ABSTRACT In the United States, approximately 43 % of adult men are affected by obesity (body mass index (BMI)>30 kg/m2). In 2017, heart disease, cancer, chronic lower respiratory disease, and stroke were among the top five causes of mortality among men, each associated with obesity.2 To improve or reduce risk factors associated with these conditions, modest weight loss of 5-10% is often prescribed through behavioral weight loss interventions. Yet, despite obesity-linked mortality among men, male participation in weight loss interventions (27%) is considerably low. Preliminary data have shown that when Black men do participate in weight loss interventions, alone and with their spouses, they experience successful weight loss. However, the motivations, behaviors and strategies associated with successful weight loss are not well understood nor studied among men across racial/ethnic groups. Identifying these motivations, behaviors and strategies is essential to increase participation in weight loss interventions as well as to improve weight loss strategies for men. Behaviors associated with weight loss and weight maintenance are influenced by individual, social and environmental factors. Understanding the social and environmental factors and their interactions has been understudied when compared to individual level factors. For men, it is suggested that family plays a role because behaviors associated with weight loss and weight maintenance typically occur within the family behavioral context. Women are often tasked with the responsibility of directing the home environment and family behaviors, especially regarding the purchasing of food and preparation of meals. As a result, weight loss interventions typically target women. This approach fails to address the influence male members in the family have on weight and weight related behaviors not only for themselves but other family members within the household. Gaining insight into how the family behavioral context and family interactions influence behavior will be important in designing family centered weight loss intervention where the male is the index partner. Our long-term goal is to develop weight loss interventions designed specifically for men that lead to weight loss maintained over time among themselves and family members. Using a mixed methods approach, the proposed supplemental research will identify the factors associated with successful weight loss among men in a family behavior context in the weight loss phase of the DELISH study. DELISH is a weight loss intervention testing the efficacy of a Mediterranean-style dietary pattern, adapted for a southeastern United States population, enrolling at least 40% males to address the low male participation in weight loss studies. The central hypothesis is that specific social factors related tofamily dynamics and functioning are associated with weight loss among men. Our aim is to learn more about these factors to inform future interventions.