A Systematic Review of Healthy Nutrition Intervention Programs in Kindergarten and Primary Education

Childhood obesity and overweight rates are increasing in an exponential way. This type of diet-related health problem has consequences, not only at present but also for children’s future lives. For these reasons, it is very important to find a solution, which could be nutrition intervention programs. The main objective of this article is to investigate the effectiveness of nutrition intervention programs in children aged 3–12 around the world. We used SCOPUS, Web of Science, and PubMed databases to carry out this systematic review and we followed the PRISMA statement. Two authors conducted literature searches independently, finding a total of 138 articles. Finally, after a thorough screening, a total of 19 articles were selected for detailed analysis. The results show that, in general, nutrition intervention programs are effective in improving knowledge and behaviors about healthy habits, and, consequently, that the body mass index value is reduced. However, it is true that we found differences between the incomes of families and geographical areas. In conclusion, we encourage school centers to consider including these types of programs in their educational program and bring awareness of the importance of families too.


Introduction
One of the main educational objectives is to promote people healthy lifestyle habits among young related to the Mediterranean diet and the regular practice of physical activity. However, diet-related health problems have a high incidence in children and adults [1,2]. Diet is an important risk factor that can be modified, having a significant impact on people's health [3]. In fact, eating behavior (such as food choices, and eating events and habits) establishes the health status of people [4]. The most common of these problems are overweight and obesity, which have increased in children in the last few years. This has occurred not only in the richest countries but also in poorer countries [5,6], and the incidence continues to grow. Since 1975, universal obesity has almost tripled [1]. In 2020, 340 million children aged 5-19 and 38.9 million children aged under 5 were obese or overweight [1].
An imbalance between energy intake and expenditure causes overweight and obesity. Energy expenditure cannot be exceeded by energy intake. In consequence, diet quality is essential to maintaining body mass index (BMI) [7].
Nevertheless, there are other diet-related health problems, such as stunting or wasting. A child is stunted when they are too short for their age; a child is wasted when they are too thin for their height (underweight). Even though the prevalence of stunting in children aged under 5 has decreased from 33.1% in 2000 to 22% in 2020, 149.2 million children suffered it in 2020 and 45.4 million suffered from wasting [8].
In the primary string search, we found 2 articles about pre-primary education.

Inclusion and Exclusion Criteria
The main criteria for this review were nutrition intervention programs in pre-primary and primary schools over the world. During the selection process the following criteria has been considered: • Articles from scientific journals were accepted, whereas other types of studies such as gray literature were refused; • Participants sample had to be made up of preschool of school children, and studies with post-primary, teachers or families as samples were refused; • Experimental or quasi-experimental articles were accepted, while articles without an intervention program, a pre-and post-intervention, or experimental group were refused; • Nutrition intervention programs in pre-primary or primary schools were included, whereas we refused articles whose variables were different from eating diet, for instance, physical activity, food wasted, smart devices, hand washing, academic achievement, or teachers' attitudes, among others;

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Articles with open access and the Spanish or English language were included. We refused articles to which we did not have full access or which were written in other languages.

Article Selection and Data Extraction
Firstly, we found 17 articles for pre-primary education and 121 for primary education. Removing articles published before 2013, studies repeated in two or more databases, and gray literature, we screened 74 articles in total. Later, we applied the inclusion criteria mentioned before and 42 studies were selected for a full reading. Finally, 19 articles published in scientific journals were included in our systematic review. This process is summarized in Figure 1.
Firstly, we found 17 articles for pre-primary education and 121 for primary ed tion. Removing articles published before 2013, studies repeated in two or more datab and gray literature, we screened 74 articles in total. Later, we applied the inclusion cri mentioned before and 42 studies were selected for a full reading. Finally, 19 articles lished in scientific journals were included in our systematic review. This process is s marized in Figure 1. The same two authors extracted the following data from the 19 articles selected thors' names, year of publication, instruments used, variables measured, sample, cou and main findings. Then, a third author validated the information.

Study Quality Assessment
The literature search and article selection were carried out by two authors i pendently. Some disagreements were found, but they were solved by the consensus o two authors. We divided the number of agreements by the total number of agreem plus disagreements, then we multiplied the answer by 100 to obtain the inter-rater r bility percent, which resulted in 95%. The same two authors extracted the following data from the 19 articles selected: authors' names, year of publication, instruments used, variables measured, sample, country, and main findings. Then, a third author validated the information.

