Childhood obesity is a critical public health issue that has substantially increased worldwide [1,2]. Obesity is associated with metabolic and cardiovascular risks at all ages, but it is particularly risky at ages 2 to 19 years due to early complications [2,3]. According to UNICEF (United Nations International Children's Emergency Fund), at least 1 in 20 children under 5 years old has obesity; the prevalence in children over 5 years and adolescents increases to 1 in 3 [4]. Mexico ranks first in childhood obesity in the world, with 37.3% of schoolchildren and 41.1% of adolescents with overweight and obesity [5]. Lifestyle is a crucial risk factor for obesity; among obesogenic environments are unhealthy diets high in saturated fat, simple carbohydrates, and sugary drinks, as well as low physical activity (PA) with long periods of sitting [6,7]. Family factors, such as dysfunctional families and parents’ low educational levels, are also fundamental in childhood obesity. Lyons et al [8] reported that family discord influences children’s eating habits, with a higher risk of eating disorders later in life. Other studies indicated that mothers’ perceptions of the child’s body image are a risk factor for childhood obesity. Mothers of children with overweight or obesity tend to underestimate their children’s weight, representing a barrier to obesity diagnosis and treatment [9]. On the contrary, psychosocial well-being is a protective factor since it reduces emotional and behavioral disorders that could lead to obesity in children and adolescents [10].

Paradoxically, mild to moderate food insecurity and childhood malnutrition are also associated with a higher prevalence of obesity [11]. Low- and middle-income countries have the highest prevalence of malnutrition: undernutrition (11.5% growth retardation and 1.4% emaciation) and overweight (8.5%), placing Mexico in seventh place for child malnutrition in Latin America. Both obesity and malnutrition are risk factors for complications such as type 2 diabetes (T2D) and cardiovascular diseases, which in turn cause high mortality rates and decreased productive life [12]. Unfortunately, T2D in adolescence and childhood has increased, reaching a diagnostic prevalence between 0.68% and 1.2% [13]. Childhood obesity negatively affects cardiac and vascular structure and function; it triggers metabolic conditions such as insulin resistance, elevated serum uric acid, and metabolic syndrome, among others [14]. Estimates suggest that in the future, obesity-attributed coronary heart disease will increase by 5% to 16% [15].

Regarding lifestyle risk factors, studies have shown that 67.6% of schoolchildren and 46% of adolescents are sedentary, while 80.1% and 91.5% spend more than 2 hours in front of a screen. This leads to an increase in BMI and, therefore, a decrease in cardiovascular health [16]. On the contrary, a healthy diet is one of the main protective factors. Each region has traditional diets that, generally, are healthy and promote biodiversity and food security with low environmental impact. The traditional Mexican diet (TMexD) is a healthy and sustainable diet that promotes dietary diversity and encourages the consumption of local foods [17]. The TMexD includes plant foods such as fruits, vegetables, and whole grains, as well as animal-based foods, which provide fiber, vitamins, minerals, antioxidants, protein, and healthy fats. Promoting TMexD among Mexican schoolchildren, especially at ages 6 to 12 years, is crucial because they are more selective and demanding when it comes to consuming food [18]. Regarding PA in childhood, recommendations include at least 60 minutes per day in addition to limiting screen time to 2 hours per day or less [19]. Therefore, it is essential to implement behavior-change interventions promoting healthy diets and PA for childhood obesity prevention [20].

Multiple studies have concluded that it is easier to prevent obesity at early stages of life than in adulthood [18]. These interventions must take into account lifestyle settings and conditions such as those found in schools, homes, families, etc [21,22]. Proposals should focus on generating changes in eating habits, increasing PA, and raising awareness about the importance of healthy lifestyles among children and adolescents [15,23]. With a comprehensive intervention and its evaluation in low-income communities, the most unprotected social sectors will be prioritized [24].

Home and school are the most influential places for children. The school is considered a suitable and safe environment for programs promoting healthy lifestyles [25]. Studies have reported that school interventions focused on reducing obesity are successful because schoolchildren are at an age where healthy habits can be instilled and maintained in the long term [26,27]. On the other hand, parents as providers also influence nutrition during school years since children usually consume what is available at home. Furthermore, researchers focus on schools as a fundamental component to ensure the development of students’ personalities and habits, as well as to promote their multiple intelligences, skills, abilities, and behaviors. From this age forward, the educational center is a privileged environment to achieve a balance of these pillars that will last throughout life [28]. Thus, it is a priority for schools to promote healthy habits [21].

Globally, there are successful programs promoting healthy habits. The Diabetes Prevention Program is one of the first T2D preventive programs that has been adapted for use in school settings [29,30]. In Mexico, programs such as “Specific Action Program 2007-2012 School and Health,” “National Strategy for the Prevention and Control of Overweight, Obesity, and Diabetes,” and others have been developed for obesity and T2D prevention and have been taken as a basis for interventions in some Mexican elementary schools [31-33].

