Consistent food tracking is important for weight loss. Many people struggle with forming and maintaining the habit because it is time consuming and generally un-enjoyable. We describe the design and initial field evaluation of HappyInu, a virtual pet-care game that we developed to promote consistent food tracking. HappyInu uses daily notifications to remind users to track, provides photo-based food tracking to make the process simpler and gives virtual and cash rewards for motivation. In our pilot study, users were excited about the game-based approach and they wanted more in-game tasks and rewards to be offered. Intrinsic rewards were more motivating than cash, particularly pleasure (fun) and the need to contribute to something meaningful. However, users played HappyInu on a casual (non-daily) basis, just as they did with other smartphone games. In this paper, we discuss users' perceptions on the role of games for behavior change and the implications on game design.