Weight-Related Behavior among Adolescents: The Role of Peer Effects

Research Article published by PLoS One 2011;6(6):e21179. Epub 2011 Jun 23

Background:

• Since the dramatic increase in average weight and obesity has occurred in genetically stable populations, the weight gains can be attributed to environmental factors related to calorie intake and/ or physical activity, such as poor dietary choices and health behaviours. Social interactions may also have contributed to the rapid rise in obesity, such as ranging from smoking, alcohol use, other health risky behaviours as well as individuals' lifestyle choices may also be directly influenced by peer behaviour. therefore, the present research provides "a comprehensive investigation of whether social interaction in friendship networks influence the following weight-related behaviours of adolescents: exercising regularly, playing an active sport, hours of TV/Video viewing, sleeping six or fewer hours, eating breakfast on weekday, frequency of eating at fast food restaurants, eating five serving of fruits/vegetables daily, and consuming calorie-dense snacks."

Research Question:

• The authors consider seven previously unexamined behaviours related to physical activity and die, in addition with Fletcher's study of TV viewing behaviour among schoolmates to investigate whether the relationship between peer and individual influence weight-related behaviours among adolescents. 

Method:

• The method used in this study was qualitative; the researchers used the data from a nationally representative sample of adolescents and to examine the association between peer and individual weight-related behaviours. 
• The data for this study are drawn from the National Longitudinal Survey of Adolescent Health, and surveyed adolescents in grades 7 to 12 in 132 schools nationwide in the U.S, and beginning with an in-school questionnaire administered to a nationally representative sample of students in grades 7 to 12 in 1994-95 (Wave 1), the study follows up with a series of in-home interviews of respondents approximately one year (Wave 2; 1996), six years (Wave 3; 2001-2002), and thirteen years later (Wave 4; 2007-2008).
• The samples in this study are drawn primarily from the wave 2 (1996) respondents in grades 7 to 12 with at least one nominated friend. In addition, the analysis is based on samples of 3,898 adolescents and their peers with average number of nominated friends per individual is 2.54. Detailed summary statistics on adolescent and peer weight-related behaviours are in Table 1 and Table 2 reports the corresponding descriptive statistics for control variables.

Key findings:

• The researchers find a significant positive association between individuals' and friends' behaviours in terms of sports, exercise and fast food consumption. The estimated associations are robust to controls for individual- and family-level factors, unobserved heterogeneity at the school level and account for non-random peer selection.  
• The estimate from the baseline model, (see column 1 of Table 3) suggest that having friends who are more engaged in weight-related behaviours is associated with an increase in individual's participation in these activities. This result holds for all weight-related behaviours except for sleeping six or fewer hours.
• In model 7, Table 4 suggest that, on average, a 10% increase in the proportion of friends who exercise is associated with a 0.79% greater likelihood that the individual exercises.
• A one-day increase in the avg. number of weekdays friends eat at fast food restaurants is associated with a 0.18 increase in the number of days the adolescent eats in a fast food restaurant.
• Important to note that the weight-related behaviours were not significantly associated with the BMI (Table 6), which could be due to genetic predisposition.

Interesting finding in relate to the topic:

• The common attributes and environmental factors that influence adolescents' weight-related behaviours are not captured by our individual- and family-level controls or by the school-level fixed effects, but the estimates presented in the study show the strong correlated effects and influence of friend networks. 
• The study finds significant peer effects for pursuing an active sport, regular exercise, and the frequency of eating in fast food restaurants, suggesting that an individual is more likely to engage in these behaviours if his or her friends do so.
• Close friendship with an obese person predicts obesity more than living near obese people or familial relation to an obese person. (Christakis 2007)

Weakness:

• Since the study was done in qualitative method, the significant outcome of the relationships between social interactions in friendship networks and weight-related behaviours of adolescents may be driven in part by the correlated effects within smaller groups.
• Although the researchers utilize both lagged and contemporaneous measure of body weight along with school-level fixed effects and parental location preferences, but it is likely that selection could be conditioned on other unobserved characteristics, such as degree of risk aversion. 
• The study failed to look at the effects of whether the spread of one behaviour in social networks (e.g. fast-food consumption) might influence the spread of another (e.e. unhealthy snacking). As well as the peer effects in obesity operate via pathways other than the ones examined here, such as economic insecurity.

Take Home Message:

• Obesity is caused by a complex range of factors that very dramatically across the population.

          - Food consumption. (Fast-food consumption, unhealthy snacking)
          - Individual Physical Activity.
          - Individual Psychology.
          - Physical Activity Environment.
          - Food Production. (Convenience of food offerings)
          - Physiology.

• The BMI calculation tool is a easy way to measure and good for population-based analysis, but it can not use to measure the body fat %  and according to the study the weight-related behaviours were not significantly associated with the BMI.
•  Proper weight management involves: a healthy relationship with food and physical activity, as well as psychological and environmental control.

References:

• Ali MM, Amialchuk A, Heiland FW (2011). Weight-Related Behavior among Adolescents: The Role of Peer Effects. PLoS ONE 6(6): e21179. Retrieved July 20, 2011 from http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0021179#pone.0021179-Barnes1
• Barnes MG, Smith TG, Yoder J (2010). Economic Insecurity and the Spread of Obesity in Social Networks. WSU School of Economic Sciences Working Paper No. 2010-2. Retrieved July 20, 2011 from http://ssrn.com/abstract=1552185 
• Davis B, Carpenter C (2009). Proximity of fast-food restaurants to schools and adolescent obesity. American Journal of Public Health 99(3): 505–510. Retrieved July 20, 2011 from http://www.plosone.org/article/findArticle.action?author=Davis&title=Proximity of fast-food restaurants to schools and adolescent obesity. 
• Dianne Hales, Lara Lauzon (2007). An Invitation to Health- Second Canadian Edition. (pp.121-136). Nelson Education Ltd. Retrieved July 20, 2011.