Objective: To explore participation, consistency of demographic and health profiles, and shortterm impacts across six Aboriginal Knockout Health Challenge (KHC) team-based weight loss competitions, 2012 to 2015.Methods: Data comprised one competition each from 2012 and 2013 and two per year in 2014 and 2015. We compared baseline and change (pre-to post-competition) in weight, fruit and vegetable consumption, physical activity and waist circumference (baseline only) across competitions using mixed models.Results: Numbers of teams and participants increased from 2012 to 2015 from 13 and 324 to 33 and 830, respectively. A total of 3,625 participants registered, representing 2,645 unique people (25.4% repeat participation). Participants were mainly female and >90% were classified obese at baseline. Baseline weight and weight lost (between 1.9% and 2.5%) were significantly lower in subsequent competitions compared with the first. Improvements in fruit and vegetable consumption and physical activity were comparable across competitions. Conclusion:The KHC has increasing and sustained appeal among Aboriginal communities, attracting those at risk from lifestyle-associated chronic disease and effectively reducing weight and promoting healthy lifestyles in the short term. Implications for public health:Community-led programs generated by, and responsive to, Aboriginal Australians' needs can demonstrate consistent community reach and sustained program-level lifestyle improvements.

Background: Community-based weight loss programs may have potential to address overweight and obesity at the population level. However, participation patterns and individual outcomes from these programs are understudied. This study examined repeat participation patterns and participant weight change between contests over seven years of an Aboriginal Australian team-based program in order to identify (1) predictors of repeat participation and (2) associations with weight change between contests. Methods: Data for the 12 contests from 2012 to 2018 were merged, with probabilistic record matching. A total of 7510 enrolments were registered for the 12 contests, representing 4438 unique people. Contest lengths varied from 10 to 16 weeks in duration. Non-repeat participants were those who only competed once in the program by the end of 2018, and repeaters were those who competed in at least two contests. Associations between repeat participation and participant baseline (i.e., first participation occasion) characteristics, change in diet and physical activity and percent change in weight during the first participation occasion were examined using crossed random effects (for person and team) regression adjusted for exposure to the program. Weight percentage change between contests was calculated for consecutive participation occasions occurring at least three months apart, converted to percent change per month. Weight change was regressed on number of repeat participation occasions adjusted for age, gender, baseline weight at first participation occasion, and weight percent change in the immediately preceding contest. Results: One-third of the 4433 participants participated more than once, with women more likely than men to repeat. A 1% reduction in weight during a competition was associated with an increase in weight of 0.05% per month between competition end and subsequent participation. Regain was smaller the heavier participants were at their first participation. Conclusions: While individuals benefit from weight loss through program participation, strengthening strategies for weight loss maintenance within or following the program could improve long-term weight outcomes and reduce weight cycling.