On-screen ideals and off-screen ordeals: a daily diary study of the bidirectional links between short-video media use and eating disorder symptoms in college students.

With the rapid proliferation of short-video platforms, concerns about their impact on mental health-particularly eating disorders-have intensified. However, little is known about the bidirectional associations between short-video media use and eating disorder symptoms, or the emotional mechanisms underlying these links. Using an intensive longitudinal design, this study collected daily data over 21 consecutive days from 200 Chinese college students. Multilevel structural equation modeling (MSEM) was employed to examine reciprocal relationships between short-video media use and eating disorder symptoms, as well as the mediating role of negative emotions at both within-person and between-person levels. At the within-person level, short-video media use and eating disorder symptoms demonstrated a mutually reinforcing relationship, with negative emotions mediating this bidirectional association. At the between-person level, both constructs indirectly predicted one another through negative emotions, although direct effects were nonsignificant. These findings suggest a potential self-reinforcing cycle between short-video media use and eating disorder symptoms, highlight the important mediating role of negative emotions, and demonstrate the methodological value of a 21-day daily diary design for capturing the bidirectional associations between these constructs, with practical implications for promoting emotional regulation and healthier digital engagement among college students.