Researchers have returned to an old study conducted to analyse the link between saturated fats, cholesterol and mortality - and found evidence that, if revealed earlier, may have substantially changed dietary guidelines.

Saturated fats: not so bad?

In 1968-1973, the Minnesota Coronary Experiment (MCE) took place. A randomised controlled trial, it was the largest and perhaps the most rigorously executed dietary trial of cholesterol lowering by replacement of saturated fat with vegetable oil rich in linoleic acid – and yet the results were never completely published. Had they been, it can be concluded from a paper published in the British Medical Journal (BMJ) – which has retrieved the original data for analysis - the basis on which many dietary recommendations still perpetuated today may have been very different.

The trial was designed to assess whether replacing saturated fats with vegetable oil would reduce cholesterol levels and coronary heart disease. The control diet was high in saturated fat from animal fats, common margarines and shortening, while the intervention diet replaced these fats with linoleic acid (from corn oil and corn oil polyunsaturated margarine).

The intervention group had significant reduction in serum cholesterol compared with controls – but experienced no benefit in terms of death from coronary heart disease. Similarly, there was no evidence of benefit in the intervention group for coronary atherosclerosis or myocardial infarcts.

The researchers concluded that available evidence from randomised 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, they said, 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.