One in eight individuals worldwide live with obesity, as defined by a body mass index (BMI) of ≥ 30.0 kg/m2 [1]. Obesity is a multifactorial disease with diverse, multi-level contributors [1, 2]. As such, many efforts, ranging from national policies to individual health initiatives, have been directed toward preventing and treating obesity [2].

At the individual level, comprehensive lifestyle intervention, also called behavioral treatment, remains a recommended treatment option [3, 4]. This approach prescribes changes in diet and physical activity and teaches strategies that facilitate behavior change [5]. Modification of eating behaviors and physical activity is also important for patients pursuing pharmacotherapy or metabolic bariatric surgery [3, 6]. Regardless of treatment approach, many patients have difficulty making changes to weight-related behaviors and sustaining these changes over time [7, 8]. Some patients may also experience suboptimal weight loss or weight recurrence (i.e., regain) despite successfully making behavioral changes due to biological adaptation and other factors [9, 10]. Additionally, many individuals experience weight-related psychosocial difficulties, such as distress due to anticipated or experienced weight stigma (i.e., prejudice or discrimination based on body weight), internalized weight stigma (also referred to as weight self-stigma and internalized weight bias, among other terms; i.e., self-devaluation or the application of negative stereotypes about weight to oneself), and body image concerns [11,12,13,14,15]. Together, these factors can cause distress and make the long-term treatment of obesity challenging, including by contributing to weight gain and impeding health behavior engagement [13,14,15].

Over the past two decades, acceptance and commitment therapy (ACT) has emerged as a promising treatment approach for those with obesity. ACT has been used both to enhance behavior change and weight loss outcomes from individual-level, behavioral interventions, as well as to improve difficulties often associated with obesity.

In this review, we provide a high-level overview of ACT, highlight seminal studies investigating the utility of ACT for obesity, and review recent research on the potential benefits for individuals with obesity, with a focus on weight and selected non-weight outcomes. Due to the size of the literature, this review focuses primarily on studies that have used ACT as part of comprehensive obesity lifestyle modification interventions (i.e., targeting eating and physical activity) or those enrolling only individuals with overweight or obesity. Additionally, our discussion encompasses ACT’s impact on several non-weight outcomes including body-related concerns, internalized weight stigma, and facets of eating regulation. ACT’s impact on dietary change more broadly (e.g., dietary intake patterns), physical activity, eating disorders, and eating dysregulation across populations is beyond the scope of this review. However, research on these topics has been summarized elsewhere and is covered in several recent studies specific to individuals with overweight or obesity [16,17,18,19,20,21].

ACT: A Brief Overview

ACT is an intervention approach that, like other so-called “third wave” or “third generation” therapies, uses mindfulness and acceptance strategies to foster behavior change and improve wellbeing [22, 23]. The overarching goal of ACT is to help individuals respond more flexibly to their thoughts, feelings, and physical sensations—sometimes referred to as “internal experiences”—so that they can better pursue living a life that is rich and personally meaningful.

One major focus of ACT is helping individuals to clarify their personal values and how these values can guide behavior. This focus is based on the premise that individuals’ wellbeing and health will be improved if individuals are engaging in actions aligned with values that are inherently meaningful and fulfilling, rather than allowing external benchmarks for success (e.g., a “goal weight”) or momentary thoughts and feelings (e.g., cravings) to dictate their behavior.

A second major focus of ACT is helping individuals to modify how they view and respond to their internal experiences so that they can pursue values-consistent behavior even when unwanted thoughts, feelings, or sensations are present. Traditional cognitive behavioral approaches focus on directly modifying and reducing unwanted thoughts and feelings. In contrast, ACT advocates for mindfully noticing and accepting these experiences as part of the human experience. This perspective is based on the tenets that efforts to directly control or change internal experiences are often unsuccessful, and that non-judgmental acceptance of such experiences more effectively allows individuals to re-direct their attention to constructive, values-consistent behavior. In ACT, individuals are taught a variety of mindfulness and acceptance skills to facilitate awareness and acceptance of internal experiences. Mindfulness skills are also often applied to increase individuals’ awareness of their values in daily life, as these can be difficult to keep in focus.

The exact ways in which ACT has been applied to obesity have varied between studies. However, many interventions have sought to (1) clarify and increase awareness of values, (2) clarify how lifestyle behaviors align with and can facilitate values-consistent living, with the hopes that doing so can enhance motivation to engage in these behaviors long-term, and (3) use mindfulness and acceptance skills to respond in adaptive ways to difficult internal experiences (e.g., cravings, negative thoughts, internalized weight stigma). Figure 1 provides a basic overview of key ACT processes as they relate to obesity-related outcomes.

