Dietary recommendations on fat intake based on limited evidence
1. Benefits of UK and US government dietary recommendations in the 1970’s and 1980’s to reduce fat intake for prevention of cardiovascular disease were not specifically proven in any randomized control trials.
2. The dietary recommendations were based on mostly small secondary randomized trials studies, which in a meta-analysis showed no significant differences in all-cause or cardiovascular mortality.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The United States and United Kingdom governments introduced new national dietary guidelines in 1977 and 1983, respectively, which recommended reducing fat intake for prevention of coronary heart disease (CHD). Specifically, they recommended limiting the consumption of fat to 30% of total energy intake and saturated fat to 10% of total energy intake. The authors of this study conducted the first systematic review of scientific evidence available to the US and UK regulatory committees at the time of their recommendations. The researchers found that there had been six small randomized controlled trials (RCT) that studied the relationship between fat and coronary heart disease. However, only one RCT had actually tested the specific dietary recommendation (i.e. the effect of a 10% saturated fat diet), which actually found that subjects following the diet actually had a higher incidence of mortality. All of the studies had limitations to their study design including a lack of adequate protocols to ensure adherence to the intervention diet and different interventions for fat restriction in each study. Furthermore, a meta-analysis of data from the six studies showed no significant differences in all-cause or coronary heart disease mortality. There were also no female participants in any of the study cohorts.
The meta-analysis had a strong study design as it thoroughly examined the literature and conducted a thorough sensitivity analysis to confirm the findings. A notable limitation is that evaluation of the studies was limited by the data available from the publication (e.g. no information on control diet fat content). Overall, these findings suggest that almost 300 million American and British citizens were recommended to change their diet based on limited, if not contradictory, evidence, and that clinicians may want to more carefully consider the evidence behind dietary recommendations in the future.
Click to read the study, published today in Open Heart
Click to read an accompanying editorial in Open Heart
Relevant Reading: Dietary fat intake and prevention of cardiovascular disease: systematic review.
In-Depth [systematic review and meta-analysis]: This study was a systematic review of studies on dietary fat intake and coronary heart disease published prior to 1983 to determine if adequate evidence was present to recommend a decrease in dietary fat intake. Six randomized control trials were found on the subject with a total of 2,467 male participants. One of the studies (by Woodhill et al,) studied the effect of a 10% saturated fat diet and found that the intervention group had a significantly higher incidence of all-cause mortality (39 vs. 28 deaths) and death due to coronary heart disease (35 vs. 25 deaths). A meta-analysis of all six studies found that the risk of all-cause mortality was 0.99 (CI95% 0.88-1.15), and that the risk of death from coronary heart disease was 0.99 (CI95% 0.78-1.25). The patients in the dietary intervention groups did have greater reductions in average cholesterol level compared to control group patients (-12.6% vs. -6.5%), found to be significant in the meta-analysis, but there was no standardized diet across studies.
Image: PD
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