Evaluating an acceptance-based lifestyle modification program to address cardiovascular disease risk among adolescent girls with overweight and obesity: Protocol for a randomized controlled trial

Abstract

Background:

Behavioral weight loss interventions achieve only limited weight loss in adolescent samples and weight regain is common. This limited intervention success may be attributed, in part, to adolescents’ lack of self-regulation skills essential for lifestyle modification and use of a one-size fits-all approach to produce weight loss in boys and girls. Interventions which teach self-regulation skills, such as Acceptance-Based Therapy (ABT), and are tailored to meet gender-specific concerns, are critical to help adolescents adapt to pervasive biological and environmental influences toward weight gain.

Objective:

This trial tests the effect of an ABT intervention on cardiometabolic health, health-related behaviors, and psychological factors among adolescent girls with overweight or obesity (OW/OB).

Methods:

Girls 14–19 years (N = 148; ≥ 40% racial/ethnic minorities) with OW/OB (BMI: ≥ 85th percentile) will be enrolled in the study. Participants will be randomized to one of two 6-month interventions, consisting of either 18 sessions of ABT or 9 sessions of a health education control, an augmented version of standard care for adolescent OW/OB, both led by bachelor’s level interventionists.

Results:

Recruitment is taking place in Philadelphia, USA, from January 2024 to January 2028. Cardiometabolic health markers (adiposity; blood pressure; blood lipids), health-related behaviors (dietary intake; physical activity; sleep), and psychological factors (quality of life; depression; disordered eating; psychological flexibility) will be measured at baseline, mid-treatment, post-treatment, 6-month follow-up, and 12-month follow-up.

Conclusions:

This study will provide valuable information on a novel intervention tailored to the needs of adolescent girls with OW/OB to address self-regulation and cardiometabolic health.

1. Introduction

Prevalence of overweight and obesity (OW/OB) among U.S. adolescents has reached an all-time high of 34.5% [1,2], contributing to psychological and physical health ramifications including an increased risk for cardiovascular disease (CVD) [3-8]. Indeed, adolescents with OW/OB are at high risk of developing CVD risk markers such as hyperlipidemia, hypertension, and insulin resistance [9] and OW/OB in adolescence is a strong predictor of CVD in adulthood [4-8]. The majority of adolescents with OW/OB fail to meet dietary [10,11] and physical activity [10,12-18] guidelines, underscoring the need for behavior change interventions to address this significant public health problem.

Behavioral interventions remain the first line of treatment for excess weight and are an integral part of obesity treatment across modalities [19-21]. However, efforts to improve the efficacy of behavioral treatments for adolescent obesity have generally been disappointing [19,20,22-27], as the amount of weight lost is limited and weight regain is common [19,20,22,24-27]. Further, prior research has identified disparities in treatment outcomes following behavioral obesity treatment such that Black individuals tended to lose less weight compared to White individuals [28] and that within the Black community, poor weight loss outcomes are especially common among women [29,30]. Thus, to improve outcomes, it is critical to identify and target novel maintaining mechanisms (e.g., self-regulation) of OW/OB in adolescent girls from diverse backgrounds.

For adolescents, adhering to dietary intake and physical activity guidelines prescribed for weight loss is exceptionally difficult due to the interaction of physiologic, environmental, and internal drives [31,32]. Indeed, physiologic factors like appetitive drive and metabolic efficiency often interact with the availability of highly palatable, energy dense foods and encouragement of sedentary behavior, and internal cues like stress or fatigue [31]. Resisting these powerful drives to consume more calories and expend less energy requires substantial self-regulation skills [33]. Self-regulation refers to automatic and conscious processes that enable individuals to control their thoughts, impulses, emotions, and behavior, and thus to postpone rewards or suppress impulses to achieve a long-term goal [34], such as weight loss. Self-regulation skills tend to be underdeveloped in adolescents [35-37], and youth with obesity demonstrate significantly lower self-regulation than normal weight youth [37-40]. As such, it is critical that behavioral interventions aim to improve self-regulation in adolescents. Developing these self-regulation skills is posited to be protective against dietary and physical activity lapses, leading to negative energy balance, decreased weight, and improved CVD risk in adolescents.

