The purpose of this study is to analyse if a multidisciplinary approach including peers is effective in the treatment of obesity in adolescence.

One in every 3 Portuguese adolescents is overweight (14% obese) (ONOCOP, 2009). Several institutions state that prevention is of upmost importance to deal with this epidemic (Council on Sports Medicine and Fitness; Council on School Health, 2006, August et al, 2008, Kohn et al, 2006), but public health stakeholders should also increase their efforts to treat those who already have excessive weight (Oude Luttikhuis et al, 2009). Several facts support this need, namely that obesity in adolescence: a) has a significant impact on both physical and psychosocial health (Lobstein et al, 2004); b) is an independent risk factor for adult obesity (Singh et al, 2008); c) is an independent risk factor for all cause mortality in adulthood - a more powerful predictor than being overweight in adult (Must et al, 1992); and d) is a major threat to the steady rise in life expectancy that occurred during the past two centuries (Olshansky et al, 2005).

Albeit this cumulative knowledge, treatment options remain elusive. A Cochrane review (Oude Luttikhuis et al, 2009) concluded that combined behavioral lifestyle interventions, when compared to standard care or self-help, provide significant and clinically meaningful reductions on weight in adolescents; and that the interventions should consider psychosocial determinants for behavior change and strategies to improve clinician-family interaction, in order to improve the desired outcomes.

The team of the TOP project has been working in this subject since 2004: the consult for obese adolescents of the Hospital de Santa Maria (HSM), a result of the collaboration between the two proponent Institutions. This has allowed the inclusion of exercise specialists in the obese adolescent' consult of the HSM, leading to an unusual (Fonseca et al, 2008), but surely necessary (Barlow et al, 2007), multidisciplinary program where, in the same Unit, adolescents are evaluated and receive medical, dietary and physical activity counselling. In compliance with the latest recommendations (Oude Luttikhuis et al, 2009), we use behavior change techniques directed not only to the adolescent but also to their parents, using the self-determination theory (SDT) rationale and motivational interviewing techniques (Teixeira et al, 2012), a treatment protocol that has been recognized by the Society for Adolescent Medicine (Fonseca et al, 2010).

Based on our previous experience and on recent literature that claims for the inclusion of peers as co-adjuvant on the weight management tasks, we hypothesize that: a) a larger and more frequent contact with the treatment staff; and b) the inclusion of peers as co-adjuvant on the weight management tasks in the TOP is necessary. Indeed, literature shows that adolescent' health related behaviors are associated with peer behaviors, in what Dishion named Social Contagion (Dishion & Dodge, 2005). Additionally, we think that regular physical activity (PA) and interactive educative sessions can provide the background to promote these two factors (Fonseca et al, 2012).

Therefore, the primary objective of this project is to develop, implement, and evaluate a treatment for adolescent obesity, which will use PA and interactive sessions to promote weight management skills, through the increase of contact time between the adolescent, parents, peers and treatment staff.

The primary outcomes will be body composition related variables, PA and sedentary behaviors. We will also look for putative moderators and mediators, derived from the behavior change rationales followed in the project, which will help understand and predict how the program has influenced the outcomes.

This project holds unique characteristics which comply with the latest recommendations for the treatment of adolescent obesity, and others that we have not been able to find in the literature: a) the inclusion of peers explicitly on the treatment protocol; b) the clinical setting of the treatment, with "real-life" subjects; c) objective measurements of the outcomes; d) the long-term treatment; and e) a well established rational (SDT and experiential learning) for the behavior change and to analyze the causal relations between predictors and outcomes.

This research is expected to contribute with increased knowledge about treatment options for adolescent obesity, specifically about the potential role of the inclusion of peers and increased time of contact through PA and interactive sessions. We also expect to contribute in a significant and clinically meaningful way to the weight management of the intervened adolescents. And, as HSM is a central hospital and a part of a medical university, the accumulated knowledge of the project will certainly be efficiently widespread to several other hospitals and obesity centers.

Inclusion Criteria:

• Obese adolescents with BMI greater than or equal to the 95th percentile
• Aged between 14 and 17
• Caucasian
• Agree to the commitment.

Exclusion Criteria:

• Adolescents with serious illnesses
• Other factors preventing the engagement in regular PA