This Randomized Controlled Trial (RCT) aims to evaluate the effectiveness of a brief Acceptance and Commitment Therapy (ACT)-based-intervention combined with treatment as usual (TAU) compared to TAU only in improving psychological conditions in a sample of adolescents with obesity (body mass index, BMI > 97th centile for age and sex). Fifty consecutive adolescents (12-17 years) of both genders with obesity will be recruited among the patients hospitalized in a clinical center for obesity rehabilitation and randomly allocated into two experimental conditions: ACT + TAU vs TAU only. Both groups will attend a three-week in-hospital multidisciplinary rehabilitation program for weight loss. The ACT + TAU condition comprises a psychological intervention based on ACT combined with a standard psychological assessment and support to the hospitalization. The TAU comprises the standard psychological assessment and support to the hospitalization. At pre- to post-psychological intervention participants will complete the Avoidance and Fusion Questionnaire for Youth, the Psychological Well-Being Scale, the Depression Anxiety Stress Scale, the Difficulties in Emotion Regulation Scale, and the Emotional Eating subscale of the Dutch Eating Behavior Questionnaire. Repeated-measures ANOVAs (2x2) will be conducted. The study will assess the effectiveness of a brief ACT-based intervention for adolescents with obesity.

Obesity in childhood and adolescence is becoming a major public health concern. In this respect, recent estimates pointed out that globally 124 million children and adolescents, aged between 5 and 19 years, were obese. In Europe, the prevalence of overweight and obese children and adolescents aged between 5 to 19 years is reported around 19%, with a higher prevalence in southern European countries.

Obesity in children and adolescents is associated with a higher risk of developing several physical and psychological problems that have an impact on their emotional development [3]. Research has reported associations between childhood and adolescent obesity and some form of psychopathology, as depression, anxiety, and attention-deficit/hyperactivity disorder. Besides, children and adolescents with obesity are more likely to suffer from psychosocial disadvantages as discrimination, social isolation, and bullying because of their weight. Moreover, obesity in childhood and adolescence is associated with poor body image, low self-esteem, and low quality of life and well-being.

This evidence suggests that obesity is a complex disease that may dramatically impair psychological health, representing a risk factor for children and adolescents' future development. This aspect calls for a better understanding of the associated risk factors and requires a multidisciplinary approach - entailing medical, nutritional, physical, and psychological components - aimed to address not only weight loss but also improving psychological conditions and treating obesity-related comorbidities.

The development of dysfunctional eating habits is one of the main factors linked to body weight, and it can be considered a barrier to weight loss [14,15]. Evidence from the literature suggests that unhealthy and dysfunctional eating habits could be related to a failure in emotional regulation strategies, that lead individuals to eat in response to difficult emotions, as in case of emotional eating defined as the tendency to eat in response of negative feelings.

Emotional regulation is defined as the ability to manage emotions, which means to recognize, understand, accept and modulate flexible responses to emotions. High emotion regulation allows individuals to act accordingly with personal goals, even in the presence of difficult emotions, while controlling for impulsive behaviors. On the contrary, when emotional regulation is lacking, emotional eating is undertaken to regulate difficult feelings.

Since emotional eating was related to higher consumption of sweet and fatty food, as an attempt to regulate negative feelings, it was found to be positively associated with weight gain and obesity, both in adult and in younger populations.

A theoretical model for explaining disordered eating suggests that momentary stimuli such as the availability of tasty food in the environment, in combination with a modern sedentary lifestyle, accompanied by difficult emotions, can lead people to move toward behaviors perceived to increase or maintain a hedonic state of pleasure, as eating tasty food immediately. The model also suggests that values clarity and behavioral commitment [to connect healthy eating habits to important life values], awareness [of their automatic thoughts], and distress tolerance [negative internal states] are specific self-regulation skills that can help individuals to deal with difficult emotions and control for their behaviors. Such skills are the main focus of Acceptance and Commitment Therapy.

Acceptance and Commitment Therapy (ACT) is a third-wave CBTs raised in the last twenty years. ACT aims to promote psychological flexibility, defined as the ability to live in the "here and now" current moment consciously while implementing behaviors to live in line with one's own values. This can be seen in opposition to experiential avoidance (or psychological inflexibility) which is the attempt to avoid un-pleasant internal states, such as thoughts, feelings, and bodily sensations. The promotion of psychological flexibility is based on three pillars: openness, awareness, and engagement. Openness refers to the willingness to develop an open and acceptable attitude toward one's personal internal states such as thoughts, emotions, and bodily sensations; Awareness refers to the ability to act intentionally with awareness about personal thought and sensations, without automatically reacting; Engagement refers to engage oneself in committed behaviors related to personal values, that is chosen life directions.

Several ACT-based protocols have been successfully applied to adolescents targeting a broad range of conditions, such as cystic fibrosis, chronic pain, ADHD, and at-risk adolescents. In a pilot study conducted by Hayes, Boyd, and Sewell, thirty adolescents referred to a psychiatric outpatient service were randomly assigned to two conditions: in one, they received an ACT intervention; in the other, participants received a standard intervention for depression. The results showed a significant decrease in depressive symptoms in patients undergoing the ACT intervention. In a study conducted by Kemani and colleagues, an ACT-based intervention was applied to adolescents with chronic pain and their family members. Results showed improved acceptance of chronic pain and psychological flexibility in adolescents, as well as decreased depressive symptoms in their parents. ACT has also been applied to adolescents with a post-traumatic stress disorder [30], proving a reduction of symptoms after a 10-week intervention.

Unfortunately, there are not many studies in the literature concerning the application of an ACT protocol for adolescents with overweight/obesity problems. However, evidence suggests that psychological flexibility is an important key factor of psychological health since it allows people to engage in meaningful challenges, in accordance with person's self-concept and important life domains. To the best of our knowledge only one pilot study published in 2019, evaluating the effectiveness of an ACT-based psychological intervention applied in combination with a 16-week lifestyle behavioral modification program in a sample of obese adolescents, was found. This study showed that the intervention was effective in promoting a reduction in BMI and an overall improvement in physical activity and psychological status of obese adolescents. Furthermore, the intervention was positively evaluated by both the adolescents and their parents who participated in the study.

Given these premises, the present study aims to evaluate the effectiveness of a brief ACT-based- psychological intervention, compared to TAU in improving psychological conditions in a sample of adolescents with obesity attending a multidisciplinary rehabilitation program for weight loss.

Inclusion Criteria:

• BMI>97th centile according to age- and sex-specific Italian charts;
• Italian mother tongue
• written and informed consent to participate from both parents and written assent from participants

Exclusion Criteria:

• any physical problems or cognitive impairment that could compromise the participation in the study.