Background and Objectives: Regarding health effects of probiotics and prebiotics in prevention and control of diseases and the lack of standard questionnaires in this field in Iran, objective of the present study was to assess validity and reliability of questionnaires designed to assess validity and reliability of probiotics and prebiotics in individuals aged 20-40 years in Tehran, Iran. Materials and Methods:After verifying content validity of the questionnaires by eight experts in fields of nutrition, psychology and psychometrics, face and construct validities (in two levels of exploratory and confirmatory factor analyses) were assessed and then the tool was validated using Cronbach's alpha coefficient (due to the multi-value of the response spectra). Results:The sampling adequacy index was higher than 0.7, which was the premise of exploratory analysis. For all the items, the standard loading factor was higher than 0.3, and the T-value was higher than 1.96. Furthermore, fit indices in confirmatory analysis were at the desired levels (0/9 and greater), and validity was verified. Cronbach's alpha value was calculated higher than 0.7, and the reliability of the questionnaire was verified.Conclusions: Results of this study showed that the researcher-prepared food frequency questionnaire developed to assess the level of probiotic and prebiotic consumptions, especially in people aged 20-40 years in Tehran, includes significant validity and reliability.

Objective: Depression and anxiety are the most common psychological disorders with extensive pathophysiology overlap, genetic correlation, and comorbidities as well as high risk of recurrence and chronicity. Due to the side effects of medication and not achieving the expected result, the use of probiotics is considered as an adjunctive treatment option without serious side effects. Methods: This is a correlational study conducted in Spring 2020 on 279 people (76 males and 203 females) aged 20-40 years in Tehran, Iran who had at least a diploma and were selected by a convenience sampling method after declaring informed consent. For collecting data, the Beck Depression Inventory, the Beck Anxiety Inventory, and a researcher-made probiotic consumption questionnaire were used and completed online. Data were analyzed using Pearson correlation test and multivariable regression analysis in SPSS v. 26 software. Results: Out of 279 participants, 209 (74.9%) had moderate probiotic consumption, 3.6% had good consumption and the rest had poor consumption. Probiotic consumption had significant negative correlation with depression (r= -0.183, P= 0.002) and anxiety (r= -0.122, P= 0.041). Despite the significant predictive power of probiotics for explaining depression, it had no significant power to predict anxiety. The regression coefficient was obtained as R=0.233; squared regression coefficient was R2=0.054, and P-values for depression and anxiety were 0.016 and 0.430, respectively. Conclusion: The use of probiotics may have reduce depression and anxiety. To obtain more accurate results, clinical trials on the use of probiotics are recommended.

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