This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The hypothesis of this protocol is that changes in fatty acid composition induced by the ketogenic diet are correlated to a reduction in seizure incidence. The Specific Aims include: 1. To determine the fatty acid composition in plasma and in circulating cell membranes in a cohort of epilepsy patients before and after initiation of the KD. 2. To evaluate whether the fatty acid content of the KD correlates with the changes seen in the fatty acid content of the plasma cell membranes. 3. To determine whether the fatty acid content of PM changes with time on the diet. 4. To evaluate the fatty acid content of the KD and compare this to fatty acid content of the pre-intervention diet. 5. To determine if changes in fatty acid composition of plasma membranes differ between lean vs overweight subjects pre and post kd. To determine if body fat content correlates with time to ketosis or response level. 6. To determine whether the 4:1 ratio KD is maintained over the course of 1 year and whether or not the fa of the diet and the membranes remain consistent over time. 7. To evaluate the FA content of the KD and to compare this to the FA content of a typical American diet.