Study Quality Assessment
The literature search and article selection were carried out by two authors independently. Some disagreements were found, but they were solved by the consensus of the two authors. We divided the number of agreements by the total number of agreements plus disagreements, then we multiplied the answer by 100 to obtain the inter-rater reliability percent, which resulted in 95%.

Study Characteristics
From the 19 articles that were selected for our systematic review, some data were extracted to know the characteristics of the studies (Table 1). In this sense, we can say that there is a great variety across geographic location. A total of 5 articles were from the United States [34][35][36][37][38], 2 from Malaysia [39,40], 2 from China [41,42], while the rest of countries did not appear in more than one study. The most studied continents were North America and Asia, with 6 out of 19 each continent, closely followed by Europe (5 articles). Most of the American articles selected were developed in the United States (5 out of 6). The age range was from 4 to 14 years old. However, most of the studies had a population aged from 6 to 12 years old, as they focused on primary education. Focusing on this stage, children aged 9 years old were the most represented group of the studies analyzed (in 73.68% of the articles). Regarding the instrument, children's and parents' questionnaires and surveys were the most used instruments [34,[36][37][38][39][40][42][43][44][45][46][47][48][49][50].

Outcomes
The effectiveness of a nutrition program depends on its aims, activities, methods, and program content, among other factors [53]. That is why we found a great variety of intervention programs. According to the articles selected, we can group nutritional programs into three categories: (1) education component programs (e.g., classroom-based learning, educational modules, and supportive educational materials), (2) practical component programs (e.g., the availability of fruit and vegetable, participation in nutritional campaigns and games), and (3) educational and practical component programs (e.g., theoretical lessons through video lessons or video laboratories, implementation of contents through meaningful activities such as gamified challenges or cooking workshops). This review included 19 intervention studies that reported a significant increase in children's consumption of a healthy diet, mainly consisting of fruit and vegetables. Overall, 6 studies of these articles included only educational components [35,36,40,41,47,51], 6 studies used practical approaches [37,38,42,44,48,50], and 7 included both approaches [34,39,43,45,46,49,52]. The intervention programs and their duration can be seen in Table 2. Table 2. Characteristics of the intervention programs.

Authors Description Intervention Duration of Sessions
García and Fernández 2022 [43] Effectiveness of the gamified proposal "Save the Mediterranean Diet". EG. The contents are presented to the students through audiovisual support. Then, they have to overcome the gamified mission. CG. Nothing was provided.
Øvrebø et al. 2022 [44] Effectiveness of a program based on free fruit and vegetable (FFV) school policies. EG. Provide a daily serving of free fruit or vegetable at lunchtime. CG. Nothing was provided. Siew et al. 2020 [40] Effectiveness of a nutrition educational package. EG. HKP educational package with three educational modules (including health awareness, nutrition, physical activity, and hygiene), and supportive educational materials (such as games, PowerPoint presentations, goal cards . . . ). CG. Nothing was provided.
Six times a year for 3 years (each session lasts one hour).

Nutritional Knowledge
In Table 3, we observe that nutrition intervention programs increase children's nutritional knowledge [40,49], especially about the appropriate daily frequency of fruit and vegetable consumption [46], and the sugar content of certain foods [35]. In addition, this knowledge about healthy habits increases, especially among children living in low-income neighborhoods [47]. On the contrary, Sharma et al. found that the EG decreased their nutrition and physical activity knowledge [37]. Finally, these school nutrition practices increase students' knowledge of active lifestyles and healthy diets [50]. This knowledge increases due to the theoretical lessons and practical activities on the subject of nutrition that take place in class [40,42].

Body Weight and Body Mass Index (BMI)
In Table 4, we find that children's participation in nutrition intervention programs causes significant changes in anthropometric variables such as weight, in some cases, over time [40]. The prevalence of normal weight increased, while the prevalence of overweight, obesity, or thinness decreased after the implementation of these programs [40,50]. Table 4. Results related to body weight and BMI.
-At a 3-month follow-up, the EG showed lower BMI scores (p < 0.05).

Authors Results
Siew et al. 2020 [40] -Significant changes in weight and BMI over time occurred in each group (p < 0.05): The prevalence of normal weight increased in the EG at the post-test, but not in the CG. The prevalence of overweight decreased in the EG at the post-test, but not in the CG. The prevalence of thinness at post-test decreased in both groups, but in the EG the decrease was greater. The CG had a higher prevalence of obesity and overweight than the EG at the post-test.
Kim et al. 2019 [51] -There were significant changes in anthropometric variables in the EG (p < 0.05).
Lin et al. 2019 [50] -The prevalence of overweight and obesity decreased in EG at post-test, but not in CG.

