The international community faces a multitude of interconnected challenges related to the economy, society, and environment. Since the Industrial Revolution, rapid economic and societal growth has enriched human life. However, this progress has come at a cost: a concurrent environmental and ecological crisis. The Intergovernmental Panel on Climate Change’s 2023 Climate Change Report [1] highlights the severity of the situation. Global annual mean temperature has risen by 1.09°C compared to pre-industrial levels, and projections indicate a 1.5°C increase by the mid-2030s if current trends persist. Alongside rising temperatures, we are witnessing rapid increases in sea surface temperature and sea levels. Extreme weather events, such as simultaneous heat waves, heavy rain, droughts, and tropical cyclones, are becoming increasingly common around the world.

Recognizing the need for a holistic approach to economic, social, and environmental issues, UNESCO spearheaded discussions that led to the global adoption of sustainability as a guiding principle. This principle now informs a wide range of policies, including dietary policies aimed at overcoming the challenges we face [2]. Examples of such policies include France’s Le programme National pour l'alimentation, the United Kingdom’s Food 2030, New York City’s NYC Food Policy, and Canada’s Regional Food System Strategy for Vancouver. All these initiatives emphasize dietary education that reflects sustainability principles [3]. In line with this global shift, the Korean Government has also embraced sustainable dietary education. In 2020, the Ministry of Agriculture, Food and Rural Affairs announced the promotion of sustainable diets through the 3rd ('20-'24) Basic Plan for Dietary Education [4].

The concept of sustainable diets has evolved beyond its previous emphasis solely on health (nutrition). It now encompasses diets that promote a range of social values across the entire food chain, incorporating considerations not only of health but also of environmental sustainability and responsible practices in food selection, storage, preparation, consumption, and waste management [4, 5]. Reviewing prior research on sustainable dietary education shows that it encompasses the domains of environment, health, and society.-In the environmental domain, studies by Kwon & Lee [6] and Oh et al. [7] demonstrated the positive impact of education programs on children’s environmentally friendly attitudes and their sustainable dietary competence. Kwon & Lee [6] used gardening activities, while Oh et al. [7] utilized food mileage and plant factory education programs. In the health domain, studies by Kim et al. [8] and Han & Lee [9] developed programs focusing on vegetables and reducing sugar consumption, respectively. These programs validated positive changes in nutrition knowledge and dietary patterns among elementary school students. For the society domain, Yoo & Kim [10] demonstrated the positive effects of character education activities based on a green diet on preschoolers’ awareness of life respect, community consciousness, and responsible behavior. Woo & Lee’s study [11] developed a sensory education textbook and teaching guidebook to improve children’s preference for traditional foods, aiming to inherit traditional food culture. They found that education using these materials positively affected student’s knowledge, table manners, and preference for traditional foods.

Building on a growing body of research on sustainable dietary education, this approach is now being implemented nationwide. In Seoul, it is known as “green school meals,” while Jeollanam-do uses the term “low-carbon green meals” [12]. These programs involve low-carbon school meals, which include Pesco (pescatarian) diets excluding beef but including fish, eggs, and other animal products. Despite the different names used in each region, they share a common goal of environmental sustainability, health, and society. The increasing adoption of sustainable dietary programs in various regions highlights the pivotal role of nutrition teachers responsible for imparting this sustainable dietary education. According to Article 8 of the Enforcement Decree of the School Meals Act [13], nutrition teachers are responsible for guiding students on dietary life, providing nutritional information and consultations, and educating the next generation on practicing sustainable dietary habits.

However, previous studies exploring sustainable practices by job domains [14, 15] have revealed that the education domain lags behind others. Additionally, research on the implementation of green school meals in Seoul found that the majority of nutrition teachers did not actively engage in educational aspects [16]. Given that the actual performance of sustainable dietary education in school settings has been reported to be low, it is crucial to identify measures that can increase the adoption of sustainable dietary education. To remove barriers and strengthen facilitations, we need to investigate the key factors that predict and explain the educational behaviors of nutrition teachers.

