Obesity can lead to many serious health conditions, including high blood pressure, diabetes, heart disease, and stroke. It is estimated that more than 65% of adults in the United States are overweight or obese, which is a significant increase over the past two to three decades. Although numerous studies have identified successful programs that help people achieve initial weight loss, few weight loss programs have shown promise for long-term success. Research has shown that a weight loss program in which there is continued contact between the program leader and the participant may improve long-term weight loss outcomes. In addition, a stepped-care approach to weight loss, in which contact between the participant and program leader increases when needed to achieve the next weight loss goal, may be beneficial. This study will examine whether a long-term weight loss program delivered in a stepped-care manner results in greater weight loss than does a standard behavioral weight loss program. Study researchers will also evaluate the cost effectiveness of both programs.

Participants in this 18-month study will be randomly assigned to either a standard behavioral weight loss program or a stepped-care weight loss program. Participants in the standard behavioral weight loss program will attend group meetings once a week for Months 1 to 6, every other week for Months 7 to 12, and once a month for Months 13 to 18. The group meetings will focus on modifying eating habits and physical activity behaviors to improve weight loss. Participants in the stepped-care weight loss program will take part in a combination of treatments, whose timing and intensity will depend on the participants' abilities to achieve predetermined weight loss goals. These treatments may include attending monthly group meetings, receiving weekly weight loss information in the mail, receiving telephone calls from study staff to discuss weight loss behaviors, taking part in individual sessions with study staff to discuss weight loss, and receiving meal replacements (e.g., Slim Fast shakes, meal bars). Participants who do not achieve their weight loss goals at select time points during the study will receive more individual attention from study staff. All participants will follow a diet that focuses on decreasing calories and fat. They will be instructed to follow a walking program 5 days a week and to keep a food and exercise diary. Participants will also have access to a Web site that will include a study calendar and information about how to change eating and exercise behaviors; the use of this Web site is optional.

Study visits will occur at baseline and Months 3, 6, 9, 12, 15, and 18. At each visit, participants' weight and height will be measured, and participants will complete questionnaires about their mood, general health, and exercise and diet habits. At baseline and Months 6, 12, and 18, participants will undergo measurements of blood pressure, fat, muscle, and waist and hip circumferences. Also at these times, physical fitness levels will be measured through a treadmill walking activity, during which an electrocardiogram (ECG) will record heart rate. For 7 consecutive days at baseline and Months 6, 12, and 18, participants will wear an activity monitor to measure physical activity levels.