Using self-determination theory to promote physical activity and weight control: a randomized controlled trial in women Marlene N. Silva • Paulo N. Vieira • Sı ´lvia R. Coutinho • Cla´udia S. Minderico • Margarida G. Matos • Luı ´s B. Sardinha • Pedro J. Teixeira Received: May 28, 2009 / Accepted: November 9, 2009 / Published online: December 11, 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Behavior change interventions are effective to the extent that they affect appropriately-measured out- comes, especially in experimental controlled trials. The primary goal of this study was to analyze the impact of a 1-year weight management intervention based on self- determination theory (SDT) on theory-based psychosocial mediators, physical activity/exercise, and body weight and composition. Participants were 239 women (37.6 ± 7.1 years; 31.5 ± 4.1 kg/m 2 ) who received either an inter- vention focused on promoting autonomous forms of exer- cise regulation and intrinsic motivation, or a general health education program (controls). At 12 months, the interven- tion group showed increased weight loss (-7.29%,) and higher levels of physical activity/exercise (+138 ± 26 min/ day of moderate plus vigorous exercise; +2,049 ± 571 steps/day), compared to controls (P \ 0.001). Main inter- vention targets such as more autonomous self-regulation (for treatment and for exercise) and a more autonomous perceived treatment climate revealed large effect sizes (between 0.80 and .96), favoring intervention (P \ 0.001). Results suggest that interventions grounded in SDT can be successfully implemented in the context of weight man- agement, enhancing the internalization of more autono- mous forms of behavioral regulation, and facilitating exercise adherence, while producing clinically-significant weight reduction, when compared to a control condition. Findings are fully consistent with previous studies con- ducted within this theoretical framework in other areas of health behavior change. Keywords Theory-based intervention Á Randomized controlled trial Á Weight management Á Autonomy promotion Á Self-regulation Á Intrinsic motivation Introduction Physical activity and exercise have been positively associ- ated with successful long-term weight control in cross-sec- tional, longitudinal, and retrospective studies (Catenacci and Wyatt 2007), and several major organizations have recommended the addition of 60–90 min per day of mod- erate intensity PA to a dietary intervention to substantially increase the odds of successful long-term weight loss (Saris et al. 2003; Donnelly et al. 2009). Unfortunately, evidence suggests that more than 70% of US adults fail to meet cur- rent PA recommendations (Spiegel and Alving 2005). In Europe, the Eurobarometer (Rutten and Abu-Omar 2004) indicates that although the amount of PA is low, a wide disparity exists (e.g., Northern European countries showing higher levels of physical activity than southern countries) with Portugal reporting the highest percentage (87.8%) of sedentary lifestyles (Varo et al. 2003) and the lowest prev- alence (40.7%) of any PA during leisure time (Martinez- Gonzalez et al. 2001). In the context of long-term weight management, it remains unclear why only about 20% of individuals seeking weight loss are able to successfully integrate PA behaviors into their lifestyles and achieve Clinical Trials.gov number NCT0051308. M. N. Silva (&) Á P. N. Vieira Á S. R. Coutinho Á C. S. Minderico Á M. G. Matos Á L. B. Sardinha Á P. J. Teixeira Faculty of Human Kinetics, Technical University of Lisbon, Estrada da Costa, Cruz Quebrada, 1495-688 Lisbon, Portugal e-mail: mnsilva@fmh.utl.pt 123 J Behav Med (2010) 33:110–122 DOI 10.1007/s10865-009-9239-y