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NC: Behavior Change Strategies (2007-2008)

Wing RR, Jeffery RW. Benefits of recruiting participants with friends and increasing social support for weight loss and maintenance. J Consult Clin Psychol 1999 Feb; 67 (1): 132-138.
PubMed ID: 10028217
Study Design:
Cohort study
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

The purpose of the study was to determine the benefits of social support for weight loss and maintenance.

Inclusion Criteria:
  • Aged 25 to 55 years
  • 15 pounds to 70 pounds (6.8kg to 31.8kg) over ideal body weight (IBW)
  • Generally good health
  • Provide informed consent.
Exclusion Criteria:

None stated.

Description of Study Protocol:


  • Participants were recruited through advertisements placed in major newspapers in Pittsburgh, PA and Minneapolis, MN
  • The advertisements asked potential applicants whether they and their friends would like to lose weight but also indicated that it was possible to join the program alone or with three other people.


  • Participants were randomly assigned either alone or with the other members of their team to one of two experimental conditions
  • A standard intervention condition or an intervention that focused on social support and included a financial contingency for weight maintenance.


The study had four conditions

  • Group One: Participants were recruited alone and given SBT
  • Group Two: Participants were recruited alone and given SBT plus the social support intervention
  • Group Three: Participants were recruited with three friends and given SBT
  • Group Four: Participants were recruited with three friends and given SBT plus the social support intervention.

Statistical Analysis

  • Analysis used general linear modeling programs of Statistical Analysis System. Primary analyses compared the four treatment groups on changes in weight from months zero to four, from months four to 10 and from months zero to 10.
  • Initial weight, center, gender, employment status and prior experience with organized weight loss programs were used as covariates. Weight loss from months zero to four was also included in weight maintenance analyses. Chi-square analyses were conducted to compare the proportion of participants who successfully maintained their weight loss vs. those who regained weight.
  • Analyses using all participants who attend the follow-up session, using the intent-to-treat approach in which participants with missing data were assumed to have returned to their baseline weight.
Data Collection Summary:

Timing of Measurements

Baseline, four months, seven months, 10 months and 16 months.

Dependent Variables

  • Weight was measured using a balance-beam scale, with participants in light street clothes and no shoes
  • BMI was calculated from weight and height, as measured with a stadiometer
  • Social support was measured at baseline using the Sallis Social Support Scales for Eating and Exercise Behavior
    • At months four, seven and 10, participants were asked to indicate how supportive other study participants had been of their weight loss efforts on scale ranging from one (not at all supportive) to five (very supportive).

Independent Variables

  • Group Two: Recruited alone and SBT plus social support
  • Group Three: Recruited with friends and SBT
  • Group Four: Recruited with friends and SBT plus social support.

Control Variables

Group One: Recruited alone and with SBT.

Description of Actual Data Sample:
  • Initial N: 166 (82 men, 84 women)
  • Attrition (final N): 90 (54%) participated in the 16-month follow-up
  • Age (mean±SD): 42.5±8.5 years
  • Other relevant demographics:
    • Participant characteristics in the four treatment groups: No differences were observed in gender, age or weight
    • Those participants who entered the study with a group of friends were more likely to be employed outside the home and less likely to have previously participated in an organized weight loss program.
  • Anthropometrics:
    • BMI: 31.2±3.7kg per m2 
    • Body weight: 84.9±12.2kg
  • Location: Pennsylvania, PA and Minneapolis, MN.

Summary of Results:

 Weight Loss in Kilograms

  SBT alone SBT + SS SBT with friends SBT with Friends + SS
Baseline to Month 4

N=30 (79%)

weight loss

Mean, SD

-7.0 (3.8)

 N=44 (92%)

weight loss

Mean, SD

-6.9 (3.5) 

N=36 (90%)

weight loss

Mean, SD

-8.6 (4.3)

N=39 (98%)

weight loss

Mean, SD

-9.3 (4.0)

Baseline to Month 10

N=29 (76%)

weight loss

Mean, SD

-5.3 (6.8)

N=36 (75%)

weight loss

Mean, SD

-6.1 (4.7)

N=33 (83%)

weight loss

Mean, SD

-8.8 (6.6)

N=38 (95%)

weight loss

Mean, SD

-8.7 (6.3)

Months 4-10


weight loss

Mean, SD

1.6 (4.0)


weight loss

Mean, SD

0.8 (2.6)


weight loss

Mean, SD

0.1 (3.5)


weight loss

Mean, SD

0.5 (3.7)

 Other Findings

  • Only 90 of the initial 166 (54%) participated in the 16-month assessment. Attendance was significantly different across the four conditions, with better attendance for those recruited with friends than for those recruited alone (65% vs. 44%); P<0.008.
  • Overall weight losses from Months zero to 16 ranged from 6.2kg to 7.9kg, with no significant differences between treatments
  • Participants recruited with friends regained slightly more weight from months four to 16 (2.7kg vs. 1.2 kg); P=0.06.
  • Weight maintenance was assessed as a dichotomous variable, comparing those who gained weight for months 4 to 10 with those who maintaind or lost additional weight from months four to 10. There was a highly significant chi-square for the four-group comparison X2 (3, N=136) = 11.7; P<0.009. Both the effect of recruitment approach X2 (1, N=136) = 4.4; P<0.04, and the effect of the social support intervention, X2 (1, N=136) = 7.1; P<0.009, were significant. For participants who were recruited alone and received SBT, 24% maintain their weight loss in full. In contrast, for partipants recruited with friends and given the social support intervention, 66% maintain their weight loss in full.
  • Overall, weight losses were greater in participants recruited with friends (4.7 vs. 3.0kg); P<0.03.
  • The Sallis Social Support Questionnaire completed at baseline was unrelated to subsequent weight loss in Groups 1, 2 or 3. In Group 4, there was a modest association, higher positive family support for health eating (r=0.36; P<0.03)and exercise (r=0.32; P<0.05) were related to poorer weight loss from baseline to month 10. In contrast, higher perceived social support from others in the group (averaged over months, four, 7 and 10) was related to greater weight losses from baseline to month 10 in Group 2 (r= -0.50; P<0.003), 3 (r=-0.59; P<0.001) and 4 (r=-0.23; P>0.10).
Author Conclusion:
  • The main finding in this study was that recruiting participants with a team of three friends and treating them with a strong social support intervention decreased the number of dropouts and markedly increased the percentage of participants who maintained their weight loss in full, over a six-month follow-up period when the social support intervention was still in effect
  • The social support manipulation was somewhat effective in this study and improved the maintenance of weight loss for both participants recruited alone and those recruited with friends.
Funding Source:
Reviewer Comments:
  • Discussion points noted by the authors
    • Participants were not randomly assigned to a recruitment condition. Thus, the differences between participants recruited with friends and participants recruited alone may have been due to differences in the type of individuals who participated in the two condtions.
    • A second concern is that the soical support intervention included several different strategies, with both intra-group cohesiveness activities and an intergroup competition with financial prizes. Thus, it is not possible to reach conclusions about the key components of this intervention.
  • No measures of physical activity were included
  • The impact of social support interventions on long-term weight loss deserves further investigation.
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? Yes
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) N/A
  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? Yes
  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.) N/A
  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? 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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  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? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  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? N/A
  6.6. Were extra or unplanned treatments described? N/A
  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? 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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  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