Research has cast doubt on recommendations that saturated fats should be replaced with vegetable oils
Long-held recommendations to replace saturated fats with vegetable oils are being questioned
This re-evaluation follows a study found this dietary substitution did not reduce rates of heart disease or survival.
The US researchers re-analysed data from a 45-year-old study designed to test the diet-heart hypothesis, that replacing saturated fat with vegetable oils rich in linoleic acid reduced the risk of coronary heart disease and death through lowering cholesterol.
In fact, the more individuals lowered their total cholesterol with the omega-6 polyunsaturated fat, the more likely they were to die from any cause.
This raises doubts around guidelines such as the Heart Foundation’s, which recommend reducing saturated fats to 7% of dietary intake to lower cholesterol and so reduce the chance of heart disease.
The study “add[s] to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid,” they wrote.
Dr Jennifer Johns, president of the Heart Foundation, said that the role of fats was not as clear-cut as it appeared to be 10 to 15 years ago.
It was important the findings weren’t sensationalised by the lay media, as occurred with last year’s Catalyst program on statins, she said, as prematurely disregarding recommendations to lower saturated fats could be harmful.
The findings would likely be considered in the next guidelines published by the Heart Foundation, but Dr Johns cautioned the study had a small sample size of highly selected patients who may have had comorbid conditions.
According to the authors, a lack of robust evidence in the form of randomised controlled trials has left the diet-heart hypothesis unsupported for half a century.
The double blind trial of 9500 patients in nursing homes or psychiatric hospitals showed a significant 14% reduction in cholesterol levels in those randomised to a diet rich in corn-based fats, compared with controls.
However, there was a 22% increased risk of death due to all causes for each 0.78 mmol/L reduction in serum cholesterol, and no reduction in myocardial infarcts or coronary atherosclerosis.
The authors also conducted a meta-analysis of five RCTs of almost 11,000 people, which found no evidence that switching to a diet of vegetable oils reduced coronary heart disease or death.
Despite the lack of evidence, the diet-heart hypothesis may have persisted for so long because of confirmation bias, Dr Lennert Veerman, leader of the Burden of Disease and Cost-Effectiveness unit at the University of Queensland, told TMR.
Dr Veerman, who also wrote the accompanying editorial in the BMJ, said the study so strongly contradicted the prevailing theory of the time that the initial authors would have thought they were wrong.
“The fat paradigm has been overemphasised in expense of others like sugar, which could have been explored much earlier,” he said.
It was time for a careful review of dietary guidelines, he said.
BMJ 2016; online 12 Apr
