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. (...)