Energy Diet is a design concept for a digital bathroom scale that displays personal health information in the form of body weight alongside environmental health information in the form of carbon weight. We intentionally conflate these two types of feedback in an effort to encourage people to regularly monitor their energy use as they weigh themselves and to reflect on the complex relationships between personal health and environmental health. To inform our design we tested paper prototypes and administered two surveys with 500 participants. We then created a working prototype that we deployed in four participants' homes for one month each. This paper discusses findings and design implications from our surveys and in-home deployment. Overall, seeing carbon weight together with body weight on a scale helped participants to conceptualize energy consumption and to reflect on a range of daily activities and their environmental impacts.