The Effects of Exenatide (Byetta ) on Energy Expenditure and Weight Loss in Nondiabetic Obese Subjects

* INCLUSION CRITERIA: * Premenopausal women and men \< 55 years of age * BMI \>30 kg/m(2) * Expressed desire for weight loss * Stable weight (variation \< 2.3 kg within past 6 months) * Ability to provide informed consent * Ability to follow verbal and written instructions * Nonsmoker * Ability to commute to study site on a regular basis for short outpatient visits over 5 weeks * For females, use of a medically approved form of contraception. For oral contraceptives, subjects will need to be on an established dose for at least 3 months to ensure stable weight and will be asked not to switch contraceptive methods during study participation. EXCLUSION CRITERIA: * Age \< 18 years * Use of other medications to treat obesity including medications obtained over the counter or internet, orlistat (Xenical, Alli), sibutramine (Meridia), topiramate (with or without phentermine (Qsymia), phentermine (Adipex P) or lorcaserin (Belviq) within the past 6 months * History of an eating disorder including anorexia or bulimia * History of surgery for the treatment of obesity (gastric banding, gastric bypass) * Diagnosis of type 1 or type 2 diabetes mellitus according to American Diabetes Association guidelines * Previous exposure to exenatide * Uncontrolled hypertension as defined by a blood pressure of 150/90 on two or more occasions or use of antihypertensive medications which may affect energy expenditure including alpha blockers, beta blockers, angiotensin receptor blockers or inhibitors of angiotensin converting enzyme * Current use of tobacco products, marijuana, amphetamines, cocaine or intravenous drug use * Chronic ethanol use (\> 3 drinks /day) * Endocrine disorders including hypo or hyperthyroidism (including subclinical disease), Cushing s disease, growth hormone deficiency or other pituitary diseases * History of pancreatitis * Personal or family history of multiple endocrine neoplasia (MEN)-2 or medullary thyroid cancer * History of unresolved gallstones * Hyperamylasemia * Fasting triglyceride level greater than or equal to 500 * Gastroparesis * Inflammatory bowel disease or malabsorption disorders * Malignancy treated with chemotherapy or radiation within the past 5 years * Current clinical depression, diagnosis of psychosis or recent use of psychotropic medication * Pregnancy within past 6 months * Breastfeeding * Failure to use medically approved contraceptive methods if subject is female * Liver function abnormalities (transaminases greater than twice normal) * Renal insufficiency (creatinine clearance \< 50 ml/min) * History of chronic infection including tuberculosis, coccidiomycoses, lyme disease or HIV infection * Pulmonary disorders, including chronic obstructive pulmonary disease, which would limit ability to follow the protocol (investigator judgment) * Cardiovascular disease including history of myocardial infarction, unstable angina or heart failure * Central nervous system disease, including history of cerebrovascular accidents, dementia, and neurodegenerative disorders * Weight \<450 pounds (maximum weight of the DXA machine as per manufacturer s manual) * Sensitivity to exenatide or any inert components in its formulation * Sensitivity to acetaminophen * Conditions not specifically mentioned above may serve as criteria for exclusion at the discretion of the investigators