Volunteers will be screened and admitted to our inpatient clinical research unit. They will undergo baseline measurements of glucose tolerance, food intake and energy expenditure in a whole room indirect calorimeter. After randomization to active drug or placebo, these measurements will be repeated. After the baseline admission, volunteers will be followed as outpatients initially on a weekly basis (for one month), followed by a monthly basis for another 5 months. Volunteers will then be readmitted for repeat measurements of food intake. All volunteers will then have the option of open label use of exenatide for another 6 months during which time they will again be followed monthly. The study is currently recruiting volunteers. Publications to date: None