The use of a food logging app in the naturalistic setting fails to provide accurate measurements of nutrients and poses usability challenges.

Objective: MyFitnessPal is the most popular commercial nutrition weight loss app. The aim of this study was to assess how individuals in naturalistic settings performed when recording their dietary intake in MyFitnessPal, and their usability experiences with the app.

Methods: Adults not regularly using MyFitnessPal (N = 43) logged their dietary intake in the app for 4 consecutive days and completed two researcher-administered 24-h recalls collected based on the Automated Multiple Pass Method.