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INTRODUCTION
Young adults are at the stage of taking responsibility for their own food choices, nutrition management, and health. Eating behaviors and habits likely persist not only during this period but also into middle and later adulthood, potentially influencing health outcomes in later life. Therefore, it is important to impart desirable eating behaviors to young adults.
Excessive sodium intake is a behavioral risk factor for noncommunicable diseases such as hypertension, heart disease, stroke, cancer, and diabetes [1]. Sodium intake among individuals aged 19 years and over in South Korea has decreased over the past ten years, however, sodium intake was 142% of the chronic disease risk reduction intake in 2022 [2, 3].
To identify factors explaining nutritional behaviors, theories such as the social cognitive theory (SCT) and the transtheoretical model (TTM) have been used. SCT suggests that personal cognitive factors, behavioral factors, and the environment interact and needs to be reflected in examining health behaviors. Personal cognitive factors include outcome expectations, self-efficacy, and knowledge. Outcome expectations are a person’s expectation regarding the consequences, either advantages or disadvantages, of doing the behavior, whereas self-efficacy refers to confidence in one’s ability to perform the behavior. Behavioral factors include behavioral capabilities, intentions, and reinforcement. Constructs such as social support, normative beliefs, barriers, and opportunities of behaviors represent environmental factors [4]. TTM describes the stages of change that people experience, and the mechanisms they use when adopting or modifying health-related behaviors. TTM suggests that behavioral change progresses in five stages: precontemplation, contemplation, preparation, action, and maintenance stages. It emphasizes the use of behavioral modification strategies appropriate to one’s stage of change, thus making it possible to plan education that customizes one’s stage of behavioral change [5]. SCT and the stages of change have been applied to research such as identifying factors related to healthy eating behaviors, planning, and evaluating the effectiveness of nutrition education programs [6-9].
Research on sodium has focused on its intake [10, 11], and the association between sodium intake and chronic diseases [12, 13]. Several studies have examined psychosocial factors related to sodium intake, and these studies were conducted in different populations such as consumers, housewives, and foodservice workers [6, 14-17]. Applying the concepts of SCT, this study aimed to investigate whether there were differences in factors such as outcome expectations, self-efficacy, eating environment, and eating behaviors according to the stages of change in adequate sodium intake among university students in Seoul, Korea. Furthermore, this study examined the association between these factors and the stages of change in adequate sodium intake according to sex. The hypothesis for this study was those in the action stage might have higher outcome expectations and self-efficacy, a more supportive eating environment, and more desirable eating behaviors than those in the pre-action stage of change in adequate sodium intake. Furthermore, the relationship between these factors and the stages of change in adequate sodium intake may differ between men and women. This study provides data for planning nutrition education tailored to the stages of change in eating adequate levels of sodium in young adults.
METHODS
Ethics statement
The study protocol was approved by the Institutional Review Board of Seoul Women’s University (approval number: SWU IRB-2021A-26). Online informed consent describing the purpose and content of the study was obtained from each participant before they completed the online survey.
1. Study design
An online survey conducted between August 2021 and March 2022 was designed as a cross-sectional study. The study was performed in accordance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement, available at https://www.strobe-statement.org/.
2. Study participants
The participants were undergraduate and graduate students from nine universities in Seoul, Korea. The investigator posted a notice describing the purpose and content of this study through channels such as websites for student communities at nine universities and bulletin boards. Participants were recruited voluntarily, and those who agreed to participate completed an online informed consent form. The sample size was 341, based on the results of a previous study on population proportion [16], with a 95% confidence level, 5% margin of error, and a 10% dropout rate. We received 353 responses to the online survey, and data from 351 students (99.4%) were used for statistical analysis, excluding incomplete responses.
3. Measurement
1) Survey questionnaire
The questionnaire was made by reviewing literature on factors of sodium intake [6, 7, 9, 14, 15, 17, 18]. The questionnaire draft was revised several times considering content validity, and a pilot test was conducted with seven university students to validate it. The final questionnaire assessed general characteristics, stages of change in adequate sodium intake, outcome expectations regarding adequate sodium intake, self-efficacy, eating environment, and eating behaviors. General characteristics include age, sex, height, weight, grade, and residence type [7].
