Healthy eating has a relevant impact on overall health. A sufficient fruit and vegetable (FV) intake, for instance, is associated with physical and mental health. However, the majority of the German population consumes less fruit and vegetables than recommended by public guidelines (e.g., “5 a day”). Even though many people intend to eat healthily, they frequently fail to translate their good intentions into action. This so-called intention-behaviour gap has been addressed in theory and empirical research, indicating that planning strategies are important predictors for overall behaviour change. The Health Action Process Approach (HAPA) states that action planning is a highly relevant self-regulatory strategy when it comes to bridging the intention-behaviour gap. With action plans, people form a mental link between situational cues (when and where) and a planned behavioural response (what), for instance: “I will eat an apple (what) at 8 am (when) in the kitchen (where)”. In empirical research, action planning has mainly been found to improve overall FV intake. This thesis aims at extending prior research by specifically focusing on high-resolution mechanisms of action planning interventions, thereby answering the question of when and how an action planning intervention unfolds its effects. The first chapter (Chapter 1) of this thesis introduces literature and empirical evidence on FV intake and action planning. In Chapters 2 to 4, three studies on action planning interventions in the context of FV intake will be presented: In Chapter 2, the frequency of plan enactment and its link to plan characteristics (i.e., plan specificity and type of the planned behaviour) and time variables (i.e., times of the day and plan calendar day) was investigated. Chapter 3 aimed at examining the frequency of cue detection and the execution of the planned behaviour and their links to overall FV intake, while accounting for interindividual as well as intraindividual differences. In Chapter 4, the short-term effects of an action planning intervention on FV intake and volitional self-regulatory outcome variables (i.e., self-efficacy and action control) were examined. The general discussion (Chapter 5) focuses on integrating the findings into the literature, discussing strengths and limitations, and providing an outlook as well as future implications for theory and practice. In the following, the main findings of this thesis will be summarized: Results of Chapter 2 indicated that plans were enacted for the majority of cases (68.7%). Fruit plans were more likely being enacted than vegetable plans. Plan specificity was unrelated to plan enactment, but specific morning plans were more likely being enacted than unspecific morning plans. Plan enactment rates decreased over the day and over the 7-day planning period. In Chapter 3, cue detection and the execution of the planned behaviour were reported in the majority of cases (63% and 69%, respectively). Within-person cue detection and between- and within-person execution of the planned behaviour were positively associated with overall FV intake. No additional effect of joint cue detection and the execution of the planned behaviour beyond each predictor’s main effect was found. In Chapter 4, FV intake and self-efficacy but not action control showed an immediate increase after an action planning intervention and subsequent maintenance of heightened levels. To conclude, this thesis (1) underlines the importance of plan enactment as conditional behavioural outcome, creating a link between action planning and unconditional health behaviour change, and (2) points to the need to integrate high-resolution temporal dynamics of health behaviour change into the research.
