We identified a high prevalence of overweight/obesity in children who studied at schools enrolled with the SHP. These values were higher than those found in Latin America [11, 42], but lower than those of children in the Brazilian urban environment [43]. Comparing with researches in other regions of Brazil, these values were lower than those reported for the South [44,45,46,47], Southeast [48,49,50], and Northeast [51, 52], but higher than those from Central-West [53,54,55], Southeast [56,57,58], and Northeast [59,60,61].
We found that being overweight/obesity was associated with high consumption of sugar-rich foods, performance of 2+ sedentary activities/day, and cardiorespiratory fitness reduction, results that were similar to those reported elsewhere [2]. In relation to high intake of foods rich in sugar, our study evaluated sugary foods and sweetened drinks containing large amount of simple carbohydrates with high energy density. These foods have been shown to be associated with obesity and diabetes positive due to positive energy balance and consequent, weight gain and body fat [62]. This confirms the importance of investing in intervention strategies and projects aimed at decreasing the consumption of candies and sweetened beverages, increasing the consumption of fruits and vegetables, and reducing fats and eating out habits [63].
Regarding sedentary activities, these were associated with reduced physical activity [2] development of cardiometabolic risk factors [64], NCDs and premature mortality [65], and quality of consumed food, such as higher candies intake [2, 64, 66]. This can be explained by the fact that sedentary activities reduce energy expenditure and tend to increase the chance of consuming unhealthy foods, thus creating a positive energy balance and consequently weight gain [2].
It is also verified that screen time on TV and computers determines children’s exposure to food advertisements which can influence food intake and preference. Food intake while watching TV and playing on the computer distracts children, promoting unintentional excessive eating [67]. According to Lipsky [66], foods mostly consumed during this period are sugary drinks, fast food, refined grains and calorie dense foods, and low amounts of fruits and vegetables. The negative association found for the cardiorespiratory fitness test can be due to (i) physical activity represents 20–40% of total energy expenditure, (ii) that 60 min of this practice contribute to weight control, and (iii) 150 min of moderate activity/week reduce blood pressure [68, 69] and visceral fat [63, 68], improve lipid profile and insulin sensitivity [63], and increase life expectancy by 0.68 years [65].
We found an association between overweight/obesity and school-related variables such as school shift and location, amounts of physical activity and offered meals, cafeteria conditions, presence of school gardens and other types of grown food, food sale in the school surroundings and its quality, and existence of nutritional diagnosis.
Studies have demonstrated that school location is related to the environmental causes of obesity, which impact food access and consumption and physical activity [70,71,72], depending on the availability of leisure spaces and food selling sites [73, 74]. Extended school shifts strengthen socialization and cultural diffusion [72, 75], contributing to increased body practices [70, 72, 75], promotion of healthy eating by having 30–50% of meals at schools [2, 70, 72, 76], increased consumption of natural/minimally processed foods, and reduced consumption of their ultra-processed counterparts [72].
Another important finding of this study relates to the fact that the greater the offer of body practices at school, the lower the prevalence of overweight/obesity, which was herein attributed to institutions that work full time and offer dance classes. A Brazilian study in public and private schools had a similar result [61], which meets the fact that physical activity can be reinforced through the scholar curriculum [9,10,11,12,13, 63, 77,78,79]. Nonetheless, it is necessary for schools to hire physical education professionals to guide activities and adapt physical structures, often assessed as inadequate [80].
We also highlight the role played by the number of meals at school, e.g., children should have at least three meals at school, where they stay for 5–7 h, making school feeding programs [2, 63, 70, 76, 81] such as the National School Feeding Program (NSFP) [82] relevant for Brazilian public schools as these offer quality food and stimulate healthy food choices [70, 76], such as fruits and vegetables [63, 80]. As for the cafeterias, this association can be explained by the influence of the atmosphere within an appropriate environment for food consumption [76].
Another relevant factor regarding school feeding was the presence of gardens that provided fruits and vegetables, cereals, tubers, and spices for school feeding, as well as the existence of a pedagogical space for food-related and nutritional education practices, allowing better knowledge on nutrition, food preparation, and healthy eating habits [83,84,85,86,87]. We did not, however, find this association in our study.
As for food sale, we observed similar results in studies that assessed the relationship between childhood obesity and the environment in which children live, emphasizing that shorter distances to and higher occurrences of places selling ultra-processed food are associated with more monotonous food choices with high caloric density, and, as consequence, with higher prevalence of overweight/obesity [73, 74, 88]. In Brazil’s case, although it is positive that NSFP [82] does not allow food sale in public schools, it is still necessary to propose legal provisions that control food trade in school surroundings [81], including the informal ones.
