The Ketogenic Diet was first described as a non-pharmacologic therapy for epileptic seizures in 1921. This therapy has undergone periods of popularity and disfavor, the latter related primarily to the rigors of the diet. However, in recent years the Ketogenic Diet has regained popularity as therapy for a select group of children whose seizures have not responded to medications or in whom side effects of the medications have become unacceptable. As part of a current comprehensive study of the Ketogenic Diet which will address questions about methods of diet initiation, and measurement of regional brain pH, we plan to evaluate the effects of the Ketogenic Diet on growth, body composition, resting energy expenditure, substrate utilization and bone density. To date, 25 patients have been enrolled (12 girls and 13 boys). The age ranged from 10 months to 17 years, with an average of 8 years. Preliminary analysis of our data shows: 1) The Ketogenic Diet produces an overall decrease in resting energy expenditure (REE) with the largest decline between the baseline and 1-month follow-up. 2) The Ketogenic Diet produces a loss of BMD despite supplementation. 3) The Ketogenic Diet produces an initial weight loss followed by weight stabilization.