DLM: Major Dietary Components for LDL-Cholesterol Reduction (2001)
- 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.
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.
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
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
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.
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.
University/Hospital: | Pennsylvania State University |
No tests for homogeneity were reported. Some studies did not report baseline lipid levels. Study quality not addressed.
Quality Criteria Checklist: Review Articles
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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 | |