To give brief examples of how these ACT skills might be applied clinically—for values, individuals may be guided in clarifying broad values that are important to them and then be encouraged to explore how engaging in health behaviors and being at a healthy weight can empower them in these areas. For example, an individual might state that they strongly value being an active, engaged parent (broad value). They may then note that they sleep better and have more energy to play with their children when exercising regularly, and that being at a healthy weight improves their mobility, enabling them to engage in a broader range of activities with their children (value-health link). One way that mindfulness skills can be applied is by encouraging individuals to practice pausing before, during, and after episodes of eating to have heightened awareness of various aspects of their internal experience, such as how much hedonic versus physiological hunger they are experiencing. An example of how acceptance might be cultivated is by asking individuals to notice behaviors that they are willing to engage in only under optimal conditions of internal experience, such as being willing to exercise after work only if they feel no anxiety about other tasks that also demand their time and attention. Individuals can then be encouraged to experiment with engaging in these behaviors even if the conditions are not optimal; for example, by increasing their willingness to sit with the anxiety they feel about the other tasks that are not getting done while they exercise. More detailed discussions of ACT’s theoretical fit with obesity and how skills can be applied clinically are provided in articles by Lillis et al. and Forman, Butryn, et al. [24,25,26]. For an overview of reviews and meta-analyses of ACT for obesity, see Table 1.

Table 1 Overview of Reviews / Meta-Analyses of ACT for obesity

Additionally, many interventions have combined content from ACT with strategies from traditional behavioral modification interventions, such as stimulus control, self-monitoring, and goal setting [5]. Within the obesity literature, interventions using ACT are therefore often referred to as acceptance-based behavioral treatments, abbreviated ABT or ABBT. For simplicity across interventions with multiple foci and approaches, we have opted to use “ACT” or “ACT-based” herein, which encompasses ABT/ABBT.

Foundational Studies of ACT for Obesity

Most early work on ACT for obesity, conducted in the mid-2000s to mid-2010s, focused on investigating ACT’s efficacy for weight loss relative to standard behavioral interventions. Building on promising pilot studies [27,28,29], results from several larger, randomized controlled trials showed that ACT-based interventions produced mean weight losses on par with or exceeding those from standard behavioral interventions [30,31,32,33].

For example, in one study, participants in an ACT-based intervention had greater weight loss relative to standard treatment at one year (M ± SD: 13.3% ± 0.83% in ACT vs. 9.8% ± 0.87% in standard) [32]. These differences had attenuated by the final follow-up at three years (4.7% ± 10.1% in ACT vs. 3.3% ± 8.2% in standard), although more individuals in the ACT-based intervention maintained ≥ 10% weight loss (a clinically significant target of such interventions) [31]. In another study among individuals with obesity and high internal disinhibition (i.e., susceptibility to eat in response to internal experiences), participants who received an ACT-based versus standard behavioral intervention had greater weight loss two years after starting treatment (M ± SE: 4.1% ± 0.88 in ACT vs. 2.4% ± 0.87 in standard) [33]. In another trial, mean weight loss at one year was comparable across ACT and non-ACT conditions (M ± SD: 10.84% ± 7.04% in ACT vs. 10.21% ± 7.98% in one non-ACT condition and 10.62% ± 7.82% in another). However, the ACT-based intervention was more efficacious for certain subgroups—here, individuals identifying as African American. Specifically, in the ACT condition, weight losses were similar for those identifying as African American and White—9.4% vs.11.5%, respectively–whereas greater differences in weight loss by race were observed for the non-ACT conditions [30].

Some of these studies also provided preliminary support that ACT could positively impact other outcomes of interest, such as internalized weight stigma, psychological distress, and quality of life [33, 34]. Additionally, a number of smaller studies investigated ACT’s efficacy for reducing weight recurrence and improving other aspects of health and wellbeing following metabolic bariatric surgery. On the whole, results were promising [35, 36]. For example, in one pilot study among patients who had undergone metabolic bariatric surgery and experienced ≥ 10% weight recurrence, weight recurrence was stopped and even reversed during a 10-week ACT intervention, with mean (± SD) weight losses of 3.58% ± 3.02% [36].

Overall, these seminal studies provided initial empirical support for ACT-based interventions as an alternative to standard behavioral treatment and raised the possibility of enhanced efficacy for certain outcomes or populations. Below, we provide an overview of more recent work in these areas.

ACT for Weight Loss and Weight Loss MaintenanceNew Populations

The influential studies on ACT discussed above focused on adults with overweight or obesity. One novel area of research has been to test ACT’s efficacy among adolescents or teenagers with overweight or obesity. Preliminary work with this population has demonstrated promising results for decreasing BMI [37,38,39]. For example, as highlighted in a 2023 scoping review of ACT for weight management among adolescents (Table 1), these studies have generally observed strong acceptability and feasibility of this approach, as well as decreases in BMI [40]. Given these preliminary findings, a fully powered randomized controlled trial is ongoing to test the efficacy of this treatment modality for this population [41].

