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• Research objectivesThe aim of this work is to understand the phenomenon of emotional acculturation and its role in the behavior of brand culture diffusion by members of a brand community.• MethodologyAn ethnographic study was carried out. The researcher integrated three WeightWatchers communities over a 12-month period. The material was drawn from observation, interviews and autoethnography.• ResultsThe study highlights a process of emotional acculturation during integration into and evolution within a brand community. This process reveals four fundamental emotions: authentic pride, hubristic pride, shame, and fear. These emotions generate different brand culture dissemination behaviors: displaying, claiming, denying, or confessing.• Conceptual and managerial implicationsThe results suggest a range of actions at individual and collective level to help people deal with their emotions more effectively. At the individual level, the facilitator can, through their community, relieve shame, frame hubristic pride, make authentic pride visible and reduce fear. On a collective level, the marketing manager must share micro-cultures (inter-group exchanges) and build a new reward system for the most acculturated members.• OriginalityWhile marketing studies focus on brand acculturation, this research is the first to look at emotional acculturation to brand culture. Unlike previous studies, it identifies individual diffusion mechanisms specific to each stage of emotional acculturation to the brand.