The purpose of this study is to evaluate the effectiveness of a technology-based system (the Body Media FIT system) for enhancing weight loss in severely obese individuals (BMI: ≥ 40 kg/m2). The investigators will compare two 6-month interventions: 1) a standard behavioral weight loss program (SBT) and 2) a standard behavioral weight loss program plus the use of the Body Media FIT system (SBT+FIT). The Body Media® FIT system is a novel weight loss tool consisting of an armband that measures energy expenditure, a digital display watch that provides "real time" physical activity and energy expenditure feedback, and access to a system website which allows individuals to track their food intake and set exercise and dietary goals. We will examine differences in physical activity, weight loss, and program adherence between groups.