Meta-analysis or Systematic Review

M - Click here for explanation of classification scheme.

POSITIVE: See Quality Criteria Checklist below.

To determine the effectiveness of school-based strategies for obesity prevention and control using methods of systematic review and meta-analysis.

• Studies published in English between 1966 and 2000
• Target age: Children three to 18 years in school setting
• Report used weight-related outcomes (BMI, body weight, etc.), included a control measurement (either with pre- and post-measures or using control group(s); and followed participants for at least six months from the beginning of the intervention
• Study aimed to prevent unnecessary weight gain or manage weight and employed interventions related to nutrition, physical activity, reduction in television (TV) viewing or combinations thereof.

Fail to meet inclusion criteria.

Recruitment

Design  

• The literature search for overweight/obesity intervention studies published between 1966 and February 2000 was conducted using MEDLINE, HealthStar, Psych Info and Embase. A review of the studies was conducted in collaboration with the CDC and Prevention’s Guide to Community Preventive Services branch and has been published
• 25 Additional searches were conducted to retrieve studies published between February 2000 and October 2004 using Medline, Ovid, Cinahl and PsychInfo
• The Cochrane Library was searched to identify systematic reviews to be used for manual bibliography searching. Other meta-analyses, review articles and articles written by prominent authors in the field of obesity were also reviewed for relevant citations.
• Data were extracted from each article by two reviewers independently, using a standardized protocol developed by the CDC. Information about study description and results was collected and methodological quality was assessed
• The quality scoring system used takes into account suitability of study design and quantifies threats to validity. This score is used as the basis for excluding studies of poor quality from the review. The two reviewers compared quality scores and data extracted; the principal investigator was consulted when differing responses could not be reconciled.

Dietary Intake/Dietary Assessment Methodology 

Not applicable.

Blinding Used 

Not applicable.

Intervention 

Not applicable.

Statistical Analysis

• Data were analyzed using RevMan software version 4.2.54. For clusters of articles reporting the same outcomes and shared intervention types (nutrition, PA or combination), meta-analysis was performed. Data entered in RevMan included the following: Pre- and post-changes in outcome measures for the intervention and the control groups, the corresponding number of participants for each treatment group in the trial and standard deviation(s) (SD) 
• The standardized mean differences (SMD) were computed with their 95% confidence interval (CI). SMD was used because the trials included in the analysis assessed weight loss in different ways (e.g., BMI, weight and ponderosity). Using SMD transformed the results of trials into a uniform scale, so that they could be pooled. The SMD gives size of the treatment effect in each trial relative to the variability observed in that trial
• To assess the net effect of different interventions on weight loss, pooled SMD and 95% CIs were computed for clusters of trials with similar interventions. Weight reduction for each intervention type (nutrition, PA, combination) compared with placebo was considered statistically significant when the 95% CI around the pooled SMD did not include zero. Comparisons across interventions were made also using the 95% CIs around the pooled SMD 
• The Q-test was used to test for heterogeneity.The Q-test is based on the w² distribution and provides a measure of the sum of the squared differences between the results observed and the results expected in each trial, under the assumption that each trial estimates the same treatment effect. The I² test was also computed to estimate the degree of inconsistency of the results of the trials.

The following describe the studies included in the review and meta-analysis:

Timing of Measurements

Children were followed for at least six months from the beginning of the intervention.

Dependent Variables

Body weight, BMI, body fat measures indicative of overweight or obesity.

Independent Variables

Interventions related to nutrition, physical activity, reduction in TV viewing or a combination of these.

Control Variables

 Pre- and post-body weight measures or a control group.