To examine the stages of change in adequate sodium intake, the item was developed based on the definition of the stages of change in the TTM [5]. Participants were asked to respond if they practiced adequate sodium intake and intended to do so if they did not. To help the participants understand adequate sodium intake, the amount of salt (limited to one teaspoon of salt per day when converting the sodium in food into salt) was suggested in the stages of change question, based on the World Health Organization’s (WHO) recommendation of a daily sodium intake goal of 2,000 mg per day [19]. Participants were categorized into the precontemplation stage if they did not practice adequate sodium intake (not limited to one teaspoon of salt per day) and did not intend to do so in the future. The contemplation and preparation stages were defined as not practicing adequate sodium intake but having the intention to do so within the next six months or the next month, respectively. The action stage was defined as practicing adequate sodium intake and have been doing so for less than six months, and the maintenance stage was defined as practicing adequate sodium intake for more than six months.
Outcome expectations regarding adequate sodium intake were constructed based on the literature [6, 7, 15]. Two subscales, the advantages (six items) and disadvantages of eating adequate sodium (eight items), were obtained through factor analysis. Cronbach’s α was 0.80 (total score of outcome expectations), 0.83 (advantages of eating adequate sodium), and 0.79 (disadvantages of eating adequate sodium). Self-efficacy consists of 13 items based on the literature [7, 14, 20]. Factor analysis revealed two subscales: self-efficacy for healthy eating behaviors (seven items) and sodium intake control (six items). Cronbach’s α was 0.85 (total score of self-efficacy), 0.88 (self-efficacy for healthy eating behaviors), and 0.75 (self-efficacy for sodium intake control).
The eating environment comprised eight items [20], and factor analysis revealed two factors: social environment (four items) and physical environment (four items). Cronbach’s α was 0.66 (total eating environment), 0.79 (social environment), and 0.45 (physical environment). Eating behaviors included twenty-five items [15, 17, 18, 20, 21] and were composed of three subscales: general eating behaviors (nine items), behaviors related to sodium intake (13 items), and behaviors related to sodium check (three items). Cronbach’s α was 0.70 (total score of eating behaviors), 0.79 (general eating behaviors), 0.76 (behaviors related to sodium intake), and 0.72 (behaviors related to sodium check).
2) Measurement and scoring of items
Each item was measured using 5-point scales ranging from ‘strongly disagree’ to ‘strongly agree’ (outcome expectations, eating environment) or ‘very difficult’ to ‘very easy’ (self-efficacy). To measure the eating environment, a response category was provided if each item did not apply to the participants. Item of eating behaviors was measured using 4-point scales from ‘0–1 days/week’ to ‘6–7 days/week’ (general eating behaviors) or ‘strongly disagree’ to ‘strongly agree’ (behaviors related to sodium intake, and sodium check).
The total score or subscale score of the variables was the summed score of each item, while reverse scoring the negative items. A higher total or subscale score indicates that participants have more positive outcome expectations, higher self-efficacy, greater influence from the eating environment, and better eating behaviors. In contrast, a higher score on the disadvantages of eating adequate sodium indicated that the participants agreed more on the disadvantages. A higher score for behaviors related to sodium intake also suggests that participants practice behaviors that increase sodium intake.
4. Statistical analysis
Statistical analyses were performed using the IBM SPSS Statistics (version 24.0; IBM Co.). According to the responses on the stages of change in adequate sodium intake, the participants were classified into the pre-action stage (precontemplation, contemplation, and preparation stage) and the action stage (action and maintenance stage).
To investigate the differences in variables by the stages of change group, t-test, χ2-test, and analysis of covariance (ANCOVA) were conducted. According to the analysis of general characteristics by the stages of change group, weight was used as a covariate in the ANCOVA to examine the relationship of variables with the stages of the change group. Factor analysis was conducted to obtain the subscales of the variables. To investigate the association of variables with the stages of change in adequate sodium intake according to sex, Spearman’s correlation analysis between variables and the five stages of change was performed. The statistical significance level was set at P < 0.05.
RESULTS
1. General characteristics of participants
With respect to the stages of change in adequate sodium intake, 77.2% of the participants were in the pre-action stage and 22.8% were in the action stage. The mean age of participants was 23.6 years and 58.1% were women (Table 1). There were no significant differences in age or sex according to the stages of change. The weight and body mass index of the action stage in women were significantly lower than those in the pre-action stage (P < 0.01, P < 0.05, respectively). Approximately 27.6% of the participants were enrolled in the College of Social Science, followed by the College of Natural Science (25.4%) and the College of Humanities (22.2%). Approximately 29.6% of the participants were seniors and 21.1% were graduate students. Sixty-three percent of the participants lived with family members, whereas 37% lived in dormitory rooms or boarding houses. College attendance, grade, and residence type did not differ significantly according to the stages of change group. The distribution of the stages of change according to sex was not significantly different (Table 2).