The scientific literature also points out that performing nutritional diagnosis at schools was also associated with being overweight/obesity [68, 69], i.e., this is an essential instrument for assessing nutritional status [9,10,11,12,13, 77,78,79], allowing better management of overweight/obesity by PHC for individual and/or collective care [68, 69]. Because children spend most of their daytime at school, it denotes a relevant social equipment for the diagnosis and monitoring of overweight/obesity, with training and standardization of this process being required for the proper, efficient care of the population [68].
It is noteworthy that, in our study, food and nutrition education interventions were not associated, having as potential reasons the low frequency of these actions [68, 69, 84, 89,90,91] and the poor quality of both approach and content [84, 89, 91, 92]. Taveras et al. [92] demonstrated that behavioral interventions helped to improve BMI/A and motivate habit changes in children with more frequency in the activities. Studies have shown the role of schools as promoters of health and permanent healthy habits [63, 69, 84, 85, 90], highlighting the relevance of intersectoral actions with the engagement of teachers and health care professionals [9,10,11,12,13, 77,78,79].
There are no studies conducted in Brazil evaluating the association between overweight/obesity and individual and school variables, whereas international studies [93, 94] do not allow comparison as these were carried out in private and public schools, and the latter did not provide free food for all children as in Brazil [82]. From the aforementioned individual variables, we found in model II that performing 2+ sedentary activities/day and having five meals/day, besides consuming 1+ portions of candy/day, were related to being overweight/obesity. In carrying out model III, the inclusion of contextual analyses considered the permanence of sedentary activities, number of meals, school location, school shift, dance classes, and candy sale in the school surroundings. We observed a reduction in variance in the models, showing that the individual and contextual variables together improve the explanation of the prevalence of overweight/obesity.
In the study by Fox et al. [93], a similarity of the relationship between overweight/obesity and candy purchase at or around the school could be observed, but it did not show any association between environment and eating habits at school and BMI/A. Li et al. [94], when evaluating the relationship among overweight/obesity and individual, family, school, and community variables, observed that children with higher participation in sports had lower BMI/A and positive association with longer sedentary activities, data that corroborate our study.
Regarding variation by ICC, the schools presented a small variation, but with a good reduction when the contextual variables of the school environment are included, however the AUC curve shows that the individual and contextual variables have low, but similar, predictive values. Regarding the measure of heterogeneity by MOR, we found that school explained almost half of the child’s chance of being overweight/obese, showing an improvement after the inclusion of contextual variables.
When evaluating the GCE for heterogeneity and variation, we found that we may not have considered other contextual and individual variables that improve prediction. Also, contexts such as the neighborhood and family may be involved in the explanation of overweight/obesity. Thus, it is relevant that new studies consider these factors. It should be added that the reduced values may be related to the fact that the school may present heterogeneity of the enrolled children, that is, some children may not live so close to the schools, which would not be related to geographic evaluation. For this reason, we used specific variables of the school environment to better understand the variation of the explanation of the school in the development of childhood obesity.
However, we reinforce the relevance of the school in the control of childhood obesity and in the promotion of strategic actions for the promotion of healthy eating habits and physical activity. Studies show that school is a space to prevent and reduce childhood obesity since it influences healthy eating, weight control and maintenance, and health in general. Furthermore, children consume up to 50% of their daily calories at school [95, 96], which is a positive point for Brazil since NSFP for a menu composed of quality food [82] and in adequate quantity, substitution of high calorie dense food; presence of school gardens improving the supply of fruits and vegetables [96] and their preference among children; and the encouragement of physical activity [95, 96], in addition to health education programs [95]. The implementation of the programs and policies presents many challenges related to the availability of trained professionals, organization of schools for the implementation and evaluation and monitoring of programs and policies [95, 96].
As a limitation of the study, it is emphasized that food consumption and daily activity practices may be under or overestimated; however, as a control, we used an age-validated instrument developed by nutritionists, physical education teachers, psychologists, and educators, in addition to children that were trained to fill the questionnaire and activity follow up [28, 34].
Sedentary and non-sedentary activities were estimated with self-reported data which can present inaccuracies, which is why we chose to use a validated instrument. For future studies, the use of questionnaires that do not aim solely for an estimate is recommended. Although the 6-min walk test was validated, differences in values can be linked to ethnicity [24, 27], culture [27], socioeconomic factors, climate [97], methodological variations during the test [24, 27], and motivation during walk [23]. However, we emphasize that our study followed the guidelines of the American Thoracic Society [22] to ensure standard measurements.