Background: Overweight in adults has increased significantly in developed countries in recent decades. This problem has attracted interests of researchers in the field of nutrition knowledge. Objectives: The purpose of this study is to evaluate the validity and reliability of the Persian version of the dietary habits and nutritional knowledge questionnaire and the nutrition knowledge questionnaire for adults, and to confirm their structural model in the Iranian population. Methods: A sample of 300 hospital employees from a hospital in Mashhad, Iran, participated in this study and completed the questionnaires. The questionnaires were translated using the forward-backward translation method. Psychometric evaluation of the Persian version of the questionnaires with a total 5 subscales was assessed based on content validity and construct validity using confirmatory factor analysis. Internal consistency and test-retest reliability were evaluated using Chronbach’s alpha and intra-class correlation coefficient, respectively. Results: For qualitative content validity, the content validity index scores for all items were ≥ 0.80 and the content validity ratio scores were 0.91, 0.87, 0.84, 0.9, and 0.85 for all subscales. The Persian version of the questionnaires were confirmed by calculating confirmatory factor analysis models fit indices. The internal consistency figures for the Nutrition knowledge questionnaire for adults subscales were 0.7, 0.75, and 0.73 and for the total scale was 0.78; for the dietary habits and nutritional knowledge questionnaire were 0.71 and 0.7 and for the total scale was 0.74. The intra-class correlation coefficient were 0.97 and 0.95 for the total scale of nutrition knowledge questionnaire for adults and the total scale of dietary habits and nutritional knowledge questionnaire respectively. Conclusions: The findings show that the Persian version of the questionnaires has good content validity as well as acceptable validity and reliability.

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