The theory of planned behavior (TPB), developed by Ajzen (1991) [17], is a widely used framework for predicting and explaining human behavior. It posits that intentions guide our actions, and these intentions are shaped by three key factors: attitudes toward behavior, subjective norms, and perceived behavioral control (PBC). The TPB has been applied across various research fields [18, 19, 20, 21] demonstrating particular effectiveness in explaining consumer behavior related to sustainable food choices and dietary habits [21]. However, no prior studies have utilized the TPB to specifically understand the behaviors of nutrition teachers regarding sustainable dietary practices. This research gap highlights the need for an empirical study in this area.

Furthermore, researchers have emphasized the necessity of extending the TPB model to encompass external factors that shape individual characteristics and behaviors, thereby enhancing its explanatory power [22]. PBC is a core construct within the TPB that reflects an individual’s subjective perception of their ability to control the resources and skills necessary for a specific behavior [17]. Subsequent research has differentiated PBC into internal PBC (IPBC) and external PBC (EPBC). Kidwell & Jewell [22] demonstrated that the expanded TPB model incorporating this distinction between IPBC and EPBC offered greater explanatory power compared to the original TPB model with a singular PBC construct.

Significantly, no prior studies investigating the educational behavior of nutrition teachers using the TPB framework have employed the expanded model with separate IPBC and EPBC constructs. The existing body of research on nutrition teachers’ educational practices suggests that their intention to engage in educational practices is not solely influenced by their confidence and abilities, but is also contingent upon external environmental conditions or constraints [23]. Hence, the adoption of the expanded TPB model, delineating between IPBC and EPBC, offers promising prospects for achieving a more profound understanding of the educational behaviors exhibited by nutrition teachers.

First, this study aims to assess the current level of awareness about sustainable dietary education among nutrition teachers based on the TPB framework. This assessment will then be used to investigate the factors influencing their intention to implement sustainable dietary education practices. Second, the study aims to demonstrate the potential of expanding the TPB model for understanding the educational behavior of nutrition teachers. This will be achieved by dividing the core TPB construct of PBC into IPBC and EPBC. Furthermore, this study seeks to establish baseline data that can be used to activate sustainable dietary education initiatives.

This study aimed to establish foundational data for promoting sustainable dietary education by exploring factors influencing nutrition teachers’ intentions to deliver such education, based on the TPB. Analyses revealed that a majority of respondents in Jeollanam-do delivered sustainable dietary education ‘0–5 times or less per year,’ indicating a relatively low frequency of such practice. This finding aligns with previous studies on the implementation of sustainable dietary education [14, 15, 16].

The low performance of education by nutrition teachers has been a persistent problem since the introduction of the Nutrition Teacher System in 2006 [14, 15, 16]. These challenges encompass various factors such as ‘work overload,’ ‘insufficient educational resources,’ and ‘systemic issues (e.g., not designated as regular class sessions) [16, 23, 26]. Therefore, specific measures are needed to increase the delivery of sustainable dietary education.

This study emphasizes the distinction between IPBC and EPBC within the TPB model. Traditionally, Ajzen [25] conceptualized PBC as a single construct encompassing both internal and external factors. Internal factors included skills, knowledge, background, and willpower, while external factors included access to support, time, and cost. Building upon this concept, Bang & Kim [18] divided PBC into IPBC and EPBC in their study of tourist behavior.

In contrast, previous TPB research on educational behavior among general teachers has typically treated PBC as a single domain [27, 28]. However, unlike general teachers, nutrition teachers have the dual responsibility of providing meal services and delivering education. Moreover, they often lack the institutional support structures commonly available in traditional classrooms, such as regular teaching schedules and standardized textbooks. Given these distinct circumstances, we argue that an expanded TPB model, differentiating between IPBC and EPBC, is essential for comprehending the specific barriers that impede nutrition teachers from delivering education. Furthermore, Jong’s study [23] found significant differences in the levels of internal and external factors hindering nutrition teachers from delivering educational behavior. Therefore, this study holds significance by demonstrating the need for the expanded TPB model, separating PBC into IPBC and EPBC, when investigating the educational behavior of nutrition teachers.

