Eligibility Criteria
Inclusion Criteria:
* Body mass index of 18-25 and 30-45 kg/m2
* Able to understand written and spoken English and/or Spanish
* Fasting euinsulinemia (fasting serum insulin of 4-10 μU/mL) for reference group or hyperinsulinemia (fasting serum insulin ≥ 13 μU/mL) for hyperinsulinemic group on screening labs
* Written informed consent (in English or Spanish) and any locally required authorization (e.g., Health Insurance Portability and Accountability Act) obtained from the participant prior to performing any protocol-related procedures, including screening evaluations.
Exclusion Criteria:
* Unable to provide informed consent in English or Spanish
* Unwillingness to use only bedpan or urinal to void or to refrain from non-emergent mobile device use during the GIST
* Documented weight loss of ≥ 5% of baseline within the previous 6 months
* Systolic blood pressure \< 90 mm Hg or \> 160 mm Hg, and/or
* Diastolic blood pressure \< 60 mm Hg or \> 100 mm Hg
* Abnormal resting heart rate: \< 60 or ≥ 110 bpm
* Sinus brady or tachycardia that has been worked up and considered benign by the recruit's personal physician may be permitted at the PI's discretion
* Abnormal screening electrocardiogram (or if on file, performed within previous 90 d):
* Non-sinus rhythm
* Heart conduction blocks
* Previously unknown ischaemic changes that persist on repeat EKG:
* ST elevations
* T-wave inversions in a vascular distribution
* Hemoglobin A1c ≥ 5.7%, and/or
* Fasting plasma glucose ≥ 100 mg/dL
* Positive qualitative β-hCG (i.e., pregnancy test) in women of childbearing potential
* Positive urine drug screen, except for lawfully prescribed medications and/or marijuana, provided that participant agrees to refrain from marijuana use during the period that they refrain from alcohol.
* Transaminases (AST or ALT) \> 3.0 x the upper limit of normal
* Total bilirubin \> 1.25 x the upper limit of normal
* Abnormal sodium, potassium, chloride, or bicarbonate levels that are considered potentially significant according to the clinical judgment of the PI.
* Creatinine equating to estimated glomerular filtration rate \< 60 mL min-1 1.73 m-2
* Hemoglobin \< 10 g/dL or hematocrit \< 30%
* Platelet count \< 100,000/μL
* Women currently pregnant, measured by serum and/or urine β-hCG
* Women currently breastfeeding
* History of having met any of the American Diabetes Association's definitions of prediabetic state during adulthood or diabetes mellitus (i.e., overt diabetes) at any time:
* Hemoglobin A1c ≥ 5.7%, or rapid rise in documented HbA1c values causing clinical concern for evolving insulin deficiency
* Plasma glucose ≥ 100 mg/dL after 8-h fast
* Plasma glucose of ≥ 140 mg/dL at 2 h after ingestion of a 75-g glucose load
* Random plasma glucose ≥ 200 mg/dL associated with typical hyperglycemic symptoms, diabetic ketoacidosis, or hyperglycemic-hyperosmolar state
* History of gestational diabetes mellitus within the previous 5 years
* Use of most antidiabetic medications within the 30 days prior to screening
* Excluded: thiazolidinediones, sulfonylureas, meglitinides, DPP4 inhibitors, GLP-1 receptor agonists, SGLT2 inhibitors, amylin mimetics, acarbose, insulin
* Metformin is acceptable provided that recruits meet all of the inclusion criteria at screening
* Known, documented history, at the time of screening, of any of the following medical conditions:
* Pancreatic pathology, including but not limited to: Pancreatic neoplasia (unless appropriately evaluated and considered benign and not producing hormones), Chronic pancreatitis, History of acute pancreatitis within the past 5 years
* Cardiovascular diseases (N.B. uncomplicated hypertension is not exclusionary)
* Atherosclerotic cardiovascular disease
* Stable or unstable angina
* Myocardial infarction
* Ischaemic or hemorrhagic stroke
* Peripheral arterial disease (claudication)
* Use of dual antiplatelet therapy (aspirin + P2Y12 inhibitor)
