This review, to evaluate the effectiveness of school-based strategies to control or prevent obesity, found combined nutrition and physical activity interventions were effective at achieving weight reduction in school settings. Given the potential for publication and language bias, the restriction of included trials by unreported quality criteria and the possible inappropriate pooling of trials, these conclusions may not be reliable.

To evaluate the effectiveness of school-based strategies to control or prevent obesity .

MEDLINE, HealthSTAR, PsycINFO and EMBASE were searched from inception to February 2000. Update searches were performed on MEDLINE, CINAHL and PsycINFO from February 2000 to October 2004. The Cochrane Library was also searched for systematic reviews. Bibliographies of review articles, meta-analyses and articles written by experts in the field were handsearched. Only published English-language papers were sought.

Controlled studies (with either pre/post measures or control groups) of children (aged three to 18 years) that were conducted in a school setting, with a follow-up period of at least six months, were eligible for inclusion. Included studies had to report common weight-related outcomes (e.g. body mass index, body weight). Exclusion criteria applied were: data presented in graphs or were categorical; unknown sample size; poor methodological quality; and lack of standard deviation.

The majority of included studies were randomised controlled trials (RCTs. Treatment and primary prevention interventions were included. Most included studies took place in elementary schools. The included studies were conducted in a variety of countries. There was a variety of interventions that were used singly or in combination (e.g. physical activity, nutrition and parent involvement).

The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.

Methodological quality was assessed using the relevant section of the Centre for Disease Control and Prevention's (CDC) Community guide data abstraction form, which takes into account suitability of study design and validity (no further details reported).

Validity was assessed by two reviewers and disagreements resolved by consulting a third reviewer.

Two independent reviewers extracted data for the outcomes weight, body mass index, body fat and skin-fold thickness into the CDCs Community guide data abstraction form. For studies that reported the same outcomes and interventions, mean change and standardised mean differences and corresponding 95% confidence intervals were calculated.

Standardised mean differences and 95% confidence intervals were pooled for trials with similar interventions. Statistical heterogeneity was assessed using the χ² test and I² statistic. When statistical heterogeneity was present the random-effects model was used (otherwise the fixed-effect model was used). Subgroup analyses were performed for gender.

Nineteen trials were included in the review (n=more than 13,029 children); 14 were randomised controlled trials (RCTs, n=>14,418 children) and five were non-randomized controlled trials (n=4,690 children); eight trials were included in the meta-analysis.

Eight trials assessed a combination of nutrition plus physical activity and found a significant reduction in body weight compared with control (standardised mean difference -0.29, 95% confidence interval (CI): -0.45 to -0.14; χ²=76.38, p<0.00001, I²=90.8%). Other interventions (nutrition and TV reduction) were each assessed in single trials and were also associated with a significant reduction in body weight compared with control. Physical activity was not associated with reduction in body weight (one trial).

Combination trials with a parent/family component were associated with improved body weight compared to control (standardised mean difference -0.20, 95% CI: -0.41 to 0.00; χ²=8.35, p =0.04, I² =64.1%, four trials). This effect decreased when both a family and environmental component were included (standardised mean difference -0.16, 95% CI: -0.32 to 0.00; χ²=5.71, p=0.02, I²=82.5%, two trials).

Combination nutrition and physical activity interventions were effective at achieving weight reduction in school settings.

The review addressed a clear question, with inclusion criteria for participants, outcomes and study designs. However, a large number of studies were excluded as they failed to meet quality criteria that were not described in the review. Only English language studies were sought, which may have increased the possibility of language bias. The review was restricted to published studies, which may have increased the possibility of publication bias (which was not assessed). The authors stated that they assessed validity, but few details were reported and results of the validity assessment were not shown. Study quality was incorporated by restricting the analysis to certain trials but no further details were reported. Validity assessment and data extraction were performed by two reviewers, decreasing the possibility of error and bias in the review process. The authors did not report that similar steps were taken for study selection. Although the authors attempted to combine similar trials in meta-analysis, statistical heterogeneity was present in most of the analyses, so pooling may not have been appropriate. Given the possibility of language and publication bias, the restriction of the review to trials that met unreported quality criteria and the possible inappropriate pooling of trials, the authors' conclusions may not be reliable.

Practice: The authors did not state any implications for practice.

Research: The authors stated that interventions that modify school policies and the physical environment in ways that support improved dietary practices and regular physical activity but do not provide behavioural programs, and evaluation of these, are needed.

Not stated.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.