The study, published in BMJ Open Heart journal, reviewed the scientific body of evidence available to US and UK dietary committees when they introduced the guidelines in 1977 and 1983 respectively.
It found that only six randomised controlled trials - considered the gold standard evidence in nutritional science - had investigated the link between dietary fats and coronary heart disease (CHD) prior to 1983.
None of these trials proved a link between higher fat consumption and increased risk of death from heart disease or other causes.
Most concluded that dietary intervention had no impact on CHD, and one stated “A low-fat diet has no place in the treatment of myocardial infarction" [heart attack].
Meta-analysis of the six trials revealed there was no overall difference in death rates between the dietary intervention and control groups.
“What our study shows is that the evidence was not there to introduce dietary fat guidelines,” lead author Zoe Harcombe told BigHospitality.
“Some of the studies swing slightly one way and others swing the other, but when the results were pooled – which is what meta-analysis is – there were no differences in all-cause mortality and heart mortality resulting from the dietary interventions.
“You can remove any one of the studies and it would make no difference, you just can’t get the body of evidence to say that dietary fat has an impact on mortality.”
No scientific basis
There is no reference to these trials in the reports from UK and US dietary committees, suggesting there was no review of the scientific evidence prior to guidelines being introduced.
Additionally, no randomised controlled trials were held to test the impact of the guidelines, which recommended that fat should make up 30 per cent of diet and carbohydrates should make up 55 per cent of diet.
In the US report, Mark Hegsted, professor of nutrition and member of the dietary guidelines committee, stated: "What are the risks associated with eating less meat, less fat, less saturated fat, less cholesterol, less sugar, less salt and more fruits, vegetables, unsaturated fats and cereal products - especially whole grain cereals. There are none that can be identified and important benefits can be expected."
Harcombe claimed that by making these assumptions without testing them, the dietary committees had taken "a leap in the dark".
“What has happened over the last 30 years is we have eaten less fat and more carbohydrates, obesity has increased tenfold in the UK and we have type 2 diabetes about to bring the NHS to its knees," she said. "What are the risks indeed?"
Dietary guidelines
Public Health England (PHE) has stepped in to defend dietary guidelines, claiming there is now an 'extensive evidence base' supporting the recommendation to eat less fat.
“The advice issued by Coma (Committee on Medical Aspects of Food Policy) in 1991 confirmed that eating too much saturated fat can raise cholesterol levels, which increases the risk of heart disease," said Dr Alison Tedstone, chief nutritionist at PHE.
However, Harcombe pointed out that most of this evidence is based on epidemiological study, which is less scientific than randomised controlled trials and can not be used to establish cause and effect.
Additionally, she said, there is growing body of scientific evidence suggesting that carbohydrates, not fat, are the problem in modern diets.
"There have been more than 20 studies published in the last 18 months which suggest we revisit public health advice to eat less fat," she said.