Health Education Research Advance Access originally published online on April 11, 2008
Health Education Research 2009 24(2):237-252; doi:10.1093/her/cyn015
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Transtheoretical model-based dietary interventions in primary care: a review of the evidence in diabetes
1 Research Centre for Health Promotion, Faculty of Sport Sciences, Department of Health Sciences, University of Jyväskylä, PO Box 35 (L), FIN-40014, Finland
2 Health Care and Social Services, University of Applied Sciences, Raastuvankatu 31–33, FIN-65100 Vaasa, Finland
3 Central Finland Central Hospital, Keskussairaalantie 19, FIN-40620 Jyväskylä, Finland
* Correspondence to: S. Salmela. E-mail: sanna.salmela{at}sport.jyu.fi
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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The objective of this study was to review the evidence concerning stage-based dietary interventions in primary care among persons with diabetes or an elevated diabetes risk. Search strategies were electronic databases and manual search. Selection criteria were randomized controlled studies with stage-based dietary intervention, conducted in primary care with at least 6 months of follow-up, and participants with either type 2 diabetes or with an elevated risk. The researchers evaluated trials for inclusion, extracted data and assessed study quality. Seven articles, based on five data sets, were included. These studies concentrated on cardiovascular diseases and being overweight, not diabetes. The quality of the studies was moderate to weak. Inadequacies in the reporting often involved unspecific information on the training of health care providers. Long-term positive outcomes (compared with controls) were found in total and monounsaturated fat intake, diastolic blood pressure, health status and well-being. The existing data are insufficient for drawing conclusions on the benefits of the transtheoretical model. More high-quality studies focusing on diabetes are needed, with greater attention to the training of providers and process evaluation. There is a need for a standardized appraisal tool for study evaluation, focusing separately on education interventions for patients and providers.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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Lifestyle counseling based on behavior change models is often held to be more effective in promoting long-lasting behavior change than traditional counseling, since the models provide explanations for health-related behaviors [1]. The transtheoretical model (TTM, stage-based model) is one of the six most commonly cited behavior change models [2] frequently assumed to be more effective than a control situation [3]. TTM [4] consists of three core constructs (‘stages', ‘processes’ and ‘levels of change’), with the ‘stage of change’ describing the status of the person undergoing the change process. The stages form a continuum, and the person may move through the stages in a bidirectional manner. In order to help patients progress to the next stage, health care providers should identify the current stage and tailor their counseling strategies individually. TTM postulates that people at different stages have different needs for counseling:
- (i) ‘Pre-contemplation’ (a healthier lifestyle is not yet considered) and
- (ii) ‘Contemplation’ (thinking about behavior change): at these stages, the need is for cognitive approaches that will increase the motivation for engaging in change.
- (iii) ‘Preparation’ (intending to change behaviors, with no effective action): here the need is for behavioral-skills training.
- (iv) ‘Action’ (modifying one's behaviors): the need at this stage is for specific interventions and concrete guidelines.
- (v) ‘Maintenance’ (stabilizing change and avoiding relapse): the need is for assistance in preventing relapse and in consolidating gains [1, 5].
- (ii) ‘Contemplation’ (thinking about behavior change): at these stages, the need is for cognitive approaches that will increase the motivation for engaging in change.
A good deal of criticism has been aimed at TTM, regarding, for example, the difficulty of applying the model to complex dietary behavior [3, 6–11]. Indeed, the effectiveness assumption does not appear to be founded on clear evidence. A previous review of five TTM-based lifestyle counseling studies [12] found positive changes in dietary fat intake in the stage-based groups, but the two studies in the review concerning fruit and vegetable intake showed considerable variation in the results obtained. The authors emphasized that the evidence was limited, due to the small number of studies. In addition, a large review carried out by Riemsma et al. [13] found mainly mixed effects in the five trials aimed at dietary change, with only two trials reporting significant effects that would support stage-based intervention. Within studies that incorporated multiple lifestyle interventions, there were five that included outcome measurements describing dietary behavior. In these studies, too, the results were contradictory.
Type 2 diabetes is on the increase, and its prevention requires effective lifestyle counseling [14].
The application of TTM in the diabetes context has been defended on the grounds that persons with diabetes who have been classified within the action or maintenance stages have been observed to display healthier eating patterns than those at other stages [15]. In diabetes counseling, TTM-based interventions have been reported as giving positive results [16, 17]. However, the studies in question are from hospital settings, despite the fact that the treatment of diabetes is usually a matter of primary health care. Because the primary care environment differs from the hospital setting, it is important to find evidence-based forms of counseling which will be particularly suited to the primary care setting. Although one previous review has examined TTM-based intervention studies performed within primary care settings [12], there are no previous reviews focusing on individuals with diabetes or with an elevated risk of diabetes. Thus, our first purpose was to review the evidence for using the TTM-based interventions in diabetes-related dietary interventions within primary care settings.
