Black and Hispanic adults suffer disproportionately from obesity and obesity-related conditions (e.g., Hispanic/White ratio: diabetes (1.7) compared to their white counterparts. While behavioral weight loss (WL) interventions are the first line in treating obesity, they have mixed outcomes. Most fail to make a persistent impact, especially in specific racial/ethnic subgroups. For example, Black women lose 50% less weight than their white counterparts, even when enrolled in fully powered, well-designed behavioral WL trials. One plausible reason for these sub-optimal results is a focus on behavior change at the individual level alone while neglecting critical social and environmental forces. Social networks have been increasingly shown to influence health behaviors, yet they have seldom been harnessed in studies targeting weight loss, especially among racial/ethnic minorities. In response to PAS-20-160 Small R01s for Clinical Trials Targeting Diseases within the Mission of NIDDK, this application will compare the effects of a social-network enhanced lifestyle intervention (hereafter termed "ROBUST" Reducing OBesity Using Social Ties) to an individual level lifestyle intervention (control) on modifying multiple network-level barriers to weight loss. We will randomly enroll 132 Black or Hispanic adults with obesity (BMI > 30 kg/m2) and invite up to two social network members of participants in the ROBUST arm to a 24 –week multi-competent lifestyle intervention. We will evaluate whether the ROBUST intervention not only addresses individual-level behaviors (i.e., healthy eating, increased physical activity) but also: 1) reduces social undermining as well as changes perceived health norms by activating communal coping - a behavioral process that involves thinking, communicating, and acting as if a health risk (i.e., Type 2 diabetes) is shared; and 2) dampens the harmful effects of increased interpersonal conflict on weight by teaching participants how to induce a positive affect and self-affirming mindset which we have shown in a previous trial (NHLBI-U01HL07843) prevents unwanted weight gain. Participants in the control arm will receive the same number of lifestyle sessions as those randomized to ROBUST. But, their social network will not be directly engaged in the study. We hypothesize that the ROBUST intervention will satisfy all a priori feasibility/acceptability criteria for recruitment, retention, and study conduct. Additionally, the ROBUST intervention will result in positive changes in multiple barriers to behavior change, leading to a more significant proportion of participants experiencing improvements in diet, physical activity, and weight loss at 24 weeks compared to the control group. If proven effective, the preliminary data gathered from this small RO1 will support a fully powered RCT that will result in an optimized multi-level obesity intervention that impacts critical clinical endpoints (i.e., BMI, insulin resistance, and hemoglobin A1...