The Influence of Peers on Diet and Exercise Among Adolescents: A Systematic Review
Introduction
Globally, adolescent obesity is a significant public health problem, with increasing prevalence in developed countries from 1980 (Ng et al., 2014). Adolescent obesity can negatively influence current and future physical (Falkstedt et al., 2007, Ford et al., 2008, Shah et al., 2013, Tirosh et al., 2011) and psychological health (Mond et al., 2011, Puhl et al., 2011), while also increasing medical costs (Estabrooks and Shetterly, 2007, Hampl et al., 2007, Hlaing et al., 2011). To prevent or mitigate the severity of these negative consequences, it is important to intervene early to either prevent adolescent obesity or reduce its prevalence and related health issues.
In order to reduce obesity rates in adolescents, the World Health Organization (WHO, 2015) issued recommendations for diet and exercise, designed to support a proper balance between calorie intake and expenditure. The WHO provides guidelines for physical activity and recommends increasing whole grain, fruit and vegetable intake and restricting total fat consumption. Interventions including healthy diets and adequate exercise are effective for controlling weight during adolescence (Berkowitz et al., 2013, Epstein et al., 2007, Savoye et al., 2011).
Many countries have developed national polices to support adolescents' healthier diet and exercise behaviors in accordance with the WHO guidelines. In the United States, the Healthy People 2020 initiative highlights behavioral interventions and dietary guidelines to reduce the prevalence of obesity in adolescents aged 12 to 19 years (Office of Disease Prevention and Health Promotion, 2015). Similarly, in the United Kingdom, the National Child Measurement Programme (NCMP) has been established to monitor the prevalence of obesity and provide information about healthy lifestyles and weight control (Public Health England, 2015). In Korea, the prevalence of adolescent obesity is lower than in North America or Europe, but is steadily increasing (Korean Centers for Disease Control and Prevention, 2014). Early interventions to prevent further growth in rates of adolescent obesity, through increased physical activity and modified eating behaviors, have become a governmental and educational priority in Korea (Noh, 2013). A first step in improving diet and exercise behaviors of all adolescents is to understand what factors influence those behaviors; this could be helpful in developing interventions to prompt healthier behaviors among adolescents with the goal of stemming the rise in rates of adolescent obesity.
Studies in many countries have identified diverse factors for diet and exercise among adolescents, although most have focused on the roles of parents and schools. Developmentally, relationships between adolescents and their parents evolve from those established in childhood, with adolescents becoming more independent from their parents over time. However, parents continue to influence perspectives and behaviors of adolescents (Laursen & Collins, 2009). Parental diet and exercise (Arcan et al., 2007, Salvy et al., 2011), monitoring behaviors (Ornelas et al., 2007, Stewart and Menning, 2009), and support (Bauer et al., 2011, Dowda et al., 2007, Hohepa et al., 2007) are found to be associated with adolescent diet and exercise behaviors.
School factors are also associated with adolescents' diet and exercise behaviors (Story, Nanney, & Schwartz, 2009). Studies have examined the availability of specific foods in schools, school breakfast and lunch programs, and school physical education programs as contributing factors to adolescents' diet and exercise (Bauer et al., 2011, Fox et al., 2009, Story et al., 2009). The availability of certain food items at school is associated with increasing intake of these foods among adolescents (Bigornia et al., 2015, Minaker et al., 2011, Rovner et al., 2011). Provision of any physical activity facilities was positively associated with improvement in adolescents' exercise behaviors in some studies (Durant et al., 2009, Haug et al., 2010), but not others (Kirby et al., 2012, Scott et al., 2007).
Peers are another contributing factor to adolescents' diet and exercise. As adolescents become more independent from their parents, they spend more time with their friends (Brown & Larson, 2009). The importance of peer relationships increases during adolescence, compared to childhood and preadolescence (Collins and Steinberg, 2008, Papalia et al., 2008), with peers' influence peakings (Brown and Larson, 2009, Collins and Steinberg, 2008). Therefore, peers could also play an important role in diet and exercise of adolescents, in addition to parental and school factors. Specifically, behaviors of close friends could influence adolescents' behaviors or could be shared by adolescents. However, the impact of the behaviors of the broader peer group, as well as the effect of close friends' behaviors, on adolescents' diet and exercise behaviors has been studied less than that of parents and school. Given the increasing importance of peer relationships during adolescence, and their potential for influencing diet and exercise behaviors, it is important to identify what is currently known about these influences in order to develop appropriate interventions that support healthy diet and exercise.
Therefore, the purpose of this systematic review was to examine the research to date on the contribution of peers to diet and exercise behaviors of adolescents. The review identifies which peer factors and diet and exercise behaviors were assessed, and whether any relationships among diet, exercise, and peer factors were found. This review was conducted and reported according to the PRISMA guidelines (Moher, Liberati, Tetzlaff, & Altman, 2009).
Section snippets
Information Sources and Search Strategy
With the assistance of the librarian from the University of Iowa, the following keywords were used to search the electronic databases PubMed and CINAHL in October 2016: [Adolescent] AND [Obesity] AND [Friends OR Peer network OR peer]. MeSH terms for PubMed and subject terms for CINAHL were also applied. Once the initial list of articles from PubMed and CINAHL was created, Web of Science and SCOPUS were searched in October 2016 to identify additional studies that cited or were related to
Results
The 32 studies included in this systematic review examined peer factors and their relationship to diet and exercise in adolescents. However, the studies differed in their focus: eleven studied diet only, seventeen examined exercise only, and four focused on both diet and exercise. In addition, the review highlighted another important differences among studies: while friendship and relations were of particular interest, studies differed in how they defined vs. peers, as well as the groups from
Discussion
The results of this review provide evidence that diet and exercise behaviors of adolescents were positively related to those of their peers, although associations differed based on gender, the type of diet and exercise, and the closeness of friends. The associations between adolescents' diet and exercise and those of their peers could be partially explained by the importance of friendship and peer relationships in adolescence (Brown and Larson, 2009, Collins and Steinberg, 2008, Papalia et al.,
Conclusion
This review of the literature summarized existing research on the relationships between adolescents' and their peers' diet and exercise. Twenty four studies were identified and then classified into three categories, depending on the type of behaviors investigated: exercise, diet, and both diet and exercise. Findings of this review indicated that diet and exercise of adolescents and their peers were significantly associated. Gender and closeness of friends could influence the associations
Acknowledgment
This study was completed as part of the PhD Dissertation of Sophia Jihey Chung at the University of Iowa, College of Nursing.
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