US scientists are questioning conventional wisdom and asking whether margarine might have been more harmful than butter all along.
Cutting down on saturated animal fat lowers cholesterol and reduces the risk of heart attack.
However, a new analysis of a study conducted in the late 1960s and early 1970s in Sydney reveals that people who followed the standard advice, and substituted margarine in place of butter, died sooner than those who did not change their diet.
Researchers at the US National Institute of Health say their findings could have “important implications for worldwide dietary recommendations”.
They decided to reinvestigate the Sydney study because it was the only randomised controlled study to examine the impact of increasing consumption of omega 6 polyunsaturated fatty acid, also known as linoleic acid.
It was conducted among 458 men aged 30-59 who had recently had a heart attack, half of whom were advised to cut their animal fat consumption and replace it with safflower oil and safflower oil margarine.
The results, published in the British Medical Journal, showed those who ate more safflower oil had a higher risk of death from all causes, including from heart disease.
However, dietitians and other experts have challenged the NIH findings.
For example, Catherine Collins, principal dietitian at St George’s Hospital, London, says understanding of the link between diet and heart disease has become “much more sophisticated” in the 40 years since the study was conducted.