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INTRODUCTION
The World Health Organization (WHO) recommends that the general population consume 400 g of vegetables and fruits daily in order to prevent the development of chronic non-communicable diseases, including cardiovascular diseases [1]. Mexican teenagers have been reported to consume a mean of 235 grams of vegetables and fruits per day, excluding potatoes, cereals and tubers. The Western diet today includes a tendency toward “fast food,” and teenagers and children are more vulnerable to attraction to this type of food, which put them in higher risk of developing cardiovascular diseases [2]. Low vegetable and fruit consumption by Mexican teenagers places them at risk of developing chronic non-communicable diseases in adulthood [3]. The consumption of vegetables and fruits in adolescents could replace high energy density foods which are rich in fats, refined sugars and sodium [3]. Hence, it is important to measure vegetable and fruit consumption in this population, and to design methods to increase the consumption of these food groups. There are reports indicating that school nutrition programs can improve children's vegetable consumption and intention, as well as their preference, attitude, and self-efficacy [45]. Various food education (FE) strategies may be implemented to encourage healthy eating habits among teenagers. One of these is the use of the school garden (SG) as an educational tool [6].
It has been reported that SGs, combined with educational activities in agriculture and nutrition, can help schoolchildren make better decisions about the food they eat [7]. This educational strategy must be accompanied by training for the teaching staff in charge of transmitting the knowledge [8]. Nutritional education for students can be provided through basic subjects that are already part of the current curriculum, both in the classroom and in the SG [9].
Most nutrition programs are aimed at preschoolers and schoolchildren (6 to 12 years old), and very little has been published regarding the effects of such intervention on adolescents [7]. Adolescence (defined as the period between 12 to 18 years of age), is a highly important stage in which decision-making can be positively shaped around an appropriate diet. In selecting this sample group for the study—adolescents attending a private school—researchers' intent was to avoid the distortions that socioeconomic status might cause in gauging the impact of FE accompanied by a SG: adolescents in lower socioeconomic groups, for example, although they may want to consume vegetables and fruits, may not have access to them or find them readily available. The objective of this study was to evaluate the effect of an educational intervention, accompanied by a SG as an educational didactic tool, on improving vegetable and fruit consumption according to the WHO recommendation, among middle-high school students attending a private school in Querétaro, Mexico.
SUBJECTS AND METHODS
Study design and participants
The study design is 3-arm, controlled, comparative impact study, which lasted for 20 weeks from January to June 2017. The principal of a private school in Queretaro, Mexico, gave researchers authorization to work with 6th to 12th grade students during school hours, and parental consent was obtained from all participants. The Review Board of the Universidad Autonoma de Queretaro approved the procedures (IRB number 02FCN2014). Forty-two individuals were required per group considering an alpha error of 0.05, a statistical power of 0.8 to detect a difference of 55 g between 2 groups, with a standard deviation of 80 g, and a lost cases percentage of 10%. A total of 126 students participated in the study. Subjects were randomly assigned to one of 3 study groups. Teenagers in the FE + SG group (n = 42), received a total of 29 FE lessons. Nineteen education lessons were given in the classroom and 10 education lessons were given in the SG, which focused on teaching adolescents about vegetable production, with the garden serving as a didactic tool. Each lesson included a driving question, an objective, materials and methods, guidelines and directives and final evaluation. Activities such as debates, real case analysis, and the use of electronic tablets accompanying the gardening activities, were part of the lessons given; each lesson lasted 60 minutes [10]. Table 1 lists the objectives of each of the class lessons. Teenagers in the FE group (n = 42), received the same 19 education lessons in the classroom (without the 10 education lessons in the SG). Teenagers in the control group (CG) (n = 42), did not receive any type of intervention.
Table 1
Objectives of each of the class lessons of food education and school garden program
Intervention materials, FE study program and gardening component
The study program was designed to promote the development of key competencies defined by the Organization for Economic Cooperation and Development [1112], based on the pedagogical approach of cognitive constructivism [1314] and the pedagogical renewal movement of Rousseau's New School [15]. In this program, information and communication technologies were used as educational tools [1617]. Inside the school premises, an outdoor vegetable garden was designed for the study, consisting of 25 boxes made of compressed recycling plastic, each measuring 1 × 1 × 0.40 meters, with access to 2 water faucets and direct sunlight for 5 hours a day. The vegetable garden was installed in a 11 × 2.5 m space with cement flooring, and was operated following the guidelines for a sustainable outdoor vegetable garden. Each box was prepared with 180 kg of substrate consisting of 50% black earth, 30% compost, 20% coconut fiber and 10% earthworm humus. Vegetables and aromatic plants acquired from a local organic greenhouse were transplanted directly into the seed bed [18192021].
