Low-fat recommendations not based on good science, meta-analysis shows

The low-fat craze of the late 20th century never would have happened if correct scientific protocol had been followed, according to a paper in the online journal Open Heart.

National dietary advice to cut fat consumption to reduce coronary heart disease “should never have been introduced” as it lacked any solid trial evidence to back it up, the authors of the paper say.

Dietary guidelines issued to millions of US and UK citizens in 1977 and 1983 recommended cutting overall dietary fat consumption to 30% of total energy intake and saturated fat to 10% of total energy intake.

However, the paper authors carried out a systematic review and meta-analysis of the randomised control trial data that would have been available to the US and UK regulatory committees at the time and found no evidence to support the dietary recommendation.

“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 researchers wrote.

“Dietary advice not merely needs review; it should not have been introduced.”

They found that the trials showed little or no significant difference between ‘treatment’ (ie, reduced fat consumption) and comparison groups in studies examining the relationship between dietary fat, serum cholesterol and the development of coronary heart disease.

In fact, reductions in serum cholesterol noted in treatment groups did not seem to have any impact on the death rates from coronary heart disease - or indeed from all causes.

The six trials examined had several limitations: no women were included in the trials, 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,” the researchers wrote.

However, Rahul Bahl, of the Royal Berkshire NHS Foundation Trust, said that just because the evidence was “very limited”, it does not follow that the risk factor identified is not a true risk factor as epidemiological and ecological evidence suggests a link between dietary fat and heart disease.

In addition, public policies generally don’t require randomised controlled trial evidence, Bahl said.

“There is certainly a strong argument that an over-reliance 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,” he wrote.

“Yet replacing one caricature with another does not feel like a solution.”