During the review process, we became aware that TTM-based intervention usually includes two kinds of intervention: (i) TTM-related training for ‘providers', aimed at changing their counseling practices, and (ii) counseling for ‘patients'. Nevertheless, the role of the provider is often neglected, despite the fact that information on the providers’ ability to apply TTM properly is needed in drawing conclusions. The review by Riemsma et al. [13] revealed that only eight of the 37 stage-based intervention articles gave details on the providers’ training (e.g. as nurses, physicians or dieticians). This is surprising, since learning new counseling practices is an extremely challenging undertaking [18]. With a view to expanding on the results obtained by Riemsma et al. [13], we also reviewed the information provided on the training of the providers.
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Methods |
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A computerized literature search on the Internet was carried out in November 2005, using the following databases:
- (i) Cochrane Central Register of Controlled Trials,
- (ii) Cinahl,
- (iii) Medline (from 1966),
- (iv) PsycINFO and
- (v) Embase.
- (ii) Cinahl,
The search strategy focused first of all on free-text words referring to (i) the TTM (e.g. ‘transtheoretical', ‘stage of change’), (ii) target behavior change (e.g. ‘diet', ‘change', ‘modification’) and (iii) type or content of the intervention (e.g. ‘counseling', ‘client education’). In addition, database-specific Medical Subject Headings were included when appropriate (e.g. ‘nutritional counseling', ‘intervention trials’). The search was limited to 1983–2005. The selection of articles was restricted to those published randomized controlled trials (RCTs) carried out in primary health care settings (primary care, general practice, family practice, family medicine, internal medicine) that included a TTM-based dietary counseling intervention and a control condition. The intervention was defined as verbal advice, written materials or computerized counseling. The participants had to be adults with diagnosed type 2 diabetes, or elevated risk as indicated by a family history of diabetes, being overweight or obesity, physical inactivity, belonging to a particular race or ethnicity, having previously identified impaired fasting glucose or impaired glucose tolerance, polycystic ovary syndrome, dyslipidemia, elevated blood pressure levels or a history of vascular disease or gestational diabetes [19]. Studies with <6 months of follow-up and studies without a clear focus on diabetes-related diseases (e.g. studies primarily on cancer) were excluded. The search was not language dependent. However, only studies in English were included in the analysis.
The selection stages are described in Table I. The selection was performed separately by three of the authors. One of the authors performed a second search manually, examining the reference lists of the publications included and the reviews published. Two of the authors collated the data into the descriptive table. Any differences of opinion were resolved through discussion.
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The computer-based search yielded 233 publications, of which 227 were excluded (reasons presented in Table I). Thus, the initial search gave us six RCTs with usable information. The manual search produced one more article. In all, a total of seven articles [20–26], based on five sets of research data [20 and 22, 21, 23 and 24, 25, 26], were included. In total, we found five articles [21, 23–26] that had not been included in previous reviews [12, 13].
The quality of the trials was assessed by means of the Quality Assessment Tool for Quantitative Studies [27, 28]. It defines eight component sections (selection bias, allocation bias, confounders, blinding, data collection methods, withdrawals and dropouts, analysis and intervention integrity) mentioning important issues that must be taken into account (see operationalization, Table II). The dictionary [29] that accompanies this tool was used as a guide in defining the items and the scoring process. After the reviewers had completed the quality form independently, the ratings were compared and a consensus reached by discussion. With the help of the dictionary, the information from the items on the form was transcribed into a summary of component ratings. Table II provides an example of the scoring process; the factors taken into consideration in the complete scoring process are set out in the final pages of the dictionary [29]. The total quality score for the patient counseling interventions was estimated by calculating the median of the eight component sections.
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The quality assessment tool was chosen because it takes into account intervention integrity, which is essential in theory-based studies. The content and construct validity of this tool have been established [30]. In this study, our aim was to evaluate the providers’ training on TTM-based counseling. For this reason, we decided to analyze training as a second intervention. The same quality assessment tool was used for both forms of intervention. However, during the process we found this tool (as well as others) to be not completely suitable for assessing the training of the providers. As a result, we made some modifications that helped us to cover the essential quality factors (Table II). In the end, however, due to major information gaps in the reports we examined, we were unable to score the quality of the training given to providers.