2. Outcome expectations by the stages of change in adequate sodium intake
The total score for outcome expectations regarding adequate sodium intake (possible score: 14–70) was 43.6 (62.3/100, Table 3). The total score was higher in the action stage than that in the pre-action stage (P < 0.001), suggesting more favorable expectations of eating adequate sodium in this group. Participants in the action stage agreed less with the disadvantages of eating sodium adequately than those in the pre-action stage (P < 0.001). More specifically, participants in the action stage perceived fewer disadvantages of eating adequate sodium than those in the pre-actin stage, such as ‘making me eat less of my favorite foods’ (P < 0.001), ‘foods and snacks are not delicious’ (P < 0.001), ‘difficult to reduce sodium alone when I eat with family members or friends’ (P < 0.01), ‘limitations in choosing processed foods’ (P < 0.05), and ‘difficult to choose a menu when I eat out’ (P < 0.05). None of the six items regarding the advantages of eating sodium differed significantly according to the stages of change group.
3. Self-efficacy by the stages of change in adequate sodium intake
The total self-efficacy score (possible score: 13–65) was 43.0 (66.2/100). Participants in the action stage scored significantly higher on total self-efficacy (P < 0.001), as well as on the subscales of self-efficacy for healthy eating behaviors (P < 0.001) and sodium intake control (P < 0.01, Table 4).
Ten of the self-efficacy items differed significantly according to the stages of change group. Those in the action stage perceived more self-efficacy in ‘choosing natural foods rather than instant foods or convenience foods’ (P < 0.001), ‘changing eating habits to reduce sodium intake step by step’ (P < 0.001), ‘cooking foods with low sodium’ (P < 0.01), ‘finding information and practicing methods for reducing sodium intake’ (P < 0.01), ‘using less seasoning on the table’ (P < 0.01), ‘checking nutrition labeling and choosing low-sodium foods’ (P < 0.01), ‘choosing snacks with less sodium or fruits instead of salty snacks’ (P < 0.01), and ‘choosing a low sodium menu when I eat out’ (P < 0.05). In addition, self-efficacy of ‘having meals composed of diverse foods regularly’ (P < 0.01), and ‘eating vegetables when I have meals’ (P < 0.01) were significantly higher in the action stage than those in the pre-action stage.
4. Eating environment by the stages of change in adequate sodium intake
The total score of the eating environment (possible score: 0–40) was 22.9 (57.3/100), and there was no significant difference between the stages of change group (Table 5). The subscale-level analysis revealed that the physical environment score was higher in the action stage (P < 0.05), while the social environment score was higher in the pre-action stage (P < 0.01). This indicates that participants in the action stage received more support from the physical environment to ensure adequate sodium intake. More specifically, participants in the action stage scored higher on the home as the environment for adequate sodium intake (P < 0.01), while participants in the pre-action stage scored higher on the support from ‘professionals’ (P < 0.01), and ‘friends’ (P < 0.01) for adequate sodium intake than the counterparts.
5. Eating behaviors by the stages of change in adequate sodium intake
The total score for eating behaviors (possible score: 25–100) was 61.2 (not presented in Table 6). Participants in the action stage scored significantly higher on eating behaviors, suggesting better eating behaviors than those in the pre-action stage (P < 0.001, Table 6). Subscale-level analysis showed that those in the action stage also scored significantly higher on general eating behaviors (P < 0.001) and behaviors related to checking sodium intake (P < 0.001), whereas they scored significantly lower on behaviors that increased sodium intake (P < 0.001) compared to those in the pre-action stage.
Fourteen of twenty-five items were significantly different according to the stages of change. Among the general eating behaviors, percentages of those having eating behaviors more frequently, including ‘eating 1–2 vegetables or vegetable side dishes at each meal’ (P < 0.01), ‘having 1–2 protein foods at each meal’ (P < 0.05), and ‘having breakfast’ (P < 0.05), was significantly higher in the action stage than the pre-action stage. Participants in the action stage also performed behaviors more likely, such as ‘using low-sodium foods’ (P < 0.001) and ‘choosing bland foods at restaurants’ (P < 0.05). Participants in the action stage than the pre-action stage performed behaviors related to sodium intake less likely, such as ‘eating hamburger, pizza or fried chicken’ (P < 0.001), ‘eating out or using delivery foods’ (P < 0.001), ‘eating instant foods’ (P < 0.001), ‘eating processed foods’ (P < 0.01), ‘eating all the liquid of soup, jjigae or noodles’ (P < 0.01), and ‘adding salt or soy sauce when the food or soup is bland’ (P < 0.05).
