NC: Weight Management (2007-2008)

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

To evaluate whether:

  • An active weight reduction strategy, based on the cognitive-behavioral therapy (CBT) approach and an initial very-low-calorie diet (VLCD) might lead to short- and long-term weight loss and alleviation of obstructive sleep apnea syndrome (OSAS)
  • Results of this intervention could be enhanced by combining it with nasal continuous positive airway pressure (CPAP) treatment during the first six months.
Inclusion Criteria:
  • Male sleep apnea patients
  • Age: 30 to 60 years
  • Body mass index (BMI): Over 35kg per m2
  • Subjective symptoms of OSAS
  • Oxygen desaturation index (ODI4): Over 10.
Exclusion Criteria:
  • Decompensated cardiac failure
  • Juvenile-type diabetes
  • Endocrine disease causing obesity
  • Severe psychiatric disorder.
Description of Study Protocol:


Sleep apnea patients. 


  • All patients entered a CBT weight reduction program lasting 24 months 
  • One follow-up visit conducted at 36 months (included interview and BMI measure)
  • Half the patients were randomly selected to have nasal CPAP treatment during the first six months of intervention. 


Both groups

  • Intervention started with an initial six-week diet using Dietta Mini (Medifood Ltd, Finland) VLCD preparations
  • Daily six-week diet contained 500kcal, 50g protein, 65g carbohydrate, one gram fat and the RDA of vitamins and minerals
  • Post six-week VLCD, started individualized CBT aimed at supporting weight reduction
  • Subjects received dietary counseling including oral and written information on eating behavior, nutrition, exercise, eating-related emotions and attitudes, health and weight and principles of weight reduction
  • Subjects encouraged to monitor eating habits, normalize eating patterns and increase exercise
  • Treatment program included individual meetings (30 to 45 minutes), with therapist (held two to four times per month during the first six months, once per month during the next six months and every second month during the second year). 

CPAP group: CPAP x six months + VLCD x six weeks + CBT x 24 months

  • CPAP treatment
    • Mean (range) pressure level was 13cmH2O (7.5 to 18.5cmH2O)
    • Nasal CPAP treatment stopped one week before six-month follow-up assessments

Non-CPAP group: VLCD x six weeks + CBT x 24 months.

Statistical Analysis

  • Normality of distributions tested using Liliefors test
  • Differences between patient groups or between time points within the same patient groups were analyzed using unpaired (inter-individual) or paired T-tests (intra-individual)
  • Bonferroni corrections used when analyzing data of more than two time points
  • Non-parametric tests used if variable not normally distributed
  • X2 test used to analyze significance of differences in frequencies between separate patient groups
  • Pearson correlation analysis used to evaluate relationships between weight loss (BMI) and objective alleviation of OSAS (ODI4, daytime sleepiness)
  • Multiple regression employed to examine relationships between baseline data and CPAP treatment and between change in ODI4 and BMI
  • All computations performed using Systat statistical software
  • Statistical significance set at P<0.05.
Data Collection Summary:


  • Overnight sleep recordings
  • Psychological assessments
  • Height and weight (BMI).

Timing of Measurements

  • Baseline, six, 12 and 24 months
  • 36 months (follow-up). 

Dependent Variables

  • Variable One: Body Weight (BMI); no description how it was measured
  • Variable Two: OSAS severity, measured via ODI4  
  • Variable Three: Daytime sleepiness, measured by Index of Subjective Sleepiness (ISS).
  • Variable Four: Emotional well-being assessed via semi-standardized interview and SCL-90R General Symptom Index (GSI).

Independent Variables

  • CPAP x first six months
  • Six-week VLCD
  • Individualized CBT x 24 months.

Control Variables

  • No CPAP
  • Six-week VLCD
  • Individualized CBT x 24 months.
Description of Actual Data Sample:
  • Initial N: 33 males
    • CPAP (N=18)
    • No CPAP (N=15). 
  • Attrition (final N): 31
    • CPAP (N=17)
    • No CPAP (N=14).
  • Age: Mean (±SD), 49.1±7.9 years.
  • Ethnicity: N/A

Other Relevant Demographics

ODI4: Mean (±SD), 51.3±31.1 (differences between groups not significant).


BMI: Mean (±SD), 43.8±5.4kg per m2 (differences between groups not significant).



Summary of Results:
  Baseline Six Months
(Mean ±SD)
(Mean ±SD)
(Mean ±SD)
(Mean ±SD)
Number of Subjects
Age (years)
Weight (kg)
BMI (kg/m2)

Differences between CPAP and non-CPAP were not statistically significant (P>0.05).

Table Two: Changes in Weight, BMI, ODI4 During Weight Reduction Intervention for Whole Study Group

  Baseline Six Months 12 Months 24 Months
Weight (kg)
BMI (kg/m2)

Compared with baseline:

  • *P<0.001
  • **P<0.05.

Other Findings

  • No statistical differencs between CPAP and non-CPAP groups in weight reduction either during the first six months, when CPAP was used or thereafter
  • Best result in weight reduction was seen at six months, after which weight gradually started to increase again. However, after 24 months, weight was still significantly lower than at baseline.
  • Differences in ODI4 values between two groups were not significant from baseline to six months
  • Differences in ODI4 values between baseline and follow-up measurements were significant in the whole group (see Table Two): ODI4 decreased and increased in relation to change in weight
  • Pearson correlation coefficients between changes in weight and ODI4 in all patients were 0.59 (P<0.01) at six months, 0.68 (P<0.01) at 12 months and 0.75 (P<0.01) at 24 months
  • Multiple-regression analysis revealed the improvement of ODI4 at six months was significantly related to baseline ODI4 (P<0.001), but not to use of CPAP (P=0.13) or to baseline weight (P=0.10)
  • Amount of weight loss was significantly related to baseline weight (P<0.001), but not to the use of CPAP in the beginning of CBT (P=0.43)
  • Daytime sleepiness decreased from 14.2±4.1 at baseline to 10.9±3.7 at six months (P<0.001), to 9.8±3.7 at 12 months (P<0.001) and to 10.8±4.0 at 24 months (P<0.001). However, correlations between changes in ISS and ODI4 or weight were not significant (-0.00 or -0.25).
  • Treatment success was defined in terms of ODI4 reduction and subjective well-being at six and 24 months: ODI4 remained the same or increased in 10% (six months) and 26% of patients (24 months)
  • Patients' emotional well-being improved from baseline, was best at the six-month assessment and returned toward baseline therafter. The difference between baseline and six months was almost significant (P=0.05, Bonferroni adjusted). There was no difference between groups.
  • Patients showing treatment failure at 24 months more often had serious problems in several life sectors, when compared to those showing treatment success. Correlations between Life Stress Index and weight reduction and a decrease in ODI4 were -0.56 (P<0.01) and -0.49 (P<0.01). 
  • Three-year follow-up: Compared to original weight, 13 patients (42% of original group) still showed at least 5% weight loss and seven patients (23%) showed 10% weight loss. Six patients had increased in weight.
Author Conclusion:
  • Satisfactory weight-loss associated with improvement of OSAS could be achieved by means of CBT weight-loss program.
  • Adding CPAP in the initial phase of the weight reduction program did not result in significantly greater weight loss.
Funding Source:
Foundation associated with industry:
Reviewer Comments:
  • No information regarding how and from where patients were recruited
  • No description of how body weight was measured.
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? 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? 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? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  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? ???
  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)? No
  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? No
  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? ???