Health Education Research, Vol. 18, No. 6, 693-705,
December 2003
© 2003 Oxford University Press
Are precontemplators less likely to change their dietary behavior? A prospective analysis
School of Public Health, University of Michagan, Ann Arbor, MI 48109, 1 Rollins School of Public Health, Emory University, Atlanta, GA 30322 and 2 Baylor University College of Medicine, Houston, TX 00000, USA
e-mail: kresnic{at}sph.emory.edu
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Abstract |
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The association between baseline stage of change and intervention outcomes is examined in a sample of African-American adults who participated in the Eat for Life Trial, a study to increase fruit and vegetable (F & V) intake conducted through Black churches. We explore whether precontemplators responded differently over time than those in the preparation stage, a group assumed to be more likely to change their behavior. Stage of change, F & V intake (by food-frequency questionnaires) and psychosocial variables were assessed at baseline and 1-year follow-up. Individuals initially classified as precontemplators reported an increase in F & V intake as large as those in the preparation stage and precontemplators’ post-test intake was equivalent to those in preparation. Precontemplators’ change in psychosocial outcomes was also as large or larger than those in the preparation stage. At least with regard to F & V, these findings raise questions regarding the validity of stage of change, one element of the Transtheoretical Model, as a predictor of future behavior and intervention response.
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Introduction |
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The Transtheoretical Model (TTM) has become one of the most widely applied frameworks for developing health behavior change interventions. According to the TTM, the behavior change process can be mapped as five discrete and generally sequential stages: precontemplation (not considering change), contemplation (considering change but not in the near future), preparation (considering change in the near future or already begun change), action (changed behavior in the short term) and maintenance (changed behavior long term). According to the TTM, at each stage individuals may use different cognitive and behavioral processes, and in order to maximize effectiveness, interventions should be tailored to an individual’s stage and decisional balance (Rossi et al., 1988
; Velicer et al., 1995b; Pallonen, 1998; DiClemente et al., 1991).
Whereas much of the original TTM research focused on smoking and other addictive behaviors (Rossi et al., 1988; DiClemente et al., 1991; Pallonen et al., 1992, 1994; Prochaska et al., 1993; Fava et al., 1995; Hennrikus et al., 1995; Velicer et al., 1995a; Herzog et al., 1999), over the past 10 years the model has been applied to a wide range of chronic disease and other health behaviors, including physical activity and diet (Curry et al., 1992; Marcus, 1992; Prochaska and Diclemente, 1992; Booth et al., 1993; Glanz et al., 1994; Prochaska et al., 1994; Cardinal, 1997; Boyle et al., 1998). Specifically, it has been used to understand and modify fruit and vegetable (F & V) intake, the focus of this manuscript (Laforge et al., 1994; Campbell et al., 1997, 1999a; Povey et al., 1999)
Cross-sectionally, the model appears useful in distinguishing individuals at varying levels of readiness to change F & V intake (Campbell et al., 1997; Cullen et al., 1998) as well as other health behaviors (DiClemente et al., 1991). However, less is known about how individuals at varying stages respond to dietary intervention nor how stage predicts behavior change independent of intervention. It is largely assumed that individuals in the precontemplation and contemplation stages are less likely to change their behavior than those in the preparation stage, and that interventions tailored to participant’s stage are more effective than those that do not take readiness into account (Campbell et al., 1994). In fact, in some smoking cessation studies, individuals have sometimes been excluded from participating altogether based on their baseline motivation, since it is often assumed that those initially less motivated would be less likely to attend and/or respond to interventions (Hays et al., 1999; Jorenby et al., 1999). Although in some prospective studies these assumptions have been verified (Heather et al., 1993; Greene and Rossi, 1998; Havas et al., 1998; Steptoe et al., 2001), other studies raise questions about the internal validity of the model (Resnicow et al., 1997; Quinlan and McCaul, 2000). Given the widespread use of the TTM and the inherent weaknesses of using cross-sectional analyses to establish the model’s utility, it is important to examine the validity of ‘stage’ (one element of the TTM model) as a predictor of behavioral change as well as a moderator of intervention effects.
