Lactate and Glycerol Contribution to Gluconeogenesis

Inclusion Criteria for All Subjects 1. Age 40-70 years. 2. The subject is otherwise in general good health, based on medical history and physical examination. Inclusion Criteria for Metabolically Healthy Subjects without Obesity 1. No evidence of T2D or prediabetes as indicated by the American Diabetes Association (ADA), i.e., HbA1c \< 5.7%, fasting glucose \< 100 mg/dL, or use of glucose-lowering medications. 2. Body mass index (BMI) ≤ 24.9 kg/m2. Inclusion Criteria for Metabolically Healthy Subjects with Obesity 1. No evidence of T2D or prediabetes as per ADA criteria. 2. 30.0 ≤ BMI ≤ 45.0 kg/m2. Inclusion Criteria for T2D Subjects 1. Evidence of T2D as indicated by ADA criteria. 2. 6.5% ≤ HbA1c ≤ 8.0%. 3. 30.0 ≤ BMI ≤ 45.0 kg/m2. Exclusion Criteria for All Subjects 1. Chronic medical conditions that may affect glucose metabolism, including active malignancy, tobacco use, HIV infection, kidney failure, liver dysfunction, alcoholism, pancreatitis, active viral/bacterial infection, current pregnancy/lactation, anemia, severe cardiac or respiratory failure, and uncontrolled hyperlipidemia (total cholesterol ≥ 260 mg/dL or triglycerides ≥400 mg/dL). 2. Current medical therapy that affects glucose metabolism such as glucocorticoid, antipsychotic, or oral contraceptive pills. 3. Type 1 diabetes mellitus diagnosis and/or history of diabetic ketoacidosis. 4. Use of weekly glucagon-like peptide-1 (GLP-1) receptor agonist therapy.