Diets low in saturated fat do not prevent heart disease or improve health and instead public health warnings need to be issued over sugar, a leading scientist has said.
The fear that saturated fat raises cholesterol is "completely unfounded" while the current recommendations to follow a low fat diet are based on flawed evidence, Dr James DiNicolantonio said.
Writing in the journal Open Heart, the leading US cardiovascular research scientist said a "compelling argument can be made for the general lack of evidence in support of a low-fat diet".
Advising people to replace saturated fat with carbohydrates or omega 6 polyunsaturated fats was not supported by scientific research.
"A change in these recommendations is drastically needed as public health could be at risk," he said, adding that the rise in diabetes and obesity over recent years correlated with the increase in carbohydrate consumption "not saturated fat".
Type 2 diabetes, which accounts for 90% of the people with diabetes around the world, is largely the result of excess body weight and physical inactivity according to the World Health Organisation.
The cause of type 1 diabetes is not known and it is not currently preventable.
DiNicolantonio said: "There is no conclusive proof that a low-fat diet has any positive effects on health. Indeed, the literature indicates a general lack of any effect [good or bad] from a reduction in fat intake.
"The public fear that saturated fat raises cholesterol is completely unfounded as the low-density lipoprotein particle size distribution is worsened when fat is replaced with carbohydrate."
Instead, he said the culprits of increasing poor health are diets high in carbohydrate and sugar and a public health campaign is "drastically needed to educate on the harms of a diet high in [these foods]".
Dr DiNicolantonio said the idea that fat causes heart disease was based on a flawed 1950s study, which used data from six countries, but excluded data from another 16.
This study "seemingly led us down the wrong 'dietary road' for decades to follow", he said.
The initial Dietary Goals For Americans, published in 1977, proposed increasing carbohydrates and decreasing saturated fat and cholesterol in the diet.
Dr DiNicolantonio said: "This stemmed from the belief that since saturated fats increase total cholesterol (a flawed theory to begin with) they must increase the risk of heart disease."
Experts also believed the diet would lead to less obesity and diabetes - when the exact opposite was true, he added.
Furthermore, evidence shows that a low-carbohydrate diet - as opposed to a low-fat diet - actually improves cholesterol.
"From these data, it is easy to comprehend that the global epidemic of atherosclerosis, heart disease, diabetes, obesity and the metabolic syndrome is being driven by a diet high in carbohydrate/sugar as opposed to fat, a revelation that we are just starting to accept," Dr DiNicolantonio said.
The idea that replacing a combination of trans-fats and saturated fats with omega 6 polyunsaturated fats (without a corresponding rise in omega 3 fatty acids) has also been shown to increase the risk of death, including from cancer and heart disease, he added.
In an accompanying podcast, Dr DiNicolantonio said: "We need a public health campaign as strong as the one we had in the 70s and 80s demonising saturated fats, to say that we got it wrong."
The best diet to boost and maintain heart health is one low in refined carbohydrates, sugars and processed foods, he recommended.
WHO calls for reduced sugar intake
Yesterday, the World Health Organisation said that sugar should account for less than 5% of what people eat each day if they are to avoid health risks, such as weight gain and tooth decay, linked to excessively sugary diets.
Issuing new draft sugar guidelines, the United Nations health agency said its recommendations were based on "the totality of evidence regarding the relationship between free sugars intake and body weight and dental caries".
Free sugars include monosaccharides and disaccharides that are added to foods by manufacturers, cooks or consumers, and sugars naturally present in honey, syrups, fruit juices and fruit concentrates.
"WHO recommends reduced intake of free sugars throughout the life-course," the agency said in a statement.
It said the 5% level should be a target for people to aim for and called it a "conditional recommendation".
It also reiterated a "strong recommendation" that sugar should account for no more that 10% of total energy intake.
"There is increasing concern that consumption of free sugars - particularly in the form of sugar-sweetened beverages - increases overall energy intake and may reduce the intake of foods containing more nutritionally adequate calories," the WHO said.
The College of Physicians of Ireland has welcomed the report as a step forward in providing the evidence to tackle obesity.
Professor Donal O'Shea said that "The government needs to take action on this to safeguard the health of the nation and to realise its vision of a Healthy Ireland."