The results of this study showed that ACT, compared with the control group and PPT, led to improved body image in women with body dysmorphic disorder, a finding that is also consistent with previous research (
15,
17,
30-
33). In addition, PPT also led to improved body image, and the results of both experimental groups were consistent with research that has confirmed the effectiveness of psychological interventions in improving body image (
34,
35). To explain this finding, it can be stated that patients with body dysmorphic disorder have fundamentally negative beliefs about their appearance and social approval (
17,
33). The ACT, on the other hand, encourages patients to accept and not engage with their thoughts rather than trying to eliminate them. This is associated with improved body image and decreased self-criticism regarding their appearance. This therapy encourages patients to separate their ideas and feelings from their identity and who they are, thus mitigating the harmful impact of negative self-perceptions regarding appearance (
32,
36,
37). In fact, this therapy assists patients in letting go of the cognitive control strategies they used to engage in, not defusing with their problematic thoughts, and managing their unpleasant emotions (
38,
39).
This disengagement and detachment from self-critical thoughts is associated with a decrease in the person's sensitivity to negative attitudes regarding their appearance and acceptance of their current self (
40,
41). The use of defusion makes people feel less resentful towards their physical features. This method reduces unpleasant emotions, as well as negative thoughts and actions related to body image (
40,
41). Shame about appearance and internal and external avoidance of confronting appearance are significant issues in body dysmorphic disorder. Individuals who participate in ACT are urged to confront their shame, which may at first make them think more negatively about their appearance but eventually improves those thoughts (
16). Another important therapeutic strategy for improving body image is the reappraisal process, which is particularly addressed in ACT. This reappraisal reduces patients' excessive attention to and obsessions with their body image (
40,
41). Similar studies have also indicated that shame declines slowly at the start and middle of treatment, but improves more quickly after treatment and follow-up, because the individual learns to confront this shame, which initially raises shame but eventually leads to improvement. In fact, the patients learn to confront and communicate with the feeling of shame that they were avoiding. In an acceptance and commitment-based therapeutic approach, awareness and openness to unpleasant thoughts and feelings, including shame, is a key way to lessen the harmful effects of these internal experiences (
16,
18).
Additionally, PPT improves individuals’ body image by emphasizing their positive and adaptive traits and strengthening their positive attitude towards intrapsychic and interpersonal issues. In fact, improving individualism, self-actualization, and positive subjective well-being can reduce negative symptoms, such as a poor self-image, particularly regarding one's body (
10,
42). Indeed, according to the PPT approach, strengthening positive thoughts can help improve symptoms of psychological problems. When symptoms such as concerns about appearance or body image increase, there is a greater need and necessity for having pleasure, meaning, and a purposeful life. This can be strengthened by increasing positive thoughts and feelings or by confronting negative thoughts (
43,
44). Additionally, in this therapy, participants are encouraged to focus on the positive characteristics of their looks, which contributes to the enhancement and reinforcement of individuals' positive appraisal of their own bodies (
43,
45). On the other hand, enhancing a positive attitude toward one's own body and giving oneself positive feedback in front of the mirror are crucial for enhancing one's body image. This intervention took into account another crucial element in enhancing body image. However, it can be argued that one of the most significant issues for patients with body dysmorphic disorder is distorted body perception, shame about their appearance, and avoidance of confronting negative thoughts about body image (
16). This is especially evident when considering the greater effectiveness of ACT compared to PPT. However, in the ACT approach, in addition to self-compassion, accepting negative thoughts and perceptions of one's body gradually reduces the effects of negative thoughts while also improving a positive attitude toward the body.
This study also found that patients with body dysmorphic disorder who received PPT and ACT showed improvements in emotion regulation. However, the rate of improvement in ACT was higher than that of PPT, which is in line with other studies (
20,
46,
47). In ACT, individuals primarily learn to put their negative experiences in a compassionate framework, which enables them to have a kind of appreciative and empathetic attitude toward themselves even in stressful situations and, consequently, experience fewer emotional problems (
46,
48). This may help to explain these findings. One of the most important components of emotion regulation is acceptance and non-avoidance of unpleasant emotions, which is one of the most important key concepts and therapeutic goals of ACT (
20,
21). Patients learn to observe emotions independently of whether they are pleasant or unpleasant, and to accept them without becoming involved, using mindfulness techniques. This acceptance leads to a reduction in the negative impact of negative emotions and an increase in self-compassion. This acceptance also enhances distress tolerance, which improves the individual's emotion regulation skills (
16).
5.1. Conclusions
Overall, the findings of this study suggest that ACT is an appropriate treatment for patients with body dysmorphic disorder, and that mental health psychotherapists can use this therapy to improve body image and emotion regulation problems in these patients. Since many of these patients are encountered in non-psychiatric settings, psychologists can help prevent the adverse effects of unnecessary medical interventions by accurately diagnosing and identifying these individuals, thereby enabling the provision of appropriate treatment. Furthermore, because issues related to body image are becoming more common in society, the severity of the disorder can be alleviated by diagnosing and recognizing these people and intervening in a timely manner using an effective ACT.
5.2. Limitations
Despite achieving our goals, the present study also had some limitations that should be considered when generalizing the findings. First, the present sample included women, which limits the generalization of the findings to men. Despite the three-month follow-up period, it seems that longer follow-up periods are needed to examine the durability of treatment. Furthermore, questionnaires were employed to measure the outcome variables in this study, which, due to the nature of the instrument and the psychological characteristics of the individual at the time of completion, could result in bias. Consequently, it is recommended that future research on the efficacy of these therapies be carried out with a longer follow-up time and in a gender-balanced sample including both men and women. Additionally, more precise and objective instruments are better suited to assess the efficacy of the therapy process.