Scientists have poured cold water on new research questioning dietary advice issued 30 years ago urging people to avoid eating fatty foods such as butter and cheese.
The guidelines, introduced in the UK in 1983 and in the US six years earlier, recommended reducing overall dietary fat consumption to 30% of total energy intake and saturated fat to 10%.
But a paper published in the online journal Open Heart says the guidelines “lacked any solid trial evidence”.
The study, which reviewed data available at the time the guidelines were issued, states: “It seems incomprehensible that dietary advice was introduced for 220 million Americans and 56 million UK citizens, given the contrary results from a small number of unhealthy men.
“The results of the present meta-analysis support the hypothesis that the available [randomised controlled trials] did not support the introduction of dietary fat recommendations in order to reduce [coronary heart disease] risk or related mortality.”
The review was led by Zoë Harcombe, of the Institute of Clinical Exercise and Health Science, University of the West of Scotland, Hamilton, and Dr James Dinicolantonio, Saint Luke’s Mid America Heart Institute, Kansas City. They argued that in characterising saturated fat as the “main dietary villain”, public health teams did not pay enough attention to other risks – especially carbohydrates, which are believed to be helping to fuel the obesity crisis.
However, the paper has prompted a flurry of criticism, with scientists lining up to question its methodology and conclusions. Some went so far to argue that the new study was potentially dangerous.
“The claim that guidelines on dietary fat introduced in the 1970s and 80s were not based on good scientific evidence is misguided and potentially dangerous,” said Christine Williams, professor of human nutrition at the University of Reading.
“Whilst it is important to ensure we continue to interrogate the evidence on diet and heart disease, this must be approached through an holistic assessment of the evidence base and recognition of the clear improvements in population cholesterol levels that have taken place over the past 30 years. There are justifiable concerns regarding evidence that saturated fats have been replaced in the diet by sugars, and this requires a reasoned assessment of alternative approaches for the future.”
The British Heart Foundation (BHF) pointed out that the guidance issued 30 years ago was based not just on randomised controlled trials, but on other evidence as well.
“Understanding the true relationship between diet and our health is not simple. Unlike drug trials, studies on diet and disease are difficult to conduct,” said Victoria Taylor, senior dietitian at the BHF.
“It would be all but impossible to carry out a research trial where you controlled the diets of thousands of people over many years. That’s why guidance in the UK is based on a consensus of the evidence available not just on randomised controlled trials.”
Taylor said the BHF continued to recommend switching saturated fat for unsaturated fat, consistent with a Mediterranean-style diet, which is associated with a lower rate of coronary heart disease.
Others argued that fat is not the only factor in managing heart disease.
“This review reminds us that like Saturday Night Fever, tartan culottes and bubble perms, the reductionist ‘single nutrient’ dietary recommendations deserve to be left in the early 80’s where they belong,” said Catherine Collins, principal dietician at St George’s hospital NHS trust, said: “As do doctors and other health professionals who persist in their persecution of single nutrients whilst ignoring a ‘whole diet’ approach.”
Collins added: “Studies had small study numbers [most with a history of heart disease], were highly varied in dietary and lifestyle approach, and reviewed outcomes over a short time scale – around five years on average. All these factors would influence the outcome – whatever dietary changes were made. In contrast to that era, today’s population studies review tens of thousands of people over decades before making recommendations on diet or lifestyle factors, improving the accuracy of findings.”
In linked editorial to the study, Rahul Bahl, of the Royal Berkshire NHS foundation trust, also sounded a note of caution.
He wrote: “There is certainly a strong argument that an overreliance in public health on saturated fat as the main dietary villain for cardiovascular disease has distracted from the risks posed by other nutrients, such as carbohydrates. Yet replacing one caricature with another does not feel like a solution.”
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Research criticising 1980s fat guidelines misguided, say scientists
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