PWM: School-based Programs to Prevent Overweight (2006)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the impact of a school-based health behavior intervention known as Planet Health on obesity and boys and girls in grades 6 to 8.
Inclusion Criteria:

All students in grades 6 or 7 in 1995 (all exposed to intervention).

Obesity defined as BMI & TSF >85th percentile of standards (Must, Dallal & Dietz, Am J Clin Nutr 1991).

Exclusion Criteria:

Excluded from study students on school lists who:

  •  transferred schools at baseline
  • were in special education classes
  • were in the wrong grade
  • excluded from analysis diet records with implausible energy intakes (<2100 or >29,000 kJ; <1% of observations)
Description of Study Protocol:

10 schools randomly assigned (using random number table) after matching by town or school size & ethnic composition.

Planet Health Education program received in 5 intervention schools (designed 16 core lessons/y + 1 additional Fruit and Vegetable (F/V) campaign to be integrated into existing curriculum & PE); regular curriculum in 5 control schools. 

Program aims:

  1.  TV viewing to <2 hours per day
  2.  moderate and vigorous physical activity 
  3.  intake of high-fat foods
  4.  fruit and vegetable intake to >5 servings per day

Data collected at baseline and after 2 school years of intervention.

Measurers blind to intervention status.

Data Collection Summary:


  • Obesity (measured BMI & TSF)
  • TV viewing (11-item Television and Video Measure questionnaire)
  • Moderate & vigorous PA (16-item Youth Activity Questionnaire; walking not included)
  • Dietary fat (Youth FFQ)
  • fruit and vegetable intake (Youth FFQ)
  • Total energy intake (Youth FFQ)


Planet Health program  group (see above)

Control Variables

  • Baseline value of behavioral variable
  • Intervention status
  • Randomization pairs
  • Gender
  • Age
  • Ethnicity
  • Baseline OB, BMI & TSF
  • Others tested (e.g., self-reported menarcheal age, smoking), but not included in final model

Statistical Analysis

  • Because schools, not students, were randomized, used GEE method for analysis of dichotomous outcomes to adjust for individual-level covariates under cluster randomization, with schools nested within experimental conditions (took into account correlation of responses within schools and school matching)
  • Separate regressions for boys and girls

Similar regressions to predict changes in behavioral measures and to assess the extent to which

Description of Actual Data Sample:

Baseline Sample: 1560 students (consent rates were 58% among schools with active consent and 89% among schools with passive consent; half of schools required active consent)

Withdrawals/Drop-Outs:  65% of eligible students (64.5% in C and 64.8% in I school); main reasons for nonparticipation in baseline anthropometry were lack of parental consent (80%), and absence (14%).

Final Sample: 1295 students, grades 6-8 (83% of baseline sample); main reasons for nonparticipation in f/u anthropometry were school transfer (52%), absence (27%), and child refusal (10%).

Location: 4 Massachusetts communities in Boston metropolitan area

Duration:  2 school years (1995-1997)

Race/Ethnicity:  63-69% W, 11-15% AA, 11-16% H

SES: Median household income in school areas = $36,020 for I schools and $34,200 for C schools (based on 1990 Census data)

Summary of Results:

Baseline comparisons – C vs. I:

  • No differences in age, anthropometric, diet, PA or sociodemographic characteristics
  • Higher AA girls (17% vs. 10%) and Hispanic boys (18% vs. 12%) in control schools

Program implementation:

  • Yr 1 training completed by 83% classroom teachers (n=86), 100% PE teachers (n=9)
  • Averaged 3.5 lessons/y by classroom teachers & 8.2 microunits/y by PE teachers

 Behavioral outcomes:   

  •  TV in girls (-0.58 hrs; 95% CI, -0.85 – -0.31 hrs; p=0.001) & boys (=0.40 hrs; 95% CI, -0.56 – -0.24 hr; p<0.001)
  •  fruit and vegetable intake in girls only (0.32 svgs/d; 94% CI, 0.14=0.50 svgs/d; p=0.003)
  •  energy increment in girls only (-575 J/d; 94% CI, -1155 = 0 J/d; p = p=0.05)
  • No change in fat intake (% kcals)
  • No change in energy intake (J/d)
  • No change in moderate/vigorous physical activity

Anthropometric outcomes:

  •  in obesity in girls only (OR= 0.47; 95% CI, 0.24-0.93; p=0.03; OB increased from 21.5% to 23.7 % in C school girls and decreased from 23.6% to 20.3% in I school girls)
  •  in remission of obesity in obese girls (OR=2.16; 95% CI, 1.07-4.35; p=0.04)
  • Largest obesity effects seen for African American girls

Relationship between behavioral and anthropometric outcomes:

  • Only TV viewing associated with reduction of obesity (OR=0.85; 95% CI, 0.75-0.97; p=0.02)
Author Conclusion:

The Planet Health intervention decreased obesity prevalence among female students over 2 school years. The success of this program implemented in public school by regular classroom and PE teachers indicates a promising approach to reducing obesity among youth.

The lack of an intervention effect among boys suggests that different causal factors may operate among boys and girls, although there is little published scientific evidence to support this hypothesis.  Alternatively, girls could be more attuned to issues of diet and activity and thus more responsive to the intervention.

While the analysis of obesity incidence and remission indicates statistically significant intervention effects only for remission, it is important to note that over this 21-month period only 33 incident cases occurred – 13 among intervention girls – which limited the statistical power of our study to detect differences.  Our finding of a significant effect on remission of obesity indicates that intervention effects may be largest among those most at risk for obesity.

Funding Source:
Reviewer Comments:


  • large sample size, long-term, multi-component trial
  • study protocols well described
  • measurers blinded to intervention status
  • analysis of relation between diet/PA behavior and adiposity


  • education only (no environmental or parental/family components) to intervention,
  • unable to adjust for maturation in boys
  • fairly low participation rate

Other Comments:

Monitored intervention safety by assessing extreme dieting behavior; found no change between baseline and followup.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? ???
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) ???
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? ???
4. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? No
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? ???
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? ???
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? ???
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? ???
  6.6. Were extra or unplanned treatments described? ???
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? ???
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? No
9. Are conclusions supported by results with biases and limitations taken into consideration? ???
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes