Background: 'Fat Talk', or the act of negatively discussing one's own or another person's body, is linked to body image constructs, body dissatisfaction, low self-esteem and disordered eating. The spaces in which young women talk about the body are changing, as social media use escalates. Understanding the interplay between social media use, body image and fat talk, in different contexts, is needed. Method: Focus group interviews were used to explore how young women (aged 15-19) experience fat talk while using social media and the possible effect on body image constructs. Using purposive convenience sampling, young women who regularly used social media and were living in an inner city of England were recruited. Thematic analysis was used for analysis and six themes were identified, both a priori and inductively, to explore the interplay between them. Findings: Over 35 women were successfully recruited into the study, with 18 of these finally participating in focus group interviews. Among participants, social media use was linked to increased self-evaluation of the body, engagement in social comparative behaviour and negative self-talk about the body. Although fat talk was reportedly common and widespread, it was unacceptable in the online space. However, body talk, other than size or shape, was permissible. Conclusion: Fat talk can be divisive; however, if it becomes unacceptable in the online space, negative self-talk may increase. If fat talk is replaced by an all-encompassing 'body talk', then this too may exacerbate existing pressures on young people and their mental health and well-being. Understanding the relationship between social media, body dissatisfaction and body talk may provide new opportunities for health education to promote a more constructive prevention discourse of the body, including body talk, in or around the online space.