6. Relationship between the factors and the stages of change in adequate sodium intake
The correlation of factors at the total score level with the five stages of change in adequate sodium intake by sex are presented in Table 7. In men, the stages of change showed a significant positive correlation with eating behaviors (ρ = 0.273, P < 0.01), self-efficacy (ρ = 0.210, P < 0.05), and outcome expectations (ρ = 0.166, P < 0.05), although the correlation coefficient was not high. Similarly, the stages of change in women were more positively correlated with self-efficacy (ρ = 0.347, P < 0.01), and eating behaviors (ρ = 0.343, P < 0.01) than outcome expectations (ρ = 0.229, P < 0.01).
The correlations of the factors at the subscale level with the five stages of change are shown in Table 8. In men, the stages of change in adequate sodium intake were significantly associated with four of nine subscales, showing a relatively high correlation with the behaviors related to sodium check (ρ = 0.454, P < 0.01), followed by self-efficacy for healthy eating behaviors (ρ = 0.247, P < 0.01). As in men, the stages of change in women were significantly correlated with the behaviors related to sodium check (ρ = 0.364, P < 0.01), and self-efficacy for healthy eating behaviors (ρ = 0.380, P < 0.01). Furthermore, the stages of change in women were also positively correlated with general eating behaviors (ρ = 0.270, P < 0.01) and physical environment (ρ = 0.237, P < 0.01), and negatively correlated with the disadvantages of eating adequate sodium (ρ = –0.286, P < 0.01) and behaviors related to sodium intake (ρ = –0.239, P < 0.01).
DISCUSSION
This study examined whether there were differences in outcome expectations, self-efficacy, eating environment, and eating behaviors according to the stages of change in adequate sodium intake. In this study, a high proportion of participants (77.2%) were classified in the pre-action stage. We attempted to measure the stages of change as accurately as possible by following the measurement of the stages of change suggested in the TTM and by suggesting an adequate level of sodium intake according to the WHO guidelines [5, 19]. Similar to our study, Tamaki et al. [22] reported that a high percentage of participants (84.8%) were assigned to the pre-action stage (precontemplation to preparation stages) in the stages of change to reduce salt intake in a study with a large sample of Japanese adults. Ahn et al. [16] reported that 47.3% of restaurant staff belonged to the precontemplation or contemplation stage of reducing sodium intake when cooking, which was lower than that in our study (63.0%). This suggests that the differences in the distribution of the stages of change depend on the characteristics of the participants or the behaviors examined.
The overall outcome expectations in the action stage were more favorable than those in the pre-action stage (P < 0.001). This was mainly due to the difference in expectations regarding the disadvantages of eating adequate sodium, such as the distaste for foods with less sodium, giving up eating one’s favorite foods, difficulty in reducing sodium alone while having meals with others, and restrictions in choosing processed foods or menus at restaurants. Consistent with this study, a previous study found that misconceptions and beliefs about the importance of salt taste were related to discretionary salt use (e.g., salt use at the table and in cooking) [23]. Based on the study results, nutrition education for those in the pre-action stage should aim to decrease negative expectations of eating adequate levels of sodium. This might be achieved through methods such as persuading negative expectations (e.g., distaste), menu planning, cooking using natural ingredients or seasonings, and consequently decreasing the threshold for salty taste. Okube & Kimani [24] reported that patients with metabolic syndrome improved their beliefs about the disadvantages of adopting a healthy lifestyle after receiving health education, suggesting that education is effective in modifying negative beliefs. In our study, the participants in both groups felt similarly on the benefits of consuming an adequate levels of sodium. In contrast, a study with Korean consumers showed that a higher percentage of participants in the action or maintenance stage compared to the pre-action stage perceived the health benefits of reducing sodium intake (e.g., decreasing blood pressure, prevention of stroke, and heart disease) [15].
Self-efficacy is important in explaining the stages of change in adequate sodium intake. Consistent with our study, Ahn et al. [14] reported that self-efficacy for sodium reduction methods in cooking in the action stage was higher than that in the pre-action stage in foodservice workers at childcare centers. Another study reported that self-efficacy was higher in the maintenance stage of reduced sodium intake, followed by the action and pre-action stage [15]. These findings suggest that nutrition education should incorporate strategies to increase self-efficacy. This might be achieved by building skills such as cooking with less sodium, reading nutrition labels for choosing processed foods with low sodium, finding information and practicing methods to reduce sodium intake, and substituting low-sodium foods with high-sodium foods. Self-efficacy in reducing sodium intake might also be increased by encouraging desirable behaviors step-by-step.