This paper examines the association between baseline stage of change and behavioral and psychosocial outcomes at 1-year follow-up in a sample of African-American adults who participated in the Eat for Life Trial, a National Cancer Institute-funded study to increase F & V intake through Black churches (Resnicow et al., 2000a,b, 2001). In particular, we examine whether precontemplators respond differently over time than those in the preparation stage, a group that is assumed to be more prepared/motivated to change their dietary behavior. Specifically, based on the assumptions of the TTM, we hypothesize that:
Precontemplators will show less change in F & V intake and the associated psychosocial mediators than those at more advanced stages of readiness.
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Method |
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Design
Fourteen churches, matched on socioeconomic status (low, mixed or high) and size, were randomly assigned to one of three treatment conditions: (1) comparison (usual nutrition education/delayed intervention), (2) culturally sensitive multicomponent self-help intervention with one telephone cue call, and (3) culturally sensitive multicomponent self-help intervention with one cue call and three telephone counseling calls. The additional three telephone counseling calls in Group 3 employed motivational interviewing (MI) techniques, whereas the first call in both Groups 2 and 3 served primarily as a cue to utilize intervention materials (e.g. watch the video, read the brochures and try recipes from the cookbook) rather than directly change F & V consumption. The delayed intervention group received the self-help intervention materials after the 1-year post-test data collection. Results of the main trial have been reported elsewhere (Resnicow et al., 2000a
, 2001). The study was powered to detect a half-serving difference of F & V between Groups 3 and 1, with a power of 0.80 and 
= 0.05, with the church as the unit of analysis adjusting for the intraclass correlation. Four churches were assigned to each of Groups 1 and 3, and six (this included two smaller churches) to Group 2. Church size ranged from 100 to 1500 members, with most churches in the range of 100–250 members. Only Baptist and Methodist (including African Methodist Episcopalian) denominations were included. Baseline and 1-year follow-up data were obtained at health fairs conducted at each church. The study was approved by the Emory University human investigations committee.
Self-help intervention materials
Individuals in the two intervention arms received a 23-min video, a cookbook, printed education materials, including a quarterly newsletter, and several ‘cues’ imprinted with the project logo and 5-a-day message (e.g. refrigerator magnet, pen, scratch pad, pot holder and erasable writing tablet). The video developed for this project, entitled Forgotten Miracles, used biblical and spiritual themes to motivate healthy eating. The story involved two families, one with a poor diet and the other with a more optimal diet. As a result of a pastor’s sermon as well as a scary dream, during which the father in the ‘poor diet’ family has a heart attack, the father begins to modify his diet. In the second half of the video, a nutritionist, played by a well-known African-American actress, conducts a workshop during which benefits of F & Vs are discussed; various obstacles about eating F & Vs (e.g. cost) are addressed and several recipes are presented. Although not developed specifically as a stage-matched intervention, the first part of the video primarily addressed ‘why to change’, while the second part focused more on ‘how to change’. In this regard, the first part could be considered tailored to those in the earlier stages of change, while the second half could be considered more tailored to individuals in the latter stages of change. Materials for the comparison group included National Institutes of Health brochures addressing F & V intake (e.g. NIH Publications 92-3248 and 91-3250).
The Eat for Life cookbook contained recipes submitted by members of the participating churches. Qualifying recipes were required to contain at least a quarter serving of fruit or vegetable per portion and to be low in fat. The cookbook also contained information about the health benefits of F & Vs, tips for shopping and storing F & Vs, and cooking techniques. Printed health education materials included a National Cancer Institute brochure (95-3862), a food guide pyramid slide card (Positive Promotions, Brooklyn, NY) and the Soul Food Pyramid (Hebni Consultants, Orlando, FL). With the exception of the quarterly newsletter, which was mailed to participants, all intervention materials were distributed at the health fair exit booth. Additional details about the intervention materials can be found elsewhere (Resnicow et al., 2000a).
Participant recruitment and retention
In each church a liaison was hired to assist in participant recruitment and retention, as well as coordination of the health fairs. Pastors were asked to encourage congregants to attend the health fairs, which were generally conducted immediately after Sunday services. Flyers were posted and announcements were placed in church bulletins. To encourage participation, churches were provided with a $10 donation for each participant (up to 60 per church) that completed the baseline assessment. To assist members who may have limited literacy skills, at health fairs, staff inquired from all participants if ‘they would like to have someone from the program read the questionnaire with them?’. At post-test, liaisons were asked to assist in encouraging baseline participants to attend the follow-up health fair. Churches received an incentive that increased from $250 to $2000 based on the proportion of baseline participants that attended the post-test health fair.