We analyzed together those articles that were based on the same research data. We excluded one study [25] from the analysis of the providers’ training because it did not consist of TTM-based counseling by providers. The remaining studies were included in the quality assessment according to a minimum of two reviewers. Strength of evidence (Table III) was defined on the basis of a quality assessment of patient counseling interventions. The reasons for not performing the meta-analysis were the poor quality of the studies included, differences between study protocols, the limited number of studies and the diversity of the outcomes. In drawing conclusions in the present review, we took into account the participants, the interventions, the controls and the outcomes and the methodological quality of the trials.
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Results |
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Study characteristics
The characteristics of the seven studies included are set out in Table IV. The results presented in Table IV (first column from the right) focus solely on those outcome measures that are related to dietary behaviors (excluding e.g. outcomes concerning physical activity).
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The participants in six of the studies [21, 20 and 22, 23 and 24, 25] had elevated cardiovascular risk factors, and in one further study [26], the participants consisted of overweight persons. The purpose of the studies was to address risk factors and behaviors such as high fat intake and overweight. Simple addition of the raw numbers of participants in the seven studies examined would give a total of 4047 persons. However, there are in fact only five sets of data (the same material having being used for more than one study), with a total of 2429 participants in the five sets. The mean number of participants per study was 486. Overall, the participants were mainly middle-aged and older adults. In four studies, the participants were predominantly women [21, 23 and 24, 26]. The mean follow-up time was 15 months. The primary outcomes involved lifestyle behavior, stages of change and physiological measures. Long-term outcomes such as incidence of diabetes were not examined.
As can be seen in Table IV, all the control groups received the usual care, but the content and intensity (duration and frequency) of counseling varied or were not reported. In most of the studies [21, 20 and 22, 23 and 24, 25], usual care was defined as ‘usual care by physicians/practice nurse’ which provides no information on the intensity of the care. There was also variation in the usual care providers, who could be physicians [21, 23 and 24, 25], nurses [20 and 22] or dieticians [26]. The intervention groups received counseling with methods and intensities that were not comparable, and the intensity differed, not only between the studies but also within the studies. The content of the counseling varied between the trials: three studies [23 and 24, 25] focused only on dietary counseling, while other studies also included counseling on, for example, exercise and smoking. Furthermore, the intervention counselors were heterogeneous (physicians, nurses, dieticians, weight-loss advisors or a combination of these), and in one study [25], the actual intervention consisted of TTM-based websites, questionnaires and monthly information packages.
Methodological quality of the trials
The results of the quality assessment of patient education and providers’ training are presented in Table V. Regarding the patient education interventions, two of the studies were graded as of moderate quality [23 and 24, 25] and three as of weak quality [21, 20 and 22, 26]. Inconsistencies were found, for example, in confounders, blinding and data collection methods. Details regarding randomization methods and allocation concealment were often not accurately reported (e.g. whether the providers were randomized before the patients were selected, allowing the possibility that the providers in an intervention group might be predisposed to recruit motivated patients). None of the six trials in which there was personal contact between patients and provider examined the effect of the providers’ training. Furthermore, the degree, content and methods of the providers’ training varied or were inadequately reported (Table V). The procedures for recruitment of the providers were often unclear, making it impossible to draw conclusions on how representative the providers actually were. It was notable that the process evaluation of patient education (how the providers actually counseled) was not reported or was inadequately reported, making it difficult to ascertain whether the intervention was properly stage based. Two studies [21, 26] in particular highlighted the providers’ poor adherence to the TTM protocol. Steptoe et al. [22] also pointed out that their intervention included a range of behavioral techniques that were also used outside the TTM. For this reason, it cannot be concluded that benefits were due to the use of TTM [22].
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Level of evidence
The number of trials included was small, and the studies assessed a variety of outcome measures. Consequently, strength of evidence had to be defined on the basis of only one to three trials, which were weak or of moderate quality (Table VI). Based on the three trials [23 and 24, 25] with 6–8 months of follow-up (intermediate effectiveness, Table VI), there was limited evidence to indicate that stage-based intervention was more effective than usual care in terms of total energy intake, total fat intake, saturated fat intake, monounsaturated fat intake, weight and movement across stages of change. On the other hand, there was also limited evidence that there was no difference concerning unsaturated fat intake, diastolic and systolic blood pressure, waist circumference or waist-to-hip ratio at 6–8 months. The evidence concerning body mass index (BMI), lipid values and distribution across stages of change was conflicting. However, it must be emphasized that overall, the evidence pertaining to the 6–8 months of follow-up was weak, since all the outcomes were based on only one study (Table VI).
