Recently, the consumption of convenience food has expanded, particularly among the younger generations and single-person households [1, 2]. In the context of convenience stores (CVS), convenience food refers to pre-prepared, processed, and packaged food, allowing consumers to consume it without the need for extensive cooking or through a simple and quick cooking process. CVS offer a convenient and easily accessible option for students to grab quickly a bite or purchase snacks during their busy schedules. Adolescence is a transitional stage leading to adulthood. Since adolescence affects not only growth and development but also health and disease conditions in adulthood, good eating habits in adolescence are desired [3, 4]. However, there are concerns on the nutritional status of adolescents [5, 6, 7, 8]. First, compared to other age groups, adolescents aged 12-18 years old typically have a higher sugar intake [5]. The “2021 Youth Health Behavior Survey” conducted by the Korea Centers for Disease Control and Prevention revealed some concerning trends regarding the consumption of sugar-sweetened beverages and fast food among students [6]. According to the survey, approximately 38% of students reported consuming sugar-sweetened beverages more than 3 times a week. This high frequency of consumption suggests a significant portion of students may be regularly consuming sugar-sweetened beverages, which can contribute to excessive sugar intake and potential health issues. Second, their excessive sodium intake cannot be overlooked. Sodium consumption from 2007 to 2015 consistently exceeded 200% of the adequate intake in high school students aged 16-18 years [7]. During adolescence, excessive sodium intake can have detrimental effects on calcium absorption, bone formation, and bone density [8]. Accordingly, Korean school meals have prioritized reducing sodium content [9, 10] and education on nutrition aims to encourage the consumption of potassium and magnesium-rich vegetables, as they facilitate sodium excretion [11, 12].

The Ministry of Food and Drug Safety (MFDS) announced the “Sodium and Sugar Reduction Plan” and set long-term goals for sodium and sugar intake. By 2025, daily sodium intake should be < 3,000 mg and sugar intake from processed foods < 10% of daily calorie intake [13]. According to recent amendments to the “Sodium and Sugar Reduction Labeling Standards”, the scope of products eligible for low-salt and low-sugar labeling has been expanded. This expansion now includes popular food items such as gimbap (rice rolls), instant cooked food soup, stew, hotpot, and commonly consumed ready-to-eat foods. This step aims to provide clearer information to consumers about the sodium and sugar content in these food products and facilitate healthier choices [14]. With this policy, the Ministry of Health and Welfare recommends the implementation of dietary action guide for adolescents [15, 16]. Along with the government, there are many actions to reduce sugar and sodium in school as well. For reduction practices, natural sugar such as grind pears and apples was used instead of added sugar in school meals, and raw tomatoes are used to reduce the amount of ketchup used. In addition, school meals are trying to reduced sodium by providing daily soup salinity measurement (0.4%-0.6%) or daily more grilled menu than stewed menu [17].

Both the government and schools have made significant efforts to reduce the sugar and sodium intake. Insufficient quality of nutrition education and limited exposure to comprehensive dietary guidelines can impact students’ behavior and understanding of healthy eating practices. Thus, the adherence to sugar, and sodium reduction policies, as well as the implementation of nutrition education programs, faces numerous challenges, especially in an environment with a growing CVS number.

This study aimed to examine the usage patterns of convenience foods, and the overall CVS use, among middle, and high school students based on the frequency of convenience food consumption at CVS. Furthermore, the study aimed to investigate the students’ attitude toward sodium and sugar reduction based on their frequency of convenience food consumption as well as their compliance with the dietary action guide provided by the Ministry of Health and Welfare.

The purpose of this study was to investigate the use patterns and eating frequency of CVS among middle and high school students and to explore the students’ attitude toward sugar and sodium reduction and their compliance with dietary action guide. The study focused on individuals who had a high frequency of consuming convenience foods, aiming to identify their specific characteristics and determine the essential elements for effective nutrition education. By understanding the traits and attitude of this group, targeted nutrition education strategies could be developed to promote healthier eating habits among this population.

Food labeling includes various information about food, such as the name of raw materials, net content, manufacturing, and expiration date, nutritional components, and warning signs on the packaging or container of the product to provide accurate purchase information for the consumers. It protects consumers by allowing consumers to choose foods that meet their needs [22]. In this study, the expiration date was carefully checked and the energy information mostly checked, indicating that education on nutrition labeling is well under way. Recently, as consumers’ interest in health increases, consumers' desire to maintain health through food is increasing, and accordingly, the importance of food labeling is emphasized as an institutional device to secure food safety [23, 24]. Nutritional facts, display the type, and content of nutrients contained in individual foods, convey appropriate information about nutrition to consumers, help in rational food selection and health management, and can be used as a nutrition education tool [25]. Korea first introduced nutrition labeling in 1995, and continues to expand, and enforce mandatory nutrition labeling items. Currently, adolescents learn about food labeling in the school curriculum, but previous research showed a relatively low level of awareness and knowledge of food labeling [26, 27]. In the 2010 National Health and Nutrition Examination Survey [27], only 31.4% of adolescents responded reading nutrition labels when purchasing or selecting processed foods. However, in a recent study, > 50% of the participants checked food and nutrition labeling [29], and in a large-scale study, 33.2%-58.7% of the participants checked the nutritional labeling [30]. The present findings showed that they mostly examined the expiration date (77.3%) and > 50% of participants paid attention to the calorie information provided on the nutrition label, while only few checked for the presence of food additives (9.3%). However, this study revealed a low proportion of participants checking sugar or sodium content in nutrition labeling. This suggests a significant knowledge gap among the participants in accurately understanding and interpreting nutrition labels. Thus, education and awareness campaigns focusing on sugar and sodium content in food products are necessary to improve their ability to make informed and healthier choices.

In this study, the convenience foods predominantly consumed by students were instant noodles (including triangular gimbap), chocolate, ice cream, and soda. Instant cup noodles and triangular gimbap have high sodium content, while chocolate, ice cream, and carbonated drinks have high added sugar content. For gimbap (including kimchi gimbap, cheese gimbap, ham gimbap, etc.), the sodium content ranged from 1,200 to 1,400 mg per serving, whereas for triangular gimbap, the sodium content varies between 300 and 700 mg per serving [31]. As for chocolate, the calorie content per 100 g was 500-600 kcal, and the sugar content 23-45 g, depending on the type [32]. For Coke, a representative carbonated drink, a single serving (250 mL) contained 112 kcal of energy and 27 g of sugar [31]. Overall, most convenience store food consumed by students had a high in sodium and sugar content. Several studies have reported an association between salt intake in adolescents and various diseases. Rafie et al. [33] showed a positive association between sodium intake and obesity among Iranian children and adolescents. In a cross-sectional data analysis from the National Health and Nutrition Examination Survey conducted between 2009 and 2016, involving 9,026 children and adolescents, sodium intake was positively associated with being overweight, obesity, and central obesity in American children, even after adjusting for energy intake [34]. Similarly, the consumption of added sugars among adolescents has been associated with various diseases such as obesity and related metabolic risks, including insulin resistance, type 2 diabetes, hypertension, and metabolic syndrome [35]. Furthermore, an association between sugar and salt intake has been reported on a study involving Chinese adolescents [36]. After stratifying by sex, grades, and puberty status, dietary sodium intake was positively associated with sugar-sweetened beverage consumption in Chinese children and adolescents, particularly in young children. Especially for participants with a high frequency of convenience store visits, significantly more reported consuming chocolate and carbonated beverages ≥ 3-5 times a month than in other groups. Therefore, the intake of added sugar can be a major health concern for these individuals. Excessive sugar intake from consuming an excessive amount of carbonated beverages has been linked to an increase in the number of obese adolescents. Indeed, it is important to provide comprehensive nutritional education for adolescents on sugar and sodium intake including the potential health risks associated with their excessive consumption.