Our analysis based on the study model confirmed that all major variables were significantly associated with nutrition teachers’ intention to provide sustainable dietary education. Among these variables, EPBC had the strongest influence. A high level of EPBC signifies that a nutrition teacher perceives greater control over external resources, which in turn strengthens intentions to deliver education and ultimately leads to its implementation. Despite its significant influence, the nutrition teacher’s overall perception of EPBC was the lowest among all the variables. Similarly, Jong’s study [23] which explored factors affecting intentions to deliver nutrition education found that external challenges, such as ‘work overload’ (55.6%), ‘not included in the regular class session and insufficient materials’ (26.2%), and ‘time constraints for delivering education’ (13.5%) were significantly higher than in internal factors like ‘lack of knowledge and confidence of nutrition teachers’ (3.2%). This confirms that the greater barrier posed by external factors in delivering education compared to internal factors.

While Jong’s study [23] focused on pre-existing nutrition education emphasizing health, this study examined sustainable dietary education, encompassing broader concepts and scope that include environment, health, and society domains. Despite the expanded curriculum and content of dietary education reflecting current trends, both studies reveal the consistent challenge of insufficient external resources for teachers to effectively deliver education. This suggests that the current external resource system remains inadequate to support educational activities among nutrition teachers.

The role of the nutrition teacher in delivering sustainable dietary education is crucial, but individual efforts alone are insufficient. Therefore, alongside content development and curriculum refinement for sustainable dietary education, active support through external resources is necessary at national, community, and school levels to empower nutrition teachers to deliver education effectively.

Since EPBC is the most influential factor for intentions to deliver education, the study further investigated differences in EPBC based on subject characteristics to identify additional measures for strengthening it. First, nutrition teachers reported a higher level of EPBC compared to dietitians. This finding aligns with Lee’s study [15], which demonstrated significantly higher self-assessment scores among full-time nutrition teachers compared to part-time dietitians. Part-time dietitians, not formally classified as teachers, may perceived less responsibility and duty toward delivering nutrition education [29]. Therefore, efforts to improve attitudes and perceptions of part-time dietitians regarding sustainable dietary education, along with systemic support, are also necessary.

Second, nutrition teachers in elementary schools had higher EPBC compared to those in middle/high schools. This aligns with Yu’s study [29], which found the lowest performance level of nutritional education in high schools, possibly due to students’ focus on academic and college entrance exams. Therefore, active support for expanding the implementation of sustainable dietary education in middle/high schools is needed.

Third, the level of EPBC was higher among those working in schools providing one meal per day compared to those with 2 or more meals. This suggests that a higher meal frequency (increased workload) translates to a lower perceived level of control over resources needed for delivering education. Therefore, establishing realistic measures and plans to improve the level of EPBC is crucial, such as reducing workload and intensity for nutrition teachers, and potentially increasing the number of nutrition teachers on staff.

Attitude emerged as the second most influential factor in intentions to deliver education in this study. A significant positive association was found between attitudes and intentions, suggesting that nutrition teachers with more positive attitudes toward sustainable dietary education are more likely to deliver such education. Similarly, Oh’s study [27] found that elementary school teachers’ attitudes had the strongest positive influence on intentions to improve mathematics instruction. These findings suggest that regardless of whether they are nutrition teachers or general teachers, positive attitudes toward education are generally linked with stronger intentions to deliver that education.

This study found that current nutrition teachers generally held positive attitudes toward sustainable dietary education. We believe this may be related to the actual practice of such education. While most respondents reported delivering sustainable dietary education ‘0 to 5 times’ per year, a significant portion delivered education more frequently. This engagement with education delivery may contribute somewhat to the positive attitudes observed among the teachers.

