General Practice

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

BMJ 1998; 316 doi: http://dx.doi.org/10.1136/bmj.316.7139.1213 (Published 18 April 1998) Cite this as: BMJ 1998;316:1213

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

Footnotes

    • Accepted 23 September 1997

    Systematic review of dietary intervention trials to lower blood total cholesterol in free-living subjects

    1. J L Tang, research fellowa,
    2. J M Armitage (Jane.armitage{at}ctsu.ox.ac.uk), senior research fellowb,
    3. T Lancaster, senior clinical lecturera,
    4. C A Silagy, professor of general practicec,
    5. G H Fowler, professor of general practicea,
    6. H A W Neil, lecturera
    1. a Division of Public Health and Primary Care, University of Oxford, Radcliffe Infirmary, Oxford OX2 6HE
    2. b Clinical Trial Service Unit and Epidemiological Studies Unit, Harkness Building, Radcliffe Infirmary
    3. c Flinders University of South Australia School of Medicine, Adelaide, Australia
    4. a Department of Social Medicine, Canynge Hall, Bristol BS8 2PR
    5. b Department of Primary Care and Population Sciences, Royal Free Hospital School of Medicine, London NW3 2PF
    1. Correspondence to: Dr Armitage
    • Accepted 23 September 1997

    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

    Footnotes

      • Accepted 23 September 1997

      Commentary: Dietary change, cholesterol reduction, and the public health—what does meta-analysis add?

      1. George Davey Smith, professor of clinical epidemiology,
      2. Shah Ebrahim, professor of clinical epidemiology
      1. a Division of Public Health and Primary Care, University of Oxford, Radcliffe Infirmary, Oxford OX2 6HE
      2. b Clinical Trial Service Unit and Epidemiological Studies Unit, Harkness Building, Radcliffe Infirmary
      3. c Flinders University of South Australia School of Medicine, Adelaide, Australia
      4. a Department of Social Medicine, Canynge Hall, Bristol BS8 2PR
      5. b Department of Primary Care and Population Sciences, Royal Free Hospital School of Medicine, London NW3 2PF
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