In response to the dietary action guide of the Ministry of Health and Welfare, it was found that there was in sufficient efforts to reduce their intake of sodium, sugar, or greasy foods. However, individuals who frequently visit CVS exhibit a greater determination to reduce their consumption of these substances. This suggests that those who frequently utilize CVS are aware of the nutritional issues associated with sugar, sodium, and fat. They may experience a sense of guilt due to their frequent consumption in their daily lives, leading to a heightened desire to actively reduce their intake. This highlights the importance of addressing nutritional awareness and promoting healthier food options within the CVS environment to support individuals in making healthier choices. Kwon [37] found no significant correlation between the level of sodium-related nutritional knowledge and actual sodium-related eating behaviors, suggesting that changes in perception may not translate into behavioral changes. Recent studies on American adolescents also reported high salt intake and low adherence to dietary guidelines [38]. Despite ongoing nutritional education for adolescents, simply providing knowledge may not be sufficient to drive significant reductions in sodium and sugar intake. Additional strategies and interventions are needed to effectively translate knowledge into behavior. This could include implementing policy changes, creating supportive environments, promoting healthier food choices, and engaging adolescents in interactive and practical activities that reinforce healthy eating habits.

Nutrition education is an effective method to help adolescents form healthy eating habits. In a study on changes in eating habits and nutrition knowledge after sodium nutrition education, Ahn et al. [39] reported a significant difference in sodium awareness between the education and control groups after education. Previously, Salam et al. [40] showed a positive score increase after nutrition education, demonstrating the educational effect of nutrition education on eating behavior in school-children. In addition, there were positive changes in items related to dietary attitudes and behaviors, indicating that nutrition education contributes to changes in children's eating behaviors. However, to maximize the effectiveness of this intervention, continuous training is needed.

The study presented evidence suggesting that frequent use of CVS by adolescents may be associated with higher sugar and sodium consumption. Additionally, although awareness of reducing sugar and sodium was high, individuals did not consistently check this information on nutritional labels. These findings underscore the need for comprehensive nutrition policies and education programs that emphasize the importance of carefully checking the details of nutrition labeling. On the other hand, the number of CVS across the country is increasing, and the convenience foods sold there are becoming more diverse and convenient [1, 2]. In addition, middle and high school students’ use of convenience foods are expected to gradually increase, considering their lack of time for meals due to excessive schoolwork and preference for stimulating and palatable foods rather than nutritive ones. By providing targeted education on the potential health impacts of consuming high-sugar and high-sodium foods, individuals can make more informed choices and adopt healthier eating habits. Concurrent efforts should focus on both raising awareness on nutrition labeling and promoting healthier alternatives at CVS.

The present study has various limitations such as its small scale and specific geographical area. Therefore, the present findings may not be directly generalizable to all adolescents or different geographic locations. Additionally, the study did not account for other socioeconomic factors that could influence sodium and sugar perceptions. However, despite these limitations, the study is significant in deriving valuable elements for nutrition education implementation in schools and organizations. It can be used for policies that can increase the ability to practice eating habits, such as checking sugar and sodium content among middle and high school students when eating at CVS. This result can serve as foundation for large scale research, considering various socioeconomic factors. This will allow for a more comprehensive understanding of the factors influencing adolescents' food choices and enable the development of more effective nutrition education programs and policies.

The adolescents in this study mostly purchased items with high sugar and sodium content rather than healthy menus at CVS. Although they know that sugar and sodium should be reduced, they did not check sugar and sodium content in food labeling. This finding was independent of the number of visits to CVS; which indicates the need to clarify the importance of checking sugar and sodium content as well as calories. Therefore, customized nutrition education is needed for targets with high frequency of convenience food consumption at CVS.

Under the current learning environment of adolescents, it is difficult to reduce the rate of use of CVS. Since instant cup noodles are the most consumed by teenagers, it is desirable to control its sodium content or to make the sodium content stand out on the food label. Similarly, the sugar content in the product should be more visible. Alternatively, highlighting the sugar content of products or highlighting points such as “no sugar” could help adolescents make healthier choices.

In conclusion, it is crucial to recognize the differences in thoughts and behaviors among adolescents when designing and implementing broad nutrition education programs. Accordingly, a multidisciplinary approach is needed including comprehensive nutrition education only focused on basic nutrition but also on the importance of critical thinking, mindful eating, and understanding the impact of food choices on overall health.