Systematic review of dietary intervention trials to lower blood total cholesterol in free-living subjects Commentary: Dietary change, cholesterol reduction, and the public health---what does meta-analysis add?

Abstract

Abstract Objectives: To estimate the efficacy of dietary advice to lower blood total cholesterol concentration in free-living subjects and to investigate the efficacy of different dietary recommendations. Design: Systematic overview of 19 randomised controlled trials including 28 comparisons. Subjects: Free-living subjects. Interventions: Individualised dietary advice to modify fat intake. Main outcome measure: Percentage difference in blood total cholesterol concentration between the intervention and control groups. Results: The percentage reduction in blood total cholesterol attributable to dietary advice after at least six months of intervention was 5.3% (95% confidence interval 4.7% to 5.9%). Including both short and long duration studies, the effect was 8.5% at 3 months and 5.5% at 12 months. Diets equivalent to the step 2 diet of the American Heart Association were of similar efficacy to diets that aimed to lower total fat intake or to raise the polyunsaturated to saturated fatty acid ratio. These diets were moderately more effective than the step 1 diet of the American Heart Association (6.1% v 3.0% reduction in blood total cholesterol concentration; P<0.0001). On the basis of reported food intake, the targets for dietary change were seldom achieved. The observed reductions in blood total cholesterol concentrations in the individual trials were consistent with those predicted from dietary intake on the basis of the Keys equation. Conclusions: Individualised dietary advice for reducing cholesterol concentration is modestly effective in free-living subjects. More intensive diets achieve a greater reduction in serum cholesterol concentration. Failure to comply fully with dietary recommendations is the likely explanation for this limited efficacy. Key messages Results from metabolic ward studies suggest that dietary change can reduce blood cholesterol concentrations by up to 15% In free-living subjects the standard step 1 diet of the American Heart Association lowers cholesterol concentration by about 3%, and about another 3% can be achieved with more intensive diets Difficulties in complying with the prescribed dietary change explain the failure to achieve the expected reductions in cholesterol concentrations It is important to be realistic about the reductions in cardiovascular risk that can be achieved by individual dietary counselling