Loose Takes on a Study of Red Meat and Type 2 Diabetes

It’s a popular cause. Red meat production is a problem for the climate. Add that to ethical concerns some people have about consuming meat, and the push to reduce red meat consumption makes total sense. But when people start spinning misleading narratives about observational research and using them to promote this otherwise worthy idea, they’re not helping. A steady stream of mass media headlines from new research in AJCN are doing this right now. They say that replacing red meat with plant protein can reduce the risk of type 2 diabetes.

But even when promoting a worthy cause, correlation does not equal causation. And that is all this new study shows. So the headlines are misleading by conveying a degree of certainty that does not exist.

A Correlation from
the Nurses Health Study

The observation that is spurring all this spin comes from the venerable Nurses Health Study. Make no mistake, this study was done quite carefully. In a sample of 216,695 mostly female individuals,  Xiao Gu et al found a moderate (40%) difference in the risk for type 2 diabetes between the heaviest consumers of unprocessed red meat and the lightest consumers.

But this is where we remember that the Nurses Health Study is venerable, but fallible. It is the same observational study that repeatedly told us hormone replacement reduces a woman’s risk of heart disease. But it turned out that more powerful, randomized and placebo-controlled studies came up with the opposite result. A potent reminder that correlation does not prove causality.

Continuing Debate

Thus, we are inclined to agree with the editorial that accompanies the red meat study, which tells us:

“The current observational study is unlikely to end the discussion on whether red meat intake increases risk of type 2 diabetes and even less likely to end the epistemological debates on how to grade quality of observational evidence when many efforts are made to reduce bias and confounding.”

The certainty expressed in press releases and headlines is out of line with unresolved issues in the evidence to date.

Click here for the study and here for the editorial. For an exuberant press release from Harvard, click here.

Carcass of Beef, painting by Chaim Soutine / WikiArt

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October 24, 2023