Measures
Stage of change
Stage of change was classified based on response to five items:
(1) Are you seriously thinking about eating more F & Vs in the next 6 months?
(2) Are you seriously thinking about eating more F & Vs in the next month?
(3) How many servings of fruit do you usually eat each day?
(4) How many servings of vegetables do you usually eat each day?
(5) About how long have you been eating this number of daily servings of F & Vs?
Individuals eating fewer than five servings of F & Vs who were not seriously thinking about eating more in the next 6 months were classified as precontemplators; individuals eating fewer than five servings of F & Vs who were seriously thinking about eating more in the next 6 months, but not in the next month, were classified as contemplators; individuals eating fewer than five servings of F & Vs who were seriously thinking about eating more in the next month were classified in preparation; individuals eating at least five servings of F & Vs but who had been doing so for less than 6 months were classified in action, whereas those doing so for more than 6 months were classified in maintenance. This algorithm is similar to that used by prior five-a-day researchers (Laforge et al., 1994; Campbell et al., 1997, 1999b).
F & V intake
Multiple measures of F & V intake were obtained to provide a converging (i.e. triangulated) estimate of true intake. All participants completed a two-item measure used to assess usual F & V intake (one item each for F & V consumed ‘each day’). As noted above, these two items were also used to stage participants. Participants also completed a seven-item F & V food-frequency questionnaire (FFQ) assessing intake in the past month, based on the Behavioral Risk Factor Surveillance System (Serdula et al., 1993). To reduce over-reporting, the response categories of 4 and 5 times per day were removed. The third instrument was a 36-item F & V FFQ developed for this study, based on the Health Habits and History Questionnaire (Block et al., 1990). We excluded from the analysis any participant who was missing more than half of the vegetable (i.e. 10 items) or fruit items (i.e. eight items) from the 36-item FFQ (n = 31 at baseline and n = 37 at post-test). Cases missing fewer than half of the fruit or vegetable items were assigned a frequency of never for those missing items. These three measures were averaged to yield a composite F & V variable. The seven- and 36-item measures included an item that assessed intake of French fries and fried potatoes. These items were excluded from the computation of F & V servings.
The three FFQ methods were validated against serum total carotenoids (sum of lutein, cryptoxanthin, -carotene and -carotene), which were obtained at baseline from approximately 90% of the participants (Resnicow et al., 2000b). Correlations of total F & V servings from the two-, seven- and 36-item FFQs with total serum carotenoids were 0.22, 0.29 and 0.35, respectively.
Psychosocial measures
We report the association between stage and several psychosocial variables that have been found to be associated with F & V intake and or stage of change in prior studies (Brug et al., 1995, 1997; Campbell et al., 1997; Havas et al., 1998; Resnicow et al., 2000a,b). Outcome expectations for F & V intake were assessed with a 19-item scale (nine fruit items and 10 vegetable items; = 0.88) based on the instrument developed by Baranowski et al. (Baranowski et al., 1995). Sample item: Eating fruit gives me more energy. Self-efficacy to eat more F & V was assessed with a 10-item scale ( = 0.90) based on the work of Sallis et al. (Sallis et al., 1988) and others (Sheeska et al., 1993; Baranowski et al., 1995). Sample item: ‘How confident are you that you could eat healthy foods like fruits and vegetables, when you are depressed or in a bad mood?’. Responses range from ‘not at all confident’ to ‘very confident’. Portion size knowledge was measured with an eight-item index that assessed awareness of standard serving sizes for F & Vs. Two serving sizes were presented and the respondent was asked to check which of the two represents a single serving. Barriers to F & V intake were assessed with a 27-item (13 fruit items and 14 vegetable items) index developed by the investigators. Sample item: Fresh fruit spoils too quickly. Items were answered on a four-point continuum ranging from ‘doesn’t affect me at all’ to ‘makes it very difficult’. Higher scores indicate more perceived barriers.
Other variables assessed
Household income was assessed with an eight-category ordinal item, with answers ranging from < $10 000 to >$70 000. Values were collapsed into three groups: <$20 000, $20 000–$39 999 and 
$40 000. Education was categorized as ‘less than high school’, ‘completed high school or equivalent’, ‘some college’ and ‘completed college’. Work status was categorized as ‘unemployed’, ‘retired’ and ‘working part- or full-time’. Participants were also asked about marital status. Use of cigarettes and alcohol in the past 30 days were assessed with single items.
