The age of onset of anorexia nervosa has been progressively decreasing in recent years. Also, the prevalence rates of childhood anorexia in many countries have grown significantly. This increase was already observed before the COVID-19 pandemic, but the confinements and the stress derived from them have caused this increase to accelerate. As in adolescent and adult patients, in childhood anorexia some of the core signs and symptoms are an extreme fear of gaining weight and avoidance of food. The consequences of the early-onset of anorexia can be very important since the maturation of the organism is more incomplete in children than in adolescents. Weight loss can have very severe consequences, since in children the percentage of body fat is lower. On the other hand, hormonal disorders derived from food deprivation also have very severe consequences for the development of different organs. General physical development and growth can be affected, with consequences such as not being able to reach normal height. The research carried out to date on the efficacy of treatments for childhood anorexia is very scarce. There are no specific treatment strategies or settings for children with anorexia, and little research has been done to tailor treatment for younger patients. Given the need to explore new treatments for anorexia nervosa specifically aimed at children, the objective of this project is to develop a program to carry out exposure to one's own body through virtual reality, gradually, with progressive increases in size until achieving a healthy weight. In the virtual exposure, patients will observe the image of an avatar in a mirror for the time necessary in each session to produce the reduction of the anxiety response. The avatars that will be developed for this purpose will have a physical constitution corresponding to children under 14 years of age, and physical proportions equivalent to those of each patient. The positive results obtained with a previous version of this treatment originally developed for adolescents and adults suggest that its adaptation to children can open new ways for exploring effective treatments for childhood anorexia.

The age of onset of anorexia nervosa (AN) has been progressively decreasing in recent years, and the prevalence of childhood AN has grown significantly. This increase was already observed before the COVID-19 pandemic, but the confinements have caused this increase to accelerate. The incidence of eating disorders (ED) was 15.3% higher in 2020 compared with previous years. The relative risk increased steadily from March 2020 onwards, exceeding 1.5 by the end of the year. The increase was primarily related to teenagers and AN. A higher proportion of patients in 2020 had suicidal ideation or attempted suicide. Although the diagnostic criteria of AN are applied equally regardless of age, there are differential characteristics between child patients and adolescents or adults in the form of presentation, epidemiology, comorbidity and, also, in outcomes. In most studies, an age of less than 14 has been used as a criterion to define the childhood presentation of this disorder, since it coincides with the legal criterion in many countries. The somatic and mental consequences of early-onset anorexia have a strong negative effect on later adult life. Regardless of the treatment applied, only about half of patients maintain their restored weight in the long term. Little research has been done to tailor treatment for younger patients. Therefore, there is an urgent need for studies on new strategies to treat this serious disorder in children. The objective of this project is to develop a program to carry out exposure to one's own body through virtual reality, with progressive increases in the body mass index (BMI). Patients will observe an avatar in a mirror for the time necessary in each session to produce habituation, extinguishing the anxiety response. The avatars will have a physical constitution corresponding to children under 14 years old, and physical proportions equivalent to those of each patient. The results obtained with the version of this treatment originally developed for adolescents and adults by the investigation group suggest that its adaptation to children can open new ways for exploring effective treatments for children AN. It will also be analyzed whether the addition of a component aimed at modifying attentional biases towards the body increases the efficacy of the exposure. The hypothesis is: if a component of virtual-reality body exposure is added to the usual treatment for AN in children, then the treatment will be more effective. Furthermore, if a component designed to reduce body attention bias is also added, then the efficacy of the treatment will be even greater. The efficacy of this treatment, aimed at reducing the fear of gaining weight, will be analyzed in a randomized controlled study in which a group of patients under 14 years of age will receive treatment as usual, another group will receive treatment as usual plus five booster sessions of virtual body exposure, and a third group will receive treatment as usual, plus five booster sessions of virtual body exposure plus modification of attentional biases towards the body.

Inclusion Criteria:

• Patients with a primary diagnosis of anorexia nervosa (DSM-V)
• Patients below 14 years old
• Patients with BMI <18.5
• Subsyndromal patients will also be included

Exclusion Criteria:

• Visual deficits
• Epilepsy or neuroleptic medication
• Psychotic disorder
• Bipolar disorder
• Medical complications
• Pregnancy
• Clinical cardiac arrhythmia

De-identified individual participant data (IPD) underlying the results reported in this study, including demographic characteristics, clinical variables, and outcome measures, will be shared.

Data will be available beginning 6 months after publication of the results and will remain available for 3 years.

De-identified individual participant data underlying the results reported in this study will be available to researchers who provide a methodologically sound proposal. Requests should be submitted to the corresponding author. Access will be granted following institutional review and approval, and a data use agreement may be required. Data will be shared securely via electronic transfer.