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De Bourdeaudhuij I, Brug J, Vandelanotte C, Van Oost P. Differences in impact between a family vs. an individual-based tailored intervention to reduce fat intake. Health Educ Res 2002;17 (4): 435-449.

PubMed ID: 12197589
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
POSITIVE: See Research Design and Implementation Criteria Checklist below.
Research Purpose:

To investigate the impact of a tailored nutrition intervention on the reduction of fat intake and on psychosocial determinants of fat intake. In addition, the study sought to determine differences in impact between a family-based intervention (tailoring two family members, one adult and one child, simultaneously) and an individual-based intervention (tailoring one family member, one adult or one child).

Inclusion Criteria:

The subjects were recruited from 52 classes, with students between 15 and 18 years old, out of two secondary schools. Adolescents and parents were invited to participate.

Exclusion Criteria:

Those outside the target/inclusion group were excluded.

Description of Study Protocol:


Subjects recruited from 52 classes, with students between 15 and 18 years old, out of two Flemish secondary schools. Parents of students were also recruited.


  • The classes were randomized in three groups before recruitment
    • One group was for recruitment of family condition participants
    • One group for recruitment of adolescents for the individual condition
    • One group for recruitment of parents for the individual condition
  • For practical reasons it was not possible to recruit respondents for both conditions from the same class, leading to the use of a quasi experimental design
  • At baseline each participant received a questionnaire designed to obtain information on the psychosocial determinants of fat intake together with a food-frequency questionnaire (FFQ) to measure energy percentages of fat
  • After completion, the questionnaires were sent to the laboratory in a prepaid envelope
  • Six weeks later, participants were mailed personalized nutrition education letters to their home addresses
  • Four weeks after the subjects had received their feedback letters, they were asked to complete and return the post-test questionnaires.

Dietary Intake/Dietary Assessment Methodology

  • Registered dieticians adapted a 56-item FFQ validated in the Netherlands for this Flemish population
  • Respondents reported on the frequency of consumption of each food item per day, per week or per month with a reference period of the past four weeks
  • Intake of total fat was computed in percentages of total energy intake
    • A computer program calculated frequency of consumption for each food item per week, which was then multiplied by a weighted fat factor based on the fat content of food items as reported in the Dutch food composition tables.

Blinding Used

Participants were only aware of their own study condition, not of the other conditions.


  • The intervention was targeted at reducing fat intake
  • Subjects received personalized feedback letters including messages based on their answers to the screening questions
    • Feedback provided about subjects' fat intake as well as about their attitudes, perceived support and self-efficacy toward fat reduction
    • Subjects' actual fat consumption was expressed in percent energy from fat and was compared with the Flemish recommendations and with the mean scores of the other adolescents, mothers or fathers participating in this study
    • Respondents with low self-efficacy expectations were told how they could deal with high-risk situations such as the presence of high fat foods in the home (avoiding such situations by making low-fat shopping lists), being alone (suggestions on low-fat alternatives for single dinners) and lack of time for food preparation (recipes for easy to cook low-fat alternatives)
    • Subjects who reported a positive intention to reduce their fat intake were advised to change these plans into direct action in the week(s) to come, preferably in the next week.