Participants of the FE + SG group were given a class in the garden once a week. Students in this group were involved in the care and maintenance of the garden as part of the lessons designed in the educational program [622]. Through the process of applying an educational strategy and observing its effects on the students' knowledge, researchers were able to draft a “Teachers' Guide to High School Food Education”. The educational material was provided to the teachers who conducted the education. The competency-based curriculum was designed based on the Mexican education system [23]. It consisted of 29 sixty-minute lessons. Ten of these lessons were designed to be taught in a SG and 19 in the classroom. The series of lessons covered 5 topics: 1) the current food system and its impact on the environment and health, 2) the seed, its cultural and biological value, 3) food security, 4) healthy eating and 5) sustainable food production. Each lesson included a driving question, an objective, materials and methods, guidelines and instructions and final evaluation. Activities such as debates, real case analysis, and the use of electronic tablets accompanying the gardening activities, were part of the lessons given.
Evaluation tools
The students' vegetable and fruit consumption were evaluated by means of 2 quantitative questionnaires: a questionnaire on the frequency of vegetable and fruit consumption [2425] and a non-consecutive 3-day food consumption diary, excluding weekends [26]. The food consumption diary indicated the quantity and measurements (cup, tablespoon, serving size). Prior training was provided to the students to complete both questionnaires. These questionnaires were administered to all 3 experimental groups, before and after the intervention. From the food consumption diary, we calculated the consumption of vegetables and fruits, as well as energy, carbohydrates, proteins and lipids, using the Mexican foods and food products composition tables (2015) [27], and the results were reported as the mean of the 3 days (kcal/day). Additionally, an evaluation of psychosocial factors related to vegetable and fruit consumption was applied to the 3 groups using the Pro Children qualitative questionnaire, validated for the Mexican population [28]. The factors evaluated were: personal cognitive skills developed, personal attitudes, personal preferences, perceptions of physical environmental regarding accessibility at home, perceptions of physical environmental regarding accessibility at school, perception of personal barriers, and social environmental perception about modeling. The impact of the SG on vegetable and fruit consumption was evaluated through a structured qualitative interview. The interview questions were grouped into 5 categories according to the example given by Mertens [2930]: students' opinion about the SG in their school, the feelings the SG generated, the knowledge they believe they developed during the activities carried out in the SG, their social environment or background regarding vegetable and fruit consumption, and their willingness to simulate or replicate the knowledge acquired in the SG at home. The structured interview was applied at the end of the intervention to 10 randomly selected individuals from the FE + SG group.
Statistical analysis
The results of the numerical scale variables are shown as the mean (95% confidence interval). To evaluate the difference in vegetable and fruit consumption, as well as nutrient intake, before and after the intervention, a paired t-test was performed. The baseline, final and change means were compared between groups through an analysis of variance, followed by a Tukey post hoc test. All analyses were tested for possible confounders, and the test assumption of normality was verified to avoid bias in the parameters. All analyses were performed using the SPSS V23 (IBM Corp., Armonk, NY, USA).
RESULTS
Vegetable and fruit consumption
A total of 126 students participated in the study (84 treatments, 42 controls; 57 male, 69 female). The study groups were homogeneous, with the following mean values: age 14.9 ± 1.8 years, weight: 58 kg, height: 164.6 cm and body mass index: 21.3 (Table 2). Students in the FE + SG group increased their vegetable and fruit consumption by 65.2 g/day compared to the CG and 44.8 g/day compared to the FE group (Table 3). Likewise, the FE + SG group showed an increase in frequency of vegetable and fruit consumption to 1.4 days more per week and FE 1.2 day per week, compared to the CG (Table 4). The CG showed no differences in vegetable and fruit consumption or in the frequency of consumption (Tables 3 and 4).
Table 2
Age and anthropometric characteristics of the participating students
Table 3
Report on consumption of vegetables and fruits (grams) before and after the intervention
Data obtained from the food consumption diary for 3 non-consecutive days, excluding weekends. All values represent the mean (95% confidence interval).
FE + SG, food education + school garden; FE, food education only; CG, Control group.
1)Significant difference between baseline and post intervention mean values in paired t-test (P < 0.05).
a,bDifferent letters represent significant difference between intervention groups in Tukey post hoc test (P < 0.05).
Table 4
Frequency of weekly consumption of vegetables and fruits (days/week) before and after the intervention
Data obtained from the food consumption diary for 3 non-consecutive days, excluding weekends. All values represent the mean (95% confidence interval).
FE + SG, food education + school garden; FE, food education only; CG, Control group.
1)Significant difference between baseline and post intervention mean values in paired t-test (P < 0.05).
a,bDifferent letters represent significant difference between intervention groups in Tukey post hoc test (P < 0.05).
