NC: Social Learning Theory (2008)

Study Design:
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Quality Rating:
Research Purpose:

The purpose of the study was to evaluate the efficacy of a nurse delivered intervention designed to improve adherence to a cholesterol-lowering diet.

Inclusion Criteria:
  • 20 years or older
  • Stabilized on cholesterol-lowering dietary or pharmacological therapy for a minimum of two weeks. If on a lipid-lowering drug, no lower limit for LDL Cholesterol was set, since the patient had established hypercholesterolemia. If not on a drug the ATP II algorithm was followed, e.g., without CHD and with two or more risk factors, dietary intervention would be initiated for a serum LDL-cholesterol of at least 130mg per dL.
  • A score on the Connor Diet Habit Survey (DHS) indicating that the individual was consuming a diet with over 30% of calories from fat and was therefore non-adherent to the Step I Diet.
Exclusion Criteria:
  • Secondary hyperlipidemia
  • Complex medical and dietary regimens (e.g., patients with type 1 diabetes)
  • Patients who were unable to comprehend and write English
  • Patients who showed signs of mental confusion
  • Patients who would be unavailable for the three-month follow-up.
Description of Study Protocol:


Patients were screened for eligibility for study at three academic medical center practice and research sites (a lipid clinic, a cardiology clinic, and a research site). Patients at the lipid and cardiology clinics completed the Connor Diet Habit Survey to assess fat and cholesterol consumption. Subjects from the research site were former participants in a study examining the behavioral correlates of cholesterol reduction. These subjects completed the DHS at least six weeks following completion of the original study.  

If patients met the criteria of dietary non-adherence as well as all other criteria, they were invited to participate in the intervention study.


The study utilized a randomized controlled two-group pre-test, post-test design to enroll only subjects who were considered non-adherent to the cholesterol-lowering diet. The institutional Review Board approved the study protocol.

Blinding Used

Dietitian evaluating the food records was blinded to treatment group


Telephone intervention every two weeks. Telephone interventions included setting a goal for each two-week period between sessions, the subject reviewing the self-monitoring notes of the previous two weeks, the interventionist providing reinforcement and encouraging the subject's self-reinforcement, and the interventionist providing verbal persuasion directed at achievement of the next goal.

Statistical Analysis

  • Pearson product moment correlations used to examine the inter-relationships between self-efficacy, outcome expectancy and adherence at baseline and between baseline and 14 weeks.
  • Mann-Whitney U-test, a non-parametric procedure was used for analysis of the change scores which were non-normally distributed. 
  • The sample T-test was used for comparison of means between treatment groups.
  • Chi-square test or Fisher's exact test was used for comparison of categorical responses between treatment groups.
  • The level of significance was set at 0.05. The intention-to-treat model was used for handling protocol deviations and the baseline values of outcomes were carried forward to represent the values at 14-weeks' post-randomization for the one subject in the intervention group who withdrew before any intervention session was conducted.
Data Collection Summary:

Timing of Measurements

Baseline and at end of intervention period, 14 weeks. 

Dependent Variables

  • Variable One: Dietary adherence; total fat intake; three-day food record, analyzed by the Minnesota Nutrition Data System software developed by the Nutrition Coordinating Center at the University of Minnesota analyzed by the Minnesota Nutrition Data System software developed by the Nutrition Coordinating center at the University of Minnesota
  • Variable Two: Dietary adherence; saturated fat intake; three-day food record, analyzed by the Minnesota Nutrition Data System software developed by the Nutrition Coordinating Center at the University of Minnesota
  • Variable Three: Dietary adherence; cholesterol intake; three-day food record, analyzed by the Minnesota Nutrition Data System software developed by the Nutrition Coordinating Center at the University of Minnesota
  • Variable Four: LDL-cholesterol; measured following a 12-hour fast on two occasions at least one week apart. If the two measures differed by more than 30mg per dL, a third assay was performed and the average of the three values used. Lipids were analyzed enzymatically in a CDC standardized laboratory that used Abbott VP Supersystem.

Independent Variables

  • Variable One: Intervention or usual treatment group
  • Variable Two: Baseline adherence to diet measured by Eating behavior and clinical history and risk profile, Connor DHS and three-day food record
  • Variable Three: Baseline self-efficacy, measured by the Cholesterol-Lowering Diet Self-efficacy Scale (CLDSES)
  • Variable Four: Outcome expectancy, measured by the Perceived Therapeutic Efficacy Scale
  • Variable Five: Participants' evaluation of the intervention components, measured by a questionnaire sent to the intervention group participants two months following the study. Participants were asked to rank order the helpfulness of the three major components of the intervention: Telephone contacts, self-monitoring and goal-setting.

Control Variables

  • Variable One: Cardiovascular risk (heart disease, hypertension, cigarette smoker, activity level-general, activity level-occupation, BMI; for females, menopausal, menopausal on HRT, hypolipicemic drugs prescribed)
  • Variable Two: Age
  • Variable Three: Gender
  • Variable Four: Race or ethnicity
  • Variable Five: Marital status
  • Variable Six: Employment, full-time, part-time and other
  • Variable Seven: Income
  • Variable Eight: Education (in years).
Description of Actual Data Sample:

Initial N

65 (41 males, 24 female).

