A randomized blinded feasibility study using the Eating Attitudes Test (EAT-26) and the Reflective Functioning Questionnaire RFQ - as the main outcome to assess two interventions for eating disorders. Six experienced therapists, and their consecutively 8-9 admitted clients, were randomly allocated to the intervention group and control group. The sample included a total of 52 participants, all women, mean age 24.2 yrs. old. In the intervention group, participants received mentalization-based psychotherapy with ECOSA - a novel developed mentalization tool and in the control group, participants received interpersonal psychotherapy that focused on resolving interpersonal problems and symptomatic recovery. Four randomized samples for each participant were checked for therapy-focused fidelity by two different psychotherapists.

Six experienced therapists (more than 10 yrs. in the eating disorders' treatment) within one eating disorder center, were randomly allocated using the excel randomization function to the intervention group and control group. All participants in the clinical sample were drawn consecutively from admitted population to these therapists in a community-based eating disorder center between September 2018 to April 2019. The sample (total of 52 patients) included 26 participants in each group, all women, (mean age 24.2±3.2). Forty two percent of participants in each group were diagnosed with BN, 13% with BED, 35% with AN and 10% with ARFID. Thirty percent of participants in each group, also met criteria for borderline personality disorder on the SCID-II .The overall sample had predominantly high socioeconomic status.

Each therapist received a written consent from 8 to 9 clients to participate in the study and record all sessions. The research student, who collected the data was blind to treatment groups. Therapists and participants were blinded to the research aims and hypothesis.

In the intervention group, therapist received mentalization-based supervision along all participants' treatments, with the suggested tool and facilitated mentalization-focused therapy. The control group's participants received ITP-interpersonal psychotherapy that focused on resolving interpersonal problems and symptomatic recovery. The control group's therapist received regular supervision - with no emphasis on mentalization or tool's usage.

Participants' sessions were recorded over 12 months of treatment. Four randomized samples for each participant were checked for therapy-focused fidelity by two different psychotherapist Measures All participants underwent on entry a standard assessment of eating disorder, including a semi structured interview to measure co-morbid disorders, by experienced psychologist. Participants in both groups completed the Eating Attitudes Test (EAT-26) and the Reflective Functioning Questionnaire RFQ as part of a larger assessment battery.

The EAT-26 is a self-administered questionnaire that reveals abnormal eating behaviors. It consists of 26 items with six components scored from 0 to 3 (Zero: "Never," "Rarely," and "Sometimes"; 1: "Often"; 2: "Very often"; and 3: "Always"). The total score range from 0 to 78, and a score ≥ 20 is considered to represent abnormal eating attitudes or behaviors. The Cronbach's alpha in this study ranged between 0.75-0.90.

The RFQ was developed as a brief, easy-to-administer screening measure to assess severe impairments or imbalances in mentalization capacities. It includes 8 items scaled on 7-point Likert-type scale scored from 0 to 3. High values on this scale indicate high uncertainty about mental states, hence difficulties with mentalizing. The Cronbach's alpha in this study ranged between 0.8-0.94.

Statistical analysis All analyses were conducted using SPSS 23®. Normality distributions and outliers for each outcome variable were examined prior to commencing analysis. Independent T-tests analysis was used to assess differences between groups at baseline and between groups' improvements. Paired T-tests within each group used to assess the improvement between baseline, and 12 months treatment. Pearson correlations were computed to assess the relationship between change in eating disorder's symptoms and change in mentalizing capacities.

Inclusion criteria:

• Participants were previously diagnosed with eating disorder (Eat-26>21)
• 17 yrs age and older
• no acute suicidality
• no physical risks due to eating disorder's symptoms

Exclusion criteria:

• age <17 yrs old
• refusal to corporate with treatment
• Need of 24 hrs medical care

All names and identification data will be omitted from the file that will be sent to statistical assessments.

The research student, who collected the data was blind to treatment groups. Therapists and participants were blinded to the research aims and hypothesis.