This directed case study is framed as a discussion between a biochemistry major and her boyfriend who is interested in trying the Keto diet. The case is intended to tie together a variety of metabolism topics in a way that engages the students and relates these topics to issues in their own lives. Together with “Melanie” and “Mike,” students explore questions about basic cellular metabolism, ketones, and the overall health impacts of this popular diet. The case was originally designed for use in the second semester of a two-semester undergraduate biochemistry course after the main topics of normal metabolism (glycolysis, gluconeogenesis, the citric acid cycle, beta-oxidation of lipids, and lipid catabolism) have been covered.