Planning to break habits : Efficacy, mechanisms, and boundary conditions of implementation intentions targeting unhealthy snacking habits

Having strong goal intentions is generally not sufficient to ensure actual goal-directed behavior. However, when goal intentions are furnished with a specific type of planning, called ‘implementation intentions’, the likelihood of successful goal-striving substantially increases. Implementation intentions are simple action plans that specify the where, when, and how of goal-striving (“If I am in situation X, then I will perform goal-directed behavior Y!”), unlike intentions which merely specify a desired end-state (“I intend to achieve Z!”). Although many studies have shown that implementation intentions help to promote the initiation of new, wanted behaviors (e.g., eating more fruits), there was little empirical evidence for the efficacy of implementation intentions in diminishing existing unwanted habits (e.g., eating less junk food). The main objective of this dissertation was therefore to investigate whether implementation intentions can also be effective in endorsing this more difficult, but important, type of behavior change. This question was investigated in the domain of eating, and specifically for unhealthy snacking behavior. Two types of implementation intentions were tested for their efficacy: implementation intentions that specify not to eat an unhealthy snack in a critical situation (negation implementation intentions), and implementation intentions that specify the replacement of unhealthy snacks with healthy snacks in a critical situation (replacement implementation intentions). In addition to investigating their efficacy, the underlying mechanisms making these different types of implementation intentions (in)effective were also investigated. Moreover, it was tested whether, by fostering the identification of critical situations, the self-regulation strategy ‘mental contrasting’ could augment the efficacy of implementation intentions. Findings showed that replacement implementation intentions are effective in diminishing unwanted habits. The underlying mechanism making these implementation intentions effective involve a simultaneous facilitation of the ‘situation-healthy snack association’ and an inhibition of the ‘situation-unhealthy snack association’. Together, these two processes increase the chance that one is able to choose the healthy snack upon encountering the critical situation. Some important boundary conditions were also identified. First of all, it was found that implementation intentions should specify the replacement of unhealthy snacks by healthy snacks in order to be effective, rather than specifying not to consume the unhealthy snack. When negation implementation intentions are formulated, unhealthy snack intake ironically actually increases. Second, the if-part of the implementation intention needs to capture the actual critical situation that triggers the unwanted behavior for the implementation intention to be successful in diminishing the unwanted behavior. Related, it was found that mental contrasting is a promising strategy for identifying these critical situations and thus for increasing the effectiveness of the implementation intentions. In conclusion, while making a specific action plan may help to break unwanted habits, there are some important boundary conditions. Only when implementation intentions with the right format (replacement), that specify truly critical situations are formulated, they are effective in breaking habits. Since the plans people make without any help generally do not adhere to these conditions, formulating effective plans may require additional self-regulation strategies, such as mental contrasting