Of course, this is only one study. It involved only institutionalized patients. Only about a quarter of the participants followed the diet for more than a year. The diets don’t necessarily look like what people really ate, then or now. But this is still a large, randomized controlled trial, and it’s hard to imagine we wouldn’t at least discuss it widely.
Moreover, the researchers conducted a meta-analysis of all studies that looked at this question. Analyzed together, they still found that more people died on the linoleic-acid-rich diets, although the results were not statistically significant. Even in a sensitivity analysis, which included more studies, no mortality benefit could be found with a diet lower in saturated fats.
It’s important to note that other meta-analyses both support and dispute this. A 2010 study argued that substituting unsaturated fats for saturated fats would reduce the rates of coronary heart disease. So did a 2015 Cochrane review. A 2014 study in Annals of Internal Medicine, though, showed the opposite.
People’s reactions to this news have been much as you’d expect. Supporters of a diet low in saturated fat have called the new study an “interesting historical footnote that has no relevance to current dietary recommendations.” Others have said that if this research had been published when the study was over, “it might have changed the trajectory of diet-heart research and recommendations.”
This isn’t the first time that data from long ago have run against current recommendations. In 2013, an analysis was published of recovered data from the Sydney Diet Heart Study, a randomized controlled trial of a similar nature performed in men with a recent heart attack or angina. Although the study was done from 1966 to 1973, results weren’t available publicly until three years ago. It, too, found that a diet higher in unsaturated fats led to a higher rate of death from heart disease.
Why wasn’t this research published decades ago? It’s possible that modern computer technology allows us to do analyses that couldn’t be performed then. It’s possible that researchers tried, but were unable to get the results published.
But it’s also possible that these results were marginalized because they didn’t fit with what was considered to be “truth” at the time. The two principal investigators on the Minnesota study were Ivan Frantz and Ancel Keys, the latter of whom may be the most influential scientist in promoting saturated fat as the enemy of heart health. (Mr. Keys died in 2004.)