Use of intervention materials was assessed in the 1-year follow-up questionnaire. Individuals who reported watching most or all of the video were coded as having watched the video. Individuals who reported using at least one recipe from the cookbook were coded as having used the cookbook.
Analyses
First, we examined using baseline data, the association between stage of change, and several demographic, behavioral and psychosocial measures. Next, using ANOVA, we examined change in F & V intake (using the composite of the three FFQ measures), outcome expectations, self-efficacy, knowledge and barriers by baseline stage of change. Change scores were computed by subtracting baseline values from post-test values.
To test the main hypothesis, change scores across stages were contrasted to precontemplators. Raw post-test values were also contrasted to precontemplators. For exploratory purposes, change scores and post-test means of all stage groups were contrasted using the Scheffe post hoc adjustment.
To test whether use of intervention materials differed by stage, 
2 analysis and logistic regression were used with video use (Y/N), cookbook use (Y/N) and call completion (Y/N) as the dependent variables. No explicit directional hypotheses are listed for intervention use, although TTM theorists might posit that precontemplators would be less likely to utilize intervention materials as they are less interested in changing their behavior. Most analyses are presented for each treatment group as well as the aggregate study sample. Finally, we present a crosstab comparing stage movement from baseline to post-test
Because churches were the unit of randomization, we accounted for clustering resulting from this design effect by including church as a random effect term through SAS PROC MIXED.
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Results |
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Sample description
At baseline, a total of 1011 individuals were recruited across the 14 churches. The number of participants per church averaged 72 (range 53–130). Of the initial sample, 861 (85%) participants were assessed at 1-year follow-up. Follow rates in the three treatment groups were 84, 85 and 87%, respectively. As shown in Table I, dropouts did not differ from cohort members with regard to stage of change, gender, income, education, cigarette use or F & V intake. Dropouts were, however, significantly younger, less likely to be married and more likely to report 30-day alcohol use. Data from church members not participating in this study are not available.
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As shown in Table II, approximately 9% of the sample was classified as precontemplators, 3% as contemplators, 62% in preparation, 4% in action and 21% in maintenance. The only demographic variable associated with baseline stage of change was age. With the exception of serving size knowledge, all of the psychosocial variables were significantly associated with baseline stage of change and generally in the direction predicted by the TTM, i.e. compared to those in the action/maintenance stages those in the precontemplator/contemplator stages showed lower (less positive) outcome expectations, self-efficacy to eat more F & V and F & V intake (based on the composite FFQ measure). Those in the action group tended to respond more similarly to precontemplator/contemplator groups than the action/maintenance groups. Those in the maintenance group reported the fewest number of barriers, with little difference across the remaining four groups.
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Across the entire study sample, regardless of treatment condition, at 1-year follow-up, precontemplators increased their F & V intake from 3.1 to 4.2 servings per day, a net increase adjusted for age, of approximately 1 serving. The age-adjusted net increase was 0.97, 1.1, 0.90 and –0.04 servings per day among the contemplator, preparation, action and maintenance groups, respectively. Pre–post change among baseline precontemplators was not significantly different than those in the preparation stage at baseline, both increased by 1.1 servings. Thus, the main hypothesis was not confirmed as precontemplators showed a similar increase in F & V intake compared to those in the preparation stage. Change in F & V intake was, however, significantly higher among each group compared to those in maintenance. This is not surprising as those in maintenance were already eating five servings per day at baseline. Findings were similar when control and treatment participants were examined separately.
Unadjusted post-test values for F & V were no different between the precontemplator and preparation groups, although they were significantly lower among the precontemplator, contemplator and preparation groups compared to action and maintenance groups (data not shown). Findings were similar when control and treatment participants were examined separately.
This pattern of findings was similar for outcome expectations, self-efficacy and barriers, i.e. precontemplators showed improvement as great or greater than those in the preparation stage. Neither change scores nor post-test values differed between precontemplators and those in preparation for any of the measures, with the exception of knowledge which increased significantly more among precontemplators than those in the preparation groups, as well as among precontemplators compared to the contemplator and maintenance groups.
Despite a larger pre–post increase, post-test values for outcome expectations were still significantly lower among precontemplators versus those in maintenance (P values not shown in table). There were no other post-test group differences for outcome expectations. Post-test values for self-efficacy were significantly lower for the precontemplator, contemplator and preparation groups compared to those in maintenance (P values not shown in table). There were no group differences in post-test scores for health knowledge or barriers. The pattern of findings was similar when control and treatment participants were examined separately.