In this study, participants in the action stage were less likely to engage in behaviors that increased sodium intake, such as eating processed or instant foods, eating out or using delivery foods, and eating all the liquids of soup or noodles. Conversely, those in the action stage were more likely to consume low-sodium foods, choose bland foods at restaurants, and engage in desirable behaviors more frequently. A study on college students also found that the high sodium intake group was more likely to engage in behaviors related to sodium intake [25]. Consistent with our study, Hwang et al. [26] reported that children and adolescents in the precontemplation or contemplation stage to eat blandly performed dietary behaviors related to high salt intake more frequently than those in the action or maintenance stage. Nutrition education should be developed to change specific eating behaviors related to sodium intake, as well as general eating behaviors. Modification of eating behaviors can be achieved through the process of monitoring eating behaviors, goal setting, substitution of behaviors, and shaping desirable eating behaviors.
It seems that the association of eating environment with the stages of change was weaker than the other variables examined in this study. However, the pre-action stage received more pressure from significant others to eat less salty foods than the action stage. The majority in the pre-action stage might not think about eating sodium adequately, resulting in more pressure from significant others for healthy eating behavior. In contrast, the physical environment of the action stage was more supportive of eating adequate levels of sodium. Similarly, the recognition of a supportive environment for reducing sodium intake and recognition of sodium labeling on processed foods or foods in restaurants were higher in the maintenance or action stage than in the pre-action stage, suggesting the importance of a supportive environment in the stages of change to reduce sodium intake [15, 16]. Based on the findings of this study, it is necessary to make the physical environment more supportive of reducing sodium intake for those in the pre-action stage. This might be achieved by providing information regarding the sodium content of foods at schools or restaurants, providing low-sodium menus at home or restaurants, and serving sauce separately rather than providing seasoned foods.
Correlation analysis showed that the stages of change in eating adequate sodium were associated with the subscales of the variables, and there were some differences in the degree of correlation by sex. For both men and women, behaviors related to sodium check (e.g., checking the sodium content of processed foods, and using low-sodium foods) were quite important in the stages of change to eat adequate sodium, suggesting the necessity of emphasizing these behaviors in the nutrition education of university students or young adults. The relationship between cognition (i.e., disadvantages, subscales of self-efficacy) or environment and the stages of change in adequate sodium intake among men was not high. In contrast, the stages of change in women were related to the subscales of variables such as cognition, behavior, and physical environment to a certain degree. Similarly, a previous study reported differences in health beliefs or behaviors related to salt consumption according to sex; adult women were more aware of the benefits of reducing sodium intake and more likely to reduce the consumption of processed foods than men [27].
The study findings suggest that nutrition education should be developed by considering the characteristics of the participants (e.g., sex). Nutrition education for young adult women can be planned using multiple paths to highlight the disadvantages of eating adequate sodium, increase self-efficacy, change behaviors related to sodium checks or sodium intake, and provide a more supportive physical environment for adequate sodium intake. Nutrition education for men might need a relatively simpler strategy, including providing tips to try or practice eating sodium adequately (e.g., reading nutrition labels, and choosing low-sodium foods).
Limitations
This study had some limitations. In assessing the stages of change, we suggested an appropriate level of sodium consumption to help the participants understand adequate sodium intake. However, there were also limitations as to how accurately participants recognized the adequate level of sodium intake, considering that sodium intake is a somewhat complex behaviors compared with other dietary behaviors (e.g., consuming five servings of vegetables per day). The participants were students recruited from universities in Seoul, Korea; thus, the findings may not be generalizable to other groups of young adults. Furthermore, this study was a cross-sectional survey, and it was difficult to explain the causal relationships between the variables. Despite these limitations, this study suggested that factors, including outcome expectations, self-efficacy, eating behaviors, and eating environment, were significantly different according to the stages of change in adequate sodium intake.
Conclusion
This study provides information for developing nutrition education or counseling, customizing needs according to the stages of change in adequate sodium intake. Nutrition education should be planned to motivate young adults in the pre-action stage to consider changes in sodium intake adequately. It is necessary to improve the negative expectations of eating adequate sodium, employ methods to increase self-efficacy, and gradually engage in desirable eating behaviors. Furthermore, the physical environment of the pre-action stage must be changed to reduce sodium intake. For those in the action stage, methods to help maintain desirable eating behaviors should be employed. Nutrition education might also be planned considering the sex of young adults. For women, multiple paths might be useful, whereas a simple strategy (e.g., providing tips to try) might be employed for men.
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