Food Thought Suppression Inventory: Item response theory and measurement invariance in Portuguese adults

The Food Thought Suppression Inventory (FTSI) is a 15-item measure to assess cognitive suppression related to food. The present study aimed to: 1) study the original 15-item FTSI in both women and men through item response theory (IRT), using a graded response model; 2) replicate the factor structure obtained previously in a women sample and test the measurement invariance across body mass index (BMI) groups. In Study 1 (N = 434), the IRT model resulted in an 11-item FTSI shortened version that was equivalent across a community sample of women and men. The original FTSI was highly correlated with the FTSI short version. The short version also presented comparable correlations as the original scale in relation to body image cognitive fusion, psychological flexibility and eating psychopathology. In Study 2 (N = 435), confirmatory factor analyses revealed that the FTSI short version fitted the data well among women with normal weight and those with overweight/obesity, with the measure demonstrating invariance across both groups. These findings indicate that the FTSI short version, comprising the highest quality items, is a reliable and valid measure to assess food thought suppression in both women and men, and maintains the same factorial structure across women's BMI groups. Clinical implications were addressed.