The healthy body image (HBI) intervention: Effects of a school-based cluster-randomized controlled trial with 12-months follow-up

grade boys (43%) and girls (mean age 16.8 years) from 30 high schools participated in a cluster-randomized controlled study with the HBI intervention and a control condition as the study arms. Data were collected at baseline, post-intervention, 3- and 12-months follow-up, and analysed using linear mixed regression models. The HBI intervention caused a favourable immediate change in positive embodiment and health-related quality of life among intervention girls, which was maintained at follow-up. Among intervention boys, however, weak post-intervention effects on embodiment and health-related quality of life vanished at the follow-ups. Future studies should address steps to make the HBI intervention more relevant for boys as well as determine whether the number of workshops or themes may be shortened to ease implementation and to enhance intervention effects.