Primary Objective is to determine the feasibility (safety and tolerability) of a strict classic ketogenic diet among a population of children with recurrent or progressive and refractory brain tumors.

Secondary Objectives are: (1) to determine the objective response rate (complete response + partial response) to a strict classic ketogenic diet among children with recurrent or progressive and refractory brain tumor; (2) to estimate the time interval to tumor progression (Progression-Free Survival), time to treatment failure (Event-Free Survival), and time to death (Overall Survival) after initiation of a strict classic ketogenic diet among a group of pediatric patients with recurrent or progressive and refractory brain tumors; and (3) to describe and characterize tolerability and toxicities from a strict classic ketogenic diet among children with recurrent or progressive and refractory brain tumors.

Exploratory Objective: Identify biomarker correlates, including MR spectroscopy and metabolites of tumor response to a strict classic ketogenic diet.

• Recurrent Brain Tumor, Childhood
• Ketogenic Diet

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.