Diets high in saturated fat do not increase heart disease risk or cholesterol levels, instead public health warnings should focus on the dangers of sugar, says a leading dietary expert.
Writing in the journal Open Heart, leading US cardiovascular research scientist Dr James DiNicolantonio 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".
He went on: "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)."
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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.
Brian Ratcliffe, professor of nutrition at Robert Gordon University, Aberdeen, welcomed the article.
"For the last three decades, accumulating evidence has not provided strong support for the dietary recommendations regarding reducing fat and saturated fat intake," he said.
"DiNicolantonio does not even touch on the evidence which shows that low-fat diets (admittedly lower than the current recommendations) have been associated with poor mood and even depression.
"Many who adhere to dietary dogma have chosen to ignore the uncomfortable facts that did not fit the hypothesis."
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He said it was too "simplistic" to blame carbohydrates and sugar for rising obesity in the US. Much of the developed world has a problem with obesity without "such obvious associations with dietary carbohydrate".
Professor Tom Sanders, head of diabetes and nutritional sciences division in the School of Medicine at King's College London, said Dr DiNicolantoni's assessment misrepresented the scientific evidence.
"Refocusing dietary advice on sugar and away from fat modification and reduction is not helpful," he said.
Prof Sanders, who advises the Global Dairy Platform, said reductions in saturated fat intake had matched falls in average cholesterol levels in the UK, Western Europe, Australasia and the US, as well as in the chance of suffering cardiovascular disease.
"Dietary advice to avoid fatty meat products, choose reduced-fat dairy produce, and to restrict intakes of cakes, biscuits and puddings, which are often both high in saturated fat and sugar, and to select foods containing unsaturated oils such as nuts, fish and vegetable oils remain good sense.
"Those who fail to learn the lessons of history are likely to repeat its errors."
Victoria Taylor, senior heart health dietitian at the British Heart Foundation, said: "As research into diet and coronary heart disease has developed, so too has our understanding of fats and cholesterol. Over the years, advice has changed from cutting out all fat to focusing on types of fats.
"In the UK, our intake of total fat meets the recommended levels but we eat too much saturated fat, so there is still work to be done. That's why we still need to swap saturated fats like lard and butter for unsaturated fats such as plant oils, nuts, seeds and oily fish.
"There have been many column inches devoted to the saturated fat debate in recent months, but fat is just one element of our diet.
"To look after our hearts long-term, we should look at our diet as a whole. Eating a Mediterranean-style diet rich in fruit, veg, pulses and fish will help lower cholesterol and reduce the risk of coronary heart disease."