The most common description of the dietary practices currently adopted during adolescence consists of fat, sugar, and sodium-rich diets, with little addition of fruits and vegetables [
In this regard, one possibility would be to adopt interventions based on behavioral theories, such as the transtheoretical model. This model makes it possible to determine
In addition to the stages of change, the model encompasses three other constructs: the
Since the basis for understanding the processes of change at different times was established, several studies among young people have shown positive results from nutritional interventions directed toward the stages of change. In addition to advancing through the stages with tailored interventions, individuals perceive more benefits and fewer barriers, present greater self-efficacy, and start to have a healthier diet, including greater fruit and vegetable intake [
The objective of this study was to assess the impact of a stage-based intervention using printed educational materials, directed toward greater fruit and vegetable intake, along with the decisional balance relating to the benefits and barriers perceived and the self-efficacy, among adolescents in public schools in Brasília, Federal District, Brazil.
This was a randomized trial in which a six-month nutritional intervention was developed during the 2009 school year. Two groups were assessed (intervention and control) in order to identify the effects of an intervention based on printed educational materials for promoting healthy dietary habits, which were distributed to the adolescents every month, both in classrooms and by mail. The materials were directed toward the participants’ stages of change. This study was approved by the Research Ethics Committee of the School of Public Health, University of São Paulo.
The sampling process aimed toward obtaining a representative sample of adolescents in the 7th and 8th school years in Brasília. In order to calculate this, the 2006 School Census was used: at that time, there were 15 public schools in Brasília with 7th and 8th year students, with a total of 5,785 students enrolled [
In addition to age (in years), the variables of sex, nutritional status, and family income (as multiples of the Brazilian minimum monthly salary) were evaluated. Nutritional status was assessed from weight and height measurements, which were taken in duplicate to investigate the body mass index according to age [
Initially, each adolescent was introduced to the concept of servings of fruits and vegetables by means of an illustrated leaflet. This showed that one serving of vegetables was equivalent to a dessert plate (or cup) of raw vegetables or half a dessert plate (or half a cup) of cooked vegetables, excluding potatoes and other starchy vegetables. In the case of fruits, for instance, one serving was equivalent to a medium-sized banana or orange, a small-sized apple, a medium-sized slice of pineapple or watermelon, a small-sized slice of papaya, or a small bunch of grapes. Next, the participants were asked about their habitual intake of such foods, in servings. Their answers were recorded in categories ranging from less than one serving a day to five or more servings a day.
In order to assess the adequacy of the fruit and vegetable intake, the recommended daily intake of these foods (400 g) [
In order to classify the adolescents in the five stages of change regarding their fruit and vegetable consumption, an algorithm was used. This consisted of a questionnaire with a limited number of questions for which the answers are mutually exclusive, with a format that is similar to what has been described by several authors [
If the self-reported habitual fruit and vegetable consumption was inadequate, that is, less than five servings a day, the adolescents were asked about their intentions with regard to increasing their consumption of these foods in the near future. If they said that they had no intention of changing their dietary habits, they were classified as at the
If the participants’ habitual consumption of fruits and vegetables was adequate, that is, five or more servings a day, they were asked how long they had had this habit. If this was a recent habit, of less than six months, they were classified in the
A seven-item scale relating to the barriers faced by individuals when trying to eat in a healthy manner was included, along with a seven-item scale relating to the benefits identified by these individuals when following an adequate diet. Each item consisted of a sentence in which the participants expressed their agreement or disagreement with its contents, by means of a five-point Likert scale, ranging from 1—“I do not agree at all” to 5—“I strongly agree.” The items were selected from previous studies, which had shown relatively moderate-to-high internal consistency coefficients (Cronbach’s
This variable was assessed using a set of eight items. The participants expressed their agreement or disagreement with the content of these items on five-point Likert scales, ranging from 1—“I’m sure I cannot do this” to 5—“I’m sure I can do it.” The items were selected using the same criteria as presented regarding preparation of the scale for decisional balance [
In the initial assessment, all participants in the intervention group were asked whether they had received any nutritional guidance over the past year from a nutritionist or other healthcare professional.
