Strict Classic Ketogenic Diet as a Therapy for Recurrent or Progressive and Refractory Brain Tumors in Children

Inclusion Criteria: * Age: Patients must be \< 21 years of age inclusive at the time of enrollment on this protocol. * Histologic Diagnosis: Histologically proven, primary brain tumor that is recurrent or progressive and refractory (nonresponsive) to standard, accepted therapy. A histopathologic diagnosis from either the initial presentation or at the time of recurrence is required for all subjects, except for diffuse intrinsic pontine glioma (DIPG). * Measurable Disease: Patients must have radiographically documented measurable tumor as assessed by RANO or RAPNO criteria. * Cranial and Spinal MRI: To document the degree of residual tumor, all patients must have an MRI of the brain with and without gadolinium performed within 2 weeks prior to study enrollment. For patients who undergo a tumor debulking surgery at the time of recurrence/progression, the following must be obtained: * Cranial pre-operative MRI scan with and without contrast. * Cranial post-operative MRI scan with and without contrast within 28 days following surgery. If possible, post-operative MRI should be performed within 48 hours of surgery, prior to the onset of edema or post-operative surgical enhancement, which can make measurements of residual tumor difficult. * Performance Level: Patients must have a performance status of \> 50. Use Karnofsky score for patients \> 16 years of age and Lansky score for patients ≤ 16 years of age. * Life Expectancy: Patients must have a life expectancy of \> 8 weeks. * Prior Therapy: Patients must have fully recovered from the acute toxic effects of all prior chemotherapy, immunotherapy, biologic therapy, or radiotherapy prior to entering this study * Growth factor(s): Must not have received within 1 week prior to entry onto this study. * Other anti-cancer or experimental agents or therapies are not permitted. Homeopathic medicines are not permitted. Multivitamins are permitted. * Organ Function Requirements: Adequate bone marrow, renal, liver, pulmonary, and central nervous system function * All patients and/or their parents or legal guardians must sign a written informed consent. * In the investigator's opinion, patients must have the ability to adhere to or tolerate the dietary protocol. * Patients must be able to eat by mouth or must be willing to have a nasogastric tube (NGT) if gastrostomy tube is not already present. Exclusion Criteria: * Pregnancy * Pregnant or breastfeeding. Female patients of childbearing potential must have negative pregnancy test result within the previous 14 days.. * Sexually active patients of reproductive potential are not eligible unless they have agreed to use an effective contraceptive method for the duration of their study participation. * Other Exclusionary Criteria: Disorder of B-oxidation, as measured by plasma aceyl-carnitine, Uncontrolled infection, History of nephrolithiasis, Diagnosis of diabetes mellitus that is being treated by medication. * The following medications are excluded: Steroids: Therapeutic systemic doses of steroids must be stopped greater than 2 weeks prior to admission to the hospital to start the diet. A steroid washout of 1 week is acceptable for patients with DIPG. Concomitant chemotherapy drugs and homeopathic drugs are not permitted.