The Minnesota Coronary Experiment study refuted much of the advice on heart health that we’ve been told since the 1960s, and especially about switching from butter to a ‘healthier’ vegetable oil. Overall, there were twice as many deaths among the group that switched from butter to corn oil, the study discovered from data that was never published.

The data gathered dust on shelves, until a team of researchers—helped by the son of one of the original researchers—took a fresh look at the work. The new research team, from the University of North Carolina Health Care centre, completed the work of researchers from the University of Minnesota.

The study, which took place between 1968 and 1973, involved 9,423 participants. Part of the study—which excluded much of the controversial findings—was finally published in 1989.

The same North Carolina team also recovered unpublished data from the Sydney Diet Heart Study several years ago to discover that there were more cases of heart disease and death among those who switched from butter to safflower oil, which contains linoleic acid.