Crystal Smit

General Introduction 1 19 THIS DISSERTATION The general objective of this dissertation was to investigate the effects of the Share H 2 O social network intervention to motivate healthy drinking behaviors in influence agents and their peers. We approached this general objective with four specific research aims. The first aim was to investigate whether a social network intervention grounded in self-determination theory improves children’s consumption behaviors. In a proof-of-principle study, we tested the effectiveness of the Share H 2 O social network intervention, in which influence agents were trained to encourage water consumption — as an alternative for SSBs — among their peers. The second aim was to explore how the intervention could be improved by gaining more insight into the role of intrinsic motivation in predicting healthy drinking behaviors compared to other dominant theoretical predictors. The third aim was to compare the effectiveness of the improved Share H 2 O social network intervention to a mass media intervention—which is widely used in the public health sector—and no intervention. Finally, our fourth aim was to acquire an in-depth understanding of the underlying processes of motivating the influence agents, and via them, their peers, to adopt healthy drinking behaviors. All studies were embedded in the MyMovez research program. The MyMovez Research Program The Share H 2 O social network intervention was part of the MyMovez research program, a large-scale five-year research project funded by of the European Research Council that aimed to develop and test methods for effective social network health campaign implementation (see Bevelander et al., 2018). In this program, participants received the Wearable Lab : a smartphone with a pre-installed research application and a wrist-worn accelerometer. Through the MyMovez research application, participants received daily questionnaires (e.g., dietary- related questions or sociometric questions) and were able to use a social media platform ( Social Buzz ), create a personalized avatar, and play a puzzle game (Zoko). In the Social Buzz participants could chat, share pictures and short videos with their peers, and also contact the researchers (Bevelander et al., 2018). In the Share H 2 O