Sharma et al. 2015 [37]
-Physical activity attitude had significant differences between groups (p = 0.041), and it increased from pre-to postintervention.
-There were no significant effects of Quest to Lava Mountain (QTLM) on physical activity. CG and EG improved their results but there were no significant differences between the groups. In addition, overweight children who participated in these programs reduced their BMI score [39,46]. Additionally, children who were in schools that followed a free fruit and vegetable policy had a better BMI [44]. On the other hand, boys of parents with no higher education had an elevated BMI and a higher chance of being overweight or obese, while girls of parents with no higher education had a lower BMI and a lower chance of being overweight or obese [44]. In turn, Nickel et al. affirmed that boys that lived in rural areas experienced a greater reduction in waist circumference (WC) [47].
Finally, these programs make children do physical activity more frequently, so they can prevent and/or treat overweight and obesity in this population [37,39,46]. However, Sharma et al. did not find significant effects of a video game-based nutritional program on physical activity [37].

Eating Behaviors
In Table 5, we observe that the nutritional quotient (NQ) score increased significantly after participating in these nutrition intervention programs, in relation to diet quality, dietary attitudes, and healthy eating behaviors [42,42,51]. Moreover, we find behavioral improvement with respect to the daily frequency of fruit and vegetable consumption [45,46,51] in both children [38] and parents [34], moderation in the intake of hypercaloric foods [51], changes in the regularity of meals away from home [51] and the frequency of eating five meals per day [39], and adherence to the Mediterranean diet [43]. Verdonschot et al. disagreed, and they did not find significant differences in fruit and vegetable consumption between EG and CG [49]. Table 5. Results related to eating behaviors.

Authors Results
García and Fernández, 2022 [43] -Adherence to the Mediterranean diet was slightly higher in the EG (pre-test 6.7 and post-test 7.8) than in the CG (pre-test 8.1. and post-test 8.1).
-Adherence to the Mediterranean diet is slightly higher in the group of girls (pre-test 7.8 and post-test 8.4) compared to the group of boys (pretest 6.9 and posttest 7.6).

Authors Results
Karpouzis et al. 2021 [45] -In EG there was an increase in self-confidence in cooking, the pleasure in food and cooking, the intake of fruits and vegetables, and in the frequency of cooking at home.
-Food waste was reduced. Children ate more of the contents of their lunch boxes and they were willing to eat imperfect fruits and vegetables post-intervention.
Teo et al. 2021 [39] -At post-intervention, the EG increased their breakfast, lunch, dinner, and snack consumption frequency.
-Boys who lived in higher-income neighborhoods in EG improved dietary intake.
-The proportion of children who had a morning snack habit decreased significantly between pre-and post-intervention (p = 0.000).
-The consumption of cookies, cakes, and chocolates decreased significantly in the EG (p = 0.000).
Marshall et al. 2020 [34] -There was a significant increase in FV intake and fiber intake in the EG.
-There was a significant decrease in total fat intake and in the percentage of daily calories from sugar-sweetened beverages (p < 0.05).
-Dietary data from parents showed significant increases in the combined fruit and vegetable intake (p < 0.05).
-There were changes in the home nutrition environment which included: an increase in the frequency of cooking behaviors, in the use of nutrition facts labels, and in the availability of fruit and vegetable foods (p < 0.05).
Verdonschot et al. 2020 [49] -There were no significant differences in (FV) consumption between EG1 and CG, and EG2 and CG. However, in EG2 there was an increase in FV consumption, and in EG1 and CG there was a decrease.
Siew et al. 2020 [40] -In the attitude score, there were no significant changes for both groups over time.
Fisher et al. 2019 [35] -In EG, there were significant differences between pre-and post-test in the knowledge of bedtime routines (p = 0.002).
-Between groups, they only found significant differences in bedtime routines knowledge (p = 0.004).
Lin et al. 2019 [50] -There were no significant differences in children's healthy eating behaviors or active lifestyle behaviors between groups.
-Children increased their interest in NASA space at the post-test, but this interest did not moderate the effect of Healthy Eating Active Living (HEAL) behaviors.

