Metabolic Flux Analysis in Metabolic Dysfunction-Associated Steatotic Liver Disease

Inclusion Criteria: * Scheduled and clinically cleared for protocol-eligible bariatric surgery at Vanderbilt University Medical Center. * BMI ≥40 kg/m², or BMI \>35 kg/m² with at least one obesity-associated comorbidity, such as type 2 diabetes, cardiovascular disease, hypertension, hyperlipidemia, obstructive sleep apnea, MASLD, osteoarthritis, or polycystic ovarian syndrome. * Able and willing to complete study procedures, including informed consent, questionnaires, blood draws, MRI/MRE imaging, stable isotope tracer infusion, and research tissue collection during planned bariatric surgery. * Able to provide informed consent in English. Exclusion Criteria: * Contraindication to MRI/MRE, including implanted cardiac defibrillator, pacemaker, or other MRI-incompatible implanted device. * Prior gastric or intestinal surgery, pancreatic surgery, or other prior surgery that, in the judgment of the study team or bariatric surgeon, would interfere with study procedures or outcome interpretation. * Active cancer or ongoing cancer treatment. * Presence or history of HIV infection. * Alcohol use above study-defined limits: more than 14 alcoholic drinks per week for men or more than 7 alcoholic drinks per week for women, or illicit drug use that would interfere with safe participation or interpretation of study results. * Anemia or other hematologic condition that would increase risk from study blood collection. * Abnormal ECG or clinically significant cardiovascular finding that would increase risk from study procedures. * Impaired renal function or other clinically significant condition that would increase risk from study participation. * Known Wilson's disease, alpha-1 antitrypsin deficiency, hemochromatosis, or other non-MASLD chronic liver disease that would confound interpretation of study outcomes. * Any medical, surgical, or safety condition that, in the judgment of the PI, clinical co-investigator, CRC staff, anesthesia team, or bariatric surgeon, would make participation unsafe or interfere with completion of study procedures.