All adolescents in both the control and the intervention group were evaluated according to the variables presented above. After the six-month intervention, all the participants were assessed again. At the end of the first and second interviews, the participants in both groups received a folder presenting the 10 steps toward healthy eating during adolescence, as described by the Brazilian Ministry of Health [
Every month, the intervention group received colorful printed magazines that promoted healthy eating and information newsletters directed toward the participants’ stages of change that had been identified at the beginning of the study, with the aim of promoting fruit and vegetable consumption. The magazines were handed out at the schools and the newsletters were mailed.
The topics presented in the six magazines developed for the study were the means for overcoming the difficulties in eating healthily; the importance of breakfast and the right distribution of meals during the day; the relationship between nutritional status and adolescents’ physical activity; the role of nutrients in adolescents’ diets, the concepts of the terms
The basis for developing the magazines was the discourse of participants in a qualitative study conducted among focus groups that preceded this study [
Since previous studies found that high percentages of the adolescents were classified in the stages of change prior to action, that is, precontemplation and contemplation [
The basis for developing the newsletters was stage-based materials for promoting regular consumption of fruits and vegetables that have been used in several studies, with satisfactory results among young adults [
The newsletters for the adolescents at the precontemplation stage covered the processes of change relating to
The materials for the adolescents classified in the contemplation and preparation stages included activities relating to the processes of change consisting of
In the newsletters targeted toward individuals at the action and maintenance stages, the strategies emphasized consisted of maintaining an adequate intake of fruits and vegetables and preventing relapse (process of change:
Comparison of the variables between the control and intervention groups at the baseline was performed using the chisquare test for categorical data and Student’s
The effect of the intervention was assessed by analyzing the changes in the components of the transtheoretical model (stages of change, decisional balance, and self-efficacy) and the changes in fruit and vegetable intake. Analysis of covariance (ANCOVA) models with adjustments for sex, age, and baseline values were used for each continuous outcome, that is, decisional balance between benefits and barriers and self-efficacy. A model for repeated measurement analysis with weighted minimum squares was used for categorized outcomes, that is, stages of change and fruit and vegetable intake. The same analyses were also performed with selection of only the group of adolescents that had not received nutritional guidance prior to the intervention.
The proportions of the adolescents who progressed through each stage of change over the course of the intervention were also assessed by means of Mantel-Haenszel chisquare analyses.
A 5% significance level was used. The analyses were conducted using the Statistical Analysis Software (SAS version 9.2; SAS Institute Inc., Cary, NC, USA) and the Statistical Package for the Social Sciences (SPSS for Windows, version 13.0; SPSS Inc., Chicago, Ill, USA).
The adolescents who participated in the survey had handed over a free and informed consent statement signed by their parents or guardians. This study was approved by the Research Ethics Committee of the School of Public Health, University of São Paulo.
This study included initial participation by 860 students: 373 in the control group and 487 in the intervention group. In total, 771 participants completed the study, representing 81% followup. The losses were due to transfers of students to other schools (
More than half of the participants were aged between 11 and 13 years, and 59.5% were female (Table
Comparability between the intervention and control groups, regarding baseline characteristics.
