An equivalent randomized controlled trial (RCT) with parallel groups will be conducted. We will perform a simple randomization with 1:1:1 allocation ratio using a computer-generated randomization (www.randomization.com). Allocation concealment will be ensured since all the patients will generate an anonymous code that will be associated to the randomization’s sequence generated by the program. Researchers will be blinded to the association made.
Since we already assessed the efficacy of an ACT-based intervention compared to a CBT-based intervention in the same context of obesity rehabilitation in a previous study , in this study, the aim was to compare the three subcomponents of the psychological flexibility model with each other.
Thus, participant enrolled for the study will be randomly allocated into three experimental conditions, targeting respectively each specific subcomponent of the psychological flexibility model:
Ninety Italian adult individuals with obesity (BMI ≥ 30) attending a multidisciplinary rehabilitation program for weight loss in a single clinical center in the North of Italy will be recruited for the study if they met the following criteria assessing in a clinical interview: (1) age between 18 and 65 years, (2) BMI ≥ 30, (3) being technology friendly to use wearable devices, and (4) written and informed consent to participate.
Exclusion criteria for the study are (1) any psychiatric disturbances (including eating disorders, diagnosed according to DSM 5 criteria) and (2) any medical conditions that could compromise participation at the study.
Demographical and clinical data will be collected via a self-report form. Demographical data include gender, age, educational level, marital status, and work status.
Primary outcomes are physical (weight and BMI) and psychological conditions (PGWBI; OQ-45.2; DASS; DERS; DEBQ; AAQ-II) and adherence to a healthy lifestyle. Secondary outcomes are subcomponents of psychological flexibility (BVI, CAQ, I-CFQ, FFMQ). All the outcomes will be collected as follows.
Weight and height will be assessed to calculate body mass index (BMI = kg/m2).
Psychological well-being. The Psychological General Well-Being Inventory (PGWBI ;). The Italian validation of Grossi and colleagues  consists of 22 self-administered items rated on a 6-point Likert scale, relative to six subscales that offer a measure of the level of subjective psychological well-being. Subscales are anxiety, depression, positive well-being, self-control, general health, and vitality. The internal consistency of the measure was good, with α values of subscales ranged from .61 to .85.
Treatment outcomes. The Outcome Questionnaire-45.2 (OQ-45.2 ;). The Italian version  is used to assess the effectiveness of clinical interventions. It is a self-report questionnaire composed of 45 items. Subscales are symptoms of distress, interpersonal relations, and social role functioning. The total α score obtained in the validated version on a clinical sample is excellent (α = .90).
Psychological inflexibility and experiential avoidance. The Acceptance and Action Questionnaire (AAQ-II ;). The Italian version  is the most widely used self-reported questionnaire that measures psychological inflexibility and experiential avoidance. It is composed of 10 items, rated on a 7-point Likert scale; the internal consistency of the Italian validated version is good (α .83).
Depression, anxiety, and stress. The Depression Anxiety and Stress Scale (DASS-21 ;). The Italian version  is administered as a measure of psychological distress. It is a self-report instrument that measures several negative internal states: depression, anxiety, and stress. It consists of 21 items rated on a 4-point Likert scale, ranging from 0 to 3. Internal consistency of the Italian validated version in the clinical sample was excellent with α value of total score of .92 and α values of subscales ranged from .83 to .91.
Emotional regulation. The Difficulties in Emotional Regulation Scale (DERS ;). The Italian version [36, 37] is administered to assess difficulties in emotional regulation. This is a self-report questionnaire consisting of 36 items, rated on a 5-point Likert scale ranging from 1 (almost never) to 5 (almost always), which explores the following subscales: non-acceptance of negative emotions, inability to undertake purposeful behavior when experiencing negative emotions, difficulty in controlling impulsive behavior when experiencing negative emotions, limited access to emotion regulation strategies that are considered effective, lack of awareness of one’s emotions, and lack of understanding of the nature of one’s emotional responses. The internal consistency of the validated version on a non-clinical sample was good with α values of subscales ranged from .77 to .89. The α value of the total score was .92.
Emotional eating. The Emotional eating subscale of the Dutch Eating Behaviors Questionnaire . The Italian version  is composed of 13 of 33 items of the DEBQ to assess emotional eating. Items are rated on a 5-point scale (1 = never, 5 = very often). Higher scores reflect higher levels of emotional eating. The internal consistency of the validated version of the emotional eating subscale in the overweight sample was excellent (α = .97).
Subcomponent of the psychological flexibility model
Values. The Brief Values Inventory (BVI ;). The Italian version  is composed of 12 items aimed to assess the success in living according to personal values. The internal consistency of the Success subscale is .70 in the Italian validation study.
