Approximately 2.5 hours after admission, the study team will begin the tracer-labeled fat infusion. The tracer-labeled fats the study team are infusing occur naturally in the body. By injecting a slightly greater amount of this substance than what is already in the body the study team will be able to measure the rate of fat breakdown and fat burning. After about 50 minutes of the infusion, three blood samples will be obtained in 5 min intervals.