Finding the critical cue: implementation intentions to change one's diet work best when tailored to personally relevant reasons for unhealthy eating.

Implementation intentions promote acting on one's good intentions. But does specifying where and when to act also suffice when goals involve complex change that requires not merely initiating a behavior but rather substituting a habit with a new response? In a pilot study and two experiments, the authors investigated the efficacy of implementation intentions to replace unhealthy snacks with healthy snacks by linking different types of cues for unhealthy snacking (if-part) to healthy snacking (then-part). The pilot study identified cues for unhealthy snacking, differentiating between situational (where/when) and motivational (why) cues. Studies 1 and 2 tested the efficacy of implementation intentions that specified either situational or motivational cues in altering snacking habits. Results showed that implementation intentions specifying motivational cues decreased unhealthy snack consumption whereas the classic specification of where and when did not. Extending previous research, for complex behavior change "why" seems more important than "where and when."