DLM: Major Dietary Components for LDL-Cholesterol Reduction (2001)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the effects of the National Cholesterol Education Program's Step I and Step II dietary interventions on major CVD risk factors in healthy and high-risk subjects by conducting a meta-analysis.
Inclusion Criteria:
All published dietary intervention studies designed to decrease blood cholesterol or to decrease body weight for the primary purpose of preventing CVD.  Additional inclusion criteria: 
  • used a randomized design.
  • A Step I diet : <=30% of total energy as fat, <=10% of energy as SFA, and <=300 mg dietary cholesterol/d or a Step II diet: <=7% of energy as SFA, <=200 mg dietary cholesterol/d or both were part of the dietary intervention.
  • Subjects were free living, prepared their own food, and were counseled by dietitians or other professionals about implementing low-fat diets
  • Intervention lasted >=3 wk to stabilize plasma cholesterol.
Exclusion Criteria:
Excluded if not included above.
Description of Study Protocol:

Recruitment

MEDLINE and the references in the papers were used to select 37 dietary intervention studies in free-living subjects from 1981 - 1997.

Design

Meta-Analysis.

Blinding Used (if applicable)

Not applicable.

Intervention (if applicable)

Step I or II dietary interventions.

Statistical analysis:

  • Plasma lipids after dietary intervention were compared with lipid concentrations in the control groups as well as with baseline lipid concentrations.
  • ANOVA was used to compare the effects of Step I with those of Step II dietary interventions and the effects of exercise with no exercise.
  • Regression analysis was used to evaluate changes in plasma T-Chol, LDL-Chol, HDL-Chol, and TG in response to changes in body weight and in dietary total fat, SFA and cholesterol.
Data Collection Summary:

Timing of Measurements

Changes in serum lipids before and after Step I or II diets.

Dependent Variables

  • Serum lipids (Total cholesterol, LDL-cholesterol, HDL-cholesterol, TG)

Independent Variables

  • Step I or II diets as defined by inclusion criteria

Control Variables

 

Description of Actual Data Sample:

Initial N:  37 intervention studies published between 1981 and 1997 were selected for the present meta-analysis, representing 9276 subjects in intervention groups and 2310 subjects in control groups.

Attrition (Final N):  See above.

Age:  Not mentioned

Ethnicity:  Not mentioned

Other relevant demographics:

Anthropometrics:

Location:  Studies from all over the world 

Summary of Results:

Other Findings:

The study designs varied remarkably; some were sequential studies but most were randomized, parallel-arm studies.

21 intervention studies included both men & women, 9 studies included only men and 7 studies included only women.

19 studies included a control group in which subjects maintained their habitual lifestyle and food consumption throughout the study. Dietary information was estimated by using either a 24-h food recall or 3-7 d food records; a FFQ was also used in some studies. Some studies did not report complete dietary information.

The length of intervention ranged from 3 wk to 4 yr.

Step I and Step II dietary interventions significantly decreased plasma lipids and lipoproteins.

Step I Intervention changes: (P<0.01 for all of the following)

  • T-Chol decreased by 0.63 mmol/L or 10%
  • LDL-Chol decreased by 0.49 mmol/L or 12%
  • TG decreased by 0.17 mmol/L or 8%
  • TC:HDL-Chol decreased by 0.50 or 10%
  • HDL-Chol did not decrease based on Step I interventions 

Step II Intervention changes (P < 0.01 for all of the following):

  • T-Chol decreased by 0.81 mmol/L or 13%
  • LDL-Chol decreased by 0.65 mmol/L or 16%
  • TG decreased by 0.19 mmol/L or 8%
  • TC:HDL-Chol decreased by 0.34 or 7% 
  • HDL-Chol decreased by 7% (P = 0.05)

Positive correlations between changes in dietary total and SFA and changes in total cholesterol and LDL and HDL cholesterol were observed (r = 0.59, 0.61, and 0.46, respectively, P < 0.001).

Multiple regression analyses showed that for every 1% decrease in energy consumed as SFA, TC decreased 0.056 mmol/L and LDL-Chol by 0.05 mmol/L.; also for every 1-kg decrease in body weight, TG decreased by 0.011 mmol/L and HDL-chol increased by 0.011 mmol/L.

Exercise resulted in greater decreased in TC, LDL-Chol, and TG and prevented the decrease in HDL-Chol associated with low fat diets.

 

Author Conclusion:

A survey of the literature of dietary interventions showed that a decrease in dietary fat and SFA has beneficial effects on CVD risk factors in free-living subjects. Plasma T-Chol , LDL-Chol, and TG and the ratio of T-Chol/HDL- Chol significantly decreased after both Step I (by 10%, 12%, 8%, and 10% respectively) and Step II (by 13%, 16%, 8%, and 7% respectively) dietary interventions.

In many of these interventions, subjects lost weight (0.5-11 kg, mean: 3.38 kg). Weight loss and exercise resulted in a decrease in plasma TG and an ­ in HDL-Chol. Both exercise and a decrease in dietary fat (related to a decrease in energy intake) increased­ weight loss (2.8 kg weight loss from exercise and 0.28 kg weight loss for every 1% decrease in energy from total fat, respectively) and the effects were additive.

The results of this review provide a good benchmark of the extent to which Step I and Step II intervention programs should target healthy lifestyle practices that include diet modification, exercise and weight control to achieve maximal CVD risk reduction.

Funding Source:
University/Hospital: Pennsylvania State University
Reviewer Comments:

No tests for homogeneity were reported.  Some studies did not report baseline lipid levels.  Study quality not addressed.

Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? ???
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? ???
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes