Risk factors involved in adolescent obesity: an integrative review

The scope of this study was to examine the risk factors for the development of obesity in adolescence. The objective was to identify risk factors for adolescent obesity by means of an Integrative Review of the Literature. The PICO strategy was used to formulate the following central line of inquiry: What are the risk factors for the development of obesity during adolescence? The VHL and EBSCOhost research databases were consulted, resulting in a selection of 25 articles for in-depth study. The phenomenon of obesity was understood as the result of biological, social, psychological, and nutritional factors. The research revealed a lack of consensus on the risks and benefits, which makes evidence-based recommendations difficult. The study identified proposals that can be implemented, such as a change in eating habits, weight control and the practice of physical exercise. Such behavioral changes can be recommended within the context of the family, schools, and health services. The review recommends prevention strategies and the recognition of school as the ideal medium for health promotion through education. From a political and social standpoint, it is necessary to challenge the prevalence of publicity of the food industry that entices adolescents to consume processed foods with high fat and sugar content.


Introduction
Adolescence is the transition phase from childhood to adulthood and covers the period between 10 and 19 years of age 1 . In Brazil, according to the 2010 Demographic Census, the adolescent population was approximately 18 million between 10 and 14 years of age and 17 million between 15 and 19 years of age 2 .
Viero and Farias 3 highlight the fact that this phase is marked by far-reaching changes, representing a potentially difficult period in terms of sundry challenges and vulnerabilities because of the transformations inherent to the process of attaining human maturity. One of these vulnerabilities is related to the emergence of obesity, which constitutes a public health problem. It is considered one of the chronic non-communicable diseases (CNCD) with a high incidence among young people nowadays, signifying that if there are no effective interventions to treat it, obesity will tend to worsen over the course of life.
Obesity is defined as a nutritional and metabolic disorder of multifactorial origin. It is a condition in which the percentage of body fat in the individual is high, due to an imbalance between the intake and expenditure of energy. Genetic, emotional and lifestyle factors are closely related to its origin or perpetuation 4 .
Obesity in adolescents can be the result of both genetics and the intake of large amounts of fat and calories. In addition, the lack of physical activities and a great deal of time spent on social media, playing interactive games, and watching television can contribute to the exacerbation of the problem 5 . Obese adolescents tend to become obese adults who suffer from clinical complications from being overweight and have a reduced life expectancy 4 .
The situation discussed here is not restricted to Brazil. The prevalence of obesity and overweight in adolescents is observed in several countries such as the United States of America and Latin Americans countries 4 . Data from the Pan American Health Organization (PAHO) 6 reveal that obesity rates in children and adolescents worldwide were 1% in 1975 (equivalent to 5 million girls and 6 million boys), and 6% in 2016 (corresponding to 50 million girls and almost 74 million boys). PAHO further points out that the number of the obese aged between 5 and 19 years has increased more than tenfold, from 11 million in 1975 to 124 million in 2016 6 . Although the factors associated with the phenomenon are multiple, the influence of marketing of the food industries and the policies that support it cannot be overlooked. Nor is the fact that, in most countries, the most nutritious and healthy foods are still expensive and inaccessible to families and communities with low purchasing power 7 .
Based on the epidemiological evidence of the increase in obesity, PAHO/WHO has been recommending member countries to implement and maintain surveillance systems for risk factors. In Brazil, the Adolescent Health Program (PROSAD) 4,8 was created in 1989 with multiple objectives, one of which was the prevention of chronic diseases, which includes obesity. This program led to some beneficial developments, such as the recent National School Health Survey (PeNSE) 9 , a strategic partnership between the Ministry of Health and the Brazilian Institute of Geography and Statistics (IBGE) with the support of the Ministry of Education and Culture (MEC). One of its objectives was to identify priorities for the development of public policies for the promotion of health among adolescents 9 . Its focus was on risk surveillance and protection against chronic diseases in Brazil. This study brought to light several unhealthy lifestyles that were common among young people, including the consumption of tobacco, alcohol and illicit drugs, inadequate nutrition, and a sedentary lifestyle.
Given the empirical importance of obesity during adolescence, this article sought to identify the risk factors for obesity among adolescents by means of an integrative review of the literature.

Methods
This study involved an integrative review of the literature (IRL), utilizing the concepts and methods proposed by Soares et al 10 as a theoretical benchmark. In the health field, the IRL concentrates on summarizing scientific findings in order to identify and understand problems, situations and vulnerabilities related to the population 10 . It calls for the authors to put forward hypotheses and draw conclusions on the issue in question, which is a complex task that is based on the proposal for collaboration and integration of various lines of action with the aim of identifying evidence-based practices 11 .
The PICO strategy 12,13 was used to formulate the central line of inquiry of this study, since it facilitates an accurate search for the scientific evidence related to the topic. PICO is an acronym where the letter P indicates the population, the letter I is related to the intervention, the letter C refers to the comparison and the letter O represents the expected outcomes. The comparative study by Methley 13 on various types of reviews suggests that the PICO strategy remains the model with the greatest sensitivity for searches in different databases.
In this respect, the acronym determined for this study was: P -adolescent; I -obesity; Cnot applicable; O -to identify the risk factors for obesity. Thus, the central line of inquiry for this article was: What are the risk factors for the development of obesity during adolescence?
The following databases were consulted for the search for articles: Virtual Health Library (VHL) and EBSCOhost in the following databases: National Library of Medicine (MEDLINE via PubMed), Latin American and Caribbean Center on Health Sciences (LILACS) and Academic Search Premier -ASP. The following official key words (Decs, 2017) were used: adolescent; chronic disease; school health; obesity.
The cross-checking was performed using the advanced search tool and the Boolean and. The search was conducted with the following key words: adolescent and chronic illness and school health and obesity in Portuguese with the respective equivalents in English. Articles in Portuguese, English and Spanish published between January 2007 and December 2017 were used as filters.
The following exclusion criteria relating to the texts located included: articles with research participants younger than ten years of age and older than eighteen years of age; articles on adolescents with communicable diseases; hospitalization situations and drug or laboratory studies.
The articles listed for this IRL were organized in a synoptic table that contained: periodical/ journal; title; authors; type of approach; participants; research scenario; year of publication; level of evidence; study location; and main results. The flowchart in Figure 1 represents the structure of the corpus of this review.
The analysis of the articles was based on the GRADE (Grading of Recommendations Assessment, Development and Evaluation) scale. GRADE is a system that was developed by a group of researchers that aims to gauge the quality of the evidence and the strength of the recommendations. The level of evidence represents the confidence in the information used to support a given recommendation and the assessment of the quality of the evidence, being classified into four levels: high, medium, low and very low 14 .
It should be pointed that this type of study does not require the approval of the Ethics and Research Committee. Only public domain articles were used and all ethical criteria regarding the preservation of authorship and citation of sources were respected.

Results and discussion
The selection of articles was conducted by means of a search in the Medline (n = 106), LILACS (n = 3) and ASP (n = 49) databases, arriving at a partial total of 158 articles. At the outset, 63 articles that did not meet the inclusion criteria were excluded (study filters - Figure 1). Following the initial analysis of the search for evidence, 52 articles were excluded after reading the titles and abstracts as they did not adequately address the PICO question. Fourteen articles were withdrawn due to the following situations: duplicate, being ineligible, the fact they were qualitative studies, review studies or because they were not available for reading. Therefore, 25 studies were included for in-depth perusal.
A thorough and critical reading of each article was carried out. The works presented a multiplicity of results associated with the risk factors of obesity during adolescence. The discussion of this study was divided into three categories that included the biological factors [15][16][17][18][19] , the social factors 20-37 and the nutritional factors 38,39 . The stated intention was to conduct a non-dichotomous discussion of the phenomenon and, effectively, the findings of this review revealed that analyzing obesity requires a viewpoint that considers the multiple aspects of this condition.

Biomedical aspects of adolescent obesity
Coutinho 40 emphasizes that the "gene map of human obesity" continues to develop rapidly each year, as more genes and chromosomal regions are related to it. This gene map identified more than 430 genes, associated with phenotypes of human obesity 41 . However, Clement & Ferre 42 report that numerous genetic markers have already been associated with obesity and its metabolic consequences, though the specific interactions between genotype and phenotype in polygenic forms of obesity continue to be only scantly understood.
For its part, the field of epigenetics brings contributions to the understanding of the multifactoriality found in this review. The authors assert that there is evidence that exposure to various environmental conditions, in early stages of life, can induce persistent changes in the epigenome. However, the evidence also suggests that some epigenetic markers are modifiable according to lifestyle habits related to diet and physical activity. This evidence can contribute to the  review study.
Excluded due to duplication, ineligible by theme and not available (n = 14) Excluded from the evaluation of titles and abstracts that did not comply with PICO prerequisites (n = 54)

Included
Elegibility Selection Identification prevention of obesity in subjects or populations with an unfavorable epigenetic profile, in the sense that the phenomenon cannot be analyzed in a fragmented manner, but as a result of factors interrelated between biology and cultural conditions 43 .
In the same vein, it is also important to point out that the authors who focused their studies on Chart 1. Synopsis of the data collected in the articles of the integrative review of 2007 to 2017, organized by authors, year of publication, place of study, title, objectives and type of study.

Number of the Article
Author To test the validity of a conceptual structure.
Cross-sectional study A20 Ricci-Cabello et al. 36 (2015) England Impact of the prevalence of concordant and discordant conditions on the quality of care for diabetes in family practices in England.
To examine the association between the prevalence of diabetes-concordant and diabetes-discordant conditions and the quality of treatment of this problem at the level of family practice in England.

2015) China
Associations between adiposity indicators and high blood pressure among Chinese children and adolescents.
To evaluate the prevalence of the increase of blood pressure using sex/age and the risk attributable to overweight and obesity in Chinese children between 7 and 17 years of age. represents a risk factor for the development of chronic diseases, one of which being obesity. One of the consequences of increased body weight is a change in blood pressure. This mechanism occurs because the adipocyte is a cell that has currently been associated with the production of several mediators that can participate as pathophysiological mechanisms of systemic arterial hypertension (SAH) associated with obesity 44 .
The studies by Dong et al. 16 and Dong et al. 17 associated obesity as a risk factor in the prevalence of SAH. The body mass index (BMI) was considered the best parameter to calculate overweight/obesity in the assessment of altered blood pressure among children and adolescents. BMI was also used in the study by Martinez, Ruelas and Granger 18 showing that obese young people with increased BMI have altered uric acid rates and this is an indication of CNCD. In Brazil, the monitoring of children and adolescents is based on the graph of height versus age and BMI versus age, both present in the Adolescent Record (Caderneta do Adolescente) 45 .
Leatherdale 19 analyzed the prevalence of modifiable risk factors that are associated with cancer. He stressed in his study that of the total of adolescents analyzed, 6.2% were obese, 13.8% were overweight, 53.1% were classified as physically inactive, 96.7% were highly sedentary and 95.1% were not eating in a healthy manner. The author associated these habits with the risk of cancer in the future. Weight control, healthy habits and attitudes are important for the prevention of obesity and, consequently, other CNCDs.
Children and adolescents with obesity have a higher risk of developing chronic diseases such as heart disease, stroke, SAH, dyslipidemia, diabetes mellitus (DM), atherosclerosis, among others 46 . These diseases are diagnosed in adults, but nowadays they have been increasingly diagnosed in children and adolescents.
With respect to the data presented in this first category, the WHO alert 47 is pertinent as, without disregarding the data, it recommends caution in the anthropometric analysis of adolescents, in the light of the major bodily and hormonal changes they experience, making it difficult to establish a definitive diagnosis of obesity at this stage of life.

Social factors involved in adolescent obesity
This category includes health problems related to the conditions in which a person lives and works. In other words, it involves social, econom-ic, cultural, ethnic/racial, gender and psychological factors 48 .
The authors Song et al. 20 and Ekta et al. 21 established that the prevalence of obesity is higher among male adolescents. The disparity between the sexes is associated with the attitude regarding the body image of men -of Oriental men in the case mentioned by the author -for whom obesity is not considered to be prejudicial to health. However, it is a well-known fact that, in general, the difference in the prevalence of obesity in male and female adolescents can be influenced by ethnicity and can be explained by the sex chromosome or by the specific effects of the gonadal hormones 49 .
The study by Singh, Yu and Kogan 22 highlighted the fact that the risk behaviors of immigrant adolescents in the USA vary according to their ethnicity, culture and length of time of immigrant status. Individuals with higher sedentary lifestyle levels are more susceptible than those born in the area. The authors note, however, that with each generation there is a decrease in the rate of physical inactivity among adolescent immigrants.
Ichiho, Robles and Aitaoto 23 reported that the main causes of mortality from heart disease, stroke and cancer are associated with high rates of overweight and obesity. In the 15-year-old age group, overweight and obesity increased dramatically. There was an increase in hours spent by adolescents watching TV and, consequently, a decrease in attendance at physical education classes.
The study by Ortega et al. 24 corroborates with that of Ichiho, Robles and Aitaoto 23 by revealing that moderate to vigorous physical activity decreases between childhood and adolescence. A sedentary lifestyle tends to increase in this transition, as does the risk of developing obesity and other chronic diseases. Therefore, the encouragement of the school and family members is important for adolescents to become interested in the practice of physical exercise, making it pleasurable and beneficial to their health.
The studies by Ichiho et al. [25][26][27][28][29] conducted in the Oceanian countries (American Samoa, Marshall Islands, Palau and Micronesia) show that, there as here, the risk factors associated with overweight and obesity include unhealthy eating habits, physical inactivity and the presence of illness and deaths from CNCD.
The studies by Mbowe et al. 30 and Ghavamzadeh, Khalkhali, Alizade 31 include the school-age community. The authors stress that the mothers' educational level, the type of school and the time spent watching TV are associated with the increase in overweight and obesity, as well as the intake of obesogenic foods and the lack of physical activities. An outcome that caused consternation in this analysis is the fact that obesity rates decreased by up to 32%, when there was an additional child in the household in a study conducted in Guatemala, where the human development index (HDI) was 0.616 in 2013 and where there is evidence of food insecurity within the family environment 50 . This outcome is undoubtedly related to the socioeconomic conditions of the youths and their families.
Patel et al. 32 , Verstraetenet al. 33 and Gulati et al. 34 assert that the obesity situation of parents is reflected in the obesity of their children. The eating behavior of adolescents is part of a complex interaction with their cultural environment, and eating habits represent a long-term routine. Environmental factors are related to parental permissiveness in the choice and preference for food on the part of adolescents.
One of the problems addressed by Crinall et al. 35 is obesity and the clinical situation of young indigenous people in Australia regarding type 2 DM. The authors listed risk factors for CNCDs, including obesity, and draw attention to interventions in culture that provoke diseases and underscore the importance of preventive actions aimed at social life and health.
The care provided by health services must be based on the receptivity of the user with a view to resolving problems. On the same lines as those pointed out by Crinall et al. 35 , Ricci-Cabello et al. 36 call for attention to be given to the care of adolescents with CNCD, including obesity. Individuals with comorbidity usually seek out the health services more frequently and are more likely to have their needs attended to. These services must be prepared to offer a welcoming and effective service.
The study by Passmore et al. 37 was carried out with aborigines (indigenous Australians) using a methodology called 'Challenge.' They developed a method that leads to weight loss and encourages physical activity and good nutrition. The set of actions helped adolescents to improve their health conditions and thus reduce obesity and the risk of other CNCDs.
In Brazil, there is also a National Program of Healthcare for the Indigenous Population 50 . However, there is little information about the relationship between health and nutrition in this group, especially in the case of adolescents. This lack of information makes it difficult to assess cases of obesity in this population segment. Castro et al. 51 , for example, compared the results of their studies with non-indigenous Brazilian adolescents with surveys carried out with indigenous people. They concluded that the anthropometric measurements associated with overweight and obesity in the latter group are similar or higher, revealing the importance of monitoring young indigenous people. And Sá 52 calls attention to several ailments that are occurring in this group, particularly endocrine, nutritional and metabolic illnesses, frequently resulting from obesity.

Nutritional aspects of adolescent obesity
In this category, two articles were analyzed. The first article addressed questions about both the consumption of foods high in calories and sodium and low in nutrients, as well as ultra-processed foods. This study was carried out in schools included in the National School Meals Program, through a periodic survey by the Center for Disease Control (CDC -USA). The second article studied the self-perception of adolescents related to weight and the labels of foods that are consumed. This study was conducted by the Los Angeles Department of Public Health (USA) with low-income adolescents and adults.
Merlo et al. 38 conducted a survey to examine schools with respect to practices stipulated by nutritional standards. The data collected through a national survey conducted in 2000, 2006 and 2014 by the CDC in the U.S. were analyzed regarding the quality of the food offered to adolescents, such as: fruits, vegetables, whole grains and sodium. The results showed that over time the supply of foods with low sodium content, substitution of salt for other seasoning, increased consumption of vegetables, whole grains and fruit supply increased over the course of 10 years. However, most teenagers in the U.S. do not abide by national recommendations for a healthy diet, with the risk of weight gain, obesity, diabetes and other illnesses. Approximately 90% of U.S. children and adolescents consume more sodium than recommended.
This study draws attention to the Brazilian Government initiative, which regulated the National School Meals Program (PNAE) in 2009 by means of Law No. 11,947 53 . This Law was created to ensure that public school canteens offer healthy meals that meet the nutritional needs of the students, educating them to adopt healthy habits 53 . In other words, the Brazilian initiative regarding the consumption of healthy foods, when examined from the study by Merlo et al. 38 , is ahead of its time, since it was published six years before the article. It was a government proposal to invest in the promotion of health in the school environment.
School are venues with the potential for working on issues of collective interest within the educational perspective. For this reason, the National Curriculum Parameters of Brazil propose that cross-sectional themes, such as health, be contemplated with the same relevance as conventional areas of teaching 54 . Until the present time, the approach evaluated has considered the consumption of healthy foods from the institutional perspective. The following study broadened the outlook of the population.
Nianogo et al. 39 carried out a study with the objective of analyzing associations of self-perceived body weight with food choice intentions and consumer response to caloric information. The results showed that the self-perception of weight does not seem to be associated with the habit of reading food labels in order to obtain information regarding calories. For adolescents, knowledge about the nutritional composition of food is important such that this group can make safe choices for their own health.
In both studies, the authors were concerned with macro-and micro-situations with respect to food and obesity, be it in the quality of food, in government strategies and in the choice of individuals regarding food consumption. Therefore, in order to think about preventive actions, access, quality of care, lifestyle, choice, among others, it is necessary to reflect upon the conditions that lead individuals to obesity. The geo-economic issue is a limiting factor in access to food from a global standpoint. Due to living in poverty, the most socially vulnerable people choose to buy and consume products that are cheap and, therefore, have high levels of fat, sugar and salt 55 , which results in an increase in obesity with worldwide undernourishment or malnutrition.
In the surveys reviewed here, it is clear that the dietary patterns of adolescents are influenced by the food manufacturers, with advertisements encouraging the consumption of processed foods high in fat and sugar, which have a special appeal among poor families and communities.
The analysis of the studies elicits a reflection on the context of the changes that most impact the lives of adolescents who are experiencing physical, psychological and social transformations, marked in particular, by the progressive emancipation from family and school.
The study made it possible to answer the research question on the risk factors that impact the development of obesity in adolescence: the geo-economic question of food processing companies; change in blood pressure; higher prevalence in males in cultures where men's body mass is perceived as the image of health; increased sedentary lifestyle among immigrants; increase in hours spent by adolescents in front of TV screens, computers and on social media to the detriment of the possibilities for physical activities; decreased attendance at physical education classes; the educational level of the mothers; the impact of obese parents on their children's obesity; excessive consumption of calorie-and sodium-rich foods, low in nutrients, and ultra-processed foods, and self-perception of own weight. These risk factors also increase the chances of the development of other CNCDs.
The analysis of the articles was based on the GRADE (Grading of Recommendations Assessment, Development and Evaluation) to gauge the quality of the evidence and the strength of the recommendations. It is observed that given the variability of the results of the studies analyzed and the locations where the empirical research was conducted, the study does not provide precise evidence 14 . However, some generalization of knowledge about risk factors is possible and enables the formulation of some proposals for action such as: helping young people to cultivate balanced eating habits at school by teaching them to avoid ultra-processed foods; encouraging the practice of physical exercise; warning about the risk of excessive use of computers, TV and social media. The situation of obesity is complex and multifactorial, and it is necessary to monitor families and adolescents by strengthening the relationship between school and the Basic Health Unit in order to develop health actions by meeting the repressed demand with multiprofessionals, home visits and food re-education programs.

Conclusion
Adolescent obesity is a public health problem that affects not only physical growth and development, but also has an impact on social and emotional issues and experiences in stigmatizing situations. The study showed that obesity in adolescence is associated with pre-existing factors that promote the surge in weight gain, which are predominantly biological, social, and nutritional. In general, each of them has a different impact depending on the circumstances, but they act in an interrelated and complex way, hence the difficulty of isolating one single associated factor.
One of the limitations of this review is the impossibility of defining the predominant factors given the variability of geography, culture and focus of the themes analyzed. This makes it difficult to make possible recommendations for the problem raised. However, based on the risk factors that were examined in the studies, it is possible to say that young people can be protagonists in the transformation of their situation and, often, of their family, to the extent that they become aware of the issues involved in obesity and become multipliers of that knowledge. In this respect, the school and the Basic Health Units have a fundamental and incomparable role.