Energy contribution from the diet
In terms of energy consumption, the FE + SG group decreased its energy consumption by 6.1% (−158 kcal), within which calories from fat decreased 11% (−77 kcal) after the intervention. Caloric intake from vegetables increased 54.8% (+18 kcal) and caloric intake from fruits increased 32.3% (+21 kcal). In the FE group, energy consumption decreased 3% (−80 kcal), while the calories obtained from the fruits increased 22.4% (12 kcal). CG showed no significant difference in total energy consumption after the intervention. However, for CG, calories from fats increased 2.4% and from carbohydrates 2.6%. At the end of the intervention, a difference was observed in total energy consumption between the FE + SG group and the CG, with the latter showing an energy consumption 7.9% higher than the FE + SG group. Caloric intake from vegetables was 35.5% higher for the FE + SG group than for the FE group and 50.4% higher than for the CG. Finally, the FE + SG group showed 34.8% higher caloric intake from fruits than CG (Table 5).
Table 5
Energy consumption (kcal) before and after the intervention
Data obtained from the food consumption diary for 3 non-consecutive days, excluding weekends. All values represent the mean (95% confidence interval).
FE + SG, food education + school garden; FE, food education only; CG, Control group.
1)Significant difference between baseline and post intervention mean values in paired t-test (P < 0.05).
a,b,cDifferent letters represent significant difference between intervention groups in Tukey post hoc test (P < 0.05).
Psychological factors related to vegetable and fruit consumption
The main findings of each of the categories of the Pro Children qualitative questionnaire applied to the 3 groups are discussed below (Table 6).
Table 6
Psychosocial factors related to vegetable and fruit consumption using the Pro Children qualitative questionnaire (n = 126)
Evaluation of personal cognitive skills developed
The group FE + SG showed greater understanding of, reflection upon, and analysis of the information they received from their environment about vegetable and fruit consumption, having learned about the characteristics of a healthy diet and recommendations on daily consumption of vegetables and fruits. They perceived that they consumed more vegetables and fruits than their peers and applied a reasoning by which they could incorporate the knowledge acquired to favorably modify their habits regarding consumption of this food group.
Evaluation of personal attitudes relating to vegetable and fruit consumption
The FE + SG group and the FE group showed greater willingness to consume vegetables and fruits on a daily basis. Both groups recognized the benefits to their health from consumption of this food group.
Evaluation of personal preferences relating to vegetable and fruit consumption
Preference for fruits was higher in the FE + SG group with an acceptance of 55.2% and 50.8% for the group FE, while a higher percentage of CG subjects mentioned not having tried any of the vegetable or fruit options mentioned.
Evaluation of perceptions of physical environmental regarding accessibility of vegetables and fruits for consumption at home
The FE + SG and FE groups reported that vegetables and fruits were more accessible for consumption at home. This enabled them to play an active role in the decision to consume these foods, as there were a variety of them available at home already. All 3 groups responded that they were always allowed to eat all the vegetables and fruit they wanted at home. However, they reported that mothers were more available than fathers to encourage their teenage children to consume vegetables and fruits. One barrier to the consumption of vegetables reported by CG was that there were not always vegetables that they liked available in their homes.
Evaluation of the physical environment regarding accessibility of vegetables and fruits for consumption at school
The FE + SG group did not perceive school to be a barrier to vegetable and fruit consumption, because they could either bring them from home, buy them or obtain them for free. They reported that recess time was not a barrier to consuming vegetables and fruits. Nor did they report still feeling hungry after eating vegetables or fruits. All 3 study groups perceive their peers' low vegetable and fruit consumption as a barrier.
Evaluation of perception regarding personal barriers to vegetable and fruit consumption
Respondents from all 3 study groups did not perceive the time it takes to consume vegetables and fruits as a personal barrier, nor the fact that they might stain when consumed or be crushed in their backpack. One barrier to vegetable and fruit consumption mentioned by CG, however, was that the vegetable and fruit group tended to be displaced by other foods, as they preferred eating foods with higher energy density.
Evaluation of socio-environmental perceptions regarding role models for vegetable and fruit consumption
Members of all 3 study groups mentioned that their mothers consumed more vegetables and fruits than their fathers. However, the FE + SG group reported that their fathers did urge them to consume vegetables and fruits every day. Respondents did not perceive that television or the Internet promoted vegetable and fruit consumption through the advertising shown there.
Interview
The categories created for each item of the interview are shown in Table 7. Opinions in the FE + SG group focused on the fact that the SG was a space that motivated them to consume vegetables and fruits, since they could access it during school hours. They also said that the SG helped them save money, because the vegetables or fruits they obtained there were free. In addition, they claimed that these foods were healthy, with a low impact on the environment, since they themselves had planted and harvested them, giving them a feeling of satisfaction and pride at having participated. The teenagers reported feeling proud of making a change in themselves and in their school to promote a healthier environment. The students reported that taking classes in the SG area made them feel free and more interested in the subject, and in fact, classes in the garden seemed more fun to them than those in the classroom.
