This is a pilot clinical trial determining the effect of a Methionine-reduced diet on serum levels in subjects with solid tumors. These are subjects who will receive systemic standard of care cancer therapy.

Inclusion Criteria:

• Age: Subjects must be 18 years of age or older.
• Diagnosis: Has a diagnosis of metastatic, recurrent, or unresectable solid tumors.
• Life Expectancy: Subjects must have an expected life expectancy of at least 3 months.
• Performance Status: Subjects must have an ECOG performance status of 0-2.
• Organ Function: Subjects must have adequate organ function, as determined by the investigator through review of standard labs.
• Pregnancy and Contraception: Women of childbearing potential (WOCBP) must have a negative pregnancy test within 7 days prior to study enrollment and must agree to use adequate contraception throughout the study period and for 30 days after the last dose of study treatment. Female patients who are considered not to be of childbearing potential must have a history of being postmenopausal (with a minimum of 1 year without menses), tubal ligation, or hysterectomy.
• Dietary Compliance: Subjects must be willing and able to comply with the methionine-reduced diet as prescribed by the study protocol.
• Informed Consent: Subjects or Legally Authorized Representatives (LAR) must provide written informed consent prior to any study-specific procedures, indicating that they understand the purpose of the study and are willing to comply with its requirements.
• Able to receive systemic standard of care cancer therapy.

Additional criteria specifically for the glioma population:

• Diagnosis: Histopathological proven diagnosis: a) newly diagnosed grade 2-3 glioma or b) all grades for recurrent glioma.
• Treatment: Subjects must be able to receive radiation therapy and/or chemotherapy as a part of their treatment.

Exclusion Criteria:

• Brain Metastases: Subjects with uncontrolled or symptomatic brain metastases. Subjects with brain metastases that have been treated, are asymptomatic, and patients who require steroids are eligible.
• Significant Clinical Illness: Subjects with uncontrolled significant clinical illnesses, including but not limited to: a) Active infections requiring systemic therapy. b) Severe cardiovascular conditions such as recent myocardial infarction (within 6 months), uncontrolled angina, congestive heart failure (NYHA class III or IV), or significant arrhythmias. (c) Uncontrolled diabetes.
• Significant Amino Acid/Metabolic Illnesses: Subjects with severe or inherited illnesses that affect metabolism of amino acids or disrupt nutrient absorption, including but not limited to: a) Severe liver disease, such as cirrhosis or severe hepatic insufficiency, that may have compromised ability to metabolize amino acids. b) Inherited metabolic disorders, such as homocystinuria or other disorders affecting sulfur amino acid metabolism, that may have potential metabolic imbalances. c) Severe gastrointestinal disorders, such as active inflammatory bowel disease (IBD), short bowel syndrome, or other conditions that significantly impair nutrient absorption, that may lead to nutritional deficiencies and gastrointestinal complications.
• Recent Surgery: Major surgery within 4 weeks of randomization (biopsies are acceptable per investigator judgement)
• Concurrent Malignancies: Subjects with another malignancy that requires active treatment during the study period or is expected to interfere with the study intervention.
• Pregnancy or Lactation: Female subjects who are pregnant or breastfeeding.
• Malnutrition: Subjects with severe malnutrition or significant nutritional deficiencies per investigator's discretion.
• Substance Abuse: Subjects with a history of substance abuse or dependency within the past 6 months that, in the opinion of the investigator, would interfere with adherence to study requirements.
• Subjects with chronic kidney disease with advanced stages 3b or higher.
• Psychiatric Disorders: Subjects with psychiatric disorders that would interfere with the ability to give informed consent or adhere to study requirements per investigator judgment.
• Subjects with known allergies or intolerances to low-methionine foods.
• Subjects with any medical or surgical conditions that, in the opinion of the investigator, would make adherence to the methionine-reduced diet unsafe or impractical.