In the morning, subjects will return to the Substrate Metabolism Laboratory. The research team will collect a blood sample from the subject's hand or forearm and a small sample of fat tissue in the subject's abdomen with a needle. Next, subjects will exercise on a treadmill at a moderate intensity for about 1 hour. Immediately after exercising the research team will collect a second blood sample. Subjects will remain in the laboratory for 1 hour after exercising, and then the research team will collect another blood and fat tissue sample. Upon completion of the experimental trial, subjects will be provided a snack before leaving the laboratory.