The BMJ recently published an interesting paper that digs up some previously unpublished data on an old study, and questions whether polyunsaturated fat provides any protection against heart disease over saturated fat. The change in oil did have a noticeable change on cholesterol levels but this didn't translate to changes in heart health.
Here are some exceprts from the editorial:
"It is widely accepted that diets rich in polyunsaturated fats protect against heart disease...This new study re-examines recovered data from a double blind randomised controlled trial that took place 45 years ago. The Minnesota Coronary Experiment (MCE) followed 9423 participants from state mental hospitals and a nursing home for 4.5 years. The trial tested whether replacement of saturated fat with vegetable oil rich in linoleic acid (an omega-6 polyunsaturated fat) reduces the risk of coronary heart disease and death through a reduction in serum cholesterol concentration.
As expected, the diet enriched with linoleic acid lowered serum cholesterol concentration. But it did not reduce mortality: in fact participants in the intervention group had a higher mortality than controls. The pooled results of the MCE and four similar trials failed to find any reduction in mortality from coronary heart disease."
'These unexpected results proved difficult to stomach for researchers at the time. The trial ended in 1973, but it took until 1989 for the results to be published.'
Here is the conclusion of the study:
Available evidence from randomized controlled trials shows that replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes. Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.