Crystal Smit

Chapter 3 48 health-psychology research (Sheeran, 2002). These findings strongly suggest that the theory of planned behavior model does not sufficiently predict changes in dietary behavior. A first possible explanation—and, thereby, a possible way to strengthen the predictive power and extend the theory of planned behavior model—might lie in the limited conceptualization of the subjective norm construct. Research has shown that the subjective norms construct in the theory of planned behavior is generally a weak predictor of intentions, which might indicate a need to adjust this norm (e.g., Armitage & Conner, 2001). However, in recent years, the rapidly expanding research of the social norms domain has further scrutinized this construct in relation to dietary intake, providing more in-depth insight about the nature and mechanisms of social norms (e.g., Higgs, 2015; Jones & Robinson, 2017; Robinson, Thomas, Aveyard, & Higgs, 2014). Promising for the theory of planned behavior model, social norms research has brought forward the importance of distinguishing between not only different types, but also different sources of normative influences in predicting dietary behaviors (for review, see Jones & Robinson, 2017; Robinson et al., 2014). With regard to the types of social norms, the literature makes a distinction between descriptive (i.e., the perceptions of the prevalence of others’ behavior) and injunctive norms (i.e., the perceptions of what others consider appropriate; Cialdini, Kallgren, & Reno, 1991). Parents and peers have been shown to be the principal sources of childhood social norms in relation to dietary behaviors (Patrick & Nicklas, 2005). Parents strongly influence their children’s dietary behaviors (Pearson, Biddle, & Gorely, 2009); however, as children get older, their peers become increasingly influential of their eating behaviors (Salvy et al., 2012). Studies investigating dietary behaviors have found that social norms affect not only behavioral intention (Stok, De Ridder, De Vet, & De Wit, 2014), but also actual consumption (Jones & Robinson, 2017; Pedersen, Grønhøj, & Thøgersen, 2015). Nevertheless, it remains unclear whether either type of norm from either source predicts changes in dietary behaviors in the long run, taking into account other