Acceptance-Based Therapy (ABT) fuses standard behavioral interventions with principles from Acceptance and Commitment Therapy [41-43], namely the clarification of ones’ values and psychological flexibility, and the ability to engage in behaviors that are consistent with their values despite uncomfortable thoughts, feelings, or cravings [44]. Through this focus on self-regulation skills, ABT aims to improve: (1) tolerance of uncomfortable internal states (e.g., anxiety, stress) and perceived reduction of pleasure (e.g., choosing physical activity instead of watching TV); (2) behavioral commitment to clearly defined values, which will increase motivation to maintain difficult weight-control behaviors; and (3) metacognitive awareness of decision-making. ABT has been highly effective for weight loss in adults [33,45-47]. In one study, adults with OW/OB randomized to ABT lost 13.3% body weight over 1 year [46], which is significantly higher than the 5–10% of weight loss achieved by other behavioral interventions during the same period [47].

ABT has proven successful for treating adolescent girls for other problems such as chronic pain, high-risk sexual behavior, anorexia, and depression [28,48-51]. Our group ran a pilot study to test the feasibility of an ABT intervention among adolescent girls with OW/OB and demonstrated high acceptability, with improvements in a variety of cardiometabolic and psychological factors [52-54]. In the pilot study, participants (N = 43) achieved reductions in excess adiposity and improvements in psychological flexibility as compared to a psychoeducation control [52]. Given these promising results, a fully-powered, randomized controlled trial is warranted to determine the efficacy of ABT to reduce CVD risk among adolescents. Although both boys and girls with OW/OB are vulnerable to obesity-related complications, we chose to focus on adolescent girls, whose lived experiences with OW/OB and preferences for a weight loss program are distinct from their male counterparts [53,54]. For example, boys report wanting weight loss programs to focus on “getting stronger” and “bigger” whereas girls want programs to address a holistic view of a healthy lifestyle, including nutrition, physical activity, and mental and emotional health [53]. Additionally, girls in behavioral weight loss interventions report not feeling comfortable discussing vulnerable topics in front of members of a different gender [53]. Thus, there is a significant to tailor interventions to meet the needs of boys and girls. To ensure feasibility, and to extend findings from the pilot study, the current study focuses on adolescent girls.

2. Current study

The current study aims to test the efficacy of a novel 6-month (18 sessions) ABT intervention tailored for adolescent girls with OW/OB in reducing CVD risk compared to a 6-month (9 sessions) group health education (HE) control intervention. The HE control condition is an augmented version of standard care for adolescent OW/OB, consisting mainly of psychoeducation around nutrition, physical activity, and other health behaviors. Distinct from standard care, we chose to provide HE in a group setting and with more frequent sessions than usual care in order to maximize participant retention. We specifically decided on nine sessions as it seemed to be the optimal dose for HE: fewer sessions would limit participants’ ability to develop a sense of commitment to the study and doing more could make sessions feel boring or be perceived as having diminishing value to participants. While both ABT and HE will be held in a group settings and include psychoeducation components, participants in ABT will be taught gold-standard behavioral techniques for weight control and learn and practice mindfulness and acceptance skills to facilitate adherence to weight control behaviors.

The primary aim of this study is to compare ABT and HE on change in BMI z-score at post-treatment and 6-month follow-up. We hypothesize that adolescents randomized to ABT will show a greater decrease in BMI z-scores compared to those in the HE group. The secondary aim is to compare ABT and HE on physiological outcomes, health-related behaviors, and psychological factors at mid-treatment (month 3), post-treatment (month 6), 6-month follow-up (month 12), and 12-month follow-up (month 18). We hypothesize that adolescents in the ABT group will show significantly greater decrease in percent body fat, blood pressure, and blood lipid levels and greater improvements in diet, physical activity, sleep, quality of life, depression, disordered eating, and psychological flexibility in all time points compared to those in the HE group. Given the limited research examining effects of adolescent obesity treatment (and specifically ABT) on cardiovascular disease risk markers and other secondary outcomes (e.g., psychological variables) [55], we may be underpowered for these aims, but preliminary examination of these outcomes will inform future work on ABT’s effects on important health markers beyond weight. As exploratory aims, we will examine (1) the extent to which ABT’s effects on physiological outcomes (BMI z-score, body composition, blood pressure, blood lipids) are mediated by improvements in behavioral (dietary, physical activity, sleep) and psychological (perceived quality of life, depression, disordered eating, and psychological flexibility) factors and (2) whether demographic (race/ethnicity, socioeconomic status) and psychological (disinhibition, dietary restraint) factors moderate the effects of the intervention.

