Abstract

Introduction: National dietary guidelines were introduced in 1977 and 1983, by the United States (US) and United Kingdom (UK) governments respectively, with the intention of reducing deaths from coronary heart disease (CHD) by reducing or modifying fat intake. The two specific guidelines recommended the consumption of no more than 30% of total calories as dietary fat and no more than 10% of calories as saturated fat. To date, no analysis of the evidence base for these recommendations has been undertaken.

Methods: A systematic review and meta-analysis was undertaken of RCTs, published prior to 1983, which examined the relationship between dietary fat, serum cholesterol and mortality from CHD and all-causes. A systematic review and meta-analysis was undertaken of RCTs, currently available, which examined the relationship between dietary fat, serum cholesterol and mortality from CHD and all-causes.

A systematic review was undertaken of epidemiological evidence published prior to 1983, which examined the relationship between dietary fat, serum cholesterol and mortality from CHD. A systematic review and meta-analysis was undertaken of epidemiological evidence currently available, which examined the relationship between dietary fat, serum cholesterol and mortality from CHD.

Results: For RCTs available at the time the dietary fat guidelines were introduced, the risk ratio (RR) for dietary fat interventions and all-cause mortality was 0.982 (95% CI, 0.878 to 1.098). The RR for dietary fat interventions and CHD mortality was 0.951 (95% CI, 0.784 to 1.155).

For RCTs currently available, the RR for dietary fat interventions and all-cause mortality was 0.991 (95% CI, 0.935 to 1.051). The RR for dietary fat interventions and CHD mortality was 0.976 (95% CI, 0.878 to 1.084).

The reductions in mean serum cholesterol levels were significantly higher in the intervention groups (effect size > 1.0); this did not result in significant differences in CHD or all-cause mortality.

The epidemiological evidence available at the time the dietary fat guidelines were introduced included one prospective cohort study that found an association between CHD mortality and saturated fat, but not total fat, intake. Five other studies found no association for total or saturated fat.

For epidemiological evidence currently available, the RR for total dietary fat and CHD deaths was 1.06 (95% CI 0.97 to 1.16). The RR for saturated fat and CHD deaths was 1.13 (95% CI 0.93 to 1.37).

There were no statistically significant relationships from any of the meta-analyses undertaken.

Only one RCT currently available examined dietary fat and CHD mortality in men and women without previous heart disease. All other RCTs lacked generalisabilty. Only one prospective cohort study currently available examined dietary fat and CHD mortality in healthy men and women. All other prospective cohort studies lacked generalisabilty.

The specific dietary fat recommendations made were untested in any trial prior to being introduced.

Conclusion: Studies examining the relationship between dietary fat and CHD mortality have largely been undertaken on men and often men with pre-existing heart disease. The evidence for males with secondary disease was not conclusive. Dietary guidelines were introduced for whole populations despite this.

 

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