Development and Psychometric Evaluation of the Transtheoretical Model-Based Sustainable Nutrition Behavior Scale (TTM-SNBS) for Adolescents

<b>Background/Objectives</b>: Sustainable nutrition is essential for human and planetary health. The Transtheoretical Model-based Sustainable Nutrition Behavior Scale (TTM-SNBS) was developed to assess sustainable nutrition behaviors and the dynamic processes of behavior change in adolescents. <b>Methods</b>: The item pool was generated through literature review and expert consultation using the Delphi technique (10 experts, three rounds). Construct validity was assessed using exploratory and confirmatory factor analyses. Reliability was evaluated through Cronbach's alpha and test-retest methods. External validity was examined through correlations with the Sustainable and Healthy Eating Behaviors Scale (SHEBS), following COSMIN standards. The study included 512 adolescents aged 14-18 years (54% female) from public high schools in Ankara, Türkiye. <b>Results</b>: Initially, 75 items were developed through expert evaluation. After preliminary testing, two items with low and negative correlations were removed; 73 were retained for validation. Factor analyses and refinement produced a 45-item final validated scale comprising one stage of change item and five subscales: cognitive processes (14 items), behavioral processes (18 items), decisional balance-pros (4 items), decisional balance-cons (4 items), and self-efficacy (4 items). Items showed good discrimination (>0.27). Cronbach's alpha values ranged from 0.67 to 0.93, and fit indices were acceptable (χ²/<i>df</i> = 2.8-4.2; RMSEA = 0.045-0.065). External validity was supported by significant positive correlations with the SHEBS. <b>Conclusions</b>: The TTM-SNBS is the first psychometrically validated, theory-based instrument to assess sustainable nutrition behaviors in adolescents. It offers a reliable and valid instrument to support future research and interventions promoting sustainable dietary practices.