Recognizing that psychological factors affect customers' healthy eating behaviors, this study investigated psychological factors which might affect customers' healthful menu item selections at casual dining restaurants based on the extended theory of planned behavior (TPB). While TPB consists of attitudes, subjective norms, perceived behavioral control, and behavioral intentions, the extended version includes two new constructs (prototype and behavioral willingness). The extended TPB also subdivided the original TPB constructs of attitudes and subjective norms into affective and cognitive attitudes and injunctive and descriptive norms, respectively.

An online survey was used; 744 responses were analyzed using structural equation modeling and hierarchical regression. Results indicated that customers' healthful menu item selection behaviors were affected by intentional (behavioral intention) and reactive (behavioral willingness) decision making processes. Affective attitudes (feelings or emotions) and injunctive norms (perceived social pressure from others) regarding healthful menu item consumption had positive effects on intention and willingness to choose those menu items, whereas cognitive attitudes (rational assessment) and descriptive norms (perception of what others commonly do) had positive effects only on behavioral intention. In addition, the prototype image of unhealthy eaters had a negative effect on willingness to choose healthful menu items, indicating that when people hold negative viewpoints about unhealthy eaters, they are more willing to choose healthful menu items. Finally, the findings confirmed the importance of alignment between descriptive and injunctive norms in forming intentions to choose healthful items. In other words, when an individual perceives that most other people consume healthful menu items and that others expect him/her to do so also, the individual is likely to have stronger intention to choose those menu items.

There are theoretical and practical implications. From the theoretical perspective, to the best of our knowledge this is the first known empirical study to investigate customers' healthful menu item selections at restaurants within an extended TPB framework. Moreover, this study confirmed the importance of alignment between descriptive and injunctive norms in promoting healthy eating at restaurants, which had not previously been investigated. From the practical perspective, this study suggests strategies for developing effective promotional and marketing materials.