Low carbohydrate diets such as the ketogenic (KD) and low glycemic index (LGIT) diets have been shown to be effective in treating drug resistant seizures in children with Angelman syndrome (AS). The investigators hypothesize that consuming a fat based nutritional formulation with an exogenous ketone throughout the day will produce urinary ketosis in children consuming both low and high carbohydrate diets, depending upon dietary background. The nutritional formulation will provide fuel substrates that push metabolism away from carbohydrates and towards fat utilization. This research is being done to assess the safety and tolerability of a nutritional formulation for use in dietary interventions in AS.