COMMENTARY

No Harm in Red Meat After All? Not Exactly

F. Perry Wilson, MD, MSCE

Disclosures

October 09, 2019

Welcome to Impact Factor, your weekly savory, smoky bite of commentary on a new medical study. I'm Dr F. Perry Wilson.

If the past few years have taught me anything, it's that two people can look at exactly the same information and come to two completely different conclusions.

But I'll give you a break from politics today and let you sink your teeth into an example right from the sciences.

Red meat—tasty chunks of skeletal muscle from various mammals—has been a staple of the human diet since before we were humans. But for decades, nutritionists, physicians, and guideline-making organizations have beaten the same drumstick: Red meat intake should be minimized for your health.

Last week, a series of studies examining the role of red meat and processed meat in the diet came out in the Annals of Internal Medicine. And to read the press clippings, the study turned the dietary world on its head.

But we need to look closer. This series of studies, if nothing else, exposes how difficult it is to understand how nutrition affects our health.

Let's start with the data. Researchers, led by Dr Bradley Johnston from McMaster University, produced four meta-analyses examining the impact of red and processed meat consumption on overall mortality, cardiovascular disease, and cancer.

They scoured the published medical literature and combined multiple studies into a single estimate of effect—a powerful technique and one that helps to synthesize a large body of work.

They published a ton of data. But let's look at some of the big findings, starting with overall mortality.

The meta-analysis identified eight cohort studies of at least 1000 patients each that linked red or processed meat consumption with all-cause mortality. They found that, on average, a reduction in red meat consumption of three servings per week was associated with a 7% reduction in mortality rate.


 

Wait—I thought this study said meat was okay to eat now. The data clearly show that reducing meat intake reduces mortality, cardiovascular disease, stroke, diabetes, etc.

And here's where we get into the idea that two people can look at the same data and come to different conclusions.

Most of the medical establishment has looked at data like these and said, "Yup, red meat is bad for you." Enter multitudes of guidelines stating that we need to cut down on red meat or avoid it altogether.

But the authors consider these data low-quality.


 

And I actually think they're right about this. The data come from observational studies, and observational studies of diet are super-problematic, because your diet is interwoven with so many other things in your life. What you eat is not just about the chemicals that go into your body; it says something about your socioeconomic status, your upbringing, the value you put on healthful behaviors.

So forget observational studies. Let's look to randomized trials. Well, it's really hard to do a randomized trial of nutrition, at least over a long enough time period to see if it really affects outcomes. People just don't eat what you tell them to. In fact, the only RCT that made it into the meta-analysis that had mortality data was the Women's Health Study.

You'll recall that the Women's Health Study randomized about 50,000 women to a low-fat or regular diet. The low-fat group did end up cutting back on their red meat consumption, but there was no difference in cardiovascular disease or cancer mortality.


 

So here we are: a bunch of cohort studies suggesting a small benefit of reducing red meat intake, and one large randomized trial (composed entirely of women) without evidence of effect.

So... what recommendations would you make?

Dr Johnston and colleagues are taking some heat for writing that adults should "continue current unprocessed and processed red meat consumption."

People are reading that as "you should eat red meat."

That is not what they are saying.

They are saying, "We're not sure if it's not okay to eat red meat." Absence of evidence is not evidence of absence. It's sort of a tricky thing to wrap your head around.

Here's an analogy: Let's imagine that I dug into the literature to determine whether popcorn causes cancer. I would find that, huh, there aren't really any studies about this. Not enough data. It would be reasonable for me to say, "I suggest that you continue your popcorn consumption" because why should I tell you to stop something you like if I don't have data to support a change?

Of course, there are ethical and environmental reasons to avoid red meat consumption, but those are well beyond the scope of this area of research and this commentary. We'll open that can of tuna some other time.

The lead author has come under some scrutiny now for failing to disclose a history of ties to the agribusiness industry.

In that light, one wonders whether the guidelines shouldn't have read something like, "We recommend continuing your current red meat intake until higher-quality data are available," which may be a reasonable thing to tell your patients.

People listen to us physicians when we say to avoid red meat, or avoid cholesterol, or avoid eggs, or drink more coffee. Much of the advice regarding specific food choices is founded on relatively shaky ground. It's not that it's wrong, necessarily—just unproven. If you want to stand on nutritional bedrock, basically all we can say is that individuals should eat the number of calories required to maintain a healthy weight. Where should those calories come from? Well, we're working on it.

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