The ultimate goal of automatic diet monitoring systems (ADM) is to make food journaling as easy as counting steps with a smartwatch. To achieve this goal, it is essential to understand the utility and usability of ADM systems in real-world settings. However, this has been challenging since many ADM systems perform poorly outside the research labs. Therefore, one of the main focuses of ADM research has been on improving ecological validity. This paper presents an evaluation of ADM’s utility and usability using an end-to-end system, FitNibble. FitNibble is robust to many challenges that real-world settings pose and provides just-in-time notifications to remind users to journal as soon as they start eating. We conducted a long-term field study to compare traditional self-report journaling and journaling with ADM in this evaluation. We recruited 13 participants from various backgrounds and asked them to try each journaling method for nine days. Our results showed that FitNibble improved adherence by significantly reducing the number of missed events (19.6% improvement, 𝑝 = .0132). Results have shown that participants were highly dependent on FitNibble in maintaining their journals. Participants also reported increased awareness of their dietary patterns, especially with snacking. All these results highlight the potential of ADM in improving the food journaling experience.