UPDATE trial Stage 2: a pre-post exploratory analysis of a behavioural support intervention to reduce ultra-processed food intake, increase minimally processed food intake, and increase physical activity in adults living with overweight or obesity

Introduction High consumption of ultra-processed foods (UPF) is associated with adverse health outcomes and weight gain. Despite increasing calls for behavioural strategies to reduce UPF intake, no theory-informed intervention targeting UPF reduction has been evaluated in UK adults in alignment with national dietary guidance. We assessed the feasibility, acceptability, and preliminary behavioural and clinical outcomes of a multi-component intervention designed to reduce UPF consumption (and increase physical activity (PA)/minimally processed food (MPF) intake). Methods In this exploratory single-arm pre-post study, adults (N=45) living with overweight or obesity and habitual UPF intake [≥]50% of total energy were offered a 6-month behavioural intervention following a controlled feeding phase (UPDATE trial, stage 1). The intervention was developed using the Behaviour Change Wheel and Capability, Opportunity, Motivation-Behaviour (COM-B) model and included one-to-one sessions with a behavioural scientist, tailored print and digital materials, peer-support meetings, and a moderated group chat. Feasibility outcomes included uptake, retention, and intervention fidelity. Secondary outcomes included COM-B constructs, dietary intake, PA, clinical and self-reported outcomes, and qualitative feedback. Results Uptake was 91% (41/45). Retention at 6 months was 68% (28/41), with 83% (34/41) providing follow-up data (intention-to-treat). Median attendance at one-to-one sessions was 86% (interquartile range (IQR): 57-100) with 56% (23/41) attending all sessions (per-protocol). Fidelity to core behaviour change techniques was high. At 6 months, COM-B scores improved for healthy eating (+7%, standard deviation (SD): 8; p<0.001) and physical activity (+5%, SD: 9; p=0.013). UPF intake decreased by 25% of total energy (95% confidence interval (95%CI): -32, -17), with a corresponding increase in minimally processed foods (+23%; 95%CI: 17, 29). Vigorous physical activity increased (+60 min/week, IQR: 0-180), weekday sitting time decreased (-61 min/day, SD: 110), and weight reduced by 3.8 kg (IQR: -8.5-1.0; p=0.001). Findings were similar in per-protocol analyses. Qualitative data indicated perceived improvements in wellbeing and habit formation. Conclusion This theory-informed intervention demonstrated good feasibility and acceptability and was associated with improvements in targeted behavioural mechanisms and health-related outcomes. A randomised controlled pilot trial is warranted to evaluate effectiveness and refine implementation.