Crystal Smit

General Introduction 1 21 Chapter 3—An integrated model of fruit, vegetable, and water intake in young adolescents The aim of the longitudinal study described in Chapter 3 was to examine the role of intrinsic motivation in predicting healthy drinking behaviors compared to other dominant theoretical predictors. The study consisted of an integrated model that investigated various theoretical perspectives to determine whichmechanism is the most predictive of changes in children’s fruit, vegetables and water consumption over time. The model was based on evidence from health research applying predictors from various theoretical perspectives, including the theory of planned behavior (i.e., self-efficacy, attitude, norms, and behavioral intentions), social norms (i.e., injunctive and descriptive norms) and the self-determination theory (i.e., intrinsic motivation). The study used four data-collection waves from the MyMovez research program that included both children and young adolescents ( N = 953; 53.9% girls; M age = 11.19, SD age = 1.36). The corresponding article to this chapter was published in Health Psychology (Smit et al., 2018) . Chapter 4—Promoting water consumption among children: A three- arm cluster randomized controlled trial testing a social network intervention The aim of the study described in Chapter 4 was to compare the effectiveness of the Share H 2 O social network intervention to a mass media intervention and no intervention. The study consisted of a three-arm cluster randomized controlled trial that tested the effectiveness of the improved Share H 2 O social network intervention on children’s water and SSB consumption. Children ( N = 451; 50.8% girls; M age = 10.74, SD age = .97) were randomly assigned to either the Share H 2 O social network intervention, active control condition or no intervention. The approach and content of the Share H 2 O social network intervention was nearly the same as in the proof-of-principle study (Smit et al., 2016); however, we attempted to improve the content of the training by incorporating more principles of the self- determination theory. The active control condition was based on the principle of mass media interventions, exposing all children simultaneously to the benefits of