Background Family-Based Treatment (FBT) is the first line of care in paediatric treatment while adult programs focus on individualized models of care. Transition age youth (TAY) with Anorexia Nervosa (AN) are in a unique life stage and between systems of care. As such, they and their caregivers may benefit from specialized, developmentally tailored models of treatment.

Methods The primary purpose of this study was to assess if parental self-efficacy and caregiver accommodation changed in caregivers during the course of FBT-TAY for AN. The secondary aim was to determine if changes in parental self-efficacy and caregiver accommodation contributed to improvements in eating disorder behaviour and weight restoration in the transition age youth with AN. Twenty-six participants (ages 16–22) and 39 caregivers were recruited. Caregivers completed the Parents versus Anorexia Scale and Accommodation and Enabling Scale for Eating Disorders at baseline, end-of-treatment (EOT), and 3 months follow-up.

Results Unbalanced repeated measures designs for parental self-efficacy and caregiver accommodation towards illness behaviours were conducted using generalized estimation equations. Parental self-efficacy increased from baseline to EOT, although not significantly (p = .398). Parental self-efficacy significantly increased from baseline to 3 months post-treatment (p = .002). Caregiver accommodation towards the illness significantly decreased from baseline to EOT (p = 0.0001), but not from baseline to 3 months post-treatment (p = 1.000). Stepwise ordinary least squares regression estimates of eating disorder behaviour and weight restoration did not show that changes in parental-self efficacy and caregiver accommodation predict eating disorder behaviour or weight restoration at EOT or 3 months post-treatment.

Conclusions Our findings demonstrate, albeit preliminary at this stage, that FBT-TAY promotes positive increases in parental self-efficacy and assists caregivers in decreasing their accommodation to illness behaviours for transition age youth with AN. However, changes in the parental factors did not influence changes in eating and weight in the transition age youth.