Ketogenic Diet in Combination With Standard-of-care Radiation and Temozolomide for Patients With Glioblastoma

Inclusion Criteria: * Adults (age ≥ 18 years) * Newly or recently diagnosed glioblastoma. Patients may enroll in the study from the time of diagnosis (prior to the initiation of standard-of-care chemoradiation) up until the initiation of post-radiation adjuvant chemotherapy (typically approximately 3-4 weeks after the completion of radiation therapy). Overall, this provides a window of approximately 3 months from the time of diagnosis for patients to enroll in this study. No recurrent glioblastoma is allowed on trial. * Being seen for treatment of glioblastoma at Cedars-Sinai Medical Center. Note: Okay if patients receiving chemotherapy or radiation therapy at another facility * Patients on low and managed doses of steroids are permitted. Up to 8 mg dexamethasone or steroid equivalent. Exclusion Criteria: * Karnofsky Performance Status of \<70 as deemed by physician or equivalent * Body Mass Index of \<22 kg/m2 (rounded to nearest integer) * Patients with disorders that affect lipid metabolism such as pyruvate carboxylase deficiency, porphyria, primary carnitine deficiency, carnitine palmitoyltransferase I or II deficiency, carnitine translocase deficiency, Beta-Oxidation Defects * Medical comorbidities that in the opinion of the investigator limits the patient's ability to complete this study * Pregnant, nursing, or implanted with an intrauterine device (IUD) that is not MR compatible * Patients who are vegan or vegetarian will be excluded, as the ketogenic diet includes foods that may interfere with these preferences * Patients on high doses of steroids will be excluded * Patients currently receiving experimental therapeutic therapy will be excluded from the trial. Note: Off-label therapy use is permitted * Inability to adhere to the protocol * Patients with history of allergic reactions to surgical steel or elastomer/rubber are excluded from the activity monitor portion of the study. Because the activity monitor uses a Bluetooth low energy Transceiver, individuals using pacemakers, implantable cardiac defibrillators, neuro-stimulation devices, cochlear implants, hearing aids, or other electronic medical equipment should also be excluded from wearing the activity monitor. They can still use the Aria scale to record weight. * Patients with mechanically, magnetically, or electrically activated implants, such as cardiac pacemakers, neurostimulators, and infusion pumps, that are not magnetic resonance imaging/positron emission tomography (MRI/PET) compatible. * Patients with ferromagnetic implants and ferromagnetic foreign bodies, such as intracranial, aneurysm clips, shrapnel and intraocular metal chips as these could become dislodged. * Patients unable to tolerate MRI/PET imaging secondary to an inability to lie supine or severe claustrophobia as assessed by the treating physician or principal investigator. * Patients unable to lie still, hold their breath, or follow imaging procedure instructions as assessed by the treating physician or PI. * Patients whose most recent renal function test does not meet Cedars-Sinai Medical center standard of care MRI contrast protocol requirements (glomerular filtration rate \<45ml/min). * Patients with a known allergy to Fludeoxyglucose F18 (F18-FDG) radioactive tracer or gadolinium-based contrast agent. * Patients with allergy to animal dander or animal-instigated asthma.