Cholesterol: Dietary modifications reduce blood cholesterol levels

Clinical bottom line (level 1a)

  1. In free-living subjects, low fat diets, changed polyunsaturated proportion diets and energy/fat changing diets all reduced average blood cholesterol levels
  2. In free-living subjects, longer periods of study were associated with smaller changes in blood cholesterol level
Tang et al: BMJ 1998; 316: 1213-1220
Expires March 2003

The study

Systematic review of RCTs with individual allocation of
  • Patients: free-living subjects
  • Intervention: global dietary modifications
  • Outcome: reduced blood cholesterol


    • Articles found in not stated using MEDLINE, EMBASE, Human Nutrition, Allied & Alternative Medicine, 1966 onwards (search terms: not stated ) and hand-searching 'American Journal of Clinical Nutrition'; searching reference lists of RCT and reviews; contact with experts

    Selection criteria: RCTs comparing a treatment with control arm, global intervention, lipid concentrations before and after intervention
    Appraisal criteria: not stated, by two independent reviewers
    Articles excluded if:
    • specific supplementation diets (65)
    • multifactorial interventions (34)
    • insufficient data (5)
    • other primary aims apart from cholesterol lowering (7)


    19 trials
    significant heterogeneity in studies of 'step 2' diets and 'increased ratio' diets

    The evidence

    • Mean reductions in blood cholesterol levels
      • American Heart Association (AHA) step 1 diet: 3.0% (95% CI1.8% to 4.1%)
      • AHA step 2 diets: 5.6% (95% CI 4.7% to 6.5%)
      • Increased ratio of polyunsaturated:saturated fats: 7.6% (95% CI 6.2% to 9.0%)
      • Low fat diets 5.8% (95% CI 3.8% to 7.8%)
      • 6 month interventions: 6.8%
      • 24 month interventions: 4.4%

    Comments

    1. Study has significant heterogeneity in some interventions which may reflect 'positive' publication bias
    2. It should also be kept in mind that this study specifically excluded studies that evaluated the effects of increased exercise and weight loss which are commonly recommended by doctors when advising patients about reducing cholesterol.

    Citation

    1. Tang JL, Armitage JM, Lancaster T, et al: Systematic review of dietary intervention trails to lower blood cholesterol in free-living subjects. BMJ 1998; 316: 1213-1220
    Contributor: Bob Phillips and Musab Hayatli, November 1999
    Reviewer: Kenneth Ballew

    Clinical Question.
    Patient free-living community subjects
    Intervention or Exposure dietary modification; low-fat diets
    Outcome blood cholesterol levels