Self-Efficacy in Weight Loss Treatment

This randomized clinical trial of weight loss treatment will examine if adding personalized, one-on-one treatment session to standard behavioral group treatment will result in greater weight loss, less weight regain after weight loss, and better adherence to the treatment protocol. Everyone who enrolls in the study will receive information on healthy eating, how to increase their physical activity and develop healthy exercise habits and ways to change their eating so that they will lose weight. This information will be provided at evening group sessions. There will be a total of 20 group meetings over an 18-month period that will be held: * every week during the first month of the study, * every other week for the second month * once a month for months 3-12 * every 6 weeks for months 13-18 Participants in the self-efficacy group will also be asked to participate in one-on-one lifestyle counseling sessions with a study interventionist throughout the study. Everyone will be asked to complete questionnaires, two 24-hour dietary recalls over the phone, and have blood tests done every six months (at the beginning of the study, at 6, 12, and 18 months) a total of 4 times for the study.