Committed Action. The Committed Action Questionnaire (CAQ ;). The Italian version  is an 8-item self-report questionnaire rated on a 7-point Likert scale, used to assess positive and negative aspects of the ability to engage themselves into committed actions driven by values. The internal consistency of the measure tested on a normative sample was good (α = .80).
Cognitive fusion. The Italian-Cognitive Fusion Questionnaire (I-CFQ ;). The Italian version  is a 7-item questionnaire administered for the assessment of cognitive fusion. The internal consistency of the Italian version is excellent (α = .82).
Acceptance. The subscale “Nonjudge” of the Five Facet Mindfulness Questionnaire, described below, is used as a measure of acceptance. The internal consistency of the subscale in the validated version is good (α = .86).
Mindfulness. The Five Facet Mindfulness Questionnaire (FFMQ ;). The Italian version  is a 39-item self-report questionnaire used as a measure of mindfulness. It is composed of five subscales: observe, describe, act with awareness, non-react, and nonjudge. The internal consistency of the total scale in the validated version is good (α = .86).
In particular, the BVI and the CAQ are administered to assess the Engagement subcomponent of the psychological flexibility model. The I-CFQ and the subscale Nonjudge of the FFMQ are administered to assess the Openness subcomponent of the psychological flexibility model. The FFMQ is administered to assess the Awareness subcomponent of the psychological flexibility model.
Indicators of healthy lifestyle recorded using wearable devices are (1) daily minutes of moderate-to-vigorous physical activity, (2) daily total amount of calories, and (3) daily steps.
According to guidelines [48, 49], a healthy lifestyle requires a weekly total amount of moderate-to-vigorous physical activity of 150 min, daily energy intake around 80% of the basal energy expenditure estimated, and a weekly mean of 10,000 total daily steps.
Patients will be consecutively recruited for the study at the beginning of the rehabilitation program, after an interview conducted by clinical psychologists members of the research team, aimed to propose the research, assess the eligibility criteria, and ask an e-mail contact to send informed consent to participate.
The responsible of the study (GC) will obtain the informed consent from all participants of the study.
During the 1-month hospitalization, all participants will attend a multidisciplinary rehabilitation program composed by medical, nutritional physical, and psychological components. Patients will follow a hypocaloric balanced diet provided by dietitians. They will take part in a nutritional counseling program provided both in individual and group sessions focused on nutritional education, information on obesity and their health-related risks, setting personal goals for weight loss, weight management, behavioral changes, and prevention of relapses.
Patients will perform physical activity once a day (1 h) with trainers and physiotherapists consisting of programs of aerobic activity, postural gymnastics, and walking.
With respect to the psychological component, they will be randomly allocated into three experimental conditions targeting respectively one specific subcomponent of the psychological flexibility model:
All conditions comprise two sessions, provided twice a week, lasting about 1 h each. Sessions are delivered by an expert clinical psychologist in ACT and will include experiential exercises and metaphors.
To assess the adherence to a healthy lifestyle following the rehabilitation program, outpatients are monitored for 1 month for diet and physical activity. At discharge, they receive wearable devices to monitor the adherence to a healthy lifestyle and are instructed on how to use wearable for the following 1 month.
At the beginning of the study (time 0), at the end of the intervention (time 1), and after 3 (time 2), 6 (time 3), and 9 months (time 4) from discharge, all demographical (such as gender, age, etc.), physical (weight and height to calculate BMI (kg/m2)), and clinical variables (PGWBI, OQ-45.2, DASS-21, DERS, DEBQ, BVI, CAQ, I-CFQ, FFMQ, AAQ-II) will be collected via an online survey (using Qualtrics platform).
In order to monitor the adherence of a healthy lifestyle after the period of rehabilitation, at discharge, participants will receive a wearable device for daily recording of habits regarding diet and physical activity. Monitoring will last 1 month after discharge.
We do not expect any adverse or unintended effects due to the trial participation. However, in case of any form of psychological discomfort, participants can consult the psychologist responsible for the division. Moreover, in case of any doubts or need for information, the participant can contact the responsible of the study. Once enrolled, patients may withdraw from the study at any stage and this will not affect their future treatment.
The clinical psychologist who will conduct the sessions, the participants, and the observers will be blinded to research aims.
All personal information about participants and records of all patients will be collected and preserved separately, in a secure place, into password-protected files kept for 5 years after the end of the trial.
All data collected will be stored in cloud computing and provided to researchers through a dedicated web platform.
The Medical Ethics Committee of Istituto Auxologico Italiano approved the study.
Schedule of enrolment, intervention, and assessment in the study is presented in Fig. 1.
