Background: Adults with intellectual disabilities (ID) are susceptible to multiple health risk behaviours such as alcohol consumption, smoking, low physical activity, sedentary behaviour, and poor diet. Lifestyle modification interventions can prevent or reduce negative health consequences caused by these behaviours. We aim to determine the effectiveness of lifestyle modification interventions and their components in targeting health risk behaviours in adults with IDs. Methods: A systematic review and meta-analysis were conducted. Electronic databases, clinical trial registries, grey literature, and citations of systematic reviews and included studies were searched in January 2021 (updated February 2022). Randomised controlled trials and non-randomised controlled trials targeting alcohol consumption, smoking, low physical activity, sedentary behaviours, and poor diet in adults (aged≥18 years) with ID were included. Meta-analysis was conducted at the intervention-level (pairwise and network meta-analysis) and the component-level (component network meta-analysis). Studies were coded using Michie’s 19-item theory coding scheme and 94-item behaviour change taxonomies. Risk of bias was assessed using the Cochrane Collaboration's Risk of Bias Assessment Tool (RoB Version 2) for RCTs and Risk of Bias in Non-randomised Studies - of Interventions (ROBINS-I) tool for non-RCTs. The study involved a Patient and Public Involvement (PPI) group, including people with lived experience, who contributed extensively by shaping the methodology, providing valuable insights in interpreting results, and organising of dissemination events. Results: Our literature search identified 12,180 articles, of which 80 studies with 4,805 participants were included in the review. The complexity of lifestyle modification intervention was dismantled by identifying six core components that influenced outcomes. Interventions targeting single or multiple health risk behaviours could have a single or combination of multiple core-components. Interventions (2 RCTS; 4 non-RCTs; 228 participants) targeting alcohol consumption and smoking behaviour were effective but based on limited evidence. Similarly, interventions targeting low physical activity only (16 RCTs; 17 non-RCTs; 1413 participants) or multiple behaviours (low physical activity only, sedentary behaviours, and poor diet) (17 RCTs; 24 non-RCTs; 3164 participants) yielded mixed effectiveness in outcomes. Most interventions targeting low physical activity only and multiple behaviours generated positive effects on various outcomes, while some interventions led to no change or worsened outcomes which could be attributed to the presence of a single core component or a combination of similar core components in interventions. The intervention-level meta-analysis for weight management outcomes showed that none of the interventions were associated with a statistically significant change in outcomes when compared to treatment-as-usual. Interventions with core-components combination of energy deficit diet, aerobic exercise and behaviour change techniques showed the highest weight loss (MD=-3.61,95% CrI -9.68 – 1.95) and those with core-components combination dietary advice and aerobic exercise showed a weight gain (MD 0.94, 95% CrI -3.93 to 4.91). Similar findings were found with the components network meta-analysis for which additional components were identified. Studies had a high and moderate risk of bias. Various theories and behaviour change techniques were used in intervention development and adaptation. Conclusion: Our systematic review is the first to comprehensively explore lifestyle modification interventions targeting a range of single and multiple health risk behaviours in adults with ID, co-produced with people with lived experience. It has practical implications for future research as it highlights the importance of mixed-methods research in understanding lifestyle modification interventions and the need for population-specific improvements in the field (e.g., tailored interventions, development of evaluation instruments or tools, use of rigorous research methodologies, and comprehensive reporting frameworks). Wide dissemination of related knowledge and the involvement of PPI groups, including people with lived experience, will help future researchers design interventions that consider the unique needs, desires, and abilities of people with ID.
ORCID: 
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)