Statistical Analysis

  • A χ2-test was used to look at condition-specific differences in drop-out (family condition, individual adolescent condition and individual parent condition)
  • T-tests and χ2-tests were executed to explore differences in mean fat scores, sex and education, between subjects who dropped out and subjects who completed the baseline and the post-test questionnaires
  • Parents' and adolescents' results were analyzed separately, investigating differences between parents in the individual versus the family condition, and differences between adolescents in the individual vs. the family condition
  • χ2-tests and T-tests were conducted to study differences in respondents' reactions to the feedback letters in both conditions
  • Mean energy percentages fat and mean determinant scores at baseline and at post-test were computed for adolescents and parents
    • The mean fat scores revealed that for both adolescents and parents fat intake was relatively low at baseline
    • Since only subjects with energy percentages higher than 35% were encouraged to change, while those with energy percentages between 30 and 35% were encouraged to maintain their relatively favorable diets, both the whole research sample and the sub-sample with fat intake above 35% of total energy intake (higher risk sample) were analyzed for time and condition effect
  • Repeated-measures ANOVAs with baseline and post-test energy percentages of fat as dependent variables were used to test for significant changes in fat intake over time
  • Repeated-measures MANOVAs with seven baseline and post-test determinants' scores (attitude, self-efficacy, social support, awareness, family perception, friend perception, intention) as dependent variables, and univariate follow-up tests were used to look at general changes in determinants of fat intake over time
  • All analysis were executed for the total sample, and the total at-risk sample, as well as for the sub-sample of adolescents and parents in both samples
  • To test for differences in intervention effects between the family condition and the individual condition, analysis of covariance were conducted, testing for significant differences at post-test in percent energy from fat, and psychosocial determinants of fat intake, while adjusting for baseline levels
  • One-tailed tests were executed to examine the hypotheses. For all analysis, P<0.05 was considered to be significant.
Data Collection Summary:

Timing of Measurements

  • Baseline
  • 10 weeks post-baseline (four weeks after feedback letter received).

Dependent Variables

  • Primary analysis: Fat intake as percent total total energy measured by FFQ
  • Secondary analysis: Psychosocial scores measured using rating/scoring questionnaires; change due to personalized letter
    • Attitude, self-efficacy, social support, awareness, family perception, friend perception, intention, stages of change (based on Theory of Planned Behavior).

Independent Variables

  • Primary analysis: Psychosocial factors affecting fat intake
  • Secondary analysis: Effect of personalized letter (time: baseline vs. post).

Control Variables

Analyses adjusted for baseline levels and scores.

Description of Actual Data Sample:
  • Initial N:
    • 55 adolescents were willing to participate together with one parent (N=110), out of 19 classes ('family condition', 15% response)
    • 71 adolescents agreed to take part in the study alone, out of 16 classes in which only adolescents were asked to participate, constituting the 'individual adolescent condition' (22% response)
    • 47 parents participated out of 17 classes in which the invitation to take part was only directed to the parents of the adolescents, constituting the 'individual parent condition' (14% response)
  • Attrition (final N):
    • 44 adolescents participated with 44 parents in the family condition
    • 50 adolescents participated in the individual condition
    • 40 parents participated in the individual condition
  • Age: Adolescents 15-18 years. Parent age not reported.
  • Ethnicity: Not reported
  • Other relevant demographics: Flemish population
  • Anthropometrics: Not reported
  • Location: Belgium.


Summary of Results:

Summary of Results

  • No significant (NS) decreased in fat intake baseline vs. post for entire study population nor for adolescents or parents separately
  • Mean fat and mean determinant scores at baseline and at post-test for adolescents and parents with an energy percentage of total fat above 35% at baseline show that for adolescents in the at-risk group, NS differences were found
  • For parents in the at risk group, again social support was found to be significantly different at post-test between both conditions [(F1, 37)=5.06, P<0.05] with parents in the family condition of at-risk group reporting more social support at post-test 
  • Multivariate analysis including all measured determinants of fat intake revealed significantly more positive determinants for the whole sample (P<0.001), as well as for adolescents (P<0.001) and parents (P<0.001) separately. Univariate tests showed that in all three groups a significant positive evolution in determinants was only found for social support (P<0.005 for whole sample; P<0.05 for adolescents; P<0.05 for parents and for intention (P<0.001 for whole sample; P<0.001 for adolescents; P<0.001 for parents).
  • Stages of change categorization: As the frequencies per category were too small to execute reliable analysis, only general trends were given. After the intervention, the number of people classifying themselves in the action phase is almost doubled, while less people report to be in contemplation, preparation and maintenance. This trend appears for adolescents and parents in both conditions.