Table 7
Generation of categories of analysis from the post-intervention interview
The students reported that their classes in the SG taught them about the vitamins and inorganic nutrients present in vegetables and fruits, and to equate their consumption with good health. They also said they learned enough to replicate the SG at home and consume this food group on a regular basis. Likewise, they reported being aware of the effects of the food system on global warming, changes in land use, and on their health. Finally, they mentioned having begun or being willing to begin a vegetable garden at their own home or at the home of a family member.
DISCUSSION
The results of the study showed a significant increase in vegetable and fruit consumption by students who received nutritional education along with the didactic tool of a SG. The increase in vegetable and fruit consumption could be due to the practical activities in the SG that accompanied the nutrition education sessions, where students were exposed to farming techniques that exemplified the principles of food sustainability.
In 2007, McAleese and Rankin [31] conducted a similar intervention in garden-based nutrition education with sixth-graders and, through a 24-hour food-recall, they reported an increase in adolescents' fruit and vegetable servings. In addition, they described an increase in vitamin A, vitamin C, and fiber intake. The FE + SG group showed a significant increase in vegetable and fruit consumption, even greater than that reported by a similar study in Mexican adolescents [3]. Despite the observed increase, the reported intake of vegetables and fruits in teenagers after they received FE + SG, was equivalent to only 54% of the WHO recommendation. Although gardening has shown to have a positive effect on vegetable and fruit consumption, it has been suggested that the persistence of gardening habits and vegetable and fruit intake increase through adulthood should be studied as well [32]. It is possible that a longer intervention could help to further increase vegetable and fruit intake to levels consistent with the WHO recommendation (400 g per day).
Some countries have launched a strategy of encouraging vegetable and fruit consumption in a “5-a-day” campaign promoted jointly by the government and civil society. The impact of these campaigns has been evaluated in adults, with no significant change in the frequency of vegetable and fruit consumption, and the authors of this study reported that the campaign's message was not well understood by the population [33]. A SG as a nutritional education tool has shown to be an effective strategy for improving dietary behavior in adolescents, according to this study's results and findings reported by other authors [3435]. As reported by Bell [36], green schools have considerable potential to promote health and well-being, so we may conclude that a nutritional education intervention through a guided gardening experience in schools improves intake of vegetables and fruits and can help promote health and well-being in adolescents. In Mexico, there is a general lack of skills and knowledge in the population on how to produce, choose, combine, prepare and distribute food according to their family budget, which can lead to food insecurity [37]. Therefore, SGs could also be a strategy for food security in low-income segments of the population, as a public policy, so that subjects about food production and nutrition are taught in schools as part of the educational curriculum [38]. To replicate the SG strategy, teachers should be trained in these areas in the manner described in this study.
Human resources, specifically teachers, were trained in FE and SG management and served as a guide in this study. This study did not evaluate adolescent's willingness to try new foods, or biological mechanisms of behavior, which could be an area of interest for future study. It has been reported that schoolchildren's exposure to educational gardens promotes consumption of a wider variety of fruits and vegetables, as well as a greater willingness to try new vegetables [6]. A wider variety of vegetables and fruits consumed would provide a higher variety of micronutrients and fiber. Peña Fernández and María Reidl Martínez reported in 2015 [39] that eating patterns in adolescents were related to emotions. Thus, bread, pasta and milk were the main foods consumed, and enjoyment, pleasure and happiness were the main emotions present during eating. Vegetable and fruit intake could be related to certain emotions in adolescents. This points to an area of research for future study because of the age-typical transformation in the brain, such as increases in novelty-seeking/risk-taking behavior and the increase in food intake associated with the growth spurt [40].
It is important to note that the school in which the study was performed had sufficient technical, economic and human resources for the program to be implemented without budget limitations. The study was funded by the school itself. The study population had physical and economic access to sufficient, safe and nutritious food to meet their dietary needs at all times. The families of participants in the study were on average high-income, a group that represents about 16.9% of Mexico's population according to the National Institute for Statistics and Geography and the National survey of Income and Spending 2018 [41]. The important thing about this strategy is that the teacher serves as a guide in the lessons, and it is the teenagers themselves who are responsible for analyzing and structuring the information and proposals. It should be noted that for the purposes of replicating this intervention, the teaching staff who are to be in contact with the students must receive training in the 5 main themes of this guide.
Further studies with a longer duration are required to evaluate the effectiveness of a SG as a didactic tool in the educational intervention to meet WHO recommendations on vegetable and fruit intake. It is also necessary to evaluate whether the strategy would have similarly favorable results in low-income populations.
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