3. Method

3.1. Participants

The present study will be conducted in the Center for Weight, Eating, and Lifestyle Science (WELL Center at Drexel University), a clinical research center in Philadelphia, Pennsylvania, USA. Given Philadelphia’s racially and ethnically diverse population, we aim for and anticipate enrolling at least 40% of adolescent girls who identify as a racial/ethnic minority into the study, which is consistent with previous similar studies conducted by our team [56]. Participants will be recruited through various methods, including digital advertising (via a company specialized in recruiting for clinical trials), posted flyers, word of mouth, and utilization of a diverse range of graphic materials to appeal to prospective participants. To reach racial/ethnic minorities, we will also obtain recruitment support through the WELL Center’s youth advisory board and other community partnerships. Study inclusion and exclusion criteria are listed in Table 1 below. The present study has been reviewed and approved by the Drexel University Institutional Review Board.

Table 1.

Study inclusion and exclusion criteria.

Inclusion criteria

Exclusion criteria

Identifies as a girl 14–19 years old BMI ≥ 85th percentile for sex-and-age

Diagnosis of CVD, diabetes, lung disease, kidney disease, cancer, severe intellectual disability, or an eating or substance use disorder Pregnant, planning to become pregnant in the next 18 months, or unwilling to report a pregnancy Have suicidality or severe psychopathology that would limit the ability to engage in the intervention Have any condition prohibiting physical activity, are diagnosed with a developmental disability Have a history of bariatric surgery Have begun or changed the dosage of any medication known to affect appetite or body composition in the last three months Report weight loss ≥5% in the previous 6 months.

3.2. Procedures

Recruitment began in January 2024 and data collection is expected to conclude by January 2028. We will recruit 6 waves, each comprised of approximately 24 participants, with 12 participants randomized to each intervention per wave. Individuals will be screened for eligibility through completion of a general interest survey and a phone screen completed with parents of adolescents under 18 or with adolescents 18 or 19 (i.e., young adults). Following the screen, participants will be invited to learn more about the study in a live or recorded virtual information session and to schedule a baseline visit. Informed consent and, if applicable, assent will be obtained and eligibility will be verified at the start of this visit. Eligible participants will proceed with the baseline assessment and subsequently be randomized to the ABT or HE intervention. In addition to the baseline assessment, participants will complete an assessment at mid-way through treatment (month 3), post-treatment, (month 6) 6-month follow-up (month 12), and 12-month follow-up (month 18) for a total of 5 assessments.

3.3. Measures

3.3.1. Demographics

We will assess race/ethnicity, age, and socioeconomic status through a demographics questionnaire, administered at the baseline visit.

3.3.2. Weight

Height without shoes will be measured to the nearest 0.1 cm using a stadiometer. Weight will be measured to the nearest 0.1 kg using a certified digital scale. All measures will be taken in duplicate and the mean will be used to calculate BMI percentile for sex-and-age. We will derive BMI Z-score and BMI change using standard calculations [57]. However, data demonstrate non-trivial errors in BMI or BMI Z-score in adolescents [58,59], thus changes in tri-ponderal mass index and changes in weight relative to the BMI at the 95th percentile based on sex- and-age (as a difference in percentage units and/or a difference in BMI units) will also be evaluated [58]. Weight will be measured at all assessment time points.

3.3.3. Body fat

Body fat will be measured via bioelectrical impedance analysis (InBody770), a reliable and valid measure of adiposity [60]. Percent body fat will be measured at all assessment time points.

