The purpose of this research study is to help us to better understand how leptin regulates blood sugar levels. Leptin is a recently discovered hormone, which is made in fat cells. Leptin is secreted by fat and acts as a signal to the brain to decrease appetite and influences how the body regulates blood sugar levels. A synthetic form of leptin (A-100), an investigational drug and has not yet been approved by the Food and Drug Administration (FDA), will be administered to participants in this study. The expected duration of your participation is 3 study visits, which will be spread over 3-4 weeks.