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Based on the five trials that had 12–24 months of follow-up (long-term effectiveness, Table VI), there was limited evidence that stage-based interventions were more effective than usual care in terms of total fat intake [20, 23], monounsaturated fat intake [23] and systolic blood pressure [20]. On the other hand, there was also limited evidence that stage-based interventions were not more effective in terms of total energy intake [23, 26], saturated fat intake [23], unsaturated fat intake [23], BMI [20, 23], diastolic blood pressure [20], blood pressure [26], waist circumference or waist-to-hip ratio [23, 26], early weight loss and regain [26] and distribution across stages of change [24]. There was moderate evidence that there was no difference in terms of weight and lipid values [20, 23, 26]. Surprisingly, the evidence concerning movement across stages of change was conflicting [21, 22, 24].
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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The present review revealed that there is a lack of stage-based dietary counseling studies in primary care settings with a clear focus on type 2 diabetes prevention and treatment. Indeed, there are not many diabetes-related trials with any other main focus (e.g. cardiovascular diseases, obesity). The studies we examined also displayed a number of defects related to data on providers’ and patient education and process evaluation. In view of these considerations, it is impossible to draw conclusions concerning the benefits of stage-based dietary counseling (in comparison with usual care) in primary care settings. However, we must emphasize that an absence of data does not equal lack of effectiveness.
The only favorable long-term differences between the groups concerned total fat intake, monounsaturated fat intake and systolic blood pressure. However, no firm conclusions can be drawn from these differences, since only one or two trials addressed these outcomes. Riemsma et al. [13] suggested that there is limited evidence concerning the benefits of TTM-based counseling. Furthermore, Van Sluijs et al. [12] provided no substantial evidence for the effect of stage-based dietary interventions in primary care. If we add our observations to the previous findings, we are led to speculate on the reasons for the popularity of TTM [3], given the lack of scientific evidence. Clearly, any recommendations for using the model should be evidence based.
Nevertheless, many issues of study quality and process evaluation arose in our analysis. We found that the training of providers played a very minor role in the studies, despite the fact that new counseling practices often disseminate slowly among professionals—or sometimes not at all [31, 32]. It seemed that most of the studies did not even recognize that two separate interventions, among providers and patients, were involved. In addition, despite several published quality assessment tools for RCTs [33, 34], we found that the existing tools were designed for evaluating patient counseling interventions and did not address the education and training of providers. Despite this, the tool we used [28] is applicable, if modified. Typical deficiencies also emerged (e.g. [35, 36]) in the reporting of RCTs, and possibly in the way they were conducted.
On the basis of these observations, we would draw attention to several significant issues for future studies. First of all, it is important to describe the content and methods included in the education and training given to providers. Furthermore, in order to reduce variation arising from individual differences among providers, it would be important to determine a baseline for the characteristics of the providers. This requirement is based on many potential confounding factors, such as counselors’ attitudes, postgraduate education, counseling practices and readiness to change such practices. The point is crucial, especially with cluster-level interventions, when baseline differences between health care settings (e.g. resources, counseling practices) are likely to exist. Furthermore, the evaluation of providers’ training should include behavior change outcomes, since it appears that counselors may quickly grasp the idea of TTM, yet may need intensive training to become skilled facilitators [6]. Miller and Mount [18] have also pointed out that training should not focus solely on developing new counseling practices but should, concurrently, selectively suppress old ones. In any case, underestimating the providers’ training constitutes a waste of resources, since it contributes to exceedingly unreliable research findings. The cost-effectiveness of brief training sessions must be questioned if they are insufficient to produce significant changes in counseling practice.
One interesting finding was the variation across and within studies. For example, in one study [20, 22], there were one to three counseling sessions lasting no >20 min. In contrast, another study [26] provided counseling by a dietician and, optionally, by a physician, with monthly telephone calls and mailed materials extending >2 years. An example of intra-study variation arose in a study that provided one to three consultations with a physician, but where only those patients that had reached the preparation or the action stages were referred also to a dietician [23 and 24], in accordance with TTM. As a reviewer, it is difficult to draw conclusions on the effectiveness of stage-based counseling when the counseling protocols include so much variation. If the benefits of using TTM-based counseling in diabetes management and prevention are to be proved, future studies will have to have protocols that are more standardized.