3.3.4. Suicidality

Participants will complete the Beck Depression Inventory-II (BDI-II) to measure depression over the last two weeks [61]. If participants report having any thoughts about suicide, a suicide risk assessment will take place. Participants will be excluded if they report severe suicidality as determined by a licensed psychologist. Where appropriate, participants will be provided with resources and/or referrals. Suicidality will be assessed at all time points.

3.3.5. Eating disorder psychopathology

To assess for disordered eating behaviors, participants will complete select portions of the Eating Disorder Examination (EDE) [62], in which a trained interviewer will ask about the frequency of compensatory behaviors (e.g., vomiting, laxative use) the participant engaged in over the past three months. Participants who report any instance of vomiting, or 12 or more instances of any combination of compensatory behaviors in the past three months or meet criteria for binge eating disorder will be ineligible. The EDE will be administered at all time points.

3.3.6. Blood pressure and blood lipids

Systolic and diastolic blood pressure will be measured using an automated blood pressure cuff. We will assess triglycerides, total cholesterol, LDL cholesterol, and HDL cholesterol using a finger stick lipid test, which will be analyzed with a Cholestech LDX Lipid Analyzer. Blood pressure and blood lipids will be measured at all study time points. Blood pressure and blood lipids will be administered at all time points.

3.3.7. Dietary intake

Dietary intake will be assessed via 30-day dietary recall using the image-based VioScreen Food Frequency Questionnaire (VioFFQ), a web-based and self-administered tool that has been validated for use in children [63]. The VioFFQ provides a healthy eating index score for foods consumed in the past month and their daily average intake of the following food and macronutrient groups: Fruits, vegetables, whole grains, protein, fat, saturated fat, added sugars, and dietary fiber. Dietary intake will be measured at baseline and post-treatment.

3.3.8. Physical activity and sleep

Daily energy expenditure, step count, minutes spent in moderate-to-vigorous physical activity, and sleep patterns will be measured via an actigraph (Fitbit Sense 2) provided to participants for the study. Participants will wear the Fitbit Sense 2 device on their non-dominant wrist for seven consecutive days following their baseline, mid-treatment, and post-treatment assessments.

3.3.9. Psychological factors

The Quality of Life Inventory (QOLI) will be used to measure obesity-specific, health-related quality of life [64]. The Eating Disorder Examination Questionnaire (EDE-Q) will assess symptoms and concerns characteristic of eating disorders [65]. The Three Factor Eating Questionnaire (TFEQ-18) will measure dietary restraint, uncontrolled eating and disinhibition, and emotional eating [66,67]. The Food Acceptance and action Questionnaire (FAAQ) will measure psychological flexibility around food-related internal experiences [68]. The QOLI and EDE-Q will be administered at all study time points. The TFEQ-18 and FAQ will be administered at all time points.

3.4. Interventions

3.4.1. Shared treatment components across conditions

See Table 2 for list of topics in both treatment conditions. Nutrition, physical activity, and sleep recommendations will be consistent across conditions. Nutritional recommendations include following a calorie goal of between 1200 and 1500 cal per day if their weight is below 250 pounds or 1500–1800 per day if their weight is above 250 pounds [20,41,53,69]. Participants will also learn about MyPlate nutritional guidelines, the traffic light diet, and be encouraged to eat a diet rich in fruits, vegetables, lean sources of protein, whole grains, nuts, seeds, and encouraged to limit sugary beverages and ultra-processed foods [20,27,69]. For each session, participants will be provided a set of healthy lifestyle handouts. The content of these handouts includes topics such as reading a nutrition label, problem solving, managing stress, sleeping an adequate amount, and self-monitoring. Physical activity recommendations include at least 60 min of daily moderate-to-vigorous physical activity five days per week and physical inactivity to be reduced by limiting nonacademic screen time and other sedentary activities to less than two hours per day [8,70,71]. Sleep recommendations include getting at least eight to ten hours of sleep per night [72]. Sessions across conditions will consist of psychoeducation, goal-setting, review of progress, and problem-solving and cover a range of topics including stress management, sleep hygiene, and obtaining social support. All participants will have access to an app-based group chat, where they can communicate with other group members and their interventionist outside of the session. No intervention components will be delivered through the app. Use of a chatting app was highly effective for maintaining communication with participants in the pilot ABT intervention [73].