Variables | Total | Control Group | Intervention Group | ||||
% | % | % | |||||
Age | |||||||
11–13 yrs | 489 | 56.9% | 207 | 55.5% | 282 | 57.9% | 0.459 |
14–16 yrs | 365 | 42.4% | 163 | 43.7% | 202 | 41.5% | |
17–19 yrs | 6 | 0.7% | 3 | 0.8% | 3 | 0.6% | |
Gender | |||||||
Male | 348 | 40.5% | 135 | 36.2% | 213 | 43.7% | 0.030 |
Female | 512 | 59.5% | 238 | 63.8% | 274 | 56.3% | |
Family income | |||||||
<2 BMMS* | 294 | 34.2% | 120 | 32.2% | 174 | 35.7% | 0.130 |
2–4.9 BMMS* | 286 | 33.2% | 118 | 31.6% | 168 | 34.5% | |
≥5 BMMS* | 200 | 23.3% | 100 | 26.8% | 100 | 20.5% | |
Didn’t know/no answer | 80 | 9.3% | 35 | 9.4% | 45 | 9.3% | |
Nutritional status | |||||||
Thinness | 23 | 2.6% | 8 | 2.2% | 15 | 3.1% | 0.544 |
Adequate | 682 | 79.3% | 304 | 81.5% | 378 | 77.6% | |
Overweight | 126 | 14.7% | 50 | 13.4% | 76 | 15.6% | |
Obesity | 29 | 3.4% | 11 | 2.9% | 18 | 3.7% | |
Fruit/vegetable intake | |||||||
Adequate | 94 | 10.9% | 43 | 11.5% | 51 | 10.5% | 0.660 |
Inadequate | 766 | 89.1% | 330 | 88.5% | 436 | 89.5% | |
Stages of change | |||||||
Precontemplation | 376 | 43.7% | 159 | 42.6% | 217 | 44.6% | 0.377 |
Contemplation | 117 | 13.6% | 46 | 12.3% | 71 | 14.6% | |
Preparation | 273 | 31.7% | 125 | 33.5% | 148 | 30.4% | |
Action | 16 | 1.9% | 8 | 2.1% | 8 | 1.6% | |
Maintenance | 78 | 9.1% | 35 | 9.4% | 43 | 8.8% | |
Total |
*BMMS: Brazilian minimum monthly salary.
At the baseline, there were no significant differences between the control and intervention groups regarding the category variables, with the exception of gender distribution, given that there was a higher percentage of girls in the control group (Table
The model for repeated measurements analysis using weighted minimum squares for categorized outcomes showed that the proposed intervention did not produce any significant changes to fruit and vegetable intake (
Comparability between the intervention and control groups regarding fruit and vegetable intake and stages of change after the proposed intervention (analysis of the repeated measurements model using weighted minimum squares).
Variables | Control Group | Intervention Group | |||
% | % | ||||
Fruit/vegetable intake | |||||
Adequate | 27 | 8.4% | 42 | 9.4% | 0.626 |
Inadequate | 296 | 91.6% | 406 | 90.6% | |
Stages of change | |||||
Precontemplation | 134 | 41.5% | 195 | 43.5% | 0.905 |
Contemplation | 67 | 20.7% | 89 | 19.9% | |
Preparation | 95 | 29.4% | 122 | 27.2% | |
Action | 5 | 1.6% | 9 | 2.0% | |
Maintenance | 22 | 6.8% | 33 | 7.4% | |
Total |
Comparability between the intervention and control groups regarding decisional balance for benefits (“pros” scores) and barriers (“cons” scores) and self-efficacy, adjusted for sex and age, after the proposed intervention (analysis of covariance, ANCOVA).
Variables | Control Group | Intervention Group | |||
Mean | Standard Error | Mean | Standard Error | ||
Pros scores | 28.73 | 0.17 | 28.97 | 0.14 | 0.2885 |
Cons scores | 13.50 | 0.16 | 13.33 | 0.13 | 0.4153 |
Self-efficacy scores | 31.62 | 0.20 | 31.69 | 0.17 | 0.7749 |
The same analyses for assessing the impact of the intervention that were conducted on the full sample were also conducted by selecting only the participants who had not received prior nutritional guidance. This analysis showed that the absence of significant effects was maintained.
