mean better health? Should health authorities, like the World Health Organization, continue to send this message? The latest scientific reviews on red meat and health shed light on these questions.

Let’s examine the science that lies beneath the headlines, and what it means for our dietary choices.

What type of study was done?

The news headlines stem from a collection of five studies, undertaken by consortium of scientists, led by Bradley C. Johnston of Canada’s Dalhousie University and presented in the Annals of Internal Medicine (see original research article). The studies did not present new data. Rather, they presented a comprehensive* analysis of existing human studies, intended to coax out overall trends (these are known as meta-analyses). Each study compared rates of disease and death from common conditions (cancer, cardiovascular disease, and diabetes) in those who consumed more red meat to those who consumed less red meat. Where possible, the studies parsed out processed red meat vs unprocessed.

*NB The new meta-analysis has been met with some criticism on its inclusion criteria. Some feel that the criteria were too strict, leading to omission of potentially relevant studies, such as the Lyon Heart Study. While the Lyon study indeed found much better health outcomes in the group consuming less red meat, this was just one of several dietary differences.

What did they find?

In many ways, the findings in this latest review were familiar: those who eat less red meat tend to have lower disease or death risk.

Greater red meat intake was consistently linked to higher overall death rate (all-causes), cardiovascular death rate, and risk of type 2 diabetes. The most notable divergence from past reviews was in the link between red meat and cancer. The link was much weaker than I (and others) expected, and only showed up between processed red meat and overall cancer. It was particularly surprising not to see support for a link to colorectal cancer – even for processed red meats. 

While many of the findings were aligned with past reviews, the authors felt that the data did not justify dietary recommendations. Why not? 

First, the authors deemed the magnitude of potential benefit as “small” (to the individual); second; they judged the quality of the body of evidence as low and inconclusive.

Before we dive in to understand these issues (magnitude and quality of evidence), let’s take a closer look at cancer risk, an often misunderstood topic.

Red meat and cancer

In 2015 the International Agency for Research on Cancer, part of the World Health Organization, classified processed red meat at their highest confidence level (Group 1), alongside other smoking guns like arsenic, asbestos, and aflatoxins. The IARC ranked unprocessed red meat as a “probable” carcinogen (Group 2A) along with a slew of contentious compounds like glyphosate, the much maligned pesticide.

It’s important to note that the IARC’s role is hazard assessment, not risk assessment. Hazard speaks to the potential harm at any dose, without regard to real-world conditions. Risk speaks to the potential for harm in the real world. Risk assessments are achieved by combining hazard assessments with estimates of real-world exposures (doses).

Hazard assessments typically evaluate the strength of all available data, including human, animal and mechanistic links. In contrast, the current review of red meat and health considered one type of evidence: human studies. It it did not assess the evidence for the multiple putative mechanisms that could form the basis for a causal length. For processed red meat, nitrates are commonly thought to be a potential driver. For unprocessed red meats, the formation of carcinogenic compounds like HCAs (heterocyclic amines) and polycyclic amines (PCAs) upon high heat cooking are regarded as potential culprits, though the required exposures are unclear.  

How big or small of a potential benefit was observed?

In most cases, the risk reduction was on the order of 10%, even for substantial dietary changes, such as cutting back red meat consumption by three portions per week. The authors rightly point out that in absolute terms, a 10% benefit is not exactly transformative – for example, going from 4% to 3.6% risk of cardiovascular deaths or 10.5% to 9.7% cancer risk (over a given time span).

It’s also important to note that changes in disease risk that are fairly trivial, and inconsistent, at an individual level can be significant at a population level. For example, consider 2,000 people who routinely consume processed red meat. Then, assume that this group was split into two: Group A consistently reduced their processed red meat by three servings per week over eleven years, and Group B did not. If the proposed benefits are true, there we would expect to see roughly a dozen fewer cases of diabetes cropping up in Group A than in Group B. The change benefits the group as the whole, but does not benefit each individual member.

Why was the evidence seen as low quality?

The authors used the GRADE framework for ranking evidence, one that was developed for clinical decision making. This framework ranks all observational studies, the ‘bread and butter’ of nutrition, as low grade. This is because it is dangerous to infer causation from correlation, given the many confounders at play.

The wrinkle in this evidence assessment is that the scope of the article was limited to human studies, and thus did not tell the full story. Most notably, it does not incorporate mechanistic considerations discussed above in “red meat and cancer risk”. Would a more complete picture have altered the authors’ conclusions? Perhaps.

Same Story Different Take

In the end, it’s not the findings of these studies that deviate from the past, but the way that they are translated (or not) into dietary recommendations.

Others have focused on a public health lens, through which tiny individual benefits can add up to massive national or global benefit. They have also taken a different view of the strength of evidence, believing that caution is warranted despite the capricious nature of observational studies, presumably because they are very consistent, and align with other lines of evidence.

If you were in charge of setting dietary recommendations, what would you advise? The steaks (hee hee) are high!

The Bottom Line

If the only dietary change you make is cutting back a bit on red meat, don’t expect any miracles. Yes, there is a long list of potential benefits, but the magnitude of potential benefits is modest at best at the individual level, and the evidence is far from solid. 

For any one person, it’s impossible to predict the precise impact of a dietary change, and the best we can do is make educated guesses, based on large populations. Your personal story will depend on many factors, including your current health, the types and amounts of red meats you currently eat, how they are prepared, how much you cut back, and what you replace your meat with. 

As you contemplate your choice, don’t forget the elephant in the room. Our food choices impact more than just our personal health. They impact the health of our planet through their toll on resources. Our food choices impact the lives of the animals we raise for food. In my books, these considerations are just as important, if not more so, than the personal health story.

Last but not least, I encourage you to fixate less on heroes and villains, and more on healthy dietary patterns, while heeding the major risk factors that we can control (e.g. smoking, alcohol, obesity, stress, and a sedentary lifestyle).

Appendix

Other perspectives on the latest meat and health studies:

Five latest studies on meat and health (2019)

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