Supplementary Material for: Biofeedback and Training of Interoceptive Insight and Metacognitive Efficacy Beliefs (InMe) to Improve Adaptive Interoception: A Subclinical Randomised Controlled Trial

Introduction
Interoception, the sensing, awareness and regulation of physiological states, is crucial for wellbeing and mental health. Behavioural interventions targeting interoception exist, but Randomised Control Trials (RCTs) testing efficacy remain limited. The present, preregistered (ISRCTN16762367) RCT tested the novel Interoceptive iNsight and Metacognitive Efficacy beliefs (InMe) intervention. InMe uses slow-breathing and cardiac biofeedback during stress to train interoceptive self-efficacy beliefs and improve self-reported interoception.
Methods
Healthy participants aged 18-30 years with low self-reported interoception were randomly assigned (1:1) to the InMe intervention (n=50) or an active control (guided imagery; n=52). Participants blinded to allocation were stratified by gender and disordered eating. Assessments included baseline (T0), post-intervention (T1), and 7-8 weeks post-intervention (T2). The primary outcome was the “Adaptive Interoception” factor of the Multidimensional Assessment of Interoceptive Awareness questionnaire.
Results
Both arms improved in the primary outcome at T1 (InMe:adjusted M difference=5.76; 95%CI[-0.03;11.56], p=0.05; Control:adjusted M difference=7.90; 95%CI[1.92;13.87], p=0.002; Marginal R2=0.09). However, only InMe sustained this improvement at T2 (InMe:adjusted M difference=9.25, 95%CI[3.37;15.13], p<0.001; Control:adjusted M difference=2.94, 95%CI[-3.07; 8.96], p=0.72), as indicated by a significant Time*Arm interaction (b=6.31; SE=2.92, 95%CI[0.56;12.05], p<0.03; Marginal R2=0.12). Secondary outcomes showed a reduction in disordered eating scores across both arms at both time points (T1:b=-1.44, SE=0.37, 95%CI[-2.17;-0.71], p<0.001; T2: b=-1.05, SE=0.37, 95%CI[-1.79; -0.32], p=0.005).
Conclusion
The InMe intervention selectively improved self-reported interoception at follow-up but did not outperform the Control for secondary outcomes. Future research should explore its efficacy in clinical populations alongside complementary therapies.