Inclusion Criteria:  Able to speak and read English or Spanish (for patients enrolled at MD Anderson and Mayo Clinic), English or Korean (for patients enrolled at Yonsei), and English or Japanese (for patients enrolled at Keio) Patients with a biopsy-confirmed diagnosis of non-metastatic gastric or GEJ adenocarcinoma, who are scheduled to undergo MIPG or MITG for curative-intention Age ≥ 18  Exclusion Criteria:  Patients with known malabsorption syndromes or a lack of physical integrity of the upper gastrointestinal tract Patients with known narcotic dependence, with average daily dose > 5 mg oral morphine equivalent Subjects deemed unable to comply with study and/or follow-up procedures, at investigators' discretion Patients who are pregnant (since are excluded from receiving standard-of-care MIPG or MITG)