Replacing butter with vegetable oils may lower your cholesterol but may not curb heart disease risk or help you live longer, a new study suggests.
US scientists have re-analysed data from two old experiments, including the Sydney Diet Heart Study, and found switching to vegetable oils rich in linoleic acid lowered blood cholesterol.
But this did not translate into improved longevity or a lower risk of heart disease.
In fact, people who had a greater reduction in blood cholesterol had a higher, rather than lower, risk of death.
The scientists say their findings, published by The BMJ, add to doubts about the widely held belief that vegetable oils rich in linoleic acid - an omega-6 polyunsaturated fat - are good for heart health.
In a linked editorial, University of Queensland senior lecturer Lennert Veerman said the benefits of choosing polyunsaturated fat over saturated fat now "seem a little less certain than we thought".
Omega 6 polyunsaturated fat sources include margarine spreads and corn, sunflower and sesame oils.
The scientists analysed data from the Minnesota Coronary Experiment (MCE), conducted 45 years ago, involving 9423 participants from state mental hospitals and a nursing home.
One group replaced their saturated fat intake with linoleic acid from corn oil and corn oil polyunsaturated margarine, while the control group had diets high in saturated fat, including butter and common margarines.
An analysis of the unpublished data from a similar trial in Sydney found the risk of death from coronary heart disease was higher in those who replaced saturated fat with vegetable oil rich in linoleic acid.
The MCE findings add to growing evidence that incomplete publication of the research has contributed to "overestimation of benefits" of replacing saturated fats with the vegetable oils, the researchers said.
