Fructose Intestinal Gluconeogenesis

Qualified participants will undergo a sugar tolerance test at baseline and then randomized to undergo four separate outpatient tracer/feeding studies in a crossover fashion. After an overnight fast, a six-hour fed tracer study will be initiated, during which participants will consume liquid meals containing stable isotopes at regular intervals and receive other isotopes intravenously. Meal composition will differ only by fructose content (High vs. Low) and tracer (oral vs. intravenous 13C-labeled fructose). Blood and urine samples will be collected frequently throughout the study. Each visit will be performed approximately three weeks apart. Vital signs and anthropometrics will be measured at each clinic visit.