Schedule of enrolment, intervention, and assessment procedures
During this intervention, patients will have the opportunity to increase their motivation to change and encourage the engagement in committed actions, consistent with their life values. Patients are invited to reflect on what is important in their lives, which values make their life worth living, and which actions they could take to live a meaningful life, in accordance with personal values. The use of metaphors and experiential exercises will facilitate the process of exploring personal values, identifying life directions and related behaviors. For example, the 80th Birthday Party metaphor requires participants to imagine there is a party in honor of their birthday and the time comes when people are starting to give speeches and try to answer the question about what they want to hear people at the party say. This exercise helps patients in wondering what person they want to be with themselves and others.
Participants attending this intervention are guided to recognize and distance themselves from stressful thoughts, feelings, and sensations. They will learn to read suffering as part of human experience, without self-judgment and self-condemnation. Rather, the psychologist will encourage patients’ assumption of an open and acceptable approach to internal experiences. Throughout the session, the psychologist will help patients to reflect on their usual, but ineffective efforts to solve personal problems, and encourage the adoption of new responsive strategies based on acceptance and defusion from personal distress. An example of a metaphor used is The Passenger on a bus. In this metaphor, patients have to imagine to be a driver bus and his every thought is a passenger that gets on and off the bus. This exercise help patients to accept, defuse from, and reduce the power of their thoughts.
The intervention comprises meditation exercises and experiences aimed to learn how to act intentionally with awareness about personal thoughts and sensations without automatically reacting. Participants are supported to recognize their actions and the context where they occur and learn to choose to respond with action consistent with their values and not automatically. The psychologist will propose breathing exercises, body scan, and other mindfulness experiences. Participants will be encouraged to sitting comfortably, close the eyes, feel themselves in contact with the present moment they are living, paying attention to their breath, noticing the rhythm, and any other aspect of the experience of breathing. Then, the therapist guides the participant’s attention on the body, noting any part of their body from the head to feet and then, the sounds around, any noises that could distract their attention on themselves.
The research group comprises licensed and clinical psychologists, researchers, and doctoral student experts in the field of clinical interventions in health care settings and research. Group sessions will be administered by a clinical psychologist with many years of expertise in ACT clinical practice both in individual and group settings, blinded to research scopes. The structure and the content of interventions are consistent with ACT theory. Two bachelor-level observers, also blinded to the research, after a period of training, will attend at least 20% of sessions to evaluate the adherence to intervention protocol, the coverage of contents, and the use of any additional strategies. They will use a checklist detailed for all the content of each intervention, including the process targeted, experiential exercises, and metaphors planned for each session. Coders have to achieve a minimum of 80% reliability with the expert trainers and each other. With lower level of agreement, the data will be dismissed .
Data will be analyzed basing on intention-to-treat. This analysis includes all randomized patients in the groups to which they are randomly assigned, regardless of their adherence with the entry criteria, regardless of the treatment they actually received, and regardless of subsequent withdrawal from treatment or deviation from the protocol. Incidence, mechanisms, and patterns of missing data will be explored. To assess if missing data follow a Missing Completely At Random, Little’s MCAR test will be employed. Missing data lower than 5% will be considered negligible. In case of further amount of missing data, multiple imputation will be used.
Sample size has been calculated for a 3 (between) × 4 (within) ANOVA using G*Power software (release 3.1.3) . Setting alpha to 0.05, power to 0.80, and possible dropout, a total sample of 90 is considered enough to detect a small effect size (f = 0.20).
Descriptive statistics (such as means, standard deviations, skewness, and kurtosis) will be conducted to explore the characteristics of the sample and assess for the normal distribution of the variables. Differences between baseline characteristics of the sample will be explored using one-way analysis of variance (ANOVA). To assess relations between variables, correlational analysis will be performed. Chi-squared for categorial variables and Pearson’s correlations for continuous variables will be used. To assess the effectiveness of the intervention, mixed between-within 3 (conditions) × 4 (times) repeated measure ANOVAs will be conducted to examine changes from time 0 to time 1, 2, 3, and 4 in means of weight, BMI, and means of scores PGWBI, OQ-45.2, DASS, DERS, DEBQ, AAQ-II, BVI, CAQ, I-CFQ, and FFMQ, between three groups. Corrected effect sizes (Hedges’s g) and significance at 95% confidence interval (95% CI) will be calculated for both between-group and within-group differences.
In order to assess adherence to healthy lifestyle recommendations, total means of each daily registered indicator of a healthy lifestyle will be calculated, as well as differences of the same parameters between groups, using one-way ANOVAs.
Analysis will be performed using IBM Statistical Package for the Social Sciences (SPSS) version 26.
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