Obesity is a public health problem, as pointed out by the Risk and Protective Factors for Chronic Diseases Surveillance Telephone Survey, which found that its prevalence almost doubled from 2006 to 2023 (from 11.8% to 24.3%) in the Brazilian adult population [1]. Among users monitored in Primary Health Care (PHC) units between 2008 and 2019, the prevalence of obesity had an annual variation of 6.4% (from 14.5% to 28.5%) [2]. This growth trend suggests that the traditional care approaches based strictly on caloric restriction and energy expenditure have not worked. On the other hand, a broader approach, including behavior change, has been shown to be important to manage obesity effectively [3,4].

In Brazil, technical materials aimed at increasing the results of obesity management have been produced by the Brazilian Ministry of Health to qualify health professionals from the Sistema Único de Saúde (SUS, Unified Public Health System) [5]. The “Instructions for Collective Approach to Manage Obesity in the SUS” presents a “Strategy for the Care of Person with Obesity in SUS” focused on PHC and Specialized Care (here, this study will henceforth be called the “Strategy”). This “Strategy” combines the stage of change and the user’s self-efficacy to organize the care actions offered by the SUS [6]. It proposes that users ready to make behavioral changes aimed at weight loss, i.e., those in the most advanced stages, regardless of self-efficacy, and those in the decision stage and with high self-efficacy, should be directed to therapeutic groups [6].

A recent scoping study identified that the stages of change and self-efficacy are constructs of the Transtheoretical Model that should be used as predictive characteristics for interventions aimed at weight loss [7]. In Brazil, a randomized controlled clinical trial conducted with overweight women, which evaluated the effects of an intervention based on the Transtheoretical Model, obtained positive results for weight loss, diet, and biochemical profile [8].

Stages of change relate to a person’s readiness to change a particular behavior [9,10], such as weight loss. People can be classified into five stages: precontemplation, when someone has no intention to change behavior – lose weight – in the next six months, requiring awareness to change; contemplation, when the person recognizes that they need to lose weight but does not have a concrete plan to do so in the near future, as in the next month; decision or preparation, when the person is determined to lose weight and plans to begin the change in the next thirty days; action, when behavior changes for healthy weight have begun and continued for less than six months, which requires support for the continuity of this change; and maintenance, when this behavior change has been maintained for six months or more, being necessary to consolidate the gains made and avoid relapses [6,9]. On the other hand, self-efficacy is the confidence the person has in themselves to change and maintain a certain behavior over time [10]. Thus, the greater the self-efficacy, the more confident the person feels to set goals and achieve them, even in the face of obstacles; and the more advanced the stage of change may reach [11].

Considering self-efficacy in planning obesity management actions can lead to a greater resolution of the care offered, inducing changes and preventing relapses. Furthermore, it can provide a better alignment between motivation and confidence for change and the adoption of intervention strategies proposed by the health team. For this, questionnaires are needed that have proven validity and are easy to apply; however, no validated questionnaire is available for Brazil, especially applicable in the SUS. Therefore, the objective of this study was to translate, cross-culturally adapt, and validate a questionnaire that assesses self-efficacy to lose body weight for use in the SUS, as well as validate self-efficacy classification criteria proposed in the “Strategy” [6] to support the care of people with obesity in the SUS.

A psychometric study was conducted to translate, cross-culturally adapt, and validate a set of items to assess self-efficacy for weight loss and validate the criteria proposed by the “Strategy” [6].

The translation and cross-cultural adaptation of the self-efficacy assessment questionnaire for weight loss led to the exclusion of one item from the original questionnaire and the alteration of the text of some items and response options. Thus, three items on the questionnaire were proposed for use in the context of the SUS. After applying the questionnaire to people with obesity, a similarity was identified between those with high self-efficacy and those who had already made behavioral changes to lose weight, i.e., those who were in the final stages of change. In addition, the questionnaire presented high specificity, i.e., identifying users in ‘pre-action’ and those who were not confident about changing their behaviors to lose body weight.

The questionnaire includes situations that challenge the process of losing body weight and influence self-efficacy, such as having to rethink strategies and try to change several times, in line with the scientific literature. DeJesus et al. [23] identified lower confidence among those with severe obesity (BMI ≥40.0 kg/m²) despite the recognition and desire to lose weight. In addition, health conditions that impact the practice of physical activity, food cravings, and lack of knowledge about adequate and healthy food for weight loss were associated with lower confidence, impacting the effort spent, as well as the persistence to tackle obstacles and unsuccessful experiences [23]. In this sense, care that does not blame and stigmatize, with co-responsibility between professionals and users [24] and motivational support [23], is strategic to achieve better results [23,24], especially in the Brazilian epidemiological scenario of growing obesity [1]. By enabling the recognition of self-efficacy, the questionnaire can contribute to a greater assertiveness in defining the care plan with agreement between the health team and the user aimed at changing behaviors to lose weight.

