Looks Like Meat’s Back on the Menu, Boys

Looks Like Meat’s Back on the Menu, Boys

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. To quote the Urukhai Ugluk in The Two Towers
“Looks like meat’s back on the menu, boys!”. 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 4 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 lets look at some of the big findings,
starting with overall mortality. The meta-analysis identified 8 cohort studies
of at least 1000 patients each that linked red or processed meat consumption with all-cause
mortality. And they found this. 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 ok to eat
now? The data clearly shows that reducing meat
intake reduces mortality, CV 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 this 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 Annals authors consider this data
low-quality. And I actually think they’re right about
this. The data comes 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 – 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, 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 ok 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 I
dug into the literature to determine if popcorn causes cancer. I would find, 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. And 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 if the guidelines
shouldn’t have read something like “we recommend continuing your current red med
intake until higher quality data is available”, which may be a reasonable thing to tell your
patients. People listen to us physicians when we say
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 those calories should come from? Well, we’re working on it.

4 thoughts on “Looks Like Meat’s Back on the Menu, Boys”

  1. I knew you were in Big Popcorn's pocket! Really great video and explanation. I wasn't aware of the potential conflicts of the lead author when I put my rather hurried video up, wish I'd given it a mention.

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