The use of digital technology for self-care, such as self-management of chronic diseases, has emerged through mobile applications and wearables, often designed, developed, and used in everyday life outside the healthcare context. The new self-care practices may be beneficial in many ways but can also potentially pose risks, and there is a corresponding need to understand underlying algorithms and biases that may affect users. In this article, we describe the design and development of a mobile app for food nutrition information as part of diabetes self-management and critically discuss its implications for patients and designers.In conclusion, this study highlights the need to carefully consider how selfmanagement tools are designed, developed, and used for self-care. We propose co-design to approach data-driven healthcare in general and data-driven decisionmaking tools in particular. Our findings show that patients need to balance overreliance and mistrust in augmented data-driven decision-making, which calls for ethical considerations and a critical approach for all future designers.