RESUMEN
BACKGROUND: Emerging adults (EAs) ages 18-25 are at high risk for overweight/obesity, but little is known about their motivations for weight loss or how these may differ from those of middle aged adults (MAs) and relate to treatment outcomes. PURPOSE: The purpose of this study was to examine potential differences in weight loss motivations between EAs and MAs and determine the association between motivation and engagement/outcomes in a weight loss trial. METHODS: Data were pooled from two behavioural weight loss interventions: one targeting EAs (n = 52) and one targeting MAs ages 40-60 (n = 101). Motivation, attendance, dietary self-monitoring and weight change were measured in both trials across 3 months of treatment. RESULTS: Emerging adults were less motivated by health concerns than MAs (p < .05). Motivation to lose weight in order to improve appearance was of similar importance for both MAs and EAs but demonstrated differential associations with treatment variables. Appearance-related motivation was associated with higher program engagement for MA but was associated with poorer weight loss for EAs. Overall engagement, weight loss and retention were worse for EAs than MAs (ps < .05). CONCLUSIONS: Specific motivations for weight loss were associated with treatment outcomes, but effects varied by developmental stage. Findings of this study highlight the potential differences between motivation to initiate weight loss efforts and motivation to successfully change weight-related behaviours. Future research should explore methods for intervening directly on motivation within the context of weight control interventions among EAs.