Changes in Health-Related Behaviours Among Adults Who Accessed Real-World Weight Management Support: 12-Month Outcomes.

Background Large weight losses are desirable, but their benefits are short-lived without sustained behaviour changes that can be maintained at the household level. This longitudinal study, conducted in a real-life setting, investigated changes in weight, dietary habits, activity levels, and physical and mental well-being of members of a community weight management programme (Slimming World), compared with a matched cross-sectional reference group from the general population. The wider influence on the dietary and activity habits of family members was also explored. Methods  Longitudinal data were collected from members at 0-4 weeks (T1), 3 months (T2), and 12 months (T4) after joining. The reference group completed surveys at each time point. Diet quality scores (NDQS) were calculated using a validated tool, hours of moderate-intensity physical activity were recorded, and mental well-being was assessed using adapted items from the SF Health Survey. Changes in members' behaviours and comparisons with the reference group were analysed using within- and between-group ANOVAs with p-adjusted post-hoc comparisons. Results Of the 1,884 members who provided baseline data, 174 (7.5% male) completed surveys at T1, T2, and T4. At baseline, mean BMI and age were 34.7 ± 7.0 kg/m² and 53.0 ± 12.0 years, respectively. Mean weight change at 12 months was -7.5%. Member NDQS increased from baseline to T1 (11.5 ± 3.2 vs 14.1 ± 2.4, p < 0.001), T2 (14.3 ± 2.7), and T4 (14.1 ± 2.9) (both p < 0.05). Physical activity increased between T1 and T2 (4.6 ± 7.4 vs 6.7 ± 10.1 hours/week, p < 0.01) and was maintained at T4 (6.5 ± 6.0, p < 0.05). At T1, T2, and T4, members had higher NDQS, greater levels of physical activity (p < 0.001), and higher mental well-being scores (p < 0.05) than the reference group. At T2, of the 122 members living with a partner, 79.5% reported influencing their partner to eat healthier meals. Among the 47 members living with children, 66.0% reported influencing them to eat healthier meals. The positive influence on partners' and children's eating behaviours observed at T2 remained stable at T4 (both p > 0.05). At T2, 40.7% of members reported encouraging others in their household to become more active, and this proportion remained consistent at T4 (40.5%, p > 0.05). Conclusion Although the low response rate across all three surveys is a limitation, the findings suggest that Slimming World's behaviour change programme is effective in supporting adults (mainly females) living with obesity to make health-related behaviour changes. Members achieved clinically significant weight loss and improvements in diet quality, physical activity, and mental well-being compared with the reference group. These changes were maintained at 12 months, with an additional positive influence reported on family members' lifestyle habits.