Table 2.

Session topics in the acceptance-based and health education interventions.

	Acceptance-based intervention	Health education intervention
Session 1	Welcome and Getting Started	Welcome and Getting Started
Session 2	Self-monitoring and Mindfulness	Meal-planning
Session 3	Portion Size and Meditation	Physical Activity and Exercise Class
Session 4	Meal-planning and Mindful Eating	Managing Stress and Coping
Session 5	Physical Activity and Exercise Class	Sleep
Session 6	Stress Management: Healthy and Unhealthy Eating	Nutrition
Session 7	Willingness and Urge Surfing	Body Image
Session 8	Values and their Impact on Weight	Social Relationships and Weight Stigma
Session 9	Eating Trigger Meditation and Values	Treatment Wrap-up and Celebrating Accomplishments
Session 10	Maintaining Motivation and Passengers on the Bus
Session 11	Social Cues and Special Events
Session 12	Body Image (Part 1) and Values Awareness
Session 13	Body Image (Part 2) and Moving Reward to Life
Session 14	Maintaining Motivation and Addressing Competing Values
Session 15	Competing Values and Hunger Awareness Meditation
Session 16	Physical Activity and Sleep
Session 17	Common Reactions to Treatment Ending and Skill Review
Session 18	Treatment Wrap-up and Celebrating Accomplishments

3.4.2. Acceptance-based therapy

Participants randomized to ABT will receive 18, 90-min group sessions over a 6-month period (weekly for 10 sessions and bi-weekly for 8 sessions) with two trained bachelor’s level interventionists. The first 10, weekly sessions will take place in person at the WELL Center, and the following 8 bi-weekly sessions will take place over HIPAA-compliant Zoom. Sessions will include a weigh-in, occurring in a private assessment room or a breakout room on Zoom, and review of progress toward participants’ goals (starting in the second session), an active learning session with extensive participation (e.g., activities to practice acceptance-based skills, such as mindfulness and willingness), a facilitated discussion, and statements of goals for the next session. In addition to the informational handouts, participants in the ABT group will receive worksheets to practice skills learned in the intervention. Participants also will be taught how to monitor their caloric intake using the Fitbit food-logging feature for the duration of the intervention; app-based food diaries are effective as a self-monitoring tool for weight loss [74].

3.4.3. Health education intervention

Participants randomized to HE will receive nine, 75-min group-based psycho-education sessions over a six month period (weekly for 4 sessions, and monthly for 5 sessions) with two trained bachelor’s level interventionists. The first 4 weekly sessions will take place in person at the WELL Center, and the following 5 monthly sessions will take place over HIPAA-compliant Zoom. Participants in the HE group will not be given any homework assignments and will receive not be taught any mindfulness or acceptance-based skills. See Table 1 for a summary of session topics.

3.5. Intervention delivery

3.5.1. Interventionists

The ABT and HE interventions will be delivered by two bachelor’s level interventionists who will be required to have a background in psychology, nutrition, or exercise science or to demonstrate an understanding of behavioral recommendations related to physical activity, nutrition, and sleep. Interventionists will complete 15 h of intensive training on basic clinical skills, behavioral weight loss, and ABT. Interventionists will also complete 2 recorded mock sessions and receive feedback from the lead investigator on rapport, delivery and integration of information, understanding of the intervention components, and interventionists’ self-awareness. We chose to use bachelor’s level interventionists to increase future scalability of the intervention. Following each session, interventionists will document deviations from the treatment manuals, note any questions, and flag audio-recorded portions of sessions that should be brought to supervision. Clinical supervision will be provided by licensed clinical psychologists to ensure fidelity and competent intervention delivery will be provided throughout treatment. Assignment to conditions will be balanced across interventionists to ensure no interventionist effects. To maximize fidelity and minimize contamination across treatment conditions, separate treatment manuals will be constructed for each condition.