The present intervention protocol addresses childhood obesity in an integrative and unconventional manner, generating multifactorial knowledge about family behavior, individual factors, and the school environment. The aim of this protocol is to measure the effect of an intervention designed for low-income Mexican schoolchildren, focused on promoting healthy lifestyles for the prevention of obesity and cardiometabolic diseases. Specific aim 1 is to analyze whether baseline anthropometric and behavioral variables are associated with psychosocial well-being, family interaction or functionality, and perceptions of childhood obesity in the home environment. Specific aim 2 is to evaluate the effectiveness of the intervention in terms of retention, motivation to change, fidelity, and acceptability of the program by schoolchildren. Specific aim 3 focuses on evaluating changes in health behaviors at the end of the intervention and after 6 months in knowledge, diet quality, exercise time, and sleep time and quality.

From October 2023 to August 2024, a total of 451 participants were recruited from 4 different elementary schools in Sonora, México. As of February 2026, the collected data are in the process of analysis and interpretation. Table 3 presents the current status of each stage of the protocol as of February 2026.

Lifestyle interventions in early life are critical to reducing future disease risk and health care costs. During recent years, most of the research has been toward adult behavior [23], but recently, successful programs have been adapted to children and adolescents [21,33], representing an opportunity to extend their benefits to youth. For a greater probability of success, participant and setting characteristics should be accounted for. Places where children spend most of their time are school and home; schools represent a structured environment for the implementation of planned activities, fostering knowledge acquisition and sustainable behavioral changes. Within schools, a broader population is reached, and participants support each other, sharing experiences [25,26,74].

Two main biological models have been proposed to explain obesity: the carbohydrate-insulin model [64] and the energy balance model [75], the latter reinforced by current evidence on the high energy contribution of UPFs. Our intervention is primarily based on the carbohydrate-insulin framework, which posits that diets high in rapidly absorbed carbohydrates—often from UPFs, also high in energy, saturated fat, and sodium—promote hyperinsulinemia and adiposity. Accordingly, the intervention focused on improving carbohydrate quality and overall dietary patterns by reducing UPF consumption, along with structured PA to improve insulin sensitivity and body composition, and therefore reduce obesity. Secondary cardiometabolic outcomes were examined within this same framework, given the influence of diet and PA on metabolic and vascular health. Taken together, it is hypothesized that these behavioral changes improve insulin sensitivity, inflammation, and vascular function, thereby reducing cardiometabolic risk.

Theories such as the SCT, the TTT, and the BCW have been used as a framework in obesity studies. The SCT characterizes behavior, with self-efficacy as the greatest motivator and mediator of actions, highlighting the importance of setting goals, social and professional support [54]. Activities are planned from informing to putting practices into action to create a healthy lifestyle through education, motivation, persuasion, development of capacities, modeling, and training. The BCW indicates that for a change in behavior, capacity, opportunity, and motivation must be present [56]. With respect to the TTT, it assumes that behavior change develops in staggered stages, and while the intervention is implemented, participants may progress through stages as they increase awareness, motivation, and engagement in health-related behaviors [55]. In the present study, the transtheoretical model was used as part of the conceptual framework, and although participants were not formally classified into discrete stages, intervention activities were designed to target key processes across stages of change, progressing from awareness and outcome expectations (precontemplation/contemplation) to self-efficacy and planning (preparation), to practice (action), and finally to reinforcement and self-monitoring (action/maintenance).

Within the intervention, components align with constructs in Table 1, targeting cognitive, psychological, and physical capability through knowledge acquisition, skills training, and observational learning, while reflective and autonomous motivation were addressed by enhancing self-efficacy, outcome expectations, self-regulation, and reinforcement processes; social opportunity was incorporated through group-based activities, reducing contextual barriers to healthy behaviors. As summarized in Table 1, theoretical constructs from the SCT, COM-B, and transtheoretical model were operationalized using psychosocial and behavioral indicators assessed, in most cases, with validated instruments.

The study’s conceptual model in Figure 2 posits that the intervention influences outcomes indirectly through internal processes and individual factors. Mediating variables such as BIP and adherence to the TMexD, among others, strengthen personal and social resources, thereby facilitating the adoption and maintenance of healthy habits. Moderating variables (such as sex and location, etc) shape the context in which these changes occur and potentially influence how individuals interpret, assimilate, and respond to the intervention, ultimately modulating observed outcomes.

Regarding child nutrition, Bujtor et al [76] identified that unhealthy dietary patterns high in fat and sugary drinks were associated with impaired body composition and inflammatory biochemical parameters (ie, inflammatory cytokines, C-reactive protein, total cholesterol, triglycerides, glucose, and insulin) [77]. Likewise, healthy dietary patterns (ie, those rich in fruits and vegetables and low in UPF and sugary beverages) should be promoted from early childhood, given that children tend to exhibit greater food selectivity. With respect to PA patterns, studies reported that almost 50% of children and adolescents usually spend more time in sedentary activities (ie, screen time), consuming more sugary and salty foods, with an increase in weight and body fat [15,78]. On the contrary, an active PA pattern is associated with improvements in adiposity [79], self-esteem, mental health [80], quality of life, cognitive abilities, academic performance, etc [81]. Even low-intensity PA promotes favorable health changes in children and young people with obesity [1].

