Weight Management

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The purpose of this study was to determine whether adding motivational interviewing to a behavioral weight control program improves weight loss outcomes and glycemic control for overweight women with Type 2 diabetes.

Inclusion Criteria:
  • Women with type 2 diabetes treated by oral diabetes medications, but not insulin
  • Overweight (BMI 27kg to 50kg to m2)
  • Generally healthy
  • Could walk for exercise.
Exclusion Criteria:
  • Pregnancy
  • Recent significant weight loss (over 10 pounds)
  • Severe debilitating disease.
Description of Study Protocol:


  • Volunteers were recruited from the Birmingham, Alabama area between 2000 and 2002 using social marketing channels, direct mail solicitation and physician referrals
  • Individuals were screened by phone and then invited to a group orientation where the study was described and informed consent obtained.


Participants all received an 18-month, group-based behavioral obesity treatment and were randomized to individual sessions of motivational interviewing or attention control (total of five sessions) as an adjunct to the weight control program.

Blinding Used

The interventionists were masked to experimental design.


Five individual sessions using motivational interviewing were an adjunct to a weight control program.

Statistical Analysis

  • Baseline comparisons between experimental conditions for study dropouts compared with completers were performed using two-sample Student's T-tests and X2 tests for continuous and categorical measures
  • The main effect of treatment on primary outcomes (weight, BMI and A1C) was analyzed using two-factor ANOVA with repeated measures on each visit. Changes in primary outcomes were further modeled using ANCOVA with adjustments for baseline weight or A1C.
  • To account for the relationship between glycemic control and weight-loss, weight change was added as covariate to the models where A1C change was the outcome. Multiple comparisons in ANOVA and ANCOVA were performed with Tukey-Kramer adjustments.
  • For variables with unequal variances between conditions, Satterthwaite adjusted P-values are presented. All treatment outcome variables were also examined using random-effects mixed models, which consider all available data.
  • Pearson correlation coefficients were used to assess the direction and magnitude of associations between weight loss and glycemic control and between adherence measures and weight and metabolic control.
  • Two sample Student's T-tests were used to examine adherence between treatment conditions.
  • Multi-variable regression models were used to test the mediational effect of behavioral adherence measures on weight change at six and 18 months.
Data Collection Summary:

Timing of Measurements

Baseline, six months, 12 months and 18 months.

Dependent Variables

  • Body weight was measured without shoes using a calibrated balance beam scale
  • Height was measured without shoes using a wall-mounted stadiometer
  • BMI was calculated as weight in kilograms divided by the square of height in meters
  • Glycemic control was indexed by A1C, measured with a Bayer CDA 2000+ Analyzer
  • Intervention process measures were also collected to determine number of group sessions attended, number of self-monitoring diaries submitted and average group leader rating of self-monitoring diary quality (on a three-point scale).

Independent Variables

  • Five individual motivational interviewing sessions were held with the first session before starting group therapy, then at three, six, nine and 12 months
  • Sessions lasted approximately 45 minutes and were delivered by licensed clinical psychologists.

Control Variables

All participants received a 42-session weight management program which met weekly for six months, biweekly for six months, and then monthly for six months. Weight-loss induction was emphasized in the first six months and weight maintenance in the subsequent 12 months.

Attention control group: Individual health education sessions served as an attention placebo, with session number and length matched to motivational interviewing to control for any impact that individual attention from a health care professional might produce. Masters degree-level health educators delivered sessions that focused on women's health topics.

Description of Actual Data Sample:

Initial N

  • 217 women
  • Intervention: 109
  • Control: 108.

Attrition (Final N)

  • At 18 months: 202
  • Intervention: 103 (94%)
  • Control: 99 (92%).




  • White: 178 (82%)
  • African-American: 39 (18%)

Other Relevant Demographics

  • Married: 54%
  • College or higher: 35%
  • Employed: 35%.

Characteristic Total Sample Motivational Interviewing Attention Control P for Comparisons Between Conditions
Weight (kg)
Obese (BMI >30kg/m2) (percentage)
A1C (percentage)
Diabetes Medications (N)
Diabetes Duration (years)


Birmingham, Alabama.

Summary of Results:



Treatment Group

Measures and confidence intervals

Control group

Measures and confidence intervals

Statistical Significance of Group Difference

Weight Change (kg)

Six months

12 months

18 months

Mean, CI.




Mean, CI.








AIC (%)

Six months

12 months

18 months













Behavioral adherence measures

Group sessions  attended (percentage)

Six months

12 months

18 months

Diaries submitted (N)

Six months

12 months

18 months

Average diary ratings (0-2 range)

Six months

12 months

18 months













































Other Findings

For African American women with Type 2 diabetes, the addition of motivational interviewing to behavioral weight control program produced greater weight loss than seen in the control group; however, this additional benefit was not sustained after 12 months, when the motivational interviewing sessions had discontinued.

By contrast, white women receiving motivational interviewing weighed significantly less than baseline at six, 12 and 18 months. Therefore, the impact of motivational interviewing on weight control was more sustained for white women and was even evident after the motivational interviewing sessions had ceased.

Author Conclusion:

Motivational interviewing can be a beneficial adjunct to behavioral obesity treatment for women with Type 2 diabetes, although the benefits are not sustained among African-American women.

Funding Source:
Government: NIH
Reviewer Comments:

Well designed study. The addition of an Attention Control group - individual health education sessions that served as an attention placebo, helped to control for any impact that individual attention from a health care provider might produce.

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) 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? N/A
  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? Yes
  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? 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? Yes
  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)? 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? N/A
  10.2. Was the study free from apparent conflict of interest? Yes