Previous unsuccessful attempts to lose weight can also reduce self-efficacy and motivation [23,25]. In this scenario, a perspective that considers more than just body weight and is more sensitive to identify other beneficial changes achieved could restore self-efficacy. Brazilian regulations even recommend recognizing improvements in quality of life and sleep as indicators of obesity treatment resolution [24]. In addition, setting short-term goals and valuing the results achieved can enhance self-efficacy during the weight loss process [26].

Strengthening self-efficacy in obesity treatment is also fundamental for maintaining results over time, as greater self-efficacy can promote treatment effectiveness and help maintain the results achieved [26,27]. In a conceptual mapping study, low self-efficacy was identified as one of the main predictors for relapses of behaviors that negatively impact maintaining results [27]. A review of qualitative studies identified that individuals with greater self-efficacy adopt strategies that promote the maintenance of results, such as changing the food environment and seeking support [28]. This evidence strengthens the importance of assessing and monitoring self-efficacy in the treatment of obesity.

However, to measure self-efficacy in people with obesity, valid instruments applicable to the reality of health services are necessary. This study presented results that evidence the quality of the measure using a short questionnaire containing only three items with potential practical implications. Criterion 2 tested presented high specificity and very low to low PPVs, confirming the lack of readiness to change behaviors aimed at losing weight among people with high self-efficacy and in ‘pre-action’ (false positives). These results corroborate the applicability of the “Strategy” [6] by including, among other criteria, the concomitant assessment of the readiness to change and self-efficacy to direct users toward obesity treatment [6]. Thus, the evaluation of these two pillars of the Transtheoretical Model is complementary [6], allowing users ready for behavioral changes (in decision and with high self-efficacy, and in action or maintenance) to be referred to the appropriate treatment.

The questionnaire was also useful for identifying cases of ambivalence, with low sensitivity and NPVs ranging from low to moderate, producing false negatives, i.e., people determined to change but with low/moderate self-efficacy. In these cases of ambivalence, motivational groups, as proposed in the “Strategy” [6], are useful tools to promote readiness to change behaviors for weight loss as well as increase self-efficacy [10]. Individuals with severe obesity reported being determined to change, despite their low self-efficacy [23], and the development of groups with supportive motivational approaches enhances the confidence [25]. Therefore, use of the questionnaire by health teams enables a more assertive referral, in which users who need greater motivation to change receive the acceptance of their anxieties and understand the obstacles hampering treatment to strengthen trust and build readiness for change. In addition, the person making the decision may be focusing on potential barriers to weight loss to justify their low confidence and postpone starting changes. The joint use of other pillars of the Transtheoretical Model, such as balancing decisions and processes of change [6], can qualify the therapeutic approach, including the discussion of strategies to face obstacles and establish confidence.

Another important aspect of the questionnaire was its applicability to health services because the high demand for curative and individual assistance is one of the barriers to qualify the management of obesity in the SUS [29]. The sequential approach used for its translation and cross-cultural adaptation provided a quick, easy-to-understand questionnaire with possible direct answers, facilitating its application in everyday work. The availability of the questionnaire and the investigation of its evident validity are further efforts to increase obesity management within the SUS. However, professionals still must be encouraged to incorporate technical materials into their routine [30], recognize obesity as a problem, and plan healthcare actions [30,31].

Despite the satisfactory results, some limitations of this study should be considered. The use of online forms may have limited the contributions of the experts and healthcare professionals. However, this method provided diverse participation from different Brazilian macroregions. In addition, the forms used in the translation and cross-cultural adaptation included spaces for writing comments and suggestions. In the validation stage, the use of online forms may also have influenced the profile of respondents, even though sociodemographic characteristics were monitored. The greater participation of individuals with higher education could be a non-predominant characteristic among the population that uses the SUS. Studies including populations with less education and from macroregions less represented in this analysis may gather more evidence on the validity of the questionnaire in different scenarios.

On the other hand, the potential of the results is encouraging. The translation and cross-cultural adaptation and validation of a questionnaire to assess self-efficacy for weight loss meet the need to provide scientific evidence to qualify the treatment offered in the SUS [5]. In addition, the comparison between the original questionnaire and the back-translation made it possible to evaluate the quality of the translation; furthermore, the participation of health professionals in the comprehensibility study and the caution in providing a short questionnaire may lead to greater applicability of the scale. Finally, the validation study for using the questionnaire to care for people with obesity in the SUS gathered evidence about its ability to identify users who need to work on self-efficacy and be ready to change before starting obesity treatment.

The self-efficacy questionnaire for weight loss was successfully translated, cross-cultural adapted, and validated. Application of this questionnaire in adults with obesity validated the recommendation of the “Strategy” to evaluate self-efficacy levels in association with the classification in the stages of change to refer users to the treatment for obesity, contributing to the professional performance in the SUS based on scientific evidence. The results support the use of the questionnaire to achieve greater assertiveness in the care offered to people with obesity in the SUS, which is urgent given the epidemiological scenario of rising obesity in the country. Therefore, its application in daily care activities is recommended both to help identify readiness to change behaviors aimed at losing body weight, as proposed by the “Instructive of Collective Approach to Obesity Management in the SUS”, and to guide the construction of care plans and coping actions.