Running head : JUNK FOOD INTAKE IN FRIENDSHIP NETWORKS 1 Adolescents ’ Intake of Junk Food : Processes and Mechanisms Driving Consumption Similarities

Adolescents’ consumption of low-nutrient, energy-dense (LNED) food often occurs out of home, and friends may be an important source of influence. This study tested whether observed similarities in LNED food intake among friends result from social influence, and also explored underlying psychological mechanisms. Three waves of data were collected over one year from grade 8 students in Australia (N = 378, 54% male), including measures of food intake and related cognitions, and friendships to grade-mates. The results of longitudinal social network models show that adolescent intake was predicted by their friends’ intake, accounting for pre-existing similarities and other potentially confounding factors. Changes to adolescents’ beliefs about LNED food do not appear to be the mechanisms underpinning influence from their friends. JUNK FOOD INTAKE IN FRIENDSHIP NETWORKS 3 Adolescents’ Intake of Junk Food: Processes and Mechanisms Driving Consumption Similarities Among Friends Although adolescents’ diets are strongly governed by their family food environment (Patrick & Nicklas, 2005), about half of their consumption of low-nutrient, energy-dense (LNED) “junk” foods occurs out of home (Briefel, Wilson, & Gleason, 2009). In developed countries such as the US and Australia, young peoples’ LNED food intake has increased substantially in recent decades (Cook, Rutishauser, & Seelig, 2001; Jahns, Siega-Riz, & Popkin, 2001), resulting in reduced diet quality and additional caloric intake (Jahns et al., 2001). This has implications for both immediate and long-term health outcomes and is thought to be one of many interrelated factors linked to increased body mass index (BMI) and rates of obesity in young people (Nicklas, Baranowski, Cullen, & Berenson, 2001; SpruijtMetz, 2011). Foods eaten out-of-home by adolescents are typically consumed in school and peer contexts, and adolescent reports confirm that lunches and snacks are often eaten with friends (Feunekes, de Graaf, Meyboom, & van Staveren, 1998). In cross-sectional studies, consumption of snack foods and overall energy intake has been found to correlate with the intake of an adolescents’ best friends (Feunekes et al., 1998), and male friends have been found to be alike in their consumption of high-calorie foods (de la Haye, Robins, Mohr, & Wilson, 2010). Even among adults, dietary similarities between socially connected peers appear to be strongest for snack foods and alcohol, with effects over time suggestive of a social influence process (Pachucki, Jacques, & Christakis, 2011). Situational food norms, which entail factors such as social influence and portion size, are theorized to have a powerful effect on food intake (Herman & Polivy, 2005). Although social influence on food consumption is known to be pervasive and complex, one consistently observed phenomenon is social modeling. Laboratory-based studies on social modeling of JUNK FOOD INTAKE IN FRIENDSHIP NETWORKS 4 eating, which pair naïve participants with experimental confederates, have shown that individuals eat more when their eating companions eat more, and less when their companions eat less (e.g. Conger, Conger, Costanzo, Wright, & Matter, 1980; Herman, Roth, & Polivy, 2003; Hermans, Larsen, Herman, & Engels, 2008; Rosenthal & McSweeney, 1979). This “matching norm” effect has also been replicated in children (Salvy, de la Haye, Bowker, & Hermans, 2012): for example, girls (aged 8-12) increased their intake of cookies when exposed to a peer who ate a larger amount of cookies, relative to a peer eating a small number of cookies (Romero, Epstein, & Salvy, 2009). Moreover, young people have been found to match the food intake of friends more so than unfamiliar peers (Salvy, Howard, Read, & Mele, 2009). Similarities in diet and eating behaviors among adolescent friends have been observed in a small number of cross-sectional survey-based studies (de la Haye et al., 2010; Feunekes et al., 1998; Fletcher, Bonell, & Sorhaindo, 2011). Researchers have proposed that in these naturalistic settings, the “matching” of eating behaviors arises through social influence processes such as modeling (Monge-Rojas, Nunez, Garita, & Chen-Mok, 2002) and is motivated by goals for peer approval (Unger et al., 2004). However, it is not clear from these studies whether similarities in friends’ consumption patterns arise from socialization, or if they can be explained by other confounding processes. One such process is friendship choices that lead to dietary similarities, as friendships are often based on preferences for similar others (Aboud & Mendelson, 1998). Although there is no evidence to suggest that similarities in diet are a salient factor in adolescents’ friendship choices, friendships are based on similarities in individual attributes and behaviors that are potentially correlated with diet including gender, race or ethnic background, and obesity (de la Haye, Robins, Mohr, & Wilson, 2011a; Simpkins, Schaefer, Price, & Vest, 2013). As such, accounting for friendship selection processes when testing for socialization is critical (Veenstra, Dijkstra, Steglich, & JUNK FOOD INTAKE IN FRIENDSHIP NETWORKS 5 Van Zalk, 2013). To further this work, the current longitudinal study tested whether associations in LNED food intake amongst adolescent friends, in the context of larger friendship networks, could be explained by social influence, when potential confounding factors were controlled. The second aim of this study was to explore the mechanisms that might underpin friends’ influence on adolescent LNED food intake. Despite the prominence of behavioral modeling theory in social psychological research and evidence of social modeling effects on food intake in adults and youth, a major limitation of the eating literature is the inability to account for the reasons why people emulate each other (Herman et al., 2003). Traditionally, health behavior theories emphasize the role of social-cognitive mechanisms in mediating the influence of the social environment on behavior. For example, the theory of planned behavior proposes that the behaviors we observe in others influence our perceptions of social norms, which, along with attitudes and beliefs about behavior control, shape our intentions and subsequent behaviors (Ajzen, 1991). More general theories of social modeling also maintain that the observation of behavior in others shapes a range of individuals’ beliefs and attitudes about these behaviors, guiding future actions (Bandura, 1977). For example, there is evidence that social factors influence not only perceptions of social norms, but also attitudes towards the behavior and perceptions of behavior control (Povey, Conner, Sparks, James, & Shepherd, 2000). Thus, we test a more general model of social cognition, whereby friends’ food intake may predict adolescent intake by affecting a range of cognitive constructs including norms, attitudes, perceived behavioral control, and intentions (see the left panel of Figure 1). However, other lines of thinking downplay the cognitive, considered aspects of food choice, and instead highlight the imitative nature of social learning with regards to eating behavior. This work proposes that environmental and social cues elicit somewhat automated, JUNK FOOD INTAKE IN FRIENDSHIP NETWORKS 6 imitative responses: akin to what is referred to as “mindless eating” (Wansink & Sobal, 2007). Support for this imitative process has been found in laboratory-based studies looking at alcohol intake, where young people not only copied the quantity of alcohol consumed by confederates, but also the rate at which they drank, suggesting a somewhat unconscious, mimicked response (Larsen, Engels, Granic, & Overbeek, 2009; Larsen, Engels, Souren, Granic, & Overbeek, 2010). Aligned to this less cognitively-driven view of socio-environmental effects on eating is Bem’s self-perception theory (1972), which proposes that beliefs associated with a particular behavior tend to be fostered by reflecting on one’s past engagement in the behavior. Thus, a substantially different model to social cognition theories might be proposed, whereby youth “mindlessly” imitate the behavior of their peers, and subsequently shape their beliefs and attitudes so that they are in line with the behaviors they have endorsed (see the right panel of Figure 1). As outlined in the literature reviewed above, despite consistent evidence of food modeling in the laboratory, the extent to which this translates to natural settings, and how this plays out over time, is unclear. Additionally, the mechanisms underpinning social influence on food intake in youth and adults are not well understood, and additional work is needed to test competing theories.