Therefore, promoting the value and effectiveness of positive attitudes through workshops or campaigns that showcase successful cases of sustainable dietary education programs is essential. Additionally, efforts to maintain and reinforce positive attitudes among nutrition teachers toward sustainable dietary education are necessary.

IPBC emerged as the third most influential factor affecting intentions to deliver education. A higher level of IPBC signifies that an individual perceives greater control over their internal resources, ultimately leading to stronger intentions to deliver education and ultimately its implementation. This interpretation highlights the importance of nutrition teachers’ perceived control over their internal resources for effectively delivering sustainable dietary education.

To improve IPBC, developing and expanding workshops and training programs related to sustainable dietary education is crucial. Our study found that participants in relevant training programs had significantly higher levels of IPBC compared to non-participants, emphasizing the need for active collaboration among various stakeholders to develop and expand such programs. Therefore, active collaboration is required among various stakeholders, including metropolitan and provincial education offices, local universities, training institutions, relevant associations, and the Korean Dietetic Association, to develop and expand workshops and training programs related to sustainable dietary training.

Subjective norms, which refer to the perceived influence of others on an individual’s behavior, emerged as the fourth and final factor affecting intentions to deliver education. A significant positive association was found between subjective norms and intentions, indicating that a higher level of perceived social pressure translates to stronger intentions to deliver education. This finding differs from Chung’s study [14], which identified subjective norms as the most influential factor in nutrition teachers’ desire to implement sustainable dietary education. It is important to note that Chung’s study [14] examined the comprehensive scope of sustainable practices for nutrition teachers, encompassing duties like purchasing, menu planning, operations, waste management, education, and promotion/management. In contrast, our study focused solely on the educational aspect of sustainable dietary practices, which is just one component of a nutrition teacher’s responsibilities.

These differing results suggest that the level of subject norms may vary depending on the specific work scope of nutrition teachers. Nevertheless, despite the observed difference in degree, subjective norms remain a significant factor influencing intentions to deliver sustainable dietary education. Therefore, it is crucial to cultivate positive subjective norms among nutrition teachers by fostering active interest, support, and cooperation from those around them, including other nutrition teachers, kitchen staffs, colleagues (principals and general teachers), and students/parents.

This study has some limitations. While this study focused on exploring the intentions of nutrition teachers to deliver sustainable dietary education, it did not directly assess their actual performance in delivering such education. Future research should address this gap by examining the actual delivery of sustainable dietary education as a dependent variable. Additionally, the study’s sample was limited to Jeollanam-do and exhibited an unequal sex distribution, warranting future studies with a more balanced representation and a broader nationwide sample. Future studies should investigate whether sustainable dietary education is being conducted in a balanced manner across all domains, including environment, health, and society.

Despite these limitations, this study is significant for several reasons. It is the first to investigate the comprehensive scope of sustainable dietary education practices in Jeollanam-do, an area where prior research on this topic is lacking. Additionally, this study contributes to the theoretical foundation by employing TPB framework to understand nutrition teachers’ perceptions and intentions regarding sustainable dietary education. It also offers strategies to activate dietary education programs and suggests the potential for expanding TPB research among nutrition teachers by differentiating PBC into IPBC and EPBC. Overall, the findings from this study can inform the development of policies and systems to support sustainable dietary education initiatives.

This study was conducted to provide foundational data for activating sustainable dietary education by exploring individual motivational factors influencing the intention of nutrition teachers in Jeollanam-do Province, South Korea, based on the TPB framework. These findings suggest that improvements in nutrition teachers’ attitudes, subjective norms, internal perceived behavioral control, and external perceived behavioral control regarding sustainable dietary education would lead to a positive increase in their intentions to deliver such education. However, it was noted that nutrition teachers' actual perceptions of external perceived behavioral control, the most influential factor on educational intention, were relatively low. We anticipate that this study will contribute to promoting sustainable dietary education by strengthening facilitating factors and addressing barriers identified in this study.