Fitness to improve the nutritional status of schoolchildren: A Review

According to the Body Mass Index, overweight and obesity in adolescents has increased. Review of clinical trials to determine the effect on adolescents’ Body mass index with twelve weeks of exercise compared to a control group. PUBMED, WOS, SCOPUS, BEIC, JSTOR, and SCIELO data sources. Inclusion criteria: 1. Adolescent population; 2. Body mass index results; 3. Clinical trials; 4. groups with exercise and control; 5. Spanish, English, and Portuguese language; 6. Publications up to February 2021; Keywords: Adolescents, Body Mass Index, Exercise and Clinical Trial. Data extraction: effect on the Body mass index and its standard deviation. 8 studies (N: 761). Exercise significantly reduced the Body mass index of adolescents - 0.57 Kg/m² (-0.7 to -0.5) p < 0.01. Statistical heterogeneity (I²: 89%). 12 weeks of exercise are effective at decreasing Body mass index in adolescents.


INTRODUCTION
Obesity is a global public health problem, with high prevalence rates and rapid growth at all ages, resulting from a positive imbalance between intake and energy expenditure. Despite being modifiable risk factors, overweight and obesity remain a global public health problem. The prevalence of obesity has doubled since 1980, with more than 1.9 billion and 39% overweight adults. By 2025, global obesity is estimated to reach 18% in men and exceed 21%. In Latin America, an estimated 58% of the population (about 360 million people) are overweight and 23% (140 million) obese. Also, 50% of men and 60% of women are expected to be overweight or obese by 2030 (1,2). In clinical practice and research, the anthropometric method is used to diagnose an adolescent, and the most commonly used indicator is body mass index (BMI) (3,4). A teenager is overweight in the 85th -95th percentile and obese in the 95th (5). In Chile, 25% of adolescents are overweight and 20% obese. However, in Spain, obesity exceeds 12.6%, and overweight 26.0% (6,7). Anzolina et al. (2016) assessed BMI cut-off points' sensitivity and specificity to predict overweight/ obesity according to DEXA estimated body fat values in adolescents. BMI showed a good deal with DEXA, sensitive and specific in identifying overweight and obesity (8).
Obesity alone does not increase cardiovascular risk. Subcutaneous fat has a greater cardiovascular risk for a centripetal android pattern associated with visceral fat. For example, some obese people do not develop insulin resistance or other cardiovascular risk factors related to metabolic syndrome. For this reason, BMI does not always predict cardiovascular risk. Overweight or obese children who become obese adults have an increased risk of type 2 diabetes, hypertension, dyslipidemia, and atherosclerosis (9). Regular physical activity reduces myocardial oxygen demand and increases cardiorespiratory capacity, with lower coronary risks. Physical activity also reduces systolic and diastolic pressure, improves insulin sensitivity and blood glucose control, reduces glycosylated hemoglobin, and improves dyslipidemia. Physical activity also controls body weight and fat levels. Arango et al. (2020) found an association between high blood pressure, overweight and low cardiorespiratory physical condition (10).
Biological, social, and behavioral changes arise in adolescence, critical to adopting a healthy lifestyle, where exercise levels decrease (11). Lifestyle depends on social and environmental influences, which have transformed adolescents' attitudes, with an intake of low-cost unhealthy foods and reduced exercise (12). In addition, globalized societies evolve into a sedentary lifestyle, fostering a teen's passive attitude, a digital native and fulltime computer user, television, remote control, and video games (13). The recommended level is 60 minutes daily of moderate to vigorous aerobic activity, incorporating strengthening three times per week.
Inadequate feeding practices are observed in adolescence (14). Obesity in youth is associated with asthma, sleep disorders, exercise intolerance, hypertension, and negative selfimage (15). Obesity in adolescence is an independent risk factor for adult obesity (16). Intervening early, preventing, and controlling obesity is essential to reduce these negative consequences (17). To obesity, it is necessary to improve dietary intake, increase exercise, reduce sedentary lifestyles, and promote healthy lifestyles (18). Therefore, it is relevant to execute strategies in adolescents with lifestyle changes, healthy diet, and daily exercises to improve their nutritional status (19).
Schools are ideal for teenagers because they spend most of their time in school having access to sports facilities for exercise. However, Dobbins et al. in 2013 report that school interventions do not increase physical activity rates in adolescents, nor do they reduce BMI (20). By contrast, Waters et al. in 2011 indicate that exercise effectively reduces body fat (21). On the other hand, Peirson et al. (2015) suggest that behavioral interventions for obesity in young people moderate BMI (22). These authors used different criteria for the type and combination of exercise, intervention time, and age of the participants when obtaining their conclusions.  (25). However, all these researches were conducted with different criteria to analyze the results and unequal age limits, heterogeneous treatment times, and various intervention types.
Because of the above, the following question arises: What is the effect of physical exercise for 12 weeks on adolescents' nutritional status? It is objective: To determine the impact of training on adolescents' nutritional status in clinical trials for twelve weeks compared to a control group. This systematic review focuses on health promotion actions that develop personal skills or behaviors, effectively reducing adolescent obesity.  (25). However, all these researches were conducted with different criteria to analyze the results and unequal age limits, heterogeneous treatment times, and various intervention types.

