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MNT: Weight Management (2015)

Matsuo T, Murotake Y, Kim M, Akiba T, Shimojo N, Kim M, Tanaka K. High general self-efficacy is associated with less weight loss under a supervised dietary modification program. Obesity Research & Clinical Practice 1986; 4: e83-e162. PubMed ID: 24345652
Study Design:
Before-After Study
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To investigate the association between general self-efficacy and body weight change during a 14 week supervised dietary modification program among the Japanese population.
Inclusion Criteria:
  • Satisfied at least one of the following criteria: Body mass index (BMI) over 25kg/m2 or waist circumference (WC) greater than 90cm
  • Written informed consent provided.
Exclusion Criteria:
Did not satisify at least one of the following criteria: Body mass index (BMI) over 25kg/m2 or WC greater than 90cm.
Description of Study Protocol:


Recruited through advertisements in local newspapers.


  • 154 obese middle-aged Japanese women were selected as subjects for an intervention program mainly comprised of diet counseling over 14 weeks
  • Diet counseling was provided by skilled dietitians in 12 group sessions and all subjects were instructed to choose and consume a well-balanced 1,200-kcal diet per day, while keeping a daily food diary
  • Body weight, waist circumference and coronary heart disease risk factors were measured before and after the intervention
  • Energy intake and activity energy expenditure were assessed before and after the intervention and general self-efficacy was assessed with the General Self-Efficacy Scale (GSES) before the intervention.

Blinding Used



Diet counseling provided by skilled dietitians in 12 group sessions, with instruction regarding a well-balanced 1,200-kcal diet.

Statistical Analysis

  • Student's paired T-tests were performed to test the significance of changes in values measured before, during and after intervention program
  • Pearson's product moment correlation was used to assess the relationship between two measurement values
  • One-way analysis of covariance (ANCOVA) used to analyze changes in values across multiple groups
  • Tukey-Kramer's post-hoc test was applied when difference was significant, according to results of ANCOVA
  • Chi-square tests used to analyze categorical values
  • Multiple regression analysis was conducted to determine a combination of predictors for weight change
  • Statistically significant difference, P<0.05.
Data Collection Summary:

Timing of Measurements

  • Self-efficacy assessed with the validated tool, GSES, before the intervention
  • Measured before and after the 14-week intervention
    • Body weight, height and waist circumference 
    • Systolic and diastolic blood pressures (SBP and DBP) 
    • Serum total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) triglycerides and fasting plasma glucose.
  • Before and at the beginning of Week 10 of the intervention
    • Total energy intake in kcal and amounts of each nutrient (carbohydrates, fat and protein in grams) assessed by a three-day weighed dietary record and dietary recall interviews
    • Activity energy expenditure (AEE), assessed by a uniaxial accerlerometry sensor and a diary of exercise.

Dependent Variables

  • Body weight
  • BMI
  • Waist circumference.
  • Blood pressure
  • Total, LDL- and HDL-cholesterol
  • Serum triglycerides
  • Total energy intake
  • Macronutrient intake
  • Activity energy expenditure.

Independent Variables


Control Variables

  • Height
  • Age.
Description of Actual Data Sample:
  • Initial N: 154 females
  • Attrition (final N): 154 females
  • Age: 51.2±8.9 years
  • Ethnicity: Japanese
  • Other relevant demographics: None
  • Anthropometrics: Baseline weight, 68.7±9.2kg; baseline BMI, 28.2±3.0kg/m2
  • Location: Chiba, Japan.
Summary of Results:

Key Findings

  • Significant reductions were observed in body weight (-7.8kg), BMI (-3.2kg/m2), WC (-7.6cm), SBP (-14mmHg), DBP (-8mmHg), TC (-23mg per dL), TG (-44mg per dL), LDL-C (-16mg per dL), FPG (-8mg per dL), total energy intake, carbohydrate intake, fat intake, ratio of fat intake to total energy intake and protein intake.
  • Significant increases in HDL-C (+2mg per dL), ratio of protein intake to total energy intake, AEE and AEE/BMI were observed
  • Significant correlations were observed between amount of weight loss and age, baseline BMI, many dietary and physical activity measurements and GSES
  • Weight loss was significantly greater for the Low GSES Group than for the High GSES Group
  • Weight loss was significantly greater within the Low "degree of confidence in one's ability relative to others" Group than within the middle or high groups of this category
  • No differences across the three groups were observed in the GSES categories of "positive attitude" or "fear of failure"
  • No difference across three GSES groups were observed in any of the analysis except AEE at baseline
  • Significant difference observed between GSES groups: The highest ratio of subjects with at least 10% weight loss was observed in the Low GSES Group, while the lowest ratio was observed in the High GSES Group
  • In multiple regression models, baseline BMI, AEE and total energy intake were significant and independent predictors for weight loss accounting for 16% of the total variance in body weight change.

Correlations of Weight Loss with Selected Values


Correlation Coefficient vs. Weight Reductions


Partial Correlation Coefficient vs. Weight Reduction

Baseline BMI -0.27 <0.01 0.009 0.25
GSES 0.25 <0.01 0.26 <0.01
Delta Total Energy Intake 0.22 <0.01 0.23 <0.01
Delta Carbohydrate Intake 0.16 0.04 0.18 0.02
Delta Fat Intake 0.25 <0.01 0.24 <0.01
Delta Protein Intake -0.01 0.9 0.03 0.74

Delta AEE










Comparison of Selected Values Across Three GSES Groups





Delta Total Energy Intake (kcal/day) -687±26 -683±21 -734±26 Not significant
Delta Carbohydrate Intake (grams/day) -93±4.0 -96±4.0 -96±4.0 Not significant
Delta Fat Intake (grams/day) -24±1.0 -23±1.0<0.01 -27±1.0 <0.05
Delta Protein Intake (grams/day) -13±2.0 -11±1.0 -13±2.0 Not significant

Delta AEE (kcal/day)




Not significant

Delta AEE/BMI (kcal/day)




Not significant
Author Conclusion:
  • High general self-efficacy is associated with less weight loss under a supervised dietary modification program among obese, middle-aged Japanese women
  • General self-efficacy accounted for a significant portion of the total body weight reduction variance that occurred in response to a weight loss intervention.
Funding Source:
University/Hospital: 2004-2006 Tanaka Project of Tsukuba Advanced Research Alliance at the University of Tsukaba
Sodegaura Health Promotion Project
Reviewer Comments:
Study limitations include measuring energy intake with three-day weighted food records which may underestimate intake and limited generalization of findings to other populations and situations.
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? N/A
  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? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? 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? 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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? Yes
  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)? No
  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