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

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • A weight control program that focused on behavioral and environmental strategies to change lifestyle habits and maintain weight loss
  • The aim of this study was to assess the long-term effectiveness of the weight control program and to identify factors influencing long-term weight loss.
Inclusion Criteria:
  • Polytechnic institute in Singapore
  • Obese students (see below for criteria) age 15 to 21 years enrolled in a weight control program
  • Comparison group did not participate in the weight control program.
Exclusion Criteria:

Not described.

Description of Study Protocol:
  • A two-year prospective non-randomized comparison group study was conducted in a polytechnic institute to assess the association between weight change (the dependent variable) and selected independent variables among obese students age 17 to 21 years enrolled in a weight control program
  • The body mass index (BMI) was used to define obesity, in which a BMI of 25 to 29.9kg per m2 was defined as mild obesity and a BMI of 30kg per m2 and above as moderate obesity
  • The weight control program, using a combined strategy of behavior modification, nutrition education and exercise, was implemented by the first author and a team of doctors and nurses from the healthy lifestyle center in the institute after attending a course on obesity management conducted by the Food and Nutrition Department of the Ministry of Health. Students were free to choose individual counseling or group therapy. The program consisted of an initial treatment phase and a maintenance phase. The initial eight-week phase comprising four weekly sessions and two fortnightly booster problem-solving sessions stressed on developing the student’s skills to change their eating habits and physical activity pattern. Students were encouraged to make their own decisions to make gradual changes to their diet and exercise by using self-monitoring of weight, diet and physical activity; making healthier food choices in reducing fat intake when eating out; cognitive restructuring; setting realistic goals; stimulus control; and reinforcement. They were also taught how to manage stress and resist peer pressure. Pamphlets produced by the Training and Health Education Department and the Food and Nutrition Department were distributed to all students.
  • The maintenance phase consisted of two problem-solving sessions held a month apart. During these sessions, students discussed ways to incorporate increased physical activity in their daily routine and cope with temptations to eat, stress and examinations. As attendance was poor due to student’s lack of time and their preference for self-help written materials, we subsequently maintained contact with them by phone and mail. Individualized messages were mailed to the students six months and a year after the initial treatment phase to disseminate practical tips on weight loss that had been used effectively by their peers. Congratulatory messages were also sent to those who were able to maintain weight loss from our monitoring and they were encouraged to share their experiences with their peers.
  • At the same time, the institute implemented new policies and made some environmental changes to foster healthier lifestyle practices. Students were encouraged to participate in sports; more water coolers were installed; and food low in fat and caloric content were coded green to help students make healthier choices. Prizes were also given to the top three students who would maintain their weight loss for a year.

Statistical Analysis

  • Statistical analyses were performed using the SPSS program. Weight loss in the group enrolled in the weight control program was first compared with the group not in the program (comparison group)
  • Bivariate methods were used initially to screen each independent variable to determine any statistical association between the list of independent variables and the dependent variable: long-term weight change among students in the program
  • The paired T-test was used to compare mean weight change from baseline to two-year follow-up by selected independent variables and correlation analysis to determine associations between the independent variables and dependent variable: long-term weight change
  • Non-collinear variables that were statistically associated with weight change at the 5% level of significance from bivariate analysis were entered stepwise into the multiple regression model to determine the best combination of variables predictive of weight change.
Data Collection Summary:

Dependent Variables

Weight change.

Independent Variables 

The same questionnaire was administered to students at enrollment and at two-year follow-up. Questions included demographic data, dietary habits, exercise frequency per week, knowledge of complications of obesity, and social support.  Dietary intake information was obtained on the weekly frequency of consuming selected food categories such as fried food, fatty meat, snacks, and number of sweet drinks consumed per day. A three-day food record of daily intake was also obtained. Baseline height and weight measurements were taken by trained nurses at the healthy lifestyle center.  Subsequently, students were asked to come weekly to the healthy lifestyle center during the first two months and monthly thereafter to weight themselves under supervision of a nurse. After two years, students were contacted to report to the healthy lifestyle center to complete the questionnaire and have their weight taken. Those who did not respond after three attempts were interviewed over the phone. To reduce errors from self-reporting, they were first asked whether they have a weighing scale at home. Those with a positive reply were asked to weight themselves then and give their weight while those without a weighting scale were asked to go to the nearest place to weigh themselves. The interviewer contacted them the next day for the weight measurements. Ten percent self-reported their weight.

Control Variables

None of those in the comparison group came to the healthy lifestyle center to weigh themselves or complete the questionnaire. Thus their height and weight measurements were based on self-reports over the phone. As they were reluctant to be interviewed over the phone, they were only asked whether they had attempted to lose weight over the past two years. 