Comparing the control and intervention groups, there were no differences between the proportions of adolescents who progressed from precontemplation (
In the present study, high prevalence of inadequate fruit and vegetable intake among school children was observed, as also shown in several national studies conducted among Brazilian adolescents from different regions. [
This, together with the high percentage of overweight adolescents found in the present study, highlights the urgent need for impactful nutritional interventions in order to promote healthy dietary practices and motivate young people to adopt the nutritional recommendations. It should be emphasized that adolescence is an important period for establishing the dietary behavior that will be maintained in adulthood, and it is a stage in which there is greater independence in relation to choosing food, compared with childhood [
It should be noted that the low fruit and vegetable intake among the participants in the present study may have been associated not only with the individuals’ ages, but also with their families’ socioeconomic conditions. Family income and schooling level have been seen to be determinants of the low intake of these foods in Brazil [
Unlike what was expected, the intervention proposed was ineffective in changing these adolescents’ dietary behavior regarding their consumption of fruits and vegetables. Other studies with similar methodology have been conducted among young people, aimed at promoting the consumption of these foods, and have shown positive results after nutritional interventions targeted at stages of change. However, it should be noted that the major difference between the present study and other studies in the literature was that they included other nutritional intervention strategies in addition to distribution of educational materials to participants in order to promote fruit and vegetable consumption and change their dietary behavior [
According to Brinley et al. [
As mentioned earlier, the printed materials used in studies by Richards et al. [
It can, therefore, be said that additional motivation strategies should be included in parallel with intervention studies based on the distribution of printed materials tailored to the stages of change. Such strategies appear to be of fundamental importance for achieving a positive impact. On the other hand, recent criticism of the use of the transtheoretical model has suggested that interventions based on this theory are, in general, more intense and personalized than are the conditions presented to the control group. In other words, such interventions promote greater proximity and involvement between the researchers and the participants in the intervention group and contacts of greater frequency and of a more personal nature than in the control group. Consequently, the positive impact observed in intervention studies in this format could be a result from their intensity and not from the fact that they were based on the transtheoretical model [
Other important matters may explain the lack of impact from the proposed intervention in this study, such as the lack of family and teacher involvement in motivating behavioral changes. The family represents a fundamental social context in which behavior, actions, and habits of life are affected [
In addition, family participation in nutritional interventions is relevant given that often it is not the adolescent who makes decisions about the food available at home. The lack of autonomy in selecting foods that are consumed at home was shown in the study by Silva et al. [
Direct involvement by teachers in interventions is a debatable point, considering that Sichieri and Souza [
Likewise, the present study may not have had sufficient duration to promote changes in dietary behavior. The six-month duration was determined based on two points: the possibility of completing the study during the school year, from its submission to and approval by the school directors, until the final assessment of the students in both groups, and the fact that changing the stage from
Although the duration of previous interventions was less than or equal to six months, the literature has shown that studies of longer duration allow greater exposure of individuals to the information transmitted and favor behavioral changes [
Another limitation of the present study relates to the assessment of food intake measurements through the categorized options. Small increases in the weekly consumption of fruits and vegetables that remained less than one serving (e.g., from two to four times a week) could not be identified through the evaluation adopted, since the first option corresponded to consumption of these foods “less than once a day.” Other forms of assessment of fruit and vegetable intake with greater sensitivity to small changes need to be incorporated, especially among groups in which there are significant percentages of individuals with inadequate dietary practices.
This study showed that a nutritional intervention exclusively based on distribution of printed educational materials targeted at individuals’ stages of change was not enough to change the dietary habits of adolescents. No significant changes to the participants’ fruit and vegetable intake, benefits, and barriers or perceived self-efficacy were identified. This indicates the complexity of the issues involved in adolescents’ dietary behavior and emphasizes the major difficulties that need to be overcome in promoting healthy dietary practices in this group.
Interventions aimed at adolescents should be adapted so that, in addition to incorporating stage-matched printed educational materials, they also include other strategies for motivating them to adopt a healthy diet. It is also important to involve the social network that surrounds adolescents, in order to provide support for behavioral changes, and consider the duration of the nutritional intervention and the assessment measurements that can identify small changes in dietary habits.
This research was supported by an award provided by the International Life Sciences Institute (ILSI), Brazil, a nongovernmental and nonprofit organization. The language translation was supported by a grant from the Deanship for Research and Post-graduation of the University of Brasília.