Intervention use and baseline stage of change
Use of the video and cookbook as reported in the post-test questionnaire did not differ between the precontemplator and preparation groups. Individuals in the maintenance group, however, were significantly more likely to use the video than those in the precontemplator [odds ratio (OR): 3.0; confidence interval (CI): 1.2–7.0], contemplator (OR: 5.3; CI: 1.9–14.9) and preparation (OR: 1.9; CI: 1.1 to 3.3) groups. Those in maintenance were also significantly more likely to report using the cookbook compared to those in the precontemplator (OR: 2.4; CI: 1.1–5.5) and contemplator (OR: 3.1; CI: 1.1–8.3) groups. Neither the percent of individuals in treatment Group 1 that received the single cue nor the percent in treatment Group 2 that received all four calls differed across any of the baseline stage groups (data not shown).
Due to the small cell sizes for contemplation and action, we conducted exploratory analyses collapsing contemplators with precontemplators and those in action with those in preparation. We then examined change in F & V intake across the three composite stages. As shown in Table IV, the pattern of findings was similar to analyses with five stages, i.e. individuals in the aggregate early stage did not differ from those in the preparation/action stage. Both of the aggregate groups, however, were significantly different from the maintenance group.
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As shown in Table V, the percent of individuals who ended in maintenance was similar between baseline precontemplators and those in preparation, 16 and 21%, respectively. Additionally, the majority, 85%, of precontemplators moved forward at least one stage, whereas only 33% of those in preparation moved forward and 15% regressed at least one stage.
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Discussion |
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Over 1 year, individuals initially classified as precontemplators reported a net increase in F & V intake as large as those in the preparation stage and precontemplators’ post-test intake was equivalent to those in preparation. Precontemplators’ change in psychosocial variables was as large or larger than those in the preparation stage and their post-test values were not significantly different. The percent of individuals in maintenance at post-test was similar between baseline precontemplators and those in preparation, 16 and 21%, respectively.
The staging algorithm used here was highly similar to that used in prior studies (Laforge et al., 1994; Campbell et al., 1997, 1999a) and the psychosocial measures generally exhibited adequate psychometric properties, and they have been used by other investigators, perhaps with the exception of the barriers measure. Thus, non-comparability of our instruments with prior studies is not a likely explanation for the findings.
A limitation of the study is the fact that we did not include a measure of processes of change or decisional balance. Such data would have allowed for more sophisticated analyses of how and why individuals changed their behavior. Stage of change is only one component of TTM. Additionally, we only conducted a single post-test assessment, 1 year from baseline. More intermediate follow-up data, e.g. 3 or 6 months, may have yielded different results.
Sampling may have been a factor as the baseline distribution of stage was somewhat different than in prior studies. The percent of participants here in contemplation, preparation and action stages was similar to prior studies. However, our sample had a lower percentage in precontemplation and a higher percentage in maintenance compared to other five-a-day studies, including one conducted in rural Black churches (Campbell, 1997, 1999a). This may reflect secular trends, since our data were collected several years after the first generation five-a-day studies (Havas et al., 1995; Campbell et al., 1997, 1999a). It is also possible that elements of our recruitment differentially discouraged precontemplators and attracted those in maintenance. It should be noted that despite the differences in stage distribution in our sample compared to other studies, mean F & V intake of 3.5 servings, based on the seven-item measure commonly used, was similar to other studies (Krebs-Smith et al., 1995; Serdula et al., 1995; Campbell et al., 1999a). Participants were recruited by liaisons in each church using a quota sampling framework, e.g. first come/first served. Therefore, it is likely that study participants were not representative of the entire church population. We do not have sufficient information from the participating churches to empirically examine the issue of sampling bias and representativeness, and external validity remains a concern.
The lack of difference between the precontemplator and preparation groups at post-test might have been related to the intervention. TTM theorists posit that individuals at different stages require different types of interventions, with precontemplators requiring more attitudinal/motivational messages, whereas those in the preparation and action stages require a more behavioral and skills-based intervention. It is possible that the MI counseling, which included an element that was tailored to participants’ interest and motivation to change, functioned like an individually tailored intervention, which could explain why precontemplators responded as well to the intervention as those in preparation (Rollnick et al., 1999). Prior studies suggest that MI may be particularly effective for those with low readiness to change (Heather et al., 1996; Butler et al., 1999). On the other hand, the pattern of findings, i.e. lack of difference between the precontemplator and preparation groups, was also evident among treatment Group 1, which did not receive the MI.
