Effects of RM-493 on Energy Expenditure in Obese Individuals

Background: \- RM-493 is a drug that stimulates parts of the brain that control eating and metabolism. It has helped to reduce body weight and improve insulin sensitivity in lab tests. However, it is not fully known whether RM-493 causes weight loss by just decreasing appetite or by increasing metabolism or both. Researchers want to see how RM-493 affects metabolism and hormones that affect the metabolic rate. They also want to see how RM-493 affects appetite by assessing feelings of hunger and fullness. They will study this drug in people who are obese but are otherwise in good health. Objectives: \- To see how RM-493 affects metabolic rate and appetite in obese but otherwise healthy individuals. Eligibility: \- Individuals between 18 and 50 years old who are obese (body mass index between 30 and 40 kg/m2) but are otherwise healthy. Design: * The study consists of three phases. The first phase is the screening visit. The second phase is an 8-day inpatient stay. The final phase is a follow-up phone call one week after the end of the second phase. * Participants will be divided into two groups. One group will receive the study drug first, followed by a placebo. The other group will receive the placebo followed by the study drug. The study drug and placebo will be given under the skin for 3 days each by a small device (OmniPod) that normally is used to give insulin to people with diabetes. * Participants will be screened with a physical exam and medical history. Blood and urine samples will be collected. They will also meet with a dietitian. The OmniPod device will be demonstrated before use. * Participants will have the following procedures during their 8-day inpatient stay: * Daily exercise routine (walking on treadmill) after setting a comfortable pace (miles per hour) during an exercise test * Wear physical activity monitors * Body composition study to measure amounts of fat and muscle * Calorie controlled study diet * Study drug/placebo dose through the Om