MATERIALS AND METHODS
Because of the above, the following question arises: What is the effect of physical exercise for 12 weeks on adolescents' nutritional status? It is objective: To determine the impact of training on adolescents' nutritional status in clinical trials for twelve weeks compared to a control group. This systematic review focuses on health promotion actions that develop personal skills or behaviors, effectively reducing adolescent obesity.
2. subjects were randomly allocated to groups (in a crossover study, subjects were randomly allocated an order in which treatments were received). 3. allocation was concealed. 4. the groups were similar at baseline regarding the most important prognostic indicators. 5. there was blinding of all subjects. 6. there was blinding of all therapists who administered the therapy. 7. there was blinding of all assessors who measured at least one key outcome. 8. measures of at least one key outcome were obtained from more than 85% of the subjects initially allocated to groups. 9. all subjects for whom outcome measures were available received the treatment or control condition as allocated or, where this was not the case, data for at least one key outcome was analyzed by "intention to treat". 10. the results of between-group statistical comparisons are reported for at least one key outcome. 11. the study provides both point measures and measures of variability for at least one key outcome. Characteristics of the participants: Table 2 presents the eight studies, which included the following countries: Egypt, the USA, South Korea, Serbia, and Canada, with 761 participants. The initial mean BMI was 29.9 ± 3 kg/m2.
Characteristics of the interventions: the intervention with exercise was for twelve weeks and produced different physiological, functional, and structural improvements in adolescents.
Estimates of the effect of exercise interventions on BMI: Figure 2 shows the eight studies included in the meta-analysis. The randomeffects model found that exercise significantly reduced adolescents' BMI by -0.57 Kg/m2 (-0.68 to -0.47) < 0.01. Statistical heterogeneity (I2: 89 %). The results of each study for this age group are presented in Table 2. Of the eight included studies targeting adolescents, these provided appropriate BMI data for inclusion in the metaanalysis. Of those included in the meta-analysis, a standardized difference in BMI change from the beginning to the end of the intervention between the intervention and control groups was -0.57 Kg/m2 (95% CI -0.68 to -0.47). This result is statistically significant but presents a high heterogeneity in the studies. Thus, the small number of studies and the heterogeneity observed from the plans in the meta-analysis limit our ability to determine the effectiveness of interventions in adolescents confidently. However, these results are promising for promoting physical activity in overweight adolescents, for improving their nutritional status and physical health.
Physical activity outcomes were measured in all studies, and all eight studies report an indicator of the positive impact of physical activity intervention in adolescents (Table 2)  Although BMI does not measure body composition (36), it has widespread use in epidemiological studies due to its ease of measurement, high data availability, and its relationship to morbidity and mortality (37). Possibly, the outcome of this review seems imperceptible, but it generates changes in body composition that are not identified with BMI and improves health-related quality of life in adolescents.
Unfortunately, BMI does not distinguish between fat mass and lean mass (38). For this, the BMI can be supplemented with the abdominal perimeter, waist-to-hip ratio, or waist-to-height ratio (39). Another option is the measurement of skin folds in adolescents to diagnose and analyze body composition changes during the treatment of childhood obesity (40). Obesity is multifactorial; therefore, exercise interventions can enhance their effectiveness, in the long run, to decrease obesity in adolescents.
A limitation of our research is language due to the lack of an accurate translation that allows us to evaluate and analyze other analyses. Also, this would influence the ability of the team to analyze other databases, to avoid publication bias. Another limitation is the body mass index which does not evaluate changes in body composition but is widely used in research and clinical evaluation of adolescents. We propose using different anthropometric methodologies (4) to assess body composition in adolescents, which are low-cost using field tools, which would allow obtaining better clinical results in the adolescents intervened. In addition, in this review, we also used a qualitative analysis, due to the heterogeneity of the studies, to evaluate the effectiveness of exercise in modifying the nutritional status of adolescents after 12 weeks of intervention.

CONCLUSION
Exercise effectively decreases BMI in adolescents after twelve weeks. Moreover, it can be implemented in schools, fostering positive attitudes towards training, guiding it according to the development level, seeking satisfaction, improving the quality of life-related to health, self-esteem, and extracurricular activities.
While it is necessary to use multiple strategies to decrease obesity, our review indicates that exercise for twelve weeks effectively reduces BMI in adolescents. However, from a clinical point of view, twelve-week exercise interventions may not effectively change adolescents' nutritional status with obesity. Exercise supplemented with healthy dietary habits throughout the school period could have more significant effects.

ACKNOWLEDGMENTS
To the Research Directorate of the Universidad Santo Tomás, Universidad Mayor, Universidad de la Frontera and Universidad Pablo de Olavide, for its constant support for research.

CONFLICT OF INTEREST AND FINANCING
No conflict or funding.

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