The prevalence of overweight and obesity is still rising among school-aged children in Western countries (1, 2). Given that eating habits persist in adulthood, the importance of establishing healthy eating practices during childhood, and maintaining them throughout adolescence, has been acknowledged for a long time (3, 4). Eating a sufficient amount of fruits and vegetables is an important factor in preventing obesity and avoiding chronic diseases (5, 6). Even so, most adolescents dislike fruit and vegetables and prefer high‐fat and high‐sugary ‘fast-food-style’ products (7-9). Research has shown that their (snack) food intake is strongly influenced by close social connections (10), which provides opportunities for prevention. The development of effective strategies to improve adolescents’ eating behaviors requires an understanding of how significant others (i.e., parents and peers) influence eating behavior (11). In addition, it is important to examine whether adolescents’ own eating behavior influences their perception of what close others do and approve of. This study is the first study that explored this bi-directionality between parental and peer social norms and snack food intake among adolescents.
People tend to conform to other persons’ consumption behavior in various social contexts (12). Specifically, empirical and cross-sectional studies have shown that people’s consumption behavior is influenced by descriptive and injunctive social norms. Perceived descriptive norms are informational non-coercive guidelines that people conform to, whereas injunctive norms exert pressure on one’s behavior and relate to the feeling of external expectations and (dis)approval of ‘(un)appropriate’ eating behavior (13). These social norms have been identified as powerful mechanisms in determining adolescents’ and adults’ consumption behavior (12, 14-19). Although the research field on social norms in adolescents is still evolving, few experimental normative studies have already shown promising findings to promote healthy consumption behavior (11). For example, an intervention study successfully targeted water drinking among schoolchildren by influencing the peer group norm (20). That is, selected peers were secretly instructed to promote water drinking by increasing their own water drinking behavior and talking about the benefits of water drinking to others, which increased water drinking and decreased the consumption of sugar-sweetened beverages among their class mates. Other experimental studies found that adolescents increased their vegetable intake after exposing them to information about the amount that their peers ate (21, 22). In addition, an online study found that an injunctive peer norm promoting fruit and vegetable intake was associated with higher self-reported fruit and vegetable intake as well as lower unhealthy snack food intake (19). These findings indicate that both descriptive and injunctive norms influence adolescents’ healthy consumption behavior. Notably, these perceived norms are typically assumed to affect subsequent eating behavior. The reversed impact of eating behaviors on perceived norms has yet to be empirically tested. Therefore, we also examined whether adolescents’ own eating behavior affected their perception of the social norm in a three-wave longitudinal study.
Although young people, and adolescents especially, are influenced by their peers’ consumption behavior (12, 17, 23), their parents also represent important figures in forming dietary patterns by serving as nutritional gatekeepers and role models (8, 24-27). It has been suggested that parental influences decline when competing with peer influences, because adolescents experience a strong need for group acceptance that leads to conforming to normative behavior of peers (16, 17, 28-30). Studies have found that even if adolescents have appropriate nutritional knowledge, they still choose fast-food-style products within their school and social environment because they think it is emotionally and socially too risky (e.g., ‘not cool’) to show interest in healthy eating (7, 17). To our knowledge, only one cross-sectional study has examined both parental and peer descriptive and injunctive norms among adolescents. The study showed that only descriptive parental norms influenced self-reported fruit and vegetable consumption (31), which did not support literature suggesting that peer norms would be more important than parental norms. Notably, they also found negative correlations between parental as well as peer injunctive norms and healthy eating behavior, which could suggest potential ‘reactance effects’ (32). Reactance effects were also found in previous studies on injunctive norms and eating behavior among adults, especially (33, 34). It has been suggested that the pressure from an injunctive norm may lead to a dismissal or even backfiring of the intended effect, because people feel pressured or threatened in their sense of freedom (32).
Surprisingly, longitudinal research investigating the relative importance of parental and peer influences on eating behavior is scarce (35-38). A study that examined adolescents’ intentions and self-reported fruit, vegetable and water consumption by integrating antecedents from different theoretical approaches (i.e., theory of planned behavior, social norms, and intrinsic motivation) in one model, found that perceived descriptive parental norms (and not injunctive nor any peer norms) predicted behavioral change on water drinking only (38). Furthermore, a longitudinal study among a student population that focused merely on descriptive peer norms showed no evidence of descriptive norms being a reliable predictor of future snacking and drinking behavior. That is, perceptions about how much peers consumed sugary snack foods and (alcoholic) drinks had limited effect on students’ eating and drinking behavior one year later (36). Altogether, more research is needed to determine the directional relationships between both parental and peer descriptive and injunctive norms on the promotion of healthy snacking behavior.
In this study, we not only examined the generally assumed ordering of norms preceding eating behavior (forward), but also considered the possibility of eating behaviors preceding perceived norms (reversed), as well as possible bi-directional associations (reciprocal) between these constructs (37). For example, when we make assumptions about how much fruits and vegetables other people consume (i.e., descriptive norm), this perception could be biased by our own eating behavior. Notably, it also provides a different explanation to what is now assumed to be reactance to injunctive norms. It may be that when people usually do not eat a lot of fruits and vegetables - and are aware of this -, they assume and perceive others thinking that they should eat fruit and vegetables. So, one’s own eating behavior may, in fact, influence our perceptions of what others expect from us. In addition, social norms and snacking behavior may be related in a bi-directional manner in which the above mentioned processes are combined into positive and/or negative feedback loops.
The current study is the first to examine changes in snacking behavior and four types of social norms that promoted fruit and vegetable intake, and the directionality of these associations among school-aged adolescents by applying cross-lagged autoregressive models to a three-wave longitudinal study. To fully understand the potential impact of norms on snacking behavior and vice versa, we included fruit and vegetable (‘core’) snack food intake as well as sweet and savory (‘non-core’) snack food intake in our study (39, 40). We took a step-wise approach by comparing four structural models to investigate the proposed cross-lagged effects for descriptive and injunctive norms separately. We had the following set of research questions (belonging to each step and model) to investigate the directionality between norms and behavior:
RQ1. To what extent are social norms and snacking behaviors stable from T1 to T2, and T2 to T3 (i.e., baseline or stability model)?
RQ2. Do parental and peer social norms at T1 predict snacking behaviors at T2, and from T2 to T3 (i.e., forward model)?
RQ3. Do core and non-core snacking behaviors predict parental and peer social norms from T1 to T2, and T2 to T3 (i.e., reversed model)?
RQ4. Are there bidirectional relationships between social norms and snacking behaviors (i.e., reciprocal model)?