HYPOTHESIS: We hypothesize that an anaplerotic agent adjunct to KD may be effective for controlling seizures and improving cognitive outcomes in children with Glut1-DS. Triheptanoin (C7) is a triglyceride containing the odd chain C7 (heptanoic) fatty acid, which occurs only in limited amounts in the natural diet. It improves the oxidation of acetyl CoA by the tricarbonic acid (TCA) cycle, leading to subsequent oxidative phosporylation by the electron transport chain to produce sufficient ATP for energy utilization. It also provides the TCA intermediates alpha ketoglutarate and oxaloacetate, which are important precursors for the neurotransmitters glutamate, GABA, and aspartate. Therefore, we expect these metabolic effects will enhance seizure control and/or neurodevelopmental function.