Description of Actual Data Sample:
  • Original sample: All 374 first year obese students were requested to enroll in the weight control program.  216 (55.4%) attended the briefing session and 167 (44.7%) students enrolled in the program.
  • Withdrawals/Drop-outs: Female students attended 56.5% of the assigned sessions compared to 46.7% among the males. Main reasons for non-attendance were lack of time and they did not think it necessary as they had been given reading materials.
  • Final sample: At two-year follow-up, 112 (67.1%) of students enrolled in the program and 86 (54.4%) of those who did not attend the briefing and were not in the program (comparison group) participated in the survey.
  • Location: A polytechnic institute in Singapore
  • Race/Ethnicity: Singapore is implied.
Summary of Results:
  • Students in the weight control program and those not in the program (comparison group) were quite similar in age (17.5 years vs. 17.3 years) and mean baseline BMI (27.5 vs. 28.1kg per m2). However, there were more females in the weight control program (44.6% vs. 28.9%) than the comparison group.
  • At two-year follow-up, a higher percentage (71.4%) of the students in the weight control program had lost weight compared to 60% of those not in the weight control program, although the difference was not statistically significant (P=0.114). 10.7% of students in the weight control program regained all the weight lost during the initial eight-week treatment phase. The other 17.9% did not lose weight at all or gained additional weight.
  • The overall mean BMI has decreased from 27.5kg per m2 at baseline to 26.4kg per m2 at the two-year follow-up with 29.5% having achieved normal weight (BMI less than 25kg per m2, P<0.005).  The mean weight loss at the two-year follow-up was 2.9kg with more weight loss in males (3.3kg) than females (2.3kg).*****


Mean BMI

Mean Weight Loss (kg)

























Different letters indicate significantly different between eight-week and two-year at P<0.005.

  • Bivariate analysis showed some gender differences in factors associated with weight loss. Self-monitoring of weight, number of behavior modification techniques and income were significantly associated with weight loss in males only, while number of dietary changes, and support of friends and family were significantly associated with weight loss in females only. Factors associated with weight loss in both males and females were increased physical activity, resisting emotional cues to eat and percentage of weight loss in the first eight weeks. For both genders, weight loss at two-year follow-up was not significantly associated with keenness in losing weight, concern about being overweight, knowledge score on complications of obesity and number of sessions attended.
  • The six independent variables found to be significantly associated with weight loss at two years but showed no collinearity with each other viz, initial percentage of weight loss, physical activity, income, number of behavior modification techniques, diet changes and support were entered stepwise into the multiple regression equation to assess their joint effects on weight loss. The same three variables were found to be significantly associated with weight loss in both males and females. These were percentage of weight loss in the initial eight-week treatment period, increase in physical activity and income status. The cumulative adjusted R square (R2) for the three variables was 59.5% of the variance in weight loss were accounted for by the joint effects of initial weight loss, exercise and income. In females, the cumulative adjusted R2 was 0.480. This means that 48% of the variance in weight loss in females were accounted by the joint effects of the three variables. In males initial weight loss was the most important single variable accounting for 33.2% of the variance in long-term weight loss. In females, initial weight loss accounted for 29.1% and physical activity 13.5% of the variance in long-term weight loss.  
  • Behavior modification techniques include:
    • Self-monitoring of weight
    • Self-monitoring of diet
    • Self-monitoring of physical activity
    • Resisting cues to eating
  • Number of dietary changes include taking less in a week of the following items:
    • Fatty meat
    • Fried foods
    • Sweet drinks
    • Snacks and desserts
    • Supper
  • Fat intake score:
    • 0-did not take less fat
    • 1-take less fatty meat or fried food
    • 2-take less fatty meat and fried food
  • Support score:
    • 0-no support
    • 1-support from family or peers
    • 2-support from family and peers.
Author Conclusion:

Directly quoted from study:

  • In conclusion, our behavioral weight control program was quite effective in maintaining long-term weight loss. Important predictors associated with long-term weight loss were initial percentage of weight loss and increased physical activity. We recommend intensive efforts during the initial stage to help students lost weight gradually through behavior modification and strategies to incorporate increased physical activity in their daily routine.
  • Our study showed a higher success rate with 50.9% of adolescents achieving a reduction in BMI of at least 5%
  • The two most important predictors were initial weight loss and increase in physical activity
  • We were able to get students to exercise by emphasizing its immediate social and psychological benefits such as decreasing stress, feeling more relaxed, looking better, being able to concentrate and study better and feeling fit and less lethargic.
Funding Source:
University/Hospital: National University of Singapore, Singapore Polytec
Reviewer Comments:
  • Crude assessment of diet which was based on self-reporting of frequency of consumption of certain food categories
  • Comparison was only for weight and weight loss-rest of analyses were for intervention group
  • High proportion of students in non-intervention group reported weight loss, but could be due to non-participation in program, the public healthy lifestyle campaign, which was campus-wide; selection bias; weight was based on self-report only in comparison group compared to 10% self-report in intervention group.
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? No
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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? No
  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.) No
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? No
  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%.) Yes
  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? N/A
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? Yes
  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? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
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? N/A
  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? No
  6.6. Were extra or unplanned treatments described? No
  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? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? No
  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? No
  7.7. Were the measurements conducted consistently across groups? No
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)? N/A
  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? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  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