* History of percutaneous coronary intervention
* Heart rhythm abnormalities (non-sinus)
* Congestive heart failure of any New York Heart Association class
* Severe valvular heart disease (e.g., aortic stenosis)
* Pulmonary hypertension
* Chronic kidney disease, Stage 3 or higher (estimated glomerular filtration rate \< 60 mL/min/1.73 m2), of any cause
* Advanced or severe liver disease, including but not limited to:
* Advanced liver fibrosis, as determined by non-invasive testing
* Cirrhosis of any etiology
* Autoimmune hepatitis or other rheumatologic disorder affecting the liver
* Biliopathy (e.g., progressive sclerosing cholangitis, primary biliary cholangitis)
* Hepatocellular carcinoma
* Infiltrative disorders (e.g., sarcoidosis, hemochromatosis, Wilson disease)
* Gallstone disease, including:
* Biliary colic (active)
* History of acute cholecystitis not treated with cholecystectomy
* History of other gallstone complications (e.g., pancreatitis, cholangitis)
* Chronic viral illness (N.B. diagnosis based only on medical history and not by laboratory confirmation)
* Hepatitis B virus (HBV), unless previously successfully eradicated with antiviral drugs that have been discontinued for at least 30 d prior to screening
* Hepatitis C virus (HCV) infection, unless previously successfully eradicated with antiviral drugs that have been discontinued for at least 30 d prior to screening
* Human immunodeficiency virus (HIV) infection
* Active seizure disorder (including controlled with antiepileptic drugs)
* Psychiatric diseases causing functional impairment that:
* Are or have been decompensated within 1 year of screening, and/or
* Require use of anti-dopaminergic antipsychotic drugs associated with significant weight gain/metabolic dysfunction (e.g., clozapine, olanzapine), monoamine oxidase inhibitors, tricyclic antidepressants, or lithium
* Other endocrinopathies:
* Cushing syndrome (okay if considered in remission after treatment, provided that no exogenous corticosteroids or other ongoing treatment are required)
* Adrenal insufficiency
* Primary aldosteronism
* Venous thromboembolic disease (deep vein thrombosis or pulmonary embolism) or any required use of therapeutic anticoagulation
* Bleeding disorders, including due to anticoagulation, or significant anemia
* Active malignancy, or hormonally active benign neoplasm, except allowances for:
* Non-melanoma skin cancer
* Differentiated thyroid cancer (AJCC Stage I only)
* Clinical concern for increased risk of volume overload, including due to medications and/or heart/liver/kidney problems, as listed above
* Clinical concern for increased risk of hypokalemia, including low potassium on screening labs (i.e., below lower limit of normal), use of certain medications, or any medical conditions listed above
* Use of prescribed medications used for any of the indications in the preceding list of excluded conditions, or their use within 30 d prior to screening, except allowances for:
* Use of drugs prescribed for indications other than the exclusionary diagnoses/purposes listed above (e.g., antiepileptic drugs used for non-seizure indications, ACEi/ARB used for uncomplicated hypertension rather than for congestive heart failure, etc.). Note, as above, that antidiabetic drugs except metformin within 30 d of screening are excluded.
* Oral or parenteral corticosteroids (at greater than prednisone 5 mg daily, or equivalent) for more than 3 days within the previous 30 days; topical and inhaled formulations are permitted.
* Beta blockers or non-dihydropyridine calcium channel blockers (verapamil or diltiazem)
* History of certain weight-loss (bariatric) surgery, including:
* Roux-en-Y gastric bypass
* Biliopancreatic diversion
* Restrictive procedures (lap band, sleeve gastrectomy) performed within the past 6 months
* Clinical concern for alcohol overuse, including recent documented history during screening and/or participant report of regularly consuming more t