There was big news in the nutrition world yesterday when the New York Times ran a large story on “an international collaboration of researchers” that have overturned long-held advice that Americans should limit their consumption of red and processed meats: Eat Less Red Meat, Scientists Said. Now Some Believe That Was Bad Advice.
The report (available online at Annals of Internal Medicine) has sparked a wildfire of commentary and controversy. The Timesarticle itself gives voice to several prominent critics of the new guideline, and Twitter is predictably engulfed in argument. Although the guideline is the result of an immense effort – “the largest such evaluations ever attempted” – with the debate still raging, we can’t yet say that it represents anything resembling a scientific consensus. There’s no telling how influential it will prove to be with consumers, with doctors, or with the technocrats that collaborate on official dietary recommendations.
Whether the new report influences future national guidelines or not, the about-face should be unsurprising to anyone half paying attention to nutrition science in recent years. A thumbs-up for red and processed meats is only the latest of several such reversals: butter, saturated fats, eggs and salt have all had their own comebacks.
What we see is the medical establishment slowly grappling with the realization that much of our received wisdom on healthy diets is simply false. Some of the most notable scientific conclusions upon which our modern understanding of nutrition was based have been decisivelydebunked. Whether these myths were spread due to honest error, stupidity or conspiracy, the results have been disastrous, especially for people with diabetes or at risk of developing it. Generations have been driven towards excessive carbohydrate consumption, sending blood sugars and insulin resistance skyrocketing, and triggering a bewildering number of negative health consequences.
To be clear, the study does not make a positive case for the wholesomeness of red and processed meats.The study publishes roughly the same statistics that anti-meat critics brandish, the ones that show that red and processed meats intake are modestly correlated with cancer, heart disease and early death. The authors weigh these statistics but ultimately dispute them, based on two arguments.
First, the authors are not convinced that the numbers can be trusted. Even after surveying an immense swathe of medical literature, the researchers concluded that there simply wasn’t much worthwhile evidence out there. Previous guidelines have been largely based on observational studies, which the authors characterize as “low- or very low-certainty evidence.” Many have sharply criticized the nutrition establishment for its reliance on this dubious form of evidence; Gary Taubes, a journalist that has written extensively in favor of low-carbohydrate diets, has been beating this drum for over a decade. Mindful of the lack of good evidence, the authors of the new guidelines labelled even their own conclusions as “weak.”
Second, the authors contend that even if the statistics were perfectly reliable (“which we believe to be implausible,”), they aren’t really bad enough to worry about. Most of the negative outcomes discussed were seen to affect fewer than one in a hundred people. A separate analysis concluded that most people just don’t care about changes of this small magnitude.
The study has also been criticized for glossing over other significant considerations: concerns over both the ethical treatment of animals and the environmental degradation that the global livestock industry is believed to cause.
So is red meat healthy now? We don’t know. We have weak evidence of weak correlations, weakly implying causation. Experts split on their interpretation. But this new reversal by some scientists serves as a poignant reminder of the very many times that we have been badly served by doctors and nutrition experts in the past.