Qian et al. 2019 [41]
-The EG improved healthy eating behaviors at the post-test. There were significant differences between the pre-and post-test (p = 0.001). Moreover, the EG showed significantly higher scores than the CG (p = 0.025) in healthy eating behaviors.
-In the EG there was a significantly larger portion of students who met the recommended level for several eating behaviors at the post-test. Here, there were differences between provinces. In Shandong, they met the recommended level for each of the nine eating behaviors (p < 0.001), and in Qinghay (lower family incomes), they met the recommended level for three of the nine behaviors (p < 0.05).
Kim et al. 2019 [51] -There were significant changes in anthropometric variables in the EG (p < 0.05).
-Total NQ score of the EG significantly increased (from 64.1 to 66.0, p < 0.05) -There was a higher fruit intake in EG than in CG (2.0 vs. 1.5, p < 0.05).
-Moderation in the intake of hypercaloric foods was greater in the EG than in CG (0.5 vs. 1.2, p < 0.05).
-Changes in meal regularity were significantly greater in EG than in CG (3.4 vs. 1.2, p < 0.05).
Brown et al. 2018 [52] -There was a significant difference between the pre-and post-test in healthy snack attitude.

Authors Results
Zhou, 2018 [42] -In EG there was a significant increase in nutritional attitude (p = 0.02) and nutritional behavior (p = 0.03) at post-test, but not in CG (p > 0.05).
Sharma et al. 2015 [37] -There was a significant decrease in the amount of sugar consumed among children in EG compared to CG (p = 0.021).
Song et al. 2015 [38] -Eating fruit for lunch is the unique factor that increased in the three groups with significant differences (p = 0.002 in CG, p = 0.006 in EG2, p = 0.011 in EG1).
-EG1 significantly changed in eating vegetables for lunch (p = 0.007), eating any fruits the day before (p = 0.023), the number of days that they ate vegetables and fruits the previous week (p < 0.001), the self-efficacy to prepare FV at home (p = 0.034) and the perceptions of their peers' fruit consumption (p = 0.025).
Regarding the preference of students; berries and cherries had a significant increase only in CG (p=.006), while pears had a significant increase only in EG2 (p = 0.032). Oatmeal and granola had a significant change in EG2 (p = 0.036) and EG1 (p < 0.001), and grapes had a highly significant increase in the three groups (p < 0.001). Moreover, EG1 had significant differences in whole-grain noodles (p = 0.011), vegetables (p = 0.003), apples (p = 0.008), peaches and nectarines (p = 0.015), and squash, zucchini, and pumpkin (p = 0.032). On the other hand, participation in these programs increased self-confidence in cooking, enjoyment of food and cooking, frequency of cooking at home, availability of fruits and vegetables at home, use of nutrition labels when shopping, and knowledge of bedtime routines [34,35]. Moreover, food waste [45], total fat intake [34], and the percentage of daily calories from morning and afternoon snacks [52], such as cookies, cakes, chocolates [37,48], and sugary drinks [34], were reduced.
Finally, both children living in urban areas and those living in higher-income neighborhoods improved dietary intake self-efficacy [38,47], which may improve children's cognitive performance [39]. However, Siew et al. and Lin et al. did not find significant changes in children's nutritional attitudes [40,50].