New Settings and Efforts to Enhance Outcomes and Scalability

In most early trials of ACT for obesity, the interventionists were doctoral-level psychologists (or psychology trainees) with advanced training in ACT, and interventions were delivered in-person in research-oriented, academic settings. Several lines of research have recently explored how ACT-based interventions for obesity might be integrated into more “real world” or routine clinical settings by modifying one or more of these features. See Table 2.

Table 2 Studies evaluating impact on weight in novel contexts

One approach has been to test the feasibility and efficacy of training physicians to deliver ACT-based interventions in primary care settings. Current data suggest this approach may be challenging, although only one study to-date has tested an ACT-based weight loss intervention delivered in this format. This study demonstrated no significant weight loss and high rates of attrition, with the authors suggesting that physicians do not have time to adequately deliver an ACT-based intervention [42].

Other studies have tested the viability of alternative treatment formats, such as telehealth, workshops, and web-based self-help, to enhance intervention scalability. One pilot study comparing an ACT-based telehealth treatment to standard behavioral telehealth treatment found that weight loss was greater in the ACT-based condition, although interpretation of results was limited by a lack of statistical power [43]. These authors are currently conducting a larger, fully powered version of this trial to determine the efficacy of this approach with greater confidence [44]. Another approach has been to deliver an ACT-based intervention in a workshop format, thus reducing interventionist contact time. A study testing this delivery format, which focused primarily on weight loss maintenance, also observed greater weight loss for the ACT versus the comparison intervention [45]. A larger, fully powered study of this approach is underway [46].

Several studies have tested self-help approaches with mixed outcomes. One study of an online, guided self-help intervention observed better weight loss for the ACT condition compared to control [19], while two other self-help interventions did not show significant differences in weight loss between the treatment and control conditions [47, 48]. Similarly, two studies examining the utility of an ACT-based intervention as a supplement to treatment for individuals experiencing minimal initial weight loss showed no differences between the ACT condition and comparator condition(s) [49, 50]. However, in at least one of these studies, findings may have been impacted by suboptimal participant engagement [48, 50].

Researchers are also actively testing which components of ACT-based interventions might optimize weight loss outcomes. This can inform treatment refinement and potentially lead to more streamlined and thus more easily scalable treatments. An ongoing trial is testing the independent and combined efficacy of each component of an ACT-based intervention on weight loss outcomes, with the goal of determining which combination of treatment components produces greater weight loss outcomes than standard behavioral treatment [51].

ACT for Selected Obesity-related Outcomes Beyond WeightBody-related Concerns & Internalized Weight Stigma

Body image dissatisfaction and internalized weight stigma are commonly reported challenges for people with obesity that may cause distress as well as undermine weight control efforts [11, 52, 53]. ACT has been posited to help individuals cope with and address these issues by fostering greater self-acceptance and psychological flexibility (i.e. the ability to be aware of and experience thoughts and feelings while responding flexibly to the circumstances and letting values guide behavior), including greater psychological flexibility specific to concerns around weight [24, 54].

A 2018 systematic review of studies utilizing ACT to target body image dissatisfaction and internalized weight stigma found that medium to large effect sizes were observed in 4 of 6 studies (several of which are discussed above), emphasizing that ACT shows promise in supporting individuals with obesity at developing more positive relationships with their bodies [55]. However, the review cautioned that additional research was needed given the limited number of studies included in the review, as well as methodological limitations of the studies that were included that may impact the validity of findings.

Since 2018, several additional studies have examined the effects of ACT-based interventions on body-related concerns and internalized weight stigma. One recent, large, randomized controlled trial evaluated the effects of a group-based ACT and mindfulness intervention on a range of physical and psychological outcomes among adults with elevated BMIs. This study found that participants receiving ACT reported lower impact of weight on quality of life than those in a treatment-as-usual control group [56]. Several randomized controlled trials of an ACT-based self-help intervention have found that this approach reduces internalized weight stigma among adults with obesity [19, 48, 57]. These findings highlight the adaptability of ACT for addressing body-related concerns and internalized weight stigma in various contexts.

Eating Regulation

Dysregulated eating habits, including emotional eating and binge eating, are common among people with obesity and make weight loss and sustained weight management challenging [58,59,60]. ACT has been theorized to help improve eating regulation by teaching individuals mindfulness and acceptance strategies that they can use to respond to their cravings and emotions in more adaptive ways. However, empirical data on ACT’s efficacy for improving eating regulation among adults with overweight or obesity are mixed.

For example, one randomized controlled trial found that an ACT-based group intervention reduced emotional eating and uncontrolled eating (which is an umbrella term used to capture difficulties in eating regulation and often includes loss of control overeating) among women with obesity compared to a treatment-as-usual group at post-treatment [61]. Another large, recent, randomized controlled trial found that ACT was more effective at reducing external eating (defined as eating in response to external food cues, regardless of internal signals of hunger and fullness) than a control group both at post-treatment and 6-month follow-up [