Dietary fat intake and prevention of cardiovascular disease: systematic review

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Abstract
Objective: To assess the effect of reduction or modification of dietary fat intake on total and cardiovascular mortality and cardiovascular morbidity. Design: Systematic review. Data sources: Cochrane Library, Medline, Embase, CAB abstracts, SIGLE, CVRCT registry, and biographies were searched; trials known to experts were included. Included studies: Randomised controlled trials stating intention to reduce or modify fat or cholesterol intake in healthy adult participants over at least six months. Inclusion decisions, validity, and data extraction were duplicated. Meta-analysis (random effects methodology), meta-regression, and funnel plots were performed. Results: 27 studies (30 902 person years of observation) were included. Alteration of dietary fat intake had small effects on total mortality (rate ratio 0.98; 95% confidence interval 0.86 to 1.12). Cardiovascular mortality was reduced by 9% (0.91; 0.77 to 1.07) and cardiovascular events by 16% (0.84; 0.72 to 0.99), which was attenuated (0.86; 0.72 to 1.03) in a sensitivity analysis that excluded a trial using oily fish. Trials with at least two years' follow up provided stronger evidence of protection from cardiovascular events (0.76; 0.65 to 0.90). Conclusions: There is a small but potentially important reduction in cardiovascular risk with reduction or modification of dietary fat intake, seen particularly in trials of longer duration. What is already known on this topic The epidemiological relation between dietary fat intake and cardiovascular disease is central in strategies aimed at risk reduction in populations and individuals Systematic review of randomised controlled trials supports manipulation of dietary fat to control serum lipid concentrations, though evidence of effect on one risk factor does not rule out an opposite or reinforced effect on another unstudied risk factor Randomised controlled trials of dietary fat reduction or modification have shown varying results on cardiovascular morbidity and mortality What this study adds Systematic review of trials of modified fat intake shows that reduction or modification of dietary fat intake results in reductions in cardiovascular events, but only in trials of at least two years' duration There is little effect on total mortality Despite decades of effort and many thousands of people randomised, there is still only limited and inconclusive evidence of the effects of modification of total, saturated, monounsaturated, or polyunsaturated fats on cardiovascular morbidity and mortality