Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: More alternatives are needed for recording people's normal diet in different populations, especially adults or the elderly, as part of the investigation into the effects of nutrition on health. Objective: To compare the estimated values of energy intake, macro and micronutrient and alcohol consumption gathered using the EVIDENT II Smartphone application against the data estimated with a food intake frequency questionnaire in an adult population aged 18-70. Methods: We included 362 individuals (52 ± 12 years, 59.1% women) who were part of the EVIDENT II study. The participants registered their food intake using the EVIDENT application during a period of 3 months and through a food intake frequency questionnaire (FFQ). Both methods estimate the average nutritional composition including energy intake, macro and micronutrients and alcohol. Through the application, the values of the first week of food recording, the first month and the entire 3-month period were estimated. The FFQ gathers data regarding the food intake of the year prior to the moment of interview. Results: The intraclass correlation for the estimation of energy intake with the FFQ and the application shows significant results, with the highest values returned when analyzing the application's data for the full 3-month period (0.304 (95% CI 0.144 to 0.434), p <.001). For this period, the correlation coefficient regarding energy intake is 0.233 (p <.001). The highest value corresponds to alcohol consumption and the lowest to the intake of polyunsaturated fatty acids (r = 0.676 and r = 0.155, p <.001), respectively. The estimation of daily intake of energy, macronutrients and alcohol presents higher values in the FFQ compared to the EVIDENT application data. Taking the values recorded during the 3-month period, the FFQ for energy intake estimation (Kcal) was higher than that of the application (a difference of 408.7 (95% CI 322.7 to 494.8), p <.001). The same is true for the other macronutrients, with the exception g/day of saturated fatty acids (0.4 (95% CI -1.2 to 2.0), p = .62). Conclusions: The EVIDENT application is significantly correlated to the food intake frequency questionnaire in the estimation of energy intake, macro and micronutrients and alcohol consumption. This correlation increases with longer application recording periods. The EVIDENT application can be a good alternative for recording food intake intake in the context of longitudinal or intervention studies. Clinical Trial: ClinicalTrials.gov Identifier:NCT02016014