Discussion
This systematic review has given an analysis of the effects of nutrition education programs on children's nutrition knowledge and eating behaviors. Through this research, we found several types of programs about nutrition at schools which the latter used to obtain different dietary outcomes. Regarding the literature, nutrition education programs increase knowledge and food attitudes [54], practical activities during the programs encourage an increase in physical activities [55] or healthy eating behaviors. However, the most effective programs are those that join both education and practice [56]. These findings are in line with most of the articles selected [34,35,38,39,[43][44][45][46][47][48][49]. However, we also found some educational programs which improved the practice scores [40] or eating behaviors [41,51] and practical programs that fostered knowledge [37,42,50].
It is very important that FV policies are promoted in educational environments. In fact, exposure to FV has been shown to contribute to effective nutrition education programs [57]. We found that children which were exposed to FV provision [44,49] or FV education [38,45,49] improved their BMI, FV intake, nutrition knowledge, and behaviors. Previous studies of free fruit and vegetables (FFV) showed a reduction in BMI mean score, a reduction in school-level obesity [58], and an increase in FV intake [59][60][61]. The interventions selected are heterogeneous among the results of prior meta-analyses and systematic reviews [62,63]; however, all of them have adequate alignment among intervention, objectives, and findings, which is an important aspect to be effective [57].
In this sense, the combination of FV provision and education [49] seems to be more effective in eating habits, indeed earlier studies affirmed that education improves nutrition knowledge [64,65]. On their part, Franceschi et al. used an app to prevent overweight and obesity, resulting in an increase in nutritional knowledge [46]. The use of technology for these intervention programs showed that they are beneficial in short-term weight loss [66,67]. However, other non-technological programs also had good results. We found that children's knowledge improved and consequently they reduced food waste [45]. The knowledge improvement could be seen in nutrition [35,37,40,42,46,49,50], bedtime routine knowledge [35], physical activity knowledge [37], and healthy living in general [47,50]. This is consistent with previous research which focused on the knowledge about healthy eating habits [68,69]. Nutrition knowledge is very important in all stages of our lives because it fosters the awareness of eating and, therefore, inspires people to practice healthy eating [70,71].
Regarding eating behaviors and physical activity, we find some articles that reported changes in behavior [34,[37][38][39][41][42][43][45][46][47][48]51], as Weber et al. [72] affirmed in Germany. Regular meal intake, especially at breakfast time, is associated with better overall food consumption [73,74], and it is essential to improving eating behavior [75,76] and physical activity [77]. This regular meal intake was significantly greater in EG [51], so we can affirm that intervention programs help to improve food intake. In this sense, the results of Teo et al. show that, after an intervention program, the frequency of healthy breakfasts, lunches, and dinners increases, improving physical activity frequency and decreasing BMI scores [39]. Moreover, the consumption of cookies, cakes, and chocolates decreased significantly [48]. In general, unhealthy snacks were less consumed after nutrition intervention programs [34,37,48,51] as was confirmed previously [78].
It was believed that nutritional knowledge fosters healthy behaviors [79]. However, in Siew et al. [40] and Lin et al. [50], we do not find significant differences in attitudes while knowledge improves [40]. On the contrary, we found significant behavior, attitudes, and knowledge changes in other articles [42,51].
Nevertheless, depending on the socio-economic groups and geographical regions there are differences in eating behaviors and, consequently in obesity rates [80]. Our results are in line with that statement. Indeed, Nickel et al. affirmed that children in low-income neighborhoods only showed improved nutrition knowledge, while children in higher-income neighborhoods improved their consumption [47]; Øvrebø et al. found differences between parents' education, resulting in different BMI [44]; and Qian et al. confirmed differences between provinces, whereby there was a better improvement in eating behaviors in higher-income families [41].
All the variables mentioned influence the body mass index (BMI), which allows us to know if a person is underweight or overweight. Through the articles selected, we find changes in BMI depending on different programs [36,40,44,46,51]. Consistent with the other two intervention programs, the BMI is lower in EG than in CG after a nutrition intervention [81,82]. In a literature search, we found contrary opinions about this topic, with some articles emphasizing the effectiveness of these types of programs [83,84] while others affirmed that these interventions were not effective [85,86]. In this sense, our results show that in two intervention programs, there were no significant differences [36,40] while three of them had significant changes and differences. This is corroborated by a previous study, which showed that a 5-2-1-0 intervention program [87] decreases the BMI percentile. A higher BMI is associated with obesity and overweight, and this is the main reason to consider implementing nutrition intervention programs at schools [88].
In short, nutrition intervention programs at schools have a strong impact on children's eating. The main objective of this study was to check the effectiveness of these programs in impacting children's nutrition knowledge and behaviors. As we verified, they improve students' knowledge about healthy diets and foster healthy attitudes and behaviors in their lives. School environments and families are essential in promoting healthy habits and modifying dietary behaviors [89,90]. However, it is more important to include fun and interactive activity-based nutrition sessions [91] because attitude, which is influenced by motivation [92], mediated eating behaviors [93].

Conclusions
Despite the results achieved in our systematic review, the impact is rather limited. In this sense, we included articles from all continents except Antarctica, but they are not representative of global nutrition education programs because there is only one article from Oceania and one from Africa. On the contrary, we found a wide variety of articles from countries in Europe and Asia, but not in America.
This is due to the limitations of year of publication and type of publication that reduce the number of possible studies, but the aim was to make the selected articles as relevant and current as possible. In fact, this was the usual reason for eliminating articles not published in peer-reviewed journals and articles published before 2013. On the other hand, we followed the PRISMA methodology, which is a great method in social science research because of its transparency and openness to suggestions and comments.
This systematic review could have important educational implications. In this sense, the promotion of healthy lifestyle habits related to healthy and balanced eating is an educational objective. Therefore, future work could analyze the influence of different types of methodologies that help to reinforce behaviors related to the consumption of healthy food.