As reported by Heggmen and Zahl [82], children from rural communities have a higher risk of overweight, obesity, and unhealthy habits. Some causes include limited access to healthy foods, less space availability for PA, and less nutrition and health education. However, children from urban communities are also at risk of obesity due to their social environment: globalization, modernization, cultural changes, and low economic conditions [74]. This proposal includes participants from rural and urban communities and schoolchildren from mestizo and indigenous origins, ensuring equity, cultural relevance, and social justice, reducing the gap and improving external validity due to participants’ diversity [25-27].

Among the indicators of effectiveness are efficacy, acceptance, knowledge acquisition, motivation, etc [70-73]. Knowledge acquisition assesses participants’ learning process; by working on the learning constructs, a change in long-term habits could be achieved [24,78]. Other critical variables are motivation and willingness to change, adherence to the intervention, retention, and dropout rates, which will be assessed by directed questions and statistical techniques (ie, intention-to-treat analysis). Fidelity consists of evaluating the practices used to ensure that the intervention is reliably and validly applied and that changes after the sessions can be attributed to the intervention and not to external factors, reducing the likelihood of errors and bias. Regarding participants’ understanding and involvement, attention, positive attitude, active participation, class work, attendance lists, etc, will be assessed using checklists. Supervision instruments monitoring the organization, planning, execution, and use of the protocols and the curriculum manual are also important [83,84]. Acceptability indicates how participants perceive the intervention; if it is not well accepted, it can generate a lack of commitment and reduced effectiveness. Once participants take ownership of the intervention, they are more likely to maintain their practices even after the intervention ends [71,72].

Among the strengths are its reach and accessibility, as it was conducted in schools where children spend a lot of time, representing a realistic and ideal environment for a large number of participants, with a lower probability of withdrawal. School age represents a critical growth period in the formation of lasting habits, and children can be multiplying intervention agents in their families. Another strength is the involvement of rural and urban schools, which promotes equity and reduces the disparity in cardiometabolic risk between both communities. The experimental design using school groups as units optimizes resources and allows for a larger number of schools to be intervened. Another advantage is the comprehensive approach for assessing family habits such as adherence to the TMexD and psychosocial variables. Individual variables such as diet, sleep, and PA times are fundamental in lifestyle habits, and evaluating the intervention in terms of feasibility, viability, retention, and acceptability allows measurement of the sustainability of acquired skills over time. Regarding the use of repeated-measures ANOVA, this is a robust tool in this type of study evaluating participants at multiple times.

Among the limitations, classrooms were randomized within schools, which, while not the optimal design for this type of study, enabled us to offer the intervention to more participants in each school. Logistical and funding constraints limit a second-year waiting-list control design, leading us to prioritize implementation across multiple schools. School schedules (eg, recess, arrival, and dismissal) are structured to minimize interaction between classrooms, reducing the likelihood of contamination. Nevertheless, we acknowledge that some contamination may occur and will address this with appropriate statistical analyses. Another limitation is the relatively low sample size for this kind of study, since this type of design requires a larger number of participants and the use of robust statistical methods. However, our research design is comparable to similar studies [74].

The age of participants may also limit their responses, since younger schoolchildren find it difficult to express themselves and remember data (ie, quantity of food and time of PA). This could be improved through greater interaction between staff and participants to build trust and facilitate recall of daily activities, enhancing the accuracy of responses. Regarding the self-reported estimates of PA and dietary intake, they depend on short- and long-term memory, showing greater variability compared to other objective measures [85,86]. However, the 3-day physical activity recall and the 24h-R are validated instruments widely used in the child population [87,88]. The use of few repetitions of the 24h-R does not ensure the measurement of between- and within-person variability; however, administering more repetitions could increase the challenges inherent in data collection in children and adolescents, who may have difficulty sharing information about their behaviors and may experience mental burden and stress [89]. Another limitation is that other important social actors in the student’s life, such as parents, will not be involved; however, the involvement of teachers, and especially classmates, is possible. The curriculum implementation depends on the time available in the school curriculum itself; however, if the intervention begins alongside the school year, it optimizes time and makes it easier to complete it. Another opportunity for future studies is to include other crucial variables such as quality of life and self-esteem, which are important at this stage. Concerning multilevel models, these require larger sample sizes, involve more complex assumptions, and may be sensitive to model misspecification. However, these are well suited for group-randomized trials, as they account for data grouping, provide valid standard errors, accommodate missing or unbalanced data, and allow the simultaneous examination of individual- and group-level effects, thereby improving statistical efficiency and inference.

In conclusion, the proposed protocol represents a comprehensive program and an effective and feasible strategy to promote healthy lifestyles and prevent cardiometabolic diseases, addressing low-income schoolchildren in Mexico. It is important to continuously evaluate and adapt the intervention to ensure sustainability and expand its impact to other schools. The implementation of this program can significantly contribute to improving children’s health and well-being by fostering positive habits from an early age and reducing the risk of obesity and cardiometabolic complications.