PROJECT SUMMARY Despite widespread efforts to implement lifestyle interventions aimed at restricting energy intake and increasing physical activity, weight loss success has been limited and obesity prevalence continues to rise. Thus, there is a critical need to develop novel strategies to prevent obesity and related cardiometabolic risks. Short sleep duration is a highly prevalent behavior and is strongly associated with obesity risk among young adults. Experimental laboratory evidence indicates that short sleep duration may increase obesity risk primarily through food-seeking behavior and overeating. We have recently demonstrated that short-term sleep extension in real- life settings in young adults with habitual short sleep reduces energy intake by a significant amount, and thus might be a potent strategy to improve weight loss outcomes in lifestyle interventions with calorie-restricting diets. To our knowledge, no prior weight loss intervention trial specifically examined the effects of extending sleep duration on weight loss outcomes in young adults. We, thus, propose a randomized clinical trial to determine whether weight loss outcomes in lifestyle interventions can be improved by adding an intervention component to extend sleep duration in overweight young adults with habitual short sleep duration. Overweight young adults who habitually sleep <6.5 hours will be randomized to either a lifestyle intervention alone (diet and activity counseling) or a lifestyle plus sleep intervention (diet, activity, and sleep counseling). All participants will receive a technology-supported intensive lifestyle intervention for weight loss with biweekly remote coaching for 6 months (Intervention). Participants assigned to lifestyle plus sleep intervention will also receive individualized sleep counseling to extend sleep duration, proven successful in our prior work, and tailored feedback. Participants will continue their assigned intervention for an additional 6 months without frequent contact (Maintenance). Sleep will be objectively assessed by accelerometry. Participants will self-monitor their diet (record all dietary intake into a custom smartphone app), physical activity (by accelerometry), and self-weigh daily on a wireless scale. Our specific aims are to determine whether lifestyle plus sleep intervention produces a greater weight loss (Aim1) and a greater reduction in objectively assessed (using doubly labeled water/energy balance method) energy intake (Aim2), as compared with lifestyle intervention alone. We will compare the change in weight (primary outcome) and energy intake (secondary outcome) at 6 months between groups. We will collect additional data on behavioral, biological, and psychosocial factors to explore their effects on intervention responses and generate novel insights. Weight change at 12 months (end maintenance) will be an exploratory outcome. If effective, data from this trial would strongly support incorporating sleep interventions ...