Validation of an Italian questionnaire on knowledge and perceived effects on health of Mediterranean Diet and other dietary patterns: the NUTRIDIET questionnaire

Background and aims: Unhealthy dietary patterns are a major contributor to non-communicable diseases. The Mediterranean Diet (MD) proved health benefits, but its adherence has declined in Italy. Nutrition knowledge (NK) significantly influences dietary behavior, but no validated tool exists to assess NK and perceptions of the MD and other dietary patterns. This study aimed to develop and validate the NUTRIDIET questionnaire among the Italian population. Methods and results: A prospective observational study was conducted on 438 Italian adults (18–65 years). The NUTRIDIET questionnaire consisted of 30 items across two sections: knowledge of dietary patterns and perceptions of their health impacts. The total score ranges 0–30 points. Reliability was assessed via internal consistency (Cronbach's alpha) and test-retest reliability. Construct validity was examined by comparing scores between participants with and without nutritional background. The questionnaire exhibited good internal consistency (Cronbach's alpha = 0.792) and test-retest reliability (R = 0.650, p < 0.001). Construct validity was confirmed by higher scores in participants with nutritional background (26.9 ± 2.8) compared to those without (21.1 ± 5.4, p < 0.001). Most items were of moderate difficulty and had a good discrimination index, distinguishing between individuals with different NK levels. Conclusion: The NUTRIDIET questionnaire is a valid and reliable tool for assessing NK and health-related perceptions of the MD and other diets in the Italian population, particularly among young adults and women. This instrument can aid in identifying knowledge gaps and programming targeted interventions to improve dietary adherence and public health outcomes.