3.5.2. Fidelity

Two independent evaluators (doctoral students and/or post-doctoral fellows with a background in acceptance-based treatments and behavioral weight loss interventions who have undergone intensive training) will independently monitor and rate treatment competence, fidelity, and contamination of treatment content across conditions for 25% of sessions. A higher proportion of sessions (e.g., 50%) will be coded earlier in treatment to ensure competency and fidelity and will decrease as the treatment progresses. (Overall, a total of 25% of sessions will be rated). A checklist of key components to be covered as well as a rating of competency will be created. Because of the substantial differences between conditions, fidelity coders cannot be blinded. Feedback will be provided to interventionists and supervisors within 72 h of the session.

3.6. Statistical analyses

Initially, descriptive statistics will be compared between the two groups at baseline. Graphical displays of the outcomes over time (both means and individual trajectories) will inform statistical modeling. Statistical significance will be defined by α = 0.05 throughout the study, with the demonstration of efficacy of the intervention determined by the primary outcome (BMI z-score). Primary analyses will be based on the intention-to-treat principle.

3.6.1. Effect size estimation

No results are available which directly compare ABT and HE among adolescent girls with OW/OB. However, effect size can be predicted by deriving estimates from trials with elements similar to the proposed study. The SD for 6-month change in BMI z-score from our preliminary data was 0.34; we used a slightly higher variability estimate in change in BMI z-score in this power analysis (SD = 0.4). Aiming to detect a clinically meaningful difference of 0.23 in BMI z-score change between the groups, we conservatively estimated an effect size of 0.57.

3.6.2. Sample size estimation

Using the method described by Raudenbush [75] and implemented with the software Optimal Design, power calculations were made for a multilevel model structure. From our power analysis, a sample size of 118 (59 for each group) is required for 80% power to detect a medium effect size (d = 0.57) with the significance level of 0.05 and five assessment points, assuming the ratio of the variability of level-1 coefficient to the variability of level-1 residual is at least one. Accounting for an 80% retention rate at the post-intervention assessment (our primary endpoint), the proposed sample size of 148 will allow us to have approximately 59 per intervention group and provide sufficient power. For any of our other outcomes of interest, this sample size would provide 80% power to detect a medium effect size (d = 0.57) or greater with the significance level of 0.05. Thus, the study is adequately powered with the proposed sample size of 148.

3.6.3. Primary Aim: Compare the trajectories of change relative to baseline in BMI z-score across the study period between ABT and HE

We will use generalized linear mixed models (GLMMs) across the primary outcome (BMI z-score; for this aim. Given our experience from the feasibility study and knowledge of these measures, most of the GLMM’s models will assume an identity link and Gaussian distribution in modeling change from baseline of continuous outcomes. Our primary test of interest is on the interaction of the fixed effects of intervention (ABT vs. HE) and time. For valid inference on the fixed effects, we will use the Kenward-Roger denominator degrees of freedom. This approach will allow us to make inferences at given time points (i.e., change in BMI-z at 6-month follow-up). We will include a random effect for group assignment to account for clustering by group. We will carefully model the appropriate within-adolescent covariance structure to ensure valid inference on the fixed effects. We will include age as a covariate.

3.6.4. Secondary Aim: Compare ABT and HE interventions on physiological outcomes, health-related behaviors, and psychological factors across the study period

Models evaluating secondary aims will follow all parameters outlined above for the primary outcomes and will evaluate CVD risk-markers (body fat percentage; triglycerides; total cholesterol; LDL cholesterol; HDL cholesterol), dietary intake, physical activity, sleep, quality of life, depression, disordered eating symptoms, and eating-related psychological flexibility as outcomes of interest.

3.6.5. Exploratory Aim 1: Examine the extent to which ABT’s effects on physiological outcomes are mediated by improvements in behavioral and psychological factors

For exploratory mediation analysis, we will use a unified approach to mediation and interaction to decompose the total effect of ABT four ways: the effect due directly from ABT (controlled direct effect), the effect due to interaction only (reference interaction), the effect due to mediation only (pure indirect effect), and the effect due to mediation and interaction (mediated interaction). Such decomposition allows for a determination of the precise role our hypothesized mediators (behavioral and psychological factors) play in the effect of ABT on physiological factors.