Attrition (Final N)

  • 65 (however, of the intervention group 24 of 31 completed all six treatment sessions, three of 31 completed five, one of 31 completed only one and one of 31 did not complete any sessions)
  • Data is given for 65 subjects before and after the 14-week intervention period.


  • Intervention Group: 53.74±11.6 years
  • Usual Care Group: 55.9±10.64 years.


  • White: 94%
  • Non-white: 6%.

Other Relevant Demographics

  Intervention Group Usual Care Group
Marital Status (percentage)




Never married
Employment Full-time








Education (in Years)



    Intervention Group Percentage Usual Care Group Percentage
History of Heart Disease (yes) 38.7 35.3
Hypertension (yes) 22.6 11.8
Cigarette Smoker

Currently (yes)



Former (yes) 29.0 41.2
Activity Level (general) Sedentary 16.1 17.6
Moderately active 35.5 44.1




Activity Level (occupation)




Walking 35.5 32.3
Heavy physical 6.5 6.5


63.7 61.6
Menopausal Females on HRT 87.5 44.4
Hypolipidemic Drugs Prescribed 41.9 50.0


    Intervention Group Percentage Usual Care Group Percentage
Body Mass Index ≥27




Females 45.5 38.5
Waist-to-Hip Ratio Males >0.90 84.2 68.4

Females >0.80




  • Baseline data collected at three academic medical center practice and research sites: A lipid clinic, a cardiology clinic and a research site
  • Patients in usual care group saw their regular MD
  • Patients in intervention group received telephone calls at their homes.
Summary of Results:

Baseline and post-intervention adherence scores* and difference scores based upon Three-Day Food Records (N=65)

Dietary Adherence

Treatment Group

Control Group

Statistical Significance

Total Fat Intake

Baseline,  M±SD




Post, M±SD




Score ±SD




Percentage score ±SD
Saturated Fat Intake Baseline,  M±SD
Post, M±SD
Score ±SD

Percentage score ±SD




Cholesterol Intake

Baseline, M±SD







Post, M±SD


Score ±SD

Percentage score ±SD
LDL-Cholesterol Value Baseline, M±SD
Post, M±SD
Score ±SD

Percentage score ±SD




*Adherence scores for each nutrient were computed as the amount consumed divided by the amount prescribed per day x100.

Other Findings

Scores for self-efficacy and for outcome expectancy for the usual care and treatment groups at baseline were very similar (72.27±18.00 and 6.61±1.97 for the usual care group and 75.59±14 and 6.57±1.9 for the intervention group). There was a non-significant difference in self-efficacy scores between baseline and end of study for each group and between groups, P=0.159). For outcome expectancy there was a significant change in the difference scores (P=0.007) and the percentage difference scores (percentage difference score for the intervention group 15.67 vs. usual care group 7.99, P=0.008).

There was an inverse relationship between baseline self-efficacy and concurrent adherence scores within the intervention group for total fat (P<0.05), saturated fat (P<0.01 and Cholesterol (P<0.05). There were inverse relationships between baseline self-efficacy and adherence within the usual care group only for Cholesterol (P<0.05). At the end of the study the only adherence scores that were related to self-efficacy measured at baseline were saturated fat (P<0.05) for the intervention group, and saturated fat (P<0.01) and cholesterol (P<0.05 for the usual care group).

A follow-up survey, two months after the end of the study was completed by 68% of the intervention subjects. 60% ranked goal setting as number one, 25% ranked the phone contacts as number one and 15% ranked self-monitoring as first in helping them make eating behavior changes.

Author Conclusion:

This study introduced an adherence-enhancing intervention in a controlled study and examined its efficacy in remediating insufficient adherence to the existing regiment that was part of usual care and its effect on LDL-C. The intervention showed improved dietary adherence in the intervention group. A large change in eating behavior occurred in the three dietary components. The change within the treatment group in the serum LDL-C is what could be expected with a change to the September 1 Diet. Use of the intervention strategies described in this paper with people who are responsive to dietary intervention may be sufficient to delay or prevent the use of lipid-lowering drugs. Considering the reported high rates of non-adherence to statin therapy, it is important to identify strategies that can improve adherence to cholesterol-lowering eating plans.

Funding Source:
Government: DHHS, PHS,
University/Hospital: University of Pittsburgh School of Nursing, Universkty of Pittsburgh Graduate School of Public Health
Reviewer Comments:

This is a well-controlled study that shows efficacy of a relatively simple and inexpensive intervention for individuals at risk for heart disease. The use of telephone interviews for intervention is easy for patients and healthcare providers, and would likely promote better adherence to treatment than if patients had to take the time to get to a clinic appointment.

The use of food records alone to describe adherence to diet may not be as accurate as possible. There was a difference between the DHS and food records at baseline, with the DHS showing less adherence to diet than the food records, but food records alone were used to report baseline versus post study dietary adherence. It would have been enlightening to see the results of both tools for measuring adherence at both the beginning and the end of the study.

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? ???
  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? 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)? Yes
  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