In the majority of the trials, because the idea of TTM is to counsel only for behaviors for which a person is at risk [37], not every participant automatically received dietary counseling. Due to this, we had to speculate on whether the analysis on effectiveness concerning dietary habits also included people who did not receive any dietary counseling. This aspect was not dealt with in any of the trials. In order to study effectiveness reliably, statistical analysis should be confined only to individuals who actually received dietary counseling at the time of intervention.
The inadequate description of usual care also raises questions, since outcomes are closely related to the intensity of the intervention [38]. In cases where usual care is not properly described, it is possible that favorable differences between the groups could simply be the result of more intensive counseling in the intervention groups, not of stage-based methods. It should be borne in mind that the mere awareness that tailored intervention is being given to patients might enhance its effectiveness [7]. In addition, progress by patients can also be due to inherent change processes, when patients identify themselves as being at a particular stage [7]. At the same time, it should be noted that progress of this kind could have taken place among both types of group (control and experimental) covered in our review, since the participants in the control groups, too, completed the questionnaire concerning their readiness to change and identified their stage.
One interesting finding was that in a single study [24] assessing the long-term change in distribution across the stages of change, no significant change was found. In respect of the three studies that assessed movement across the stages of change, only one study [22] found significant change. According to TTM, it is not possible to effect lifestyle changes without such movement. In this context, we would have to question the ability of stage-based counseling to promote such movement—yet we also need to ask whether the counseling was truly based on the principles of TTM [10, 21, 39]. It is inappropriate to use TTM without evidence on its effectiveness. On the other hand, condemnation of the model is unjust if it is based on possibly inadequate implementation of the model. It seems that the only way to resolve this uncertainty is to make a proper process evaluation of the counseling sessions, using direct observation of counseling [18]. None of the studies included had carried out this kind of evaluation, a point which leaves many questions unanswered. If the model is to be considered for future application, it will be extremely important to mount a concentrated effort with a view to collecting scientific evidence concerning its benefits.
Limitations of the study
There are several factors that might affect the results of this review. The findings are based on only seven articles and five sets of data. Because of limited time, we decided not to contact the authors for additional information if an article was inadequate. Nor can we exclude the possibility of publication bias. It is also possible that our literature search failed to identify all the potential articles, given that no universally applicable definition of primary health care has been formulated so far [40]. However, we were able to find five articles that were not included in these earlier reviews [12, 13]. On the other hand, our computer-based search failed to find at least one study published in an Internet-based periodical [25], probably because this online periodical was not included in the databases used for this review. It might be advisable to include search engines (e.g. Google Scholar) in search strategies, as has been recommended [27] for the location of unpublished and difficult-to-find literature.
Despite using a validated critical appraisal tool, we found that the quality assessment process was very challenging, due to several choices of interpretation. For example, selection bias was defined as unlikely if ‘the authors have done everything reasonably possible to ensure that the target population is represented’ [29]. Based on the reports, it is difficult to say what actually is ‘everything reasonably possible'. In conclusion, there still seems to be a need for better assessment tools. In addition, the dispersal of reported results and evaluations across separate articles is problematic from the reviewer's point of view, when one is analyzing the quality of studies. It would be helpful if authors were to make known their intention to further report on their research results in any subsequent publications.
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Conclusions |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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There are currently too few studies of sufficient quality to determine the benefits of using stage-based dietary counseling, as opposed to traditional counseling, in primary care settings, among individuals with diabetes or with an elevated risk of diabetes. Because the effectiveness of TTM-based counseling is strongly dependent on the effectiveness of the education and training given to providers, such studies should be treated as studies with two separate educational interventions, each with its own evaluation. Thus, we would support a previous conclusion [41], i.e. that a modified critical appraisal tool should be created for evaluating studies with two separate educational interventions. In order to assess whether the providers have truly changed their counseling behavior, a multilevel assessment of behavior change outcomes should be included as part of an evaluation of the outcomes of providers’ training. In addition, a careful process evaluation of the counseling sessions is required.
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Funding |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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The Juho Vainio Foundation; the Yrjö Jahnsson Foundation; the Ministry of Social Affairs and Health; the Social Insurance Institution of Finland and the Ministry of Education. Funding for Open Access Publication: the Research Centre for Health Promotion, University of Jyväskylä.
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Conflict of interest statement |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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None declared.
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Acknowledgements |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsFundingConflict of interest statementAcknowledgementsReferences |
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We gratefully acknowledge the assistance of the following: Information Specialist Anita Pälvimäki, Jyväskylä University Library, for help with search strategy planning, and English lecturer Donald Adamson, University of Jyväskylä, for proofreading.
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References |
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