Similarly, the self-help materials, although not a priori tailored to those in the early stages of change, could be considered targeted to such individuals. This could perhaps explain the large increase among precontemplators. Again, however, the pattern of findings, i.e. lack of difference between the precontemplator and preparation groups, was also evident among the control group, which did not receive any stage-based intervention.
Finally, our statistical analyses utilized church as the primary unit of analysis, which resulted in a reduced number of degrees of freedom. This more conservative statistical approach increases the likelihood of null findings. However, we repeated our analyses using an individual-level error term and the pattern of findings, and therefore our conclusions were not appreciably altered.
One interpretation of our findings is that the first three stages of change, at least with regard to F & V intake, are not useful predictors of future behavior change. One reason for this is that at the first three stages, changing intentions changes stage and intentions can fluctuate depending on a variety of cognitive, psychologic or contextual events. Stage may represent more a state than a trait; and a trait that this is highly fluid. Test–re-test studies, over hours/days/weeks, in the absence of intervention are needed to determine the stability of the stage of change construct. Lack of predictive validity may simply reflect low reliability.
Additionally, as noted by Herzog et al., the time cutpoints typically used to distinguish stage, 1 and 6 months, may not correspond to how individuals conceptualize or plan change and therefore response to such questions may not provide a valid gauge of interest in or potential for change (Herzog et al., 1999). In particular, the cutpoints of 30 days and 6 months typically used to stage individuals may be more appropriate (and valid) for behaviors such as smoking cessation, for which there is a clear quit day and where abstinence is usually the goal. For diet, the nature of change is less discrete and therefore individuals may be less able to conceptualize their behavior change plans using these defined time periods.
One conclusion that can be drawn from this study is that precontemplators, at least with regard to F & V intake, should not be excluded from intervention studies, as they may ultimately be just as likely to change their behavior as those in more advanced stages, even without stage-tailored intervention. Another conclusion is that there may be little benefit in segmenting participants into the first three ‘motivational’ stages. One solution, utilized by some researchers, is to combine the first three stages into an aggregate ‘preaction’ stage (Glanz et al., 1998b; Kristal et al., 2000). Examination of group differences in F & V intake and psychosocial variables by stage in our study, both at baseline and 1-year follow-up, supports the lack of differentiation between the first three stages. Aggregating these stages, however, virtually eliminates any ‘cognitive’, i.e. intentions, distinction across the three stages and creates groups based almost exclusively on behavioral status. It is not clear if such a three-stage model provides meaningful theoretical significance. Again, it is important to note that our study did not include any measure of processes or pros and cons for change, and combining stage information with these variables may significantly enhance investigators’ ability to predict subsequent behavior change.
Although our findings may not generalize to other populations or other health behaviors, at least with regard to F & Vs, these findings raise questions regarding the validity of stage of change as a predictor of future behavior and intervention response. Whereas some studies have found the TTM to be a useful predictor of behavior change as well as a framework for developing interventions (Curry et al., 1992; Prochaska et al., 1992; Heather et al., 1993; Glanz et al., 1998a; Rakowski et al., 1998; Velicer et al., 1999), other studies, particularly longitudinal examinations, have failed to verify the internal assumptions of the model (Aveyard et al., 1999; Herzog et al., 1999; Povey et al., 1999; O’Neil et al., 2000; Quinlan and McCaul, 2000). It should also be noted that at baseline several psychosocial characteristics did differ by stage in the direction predicted by the TTM.
The TTM has been criticized on theoretical grounds (Bandura, 1997; Povey et al., 1999) and conceptual difficulties applying the model to dietary behavior, as opposed to addictive behaviors, have been noted elsewhere (Ni Mhurchu et al., 1997; Povey et al., 1999). Additional research, ideally prospective in nature, is needed to determine the utility of stage and the broader TTM as a framework for understanding and modifying diet as well as other health behaviors.
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Acknowledgements |
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Eat for Life was supported by National Cancer Institute grant CA-69668
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References |
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Received on September 14, 2001; accepted on September 25, 2002
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