National diet recommendations for fat content were not evidence based

From a systematic review of the literature available before the recommendations:

National dietary guidelines were introduced in 1977 and 1983, by the US and UK governments, respectively, with the ambition of reducing coronary heart disease (CHD) by reducing fat intake. To date, no analysis of the evidence base for these recommendations has been undertaken. The present study examines the evidence from randomised controlled trials (RCTs) available to the US and UK regulatory committees at their respective points of implementation.

Methods

A systematic review and meta-analysis were undertaken of RCTs, published prior to 1983, which examined the relationship between dietary fat, serum cholesterol and the development of CHD.

Results

2467 males participated in six dietary trials: five secondary prevention studies and one including healthy participants. There were 370 deaths from all-cause mortality in the intervention and control groups. The risk ratio (RR) from meta-analysis was 0.996 (95% CI 0.865 to 1.147). There were 207 and 216 deaths from CHD in the intervention and control groups, respectively. The RR was 0.989 (95% CI 0.784 to 1.247). There were no differences in all-cause mortality and non-significant differences in CHD mortality, resulting from the dietary interventions. The reductions in mean serum cholesterol levels were significantly higher in the intervention groups; this did not result in significant differences in CHD or all-cause mortality. Government dietary fat recommendations were untested in any trial prior to being introduced.

Conclusions

Dietary recommendations were introduced for 220 million US and 56 million UK citizens by 1983, in the absence of supporting evidence from RCTs.

In the discussion section the authors say:

This undermines the role of serum cholesterol levels as an intermediary to the development of CHD..

Recent findings about the pleiotropic effects of statins have also contributed to the notion that cholesterol doesn't matter, a notion that is mistaken. The cholesterol hypothesis is supported by mechanistic understanding of atherosclerosis, non-statin based lipid lowering trials and strong epidemiologic evidence. That said, the idea that we could impact the epidemic of atherosclerosis by a national diet recommendation to reduce fat content was pretty stupid. I believe one reason for the failure of the early diet trials was the isocaloric substitution of carbohydrate which activated the metabolic syndrome in those who were genetically predisposed.