Author Conclusion:
  • The tailored fat feedback resulted in a decrease in percent energy from fat and an increase in psychosocial determinants related to eating a low fat diet in the subgroup of respondents with percentage energy from fat above 35%.
  • In the total research sample, with a mean baseline percent energy from fat of 36.3%, only determinants towards eating a low fat diet increased significantly, but fat intake did not change
  • A clear increase in the intention to eat a low-fat diet in the future was the most important evolution in determinants of fat intake found in all subgroups
  • In contrast to the hypothesis, the decrease in percent energy from fat was not found to be larger in adolescents and parents in the family condition as compared with the individual condition.
Reviewer Comments:

Author limitations

  • Considering respondents' overall positive responses and relatively low-fat intake levels, it could be argued that especially highly motivated adolescents and parents (especially mothers) participated. Selection bias is probable. This is probably due to the quasi experimental design and the recruitment strategy in which adolescents in classes were asked to volunteer. Generalization of the results to the Belgian population of families as a whole is therefore difficult.
  • A true 'family approach' in nutrition education must undoubtedly include as many family members as possible, especially the least-motivated ones, to be effective. This study included at most one parent and one adolescent per family.
  • The present study investigated only the short-term impact of the interventions. It is possible that other results appear in the longer run.
  • A further limitation of the present study is the use of self-reports to assess tailoring effects. More objective criteria like body mass index, cholesterol levels or other blood parameters would give more verifiable results.
  • Due to the fact that the feedback letters were tailored manually and not computerized, a large time interval (six weeks) was present between the completion of the screening questionnaires and the receipt of the feedback letters by mail. This may be one of the reasons for the relatively high drop-out between baseline and post-test.

Research Design and Implementation 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)
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to nutrition or dietetics practice?
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies)
Validity Questions
1. Was the research question clearly stated?
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated?
  1.3. Were the target population and setting specified?
2. Was the selection of study subjects/patients free from bias?
  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?
  2.2. Were criteria applied equally to all study groups?
  2.3. Were health, demographics, and other characteristics of subjects described?
  2.4. Were the subjects/patients a representative sample of the relevant population?
3. Were study groups comparable?
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?
  3.3. Were concurrent controls used? (Concurrent preferred over historical controls.)
  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?
  3.5. If case control or cross-sectional 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. Criterion may not be applicable in some cross-sectional studies.)
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?
4. Was method of handling withdrawals described?
  4.1. Were follow-up methods described and the same for all groups?
  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%.)
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for?
  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?
5. Was blinding used to prevent introduction of bias?
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?
  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.)
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status?
  5.5. In diagnostic study, were test results blinded to patient history and other test results?
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described?
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied?
  6.2. In observational study, were interventions, study settings, and clinicians/provider described?
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?
  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?
  6.6. Were extra or unplanned treatments described?
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?
  6.8. In diagnostic study, were details of test administration and replication sufficient?
7. Were outcomes clearly defined and the measurements valid and reliable?
  7.1. Were primary and secondary endpoints described and relevant to the question?
  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?
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?
  7.5. Was the measurement of effect at an appropriate level of precision?
  7.6. Were other factors accounted for (measured) that could affect outcomes?
  7.7. Were the measurements conducted consistently across groups?
8. Was the statistical analysis appropriate for the study design and type of outcome indicators?
  8.1. Were statistical analyses adequately described and the results reported appropriately?
  8.2. Were correct statistical tests used and assumptions of test not violated?
  8.3. Were statistics reported with levels of significance and/or confidence intervals?
  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)?
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?
  8.6. Was clinical significance as well as statistical significance reported?
  8.7. If negative findings, was a power calculation reported to address type 2 error?
9. Are conclusions supported by results with biases and limitations taken into consideration?
  9.1. Is there a discussion of findings?
  9.2. Are biases and study limitations identified and discussed?
10. Is bias due to study’s funding or sponsorship unlikely?
  10.1. Were sources of funding and investigators’ affiliations described?
  10.2. Was the study free from apparent conflict of interest?