National dietary advice on fat consumption issued to millions of citizens in 1977 and 1983 lacked any solid trial evidence to back it up, and "should not have been introduced," concludes a paper in Open Heart. Both sets of dietary guidelines recommended reducing overall dietary fat consumption to 30% of total energy intake, and specifically, saturated fat to 10% of total energy intake. Both acknowledged that the evidence was not conclusive but mainstream media nonetheless omitted any qualification, nutritionists wrote books, and everyone believed they were on the path to cutting coronary heart disease.
So how did such flawed recommendations get into existence? This is the same decade that DDT got banned with as little evidence, so it is no surprise. We got the Environmental Protection Agency to make sure politicians did not ban everything that got published in a bestselling book but the dietary fats argument was too compelling for anyone to refute. It was career suicide for government researchers. So there was no equivalent health branch tasked with sorting out health advice. Recently, in the absence of any analysis of the evidence used to corroborate the dietary recommendations, a team of researchers carried out a systematic review and meta-analysis of the randomized control trial data that would have been available to the US and UK regulatory committees at the time.
After a comprehensive search of research databases, they found six relevant trials, covering seven different dietary interventions, spanning an average of five years, and involving 2,467 men. All the trials had been published before 1983 and had looked at the relationship between dietary fat, serum cholesterol, and the development of coronary heart disease.
Five out of the six did not consider either the overall or saturated fat recommendations. And all but one focused on secondary rather than primary prevention. The pooled data revealed a total of 740 deaths from all causes, and 423 from coronary heart disease. There was no difference in deaths from all causes between the 'treatment' and comparison groups, with 370 deaths in both. And there was no significant difference in deaths from coronary heart disease, with 207 in the 'treatment' groups and 216 in the comparison groups.
The falls in serum cholesterol were significantly greater in the 'treatment' groups, but this did not seem to have any impact on the death rates from all causes or from coronary heart disease, the analysis showed. The researchers highlight several caveats in the evidence available at the time: no women were included; no trial tested the dietary recommendations; 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. "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.
"Dietary advice not merely needs review; it should not have been introduced."
But in a linked editorial, Rahul Bahl, of the Royal Berkshire NHS Foundation Trust, disputes the new paper, saying that the scientific method is not a trump card here and just because they can't prove harm does not mean it isn't harmful - because there is epidemiological and ecological evidence suggesting a link between dietary fat and heart disease, which most scientists would dispute.
And, of course, public policies don't require randomized controlled trial evidence, Bahl notes. If people in New York City want to ban Big Gulps and San Francisco wants to ban Happy Meals, they need only find epidemiological papers they like and pass laws. There is no required standard for evidence. Bahl's statements about policy without evidence won't make climate change skeptics feel like the science is against them even if policy is.
"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," he writes. "Yet replacing one caricature with another does not feel like a solution."
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