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Objectives: Dietary intentions are supposed to engender planning processes, which in turn stimulate dietary behaviour change. However, some studies failed to find such mediation effects, which suggest more complex and not yet unravelled relationships between these factors. One explanation may be that mediation works better under certain circumstances or only for specific subgroups. This study addresses this reasoning by examining autonomy beliefs and sex as putative moderators of the hypothesized mediation chain. Design and methods: In a longitudinal design with three measurement points in time (1 week and 1 month apart), 912 women and 214 men were surveyed. Planning, intention, dietary autonomy beliefs, and sex were used to predict fruit and vegetable intake within a conditional process model designed to identify mechanisms of change. Results: The intention–planning–behaviour chain was qualified by a triple interaction involving autonomy beliefs and sex as moderators between intention and planning. Higher dietary autonomy resulted in higher levels of planning fruit and vegetable intake. For men, even in case of higher intention, at least medium levels of autonomy beliefs were necessary to facilitate planning processes. For women, already lower levels of autonomy beliefs can engender postintentional planning strategies and seem to even compensate lower intention. Conclusions: Intention and planning are key predictors of dietary change. However, these variables work better under specific conditions (with a sufficient level of autonomy), and differently in subgroups (men vs. women). These results may explain the inconsistent findings of previous studies on the mediating effect of planning and allow for a better description of the mechanisms by which intentions may influence behaviour.


Institute for Positive Psychology and Education

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Journal Article

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