GLAD-KE GLioma Biomarker and Safety Assessment During Dietary Ketone Elevation Subtitle: A Surgical Biomarker Discovery Study of Ketogenic Therapy in Recurrent Glioma

This study is being done to see if a Ketogenic Diet (KD) or short-term Ketone supplement (KS) is feasible and safe for patients with recurrent Glioma who are undergoing a clinically indicated surgery.

Inclusion Criteria: * Histopathologic diagnosis of a glioma that has received prior irradiation and is presumed recurrent. * Clinical indication for open biopsy or surgical resection. * On MRI, a 2x2x2 cm enhancement absent of bleed, calcification, or other features that can obscure MRS signal. * Karnofsky performance status ≥ 70. * Age \> 18 years. * Willing to submit archival tumor sample if available. * Patients must have the following organ and marrow function: * Absolute neutrophil count \>1,000/mcL * Total bilirubin \< 1.5 x institutional upper limit of normal (ULN) OR total bilirubin \>1.5 × ULN with direct bilirubin \< 1.5 × ULN; * AST (SGOT) and ALT (SGPT) \< 2.5 x institutional ULN * PT or PTT \< 1.5 x institutional ULN * Estimated glomerular filtration rate (eGFR) ≥ 50 mL/min/1.73 m2 calculated by the CKD-EPI equation * Patients must be maintained on a stable or decreasing dose of systemic corticosteroid regimen of dexamethasone \< 4mg (no increase for 5 days) prior to start of study intervention (Day 1). Topical and inhaled steroid treatment is allowed. * Patient must be able to provide written informed consent. * Female participants of childbearing potential must have a negative serum pregnancy test prior to study start. * Patients who have received prior ketogenic therapy (including supplements and diet) may enroll, but must have stopped prior therapy ≥ 7 days prior to day 1. * Patient willing to minimize carbohydrate-containing medications. Exclusion Criteria: * Patients with a history of a metabolic disorder including documented defect in urea metabolism (including documented history of gout), carnitine deficiency (primary carnitine deficiency, carnitine palmitoyl transferase I or II deficiency, carnitine translocase deficiency), fatty acid metabolism, beta-oxidation defects, pyruvate carboxylase deficiency, mitochondrial function, porphyria, or treatment refractory nephrolithiasis. * Active uncontrolled infection. * BMI \< 20.0. * Active bowel obstruction, ileus, or active or remote pancreatitis, known gastroparesis/delayed gastric emptying. * Known history of clinically significant heart failure (NYHA \>2), recent myocardial infarction, or symptomatic atrial fibrillation. * Diabetes mellitus, defined as HbA1c ≥6.5% or use of medications to treat diabetes (note, use of medications for weight loss that have been FDA approved for diabetes is acceptable) * Conditions that may increase the risk of study intervention or significantly reduce compliance (i.e. cognitive impairment, frank dementia, etc.). * Other concurrent experimental therapies. * Food restrictions that would limit study diet adherence. * Contraindication to receiving an MRI (cardiac pacemaker, insulin pumps, non-MRI-compatible stents/clips/plates/rods, non-removable glucose monitor, other non-removable ferromagnetic objects in the body, etc.).