Microbiome Composition and Biomarker Discovery in Refractory Pediatric Epilepsy

Inclusion Criteria: * Study participant and/or legal representative must be willing and able to give informed consent/assent for participation in the study. * Study participant and/or legal representative must be willing and able to comply with all study requirements, in the opinion of the Investigator(s). * Study participant is \<18 years of age at the Screening Visit. * Study participant has refractory epilepsy. Exclusion Criteria: * Study participant has a known cardiac disorder including arrhythmias or hypertension. * Study participant has carnitine deficiency (primary), carnitine palmitoyltransferase I or II deficiency, or carnitine translocase deficiency. * Study participant has beta-oxidation defects - medium-chain acyl dehydrogenase deficiency, long-chain acyl dehydrogenase deficiency, short-chain acyl dehydrogenase deficiency, long-chain 3-hydroxyacyl-coenzyme A deficiency, or medium-chain 3-hydroxyacyl-CoA deficiency. * Study participant has a pyruvate carboxylase deficiency. * Study participant has porphyria. * Study participant is unable to maintain adequate nutrition. * Study participant has a surgically remediable cause for refractory epilepsy. * Study participant has a suspected mitochondrial disorder or has been diagnosed with a disorder in which a high-fat diet is contraindicated. * Study participant has previously received a ketogenic diet or modified Atkins diet. * Study participant has a chronic systemic disease like chronic kidney disease, chronic liver disease, heart disease (congenital and acquired), or chronic respiratory illness. * Study participant's family is expected to have compliance problems with treatment and/or seizure registration. * Study participant's seizures are under acceptable control. * Study participant has had a vagus nerve stimulator implanted within the last 18 months, has started a new antiepileptic drug (AED) within the last 2 months, or has changed his/her antiepileptic drugs within the last month. * Study participant has a medical condition, for example a metabolic disease, where ketogenic diet is contraindicated. * Study participant's nutritional status is not good enough or intake of fluid is too small to permit treatment with ketogenic diet. * Study participant has, within the last 2 months, been using medications or herbal medicine that have a considerable effect on glucose metabolism, such as oral glucocorticoids. * Study participant has, within the last 2 months, been using medications or herbal medicine that have a considerable effect on metabolism of AEDs. * Study participant uses herbal medicine which can interact with AEDs or a ketogenic diet. * Study participant has participated in another study of an investigational drug within the previous 3 months before Screening (or within 5 half-lives for the investigational drug, whichever is longer) or is currently participating in another study of an investigational drug.