Implementing a multimodal lifestyle intervention for depression and overweight in primary and secondary care: protocol for an implementation study exploring what works, how, and under what conditions

Depression is a common mental health disorder which frequently co-occurs with increased body mass index or increased waist circumference (hereafter ‘overweight’), causing heightened cardiovascular risk. Unhealthy lifestyle behaviours underlie both conditions. The Multimodal Lifestyle Intervention (MLI) LEEF integrates physical activity, nutrition, and behavioural strategies, tailored to motivational challenges common in depression, offering a dual focus on mental and physical health. However, unpublished process data revealed very limited referral to MLI‑LEEF from both primary and secondary care, and consequently low initiation rates, signalling clear implementation challenges. This study addresses this gap by translating prioritised implementation determinants into conceptually and empirically grounded implementation strategies and examining what works, how, and under which conditions.