Why Was Data Proving That Butter Isn’t Bad for You Hidden Away for Decades?

New research—based, oddly enough, on old data—suggests that consuming vegetables oils high in linoleic acids does not, in fact, reduce the risk of heart disease or overall mortality.

Apr 13 2016, 10:00pm

Photo via Flickr user tarale

Several generations of Americans have been told to avoid saturated fats and to get their cholesterol levels down. And while the French have been happily consuming butter all along, we Americans have had to console ourselves with the likes of vegetable oil.

Until now. New research—based, oddly enough, on old data—suggests that consuming vegetable oils high in linoleic acids does not, in fact, reduce the risk of heart disease or overall mortality. What it does do is reduce cholesterol levels. But despite lower cholesterol levels, people who ate these vegetable oils had a higher—not lower—rate of death. And we're not talking small numbers. The oils in question include corn oil, safflower oil, soybean oil, sunflower oil, and cottonseed oil.

Most startling of all, perhaps, is that the data proving that America's national food policy about butter was wrong has been available, but ignored, for four decades.

Are you suddenly wondering about the conspiracies afoot in America's nutritional policy circles? Maybe you should be.

READ MORE: The Danish Butter Industry Would Like You to Know That Butter Is Bad for You

Americans' fear of butter dates back to the 1960s, when studies were said to show that lowering blood cholesterol levels reduced heart attacks and mortality. Diets low in saturated fat and relatively high in linoleic acid and other unsaturated fats were seen to be the solution. The American Heart Association and the US Dietary Guidelines affirmed this view.

Problem: Randomized controlled trials—the gold standard for medical research—never actually showed that linoleic-acid-based oils reduced heart attacks or deaths.

Data from one large randomized and controlled trial dating back to 1968 has been available for decades, though. The Minnesota Coronary Experiment, conducted at the University of Minnesota between 1968 and 1973, involved almost 10,000 patients from six mental hospitals and a nursing home. Only partial results from that trial had been reported—until now.

While investigating the health effects of linoleic-acid-rich oils, Chris Ramsden, a medical investigator at the National Institutes of Health, stumbled upon the earlier Minnesota experiment. "Looking closely, we realized that some of the important analyses that the MCE investigators had planned to do were missing from the paper," said Daisy Zamora, a co-author of the new study.

A team was assembled to recover much of the raw data from the Minnesota study. It had been stored away for decades in files and on magnetic tapes. A University of Minnesota master's degree thesis written by Steven K. Broste, a student of one of the original investigators, was also uncovered.

READ MORE: Everything You Thought You Knew About Fat Is Wrong

And guess what? The recovered data and the master's thesis both confirmed one thing: although the participants in the study who ate a diet heavy in linoleic-acid-heavy oils did in fact have lower cholesterol levels, they also happened to have almost twice—TWICE—the number of heart attacks as the control group.

The newly analyzed data was added to existing data from several other studies. The resulting meta-analysis of the combined data found this: There is no evidence that getting rid of butter and replacing it with corn oil will reduce death from heart disease or death from all causes.

No one is sure why oils containing linoleic acid would lower cholesterol but worsen heart attack risk. But the data says it all. So please pass the butter.