Body-positive content is prevalent on social networking sites (SNS). Research shows that engagement with body positive content reduces aspects of negative body image and increases aspects of positive body image. However, the mechanisms accounting for the impact of body-positive content on body image are not well understood. In this study, we used the tripartite influence model (Thompson et al., 1999) and acceptance model of intuitive eating (Avalos & Tylka, 2006) to examine how engagement with appearance-ideal and body-positive content on Instagram relates to aspects of negative and positive body image. Structural equation modelling of cross-sectional data from 454 female participants (Mage = 22.65) revealed that engagement with appearance-ideal content was indirectly associated with (higher) negative and (lower) positive body image through lower internal body orientation and body acceptance by others, and (in case of negative body image) through higher thin-ideal internalisation. Engagement with body-positive content predicted (higher) positive body image but not negative body image; appearance comparison, thin-ideal internalisation, internal body orientation, and body acceptance by others did not mediate this effect. These findings illustrate the value of combining elements of the tripartite influence model and acceptance model of intuitive eating to understand the relationship between SNS and body image.