(1) Dietary behavior is highly relevant for patients after bariatric surgery. No instrument exists assessing adherence to medical guidelines concerning the dietary behavior of patients after bariatric surgery. The aim of this study was to develop and validate such an instrument. (2) Data from patients after bariatric surgery (n = 543) were collected from March to May 2022. The development of the DBI-S was theory-based and interdisciplinary. Items’ and content validity of the DBI-S were examined. (3) The final version of the DBI-S consists of 13 items. Convergent validation was confirmed by significant correlations between DBI-S score and attitude towards healthy food (r = 0.26, p = <0.001) and impulsivity (r = −0.26, p = <0.001). Criterion validity was confirmed by significant correlations between DBI-S score and pre-/post-surgery BMI difference (r = −0.14, p = 0.002), pre-/post-surgery weight difference (r = 0.13, p = 0.003), and quality of life (r = 0.19, p = <0.001). Cluster analysis confirmed the ability to distinguish between two dietary behavior clusters (rather healthy and rather unhealthy). (4) The DBI-S is an economic and valid instrument to assess the adherence of post-bariatric surgery patients to the relevant dietary behavior recommendations and guidelines and can distinguish between rather unhealthy and healthy dietary behavior.
Keywords: bariatric surgery; body mass index; cluster analysis; dietary behavior; dietary recommendation; validation; weight.