One of the most widely advocated pieces of dietary advice from the 1970s and 1980s - to cut intake of fat and saturated fat in order to reduce the risk of a heart attack - was wrong and should never have been introduced, according to new research.
The advice given to millions of people between 1977 and 1983 lacked any solid trial evidence to back it up, the research published in the Open Heart journal says.
In the US and the UK, dietary guidelines recommended reducing overall dietary fat consumption to 30 per cent of total energy intake, and specifically, saturated fat to 10 per cent of total energy intake. Both acknowledged that the evidence was not conclusive.
In the current research, the data available at the time was reviewed and the results of six relevant trials re-examined. These showed cholesterol levels fell more in the group treated with dietary intervention but this did not seem to have any impact on the death rates from all causes or from coronary heart disease.
The researchers highlight several caveats in the evidence available at the time: no women were included; no trial tested the dietary recommendations and no trial concluded that dietary guidelines should be drawn up.
“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,” write the researchers.
They go on to say: “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.”
And they conclude: “Dietary advice not merely needs review; it should not have been introduced.”
A linked editorial in the journal says the most up to date review of the evidence also concluded that the evidence on which current dietary guidance is based was “very limited,” but this doesn’t mean that the risk factor identified is not a true risk factor.
There is epidemiological and ecological evidence suggesting a link between dietary fat and heart disease, it says. “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.”
In Ireland, the 2007 nutrition guidelines from the Irish Heart Foundation say there is strong scientific evidence for getting less than 10 per cent of dietary energy from saturated fat and moderate evidence for getting less than 30 per cent of energy from total fat.