 Specific Aims Over 50 of Americans are overweight. These individuals are at increased risk of morbidity and mortality. Weight losses of 5-10 of body weight have been shown to lower these risks. The majority of individuals who lose weight do so on their own, without the help of formal programs. Developing ways to improve weight loss in such individuals is a major public health challenge. We believe that the Internet holds tremendous promise for reaching large numbers of overweight individuals and assisting them in their weight loss efforts. Our previous research has shown that a structured behavioral weight loss program offered via the Internet, with regular feedback from a therapist, can produce average weight losses of 9 lbs. at 6 months. The purpose of this project is to compare the weight losses achieved at 6 months using 3 different types of Internet programs, all of which are used in combination with SlimFast as the dietary component.Subject PopulationTwo hundred twenty-five overweight individuals will be recruited, aged 20-65 with a BMI of 27-40 who want to lose weight using SlimFast. Participants must be willing to attend an initial orientation and weigh-in session and follow-up weigh-in sessions and agree that they will not begin a second weight loss program within the next 12 months. Interested participants will be required to have access to a computer with Internet connection from their home or their workplace.MethodsDesignParticipants will be randomly assigned to one of three conditions: 1 SlimFast Current SlimFast Website; 2 SlimFast Current SlimFast Website Computer-Generated E-mail feedback; or 3 SlimFast Current SlimFast Website Therapist-Assisted E-mail feedback. All 3 groups will be placed on a calorie-restricted diet 1200-1500 kcalday that utilizes SlimFast for 2 meals per day and a healthy evening meal. They will be encouraged to increase their exercise to 1000 kcalweek based on walking. Group 1 will receive all other input from the SlimFast website. Group 2 will receive weekly computer-generated feedback based on diet, physical activity and weight loss information. Group 3 will receive weekly e-mail messages from a trained therapist that will provide feedback based on diet, physical activity and weight loss information.Data AnalysisAll participants will be weighed at baseline, 3 months, and 6 months to document the weight changes they experience. The primary analysis will compare weight change from baseline to 6 months for the 3 conditions. An intent-to-treat analysis will be used, where dropouts are considered to have regained back to baseline weight. Secondary analyses will examine baseline predictors of weight loss and the association between use of the various Internet components and outcome. 