3.6.6. Exploratory Aim 2: determine whether demographic (race/ethnicity, socioeconomic status) and psychological (disinhibition, dietary restraint) factors moderate the effects of the intervention

We will assess the moderating effect of baseline demographic factors (race/ethnicity, SES) and psychological factors via statistical interactions (e.g., SES x intervention x time). The mixed model framework allows for outcomes to be missing at random. It is possible that this assumption will not be met, and the observed dropout will be non-ignorable. Models that accommodate non-ignorable missingness will be fit, specifically joint modeling approaches that model the outcomes as described above while also modeling the likelihood of dropout via selection models. These models will be used as a sensitivity analysis to compare with the framework described above.

4. Discussion

4.1. Study implications

Existing studies for behavioral weight loss interventions among adolescents have demonstrated minimal success, evidenced by modest weight loss and weight regain following the intervention [19,20,22,24-27]. Although standard behavioral interventions for weight loss typically include use of structured goals around caloric intake and physical activity, self-monitoring of weight and eating, feedback from an interventionist, and support with additional behavioral skills like problem-solving and stimulus control, they do not specifically address self-regulation skills, and are therefore modestly to moderately efficacious [76]. ABT interventions, which fuse behavioral recommendations with principles of mindfulness and acceptance, show high promise in this area because they build upon these behavioral approaches bytargetting self-regulation skills to promote initiation and maintenance of lifestyle modifications even when such changes are uncomfortable or difficult [77]. Furthermore, our pilot trial demonstrated preliminary efficacy for ABT in decreasing BMI percentile and improving psychological outcomes among adolescent girls and those of racial/ethnic minority identity [52]. If hypotheses are supported in this fully-powered trial, results will provide evidence for ABT as an effective way to intervene on CVD risk among adolescent girls.

4.2. Future directions

Should ABT prove efficacious, a trial comparing ABT to standard group lifestyle modification to parse out incremental effects of the acceptance-based self-regulation skills would be warranted. Future work could disseminate and assess the effectiveness of ABT in community-based settings and focus on maximizing potential for dissemination. For example, other possible settings to test ABT include schools and primary care offices. To increase scalability, future work could focus on examining effective training methods for other types of providers, such as school nurses, community health workers, and lay individuals from the community. Future trials could also consider teaching ABT skills through digital apps to increase accessibility. Furthermore, future work could test different lengths, intensities, and formats of ABT to maximize both efficacy and scalability. Lastly, future work should focus on developing ABT interventions that would meet the needs of adolescent boys (e.g., fitness-oriented ABT, gamified versions).

4.3. Strengths and limitations

This trial is well-equipped to provide valuable and clinically relevant information for weight loss interventions for adolescents. This would be the first fully-powered randomized controlled trial to test the efficacy of an ABT intervention compared to an HE control condition among adolescent girls with OW/OB. Given the planned sample diversity, this study will also provide valuable information about the efficacy of ABT for weight loss among racial and ethnic minorities. The 6-month and 12-month follow-ups also provide insight on the long-term effects of the intervention. Furthermore, should the intervention prove to be efficacious, the utilization of Bachelor’s-level interventionists and a hybrid intervention delivery makes this intervention highly scalable.

Formulated upon an extant pilot RCT led by authors of this protocol, this trial was designed with a particular scope and is therefore not without its limitations. Without parent involvement or parent-reported measures, trial results cannot shed light on the role of families in weight-loss intervention success. Furthermore, because a lower-intensity, HE group is the comparison rather than a group-based behavioral weight loss intervention, study results cannot indicate whether ABT outperforms other first-line lifestyle modification programs matched on intervention intensity, which could be the focus of a subsequent trial. Lastly, given that we powered the study on differences in BMI z-score and the minimal research to inform potential effects of ABT on secondary measures (e.g., physiological, psychological outcomes), it is possible we were underpowered to detect differences in secondary measures. However, the study will provide valuable initial information on ABT’s potential effects on health markers beyond weight.

Data availability

No data was used for the research described in the article.