The combined prevalence of overweight and obesity (BMI> 85th percentile) in this group was high in keeping with the growing trend of childhood obesity in Mexico and worldwide [5
]. Although no significant gender differences were found, higher obesity prevalence was identified in boys. (BMI > 95th
percentile). The data matches the findings of school populations nationwide [1
]. It must be pointed out that this is a low socioeconomic level urban population, two factors that have been closely associated to increased prevalence of obesity [24
Similar to that reported in Latin American school populations [25
], we found that the studied population has a high level of sedentarism, regardless of the period during which we evaluated their physical activity. Consequently, no differences were identified upon making comparisons between the two periods. Although 70% of the schoolchildren reported practicing some sport, it is more common for children to spend over three hours a week watching television or playing video games than practicing sports, especially during the vacation period. This same sedentary trend in schoolchildren during the summer vacations coincides with that reported by Tovar et al., where urban children who spend more time at home during the vacation period are involved in less demanding or sedentary activities. Moreover, they tend to practice unhealthy eating habits more often, such as: increased consumption of processed foods, low intake of fruits and vegetables and watching television during meals [26
]. Other authors have also found this pattern of physical inactivity and bad habits in urban children and have associated it with the increasing inclusion of both parents in the professional world, thus decreasing their attention to the activities of the children due to lack of time [27
]. In the present study, the proportion of economically active mothers is low (33.9%), so the changes in eating habits of schoolchildren, in general, are associated more with the fact of being on vacation, when parents and the rest of family members tend to be more flexible in the schedules and activities of the children.
An important finding of this study was proving that the daily routine of the schoolchildren changes during the vacation period and, contrary to what was expected, the lack of physical activity and changes in some habits did not influence the schoolchildren´s nutritional status negatively. These results were quite similar to that observed in an adolescent population in the State of Morelos, where no relationship between overweight and obesity and the time spent watching television, forms of physical activity and sedentarism was identified [28
]. Despite these results, it is important to mention that the use of television and video games in schoolchildren has been closely associated with weight gain so it should be considered as risk factor for the occurrence of overweight and obesity [29
]. Additionally, we can observe other risk factors in this population, such as the large percentage of children who do not usually eat breakfast, whether going to school or on vacation. It was expected that children would eat breakfast more often when their schedule is less rigid; however, it was only observed that children tend to watch more TV while eating breakfast during the summer. It is worth mentioning that skipping breakfast is associated with weight gain in children and adolescents. Likewise, people who do not eat breakfast tend to eat a lot at dinner, thus promoting weight gain [30
]. Another unhealthy habit and recently identified as a risk factor in developing childhood obesity, is reduced sleep time. The same pattern was observed during the vacation period, when schoolchildren´s bedtime is altered [33
Concerning the eating habits of schoolchildren, the high consumption of sweetened drinks, especially soft drinks, compared to water consumption and low intake of milk are astounding. Currently, Mexico is one of the countries with the highest consumption of energy drinks, which replace milk consumption and contribute significantly to the energy intake of children and adolescents, subsequently causing overweight and obesity [12
]. Furthermore, it has been mentioned that the characteristics of public schools throughout the country, promote the consumption of energy drinks within the school and its surroundings [35
]. It is interesting to observe that the consumption of sweets and snacks is also more frequent during the school period, suggesting that children have access to them just as they have access to sugar-sweetened beverages. Regarding their eating patterns, something very similar to that observed in other school populations was noted: meat consumption is excessive while the intake of fruits, vegetables, milk and dairy products is inadequate [36
]. An important fact worth underscoring is that normal-weight children were those who practiced less healthy physical activity and eating habits more often than children classified as overweight and obese, contrary to what other studies have reported where obese children practice more sedentary activities and eat less fruits and vegetables [38
]. However, it is important to consider that individuals with obesity problems tend to underestimate their consumption of food [40
]. In theory, this could limit the results of this study, since we employed self reporting and not the direct observation of food consumption.
The study has another shortcoming: sample size. It is relatively small and did not allow us to identify the influence of changes in certain habits of schoolchildren regarding their nutritional status. Another factor to be taken into consideration is the difficulty in measuring the dietary habits of schoolchildren. Therefore, it is advisable to apply multiple-choice surveys to facilitate answers and data collection, instead of open questions as used in this study.
Despite these limitations, this study proved that summers do influence the habits of schoolchildren. However, it is a period that has not been studied enough. So far, controversy on the success of school programs for the prevention of childhood obesity still prevails, and the explanation might be partly due to the fact that most of them have not taken into account the vacation period as part of the intervention. Assessments of the eating habits and activities of children while they are purely influenced by a family environment are essential to understand all the factors involved in the development of overweight and obesity in schoolchildren. In order for school interventions to be effective, they should not only consider providing nutritional education and encouraging the schoolchildren engage in physical activities; they must also focus on parents in order to create a healthier environment at home. Some variables which are linked to "parental education, nutrition and promoting exercise", are also closely related both, to parental education, cognitive levels and neuro-endocrinological roots [42
]. That is why those interventions that succeed in changing the lifestyle of children, even when they are outside the classroom, will be able to prevent and stop the huge public health problems brought about by obesity in schoolchildren.