• Initial N: 64 published trials identified
• Attrition (final N): 19 trials (representing >13,029 children) included in review; eight included in meta-analysis
• Age: Three to 18 years
• Ethnicity:
  • 10 studies conducted in US
  • One described as multiethnic
  • One including Native Americans
  • Nine conducted overseas
• Other relevant demographics: School children, with one US study specifying inner city school students
• Anthropometrics:
  • BMI
  • Skinfolds
  • Weight
  • Percent body fat
  • Central adiposity
  • BMI z-scores
  • WHR.
• Location: 10 studies conducted in US:
  • California
  • Massachusetts
  • New York
  • Connecticut
  • Minnesota
  • Midwest 
  • Nine conducted overseas:
    • Thailand
    • England
    • Australia
    • Israel
    • Greece
    • Taiwan
    • Chile
    • UK.

 

 

Intervention	Standardized Mean Differ with 95% CI	P-value
Combination	-0.29 (-0.45 to -0.14)	<0.05
Nutrition alone	-0.39 (-0.56 to -0.23)	<0.05
Physical activity alone	1.87 (1.31 to 2.42)	NS
TV reduction alone	-0.35 (-0.63 to -0.06)	<0.05

Other Findings

• When including only studies with a parent/family component in the analysis, the combination intervention improved body weight in school children ((SMD-0.20, 95% CI (-0.41–0.00)). The magnitude of the SMD for the combination intervention decreased [(SMD -0.16, 95% CI (-0.320-0.00)] when including only studies with both a family component and an environmental component
• In sub-group analysis by gender, the PA study showed better statistically significant weight reduction in girls (SMD -0.38, 95% CI (-0.74 to -0.02). The weight reduction in girls (SMD -0.38, 95% CI (0.74 to -0.02)) did not differ significantly when compared to boys (SMD -0.14, 95% CI (-0.17–0.44)).
• In studies employing combination interventions, girls showed non-significant (NS)
• Improvement in weight reduction compared with boys. Girls in the PA intervention showed NS better improvement compared to girls in trials that used combination interventions. However, in the combination interventions, boys showed NS better improvement compared with boys in the PA intervention trial.
• Significant heterogeneity shown using Q test and I² test within cluster analyses.

• The robustness of these findings is limited, as there is a high degree of heterogeneity, as measured by w² or I². The consistency of a meta-analysis depends on the similarity of magnitude of the treatment effects of the trials included in the analysis. To critically appraise these findings, the presence of any underlying potential source of heterogeneity has to be explored. Typically, heterogeneity is associated with reporting bias, differences in the intensity or duration of interventions, the underlying risk, the effect size and irregularities of data
• This meta-analysis helps to address uncertainty about the utility of school-based interventions to combat the childhood obesity epidemic. Although behavioral programs directed at weight control in schools may eventually prove to be less critical than the establishment of school policies and environmental modifications that promote health behavior change (without requiring significant motivation on the part of the student), most have in fact demonstrated success. In these analyses, we observed a pooled effect size of -0.29 in clusters of studies using combination nutrition and physical activity interventions
• Results of the analyses of studies using TV reduction, nutrition alone and physical activity alone should be interpreted cautiously, as only one study was available in each category. Nevertheless, these results indicate that the major contributing factor to the success of combination nutrition and physical activity interventions may be the nutrition component
• School policies and programs going forward should be informed by the evidence available to date, but not limited by it. Consistent patterns not yet assessable by meta-analysis have emerged. Weaving nutrition, physical activity or TV reduction lessons into the standard curriculum, so that key messages are reinforced in multiple contexts, appears useful. Programs appear to have been enhanced when physical activity was not merely encouraged, but made a routine part of the school day
• Conclusions drawn from this meta-analysis are consistent with those reported in previous systematic reviews. Authors found that combination interventions (nutrition and PA) with a parent or family component produced significant weight reduction. This result is supported by a recent meta analysis of seven intervention studies on weight loss for overweight children. On the other hand, results from interventions aimed at obesity prevention have not been as promising
• A recent meta-analytic review of 64 obesity prevention programs (46 trials) for children and adolescents showed that 79% of programs did not produce statistically reliable weight-gain-prevention effects.

Overall Impression:

Thorough review and meta-analysis resulting from strong, standardized procedures and conservative interpretation of the results.