While high protein diets are increasing in popularity, there is a lack of data on their potential adverse effects. We describe two patients on high protein supplements and exercising for physical fitness. Both developed intermittent abdominal pain, transient elevations in transaminases and hyperalbuminemia without there being any identifiable cause. The symptoms and abnormalities on the laboratory tests resolved after the high protein intake was discontinued. While the pathogenesis and importance of these abnormalities need further study, the findings raise concerns regarding the safety of high protein diets combined with high intensity exercise.