Purpose <p>Currently, there is a growing awareness among individuals about health and nutrition. Therefore, it is important to comprehend the factors that influence eating habits and attitudes. This study aims to investigate the potential mediation effect of eating attitudes in the relationship between social media use and well-being, as well as to explore whether the moderating effect of the level of orthorexia nervosa influences this relationship.</p> Methods <p>The sample consisted of 599 adults (<i>M</i>_age = 29.82, <i>SD</i> = 9.39; 68% female) from Turkey and Northern Cyprus. Participants were recruited via convenience sampling through university networks, reflecting a culturally diverse context rooted in Mediterranean and Middle Eastern dietary norms. The study used the Social Media Usage Purposes, Eating Attitudes Test Short Form, Orthorexia nervosa Questionnaire-11, and the WHO-Five Well-being Index. A cross-sectional design was employed, and data were analysed using Hayes’ Process Macro (Model 58) to test for moderated mediation.</p> Results <p>The study found that eating attitudes played a partial mediating role in the relationship between social media use and well-being among adults. Social media use positively predicted eating attitudes (<i>β</i> = .83, <i>p</i> &lt; .001) and well-being (<i>β</i> = 1.05, <i>p</i> &lt; .05), and eating attitudes significantly predicted well-being (<i>β</i> = .94, <i>p</i> &lt; .001). Also, orthorexia nervosa moderated the mediating effect of eating attitudes in the relationship between social media use and well-being. Interestingly, the moderating effect was stronger among individuals with low levels of orthorexia nervosa, contrary to initial expectations.</p> Conclusions <p>The current study suggests that eating attitudes are a key behavioral mechanism linking social media use and well-being, and this pathway is influenced by individuals’ orthorexia nervosa tendencies. These findings could aid in the development of interventions for eating disorders at both clinical and social levels and guide individuals towards healthier lifestyles. Importantly, while orthorexia nervosa moderated the indirect relationship between social media use and well-being, the study did not find a direct association between orthorexia nervosa and social media use.</p> Level of evidence <p>Level III. Evidence obtained from well-designed cohort or case–control analytic studies.</p>