Adolescent health is an important issue that has implications for adult health. Analyzing adolescent health behaviors is a social-scientifically meaningful approach to understanding healthy growth. Improper health behavior during the adolescent period can have negative impacts on physical and mental growth. Korea, the United States, the United Kingdom, and Japan all follow the World Health Organization guidelines for healthy behavior. According to these guidelines, there has been an increase in the adolescent obesity rate (Dave and Rashad, 2009).

In a report that deals with 200 countries from 1975 to 2016, there has been an increase in BMI among children and adolescents in most high-income countries, and this trend is set to accelerate in some parts of Asia (NCD Risk Factor Collaboration, 2016). In Korea, obesity is defined by a body mass index (BMI) above 25 kg/m². Adult BMI is not comparable to adolescent BMI because BMI is calculated using an age-specific percentile. According to the Standard Growth Chart for Children and Adolescents, published by the Korea Centers for Disease Control and Korean Pediatric Society (2007) and calculated using BMI across one age group, the 0 to 5th percentile is defined as underweight, the 5th to 85th percentile as normal weight, the 85th to 95th percentile as overweight, and the 95th to 100th percentile as obese (Barlow et al., 2007). The report states that obesity in 12- to 18-year-old adolescents has increased to 12.7%. The average BMI among middle and high school students was 20.7 kg/m², and the Korea Youth Risk Behavior Web-based Survey (KYRBWS) in 2014 reports the BMI for the obese and nonobese groups as being 27.0 kg/m² and 19.9 kg/m² respectively. Following classification criteria, which were defined based on BMI, over 80% of adolescents are of normal weight. This result offers some explanation for the increase in student obesity across elementary, middle, and high school, which grew from 14.3% in 2010 to 15.3% in 2013 to 15% in 2014 (Griffiths et al., 2006; Korean Ministry of Education, 2014; Song et al., 2019). However, previous studies have focused primarily on health behaviors and related factors in overweight and obese adolescents, and there has been little investigation into the health behaviors of normal-weight adolescents, who make up over 70% of all adolescents.

Inappropriate subjective weight perception is linked with behavior designed to control weight (Idema et al., 2019), and one study reported that many normal-weight adolescents perceive their body shape inaccurately and do inappropriate weight loss behaviors to remedy the perceived abnormality (Viner et al., 2006). Adolescent interest about appearance, weight, and body shape and obese in normal weight, and underweight adolescent although they have not had overweight and preference a very slim body shape ideally (Addo et al., 2019). Inappropriate overweight perception among adolescents has fluctuated in 33 European and North American national survey results between 2002 and 2014; it has increased in males across 21 countries, most significantly in Russia, Estonia, and Latvia. In surveys conducted in the United Kingdom, France, Germany, Norway, and Scotland, the correlation between overweight perception and dissatisfaction has also increased (Whitehead et al., 2017). Inappropriate weight control behavior among normal-weight adolescents is enacted in pursuit of a slim body shape, which causes feelings of inferiority and low self-esteem with regards to school life and appearance, and has a negative effect on students’ adjustment to school life, class activity, and peer relationships (Hoare et al., 2019).

Furthermore, regarding adolescent health behaviors across the world, mental health ought to be taken into account. In adolescents aged 15 to 19, depression and anxiety manifest markedly in late adolescence (Beauchamp et al., 2018). Obesity is related to the effect of stress on cognitive ability, academic achievement, psychological adjustment, and mental health promotion sequentially (Graf et al., 2005). Adolescent stress management is also a pressing research issue for understanding healthy growth. Weight and obesity are concerned a low level of perception for subjective health status in measuring a feeling of happiness (Doll et al., 2000). Male adolescents tend to underestimate their weight, whereas female adolescents tend to overestimate their weight. Owing to this, there is a high risk of depression among adolescents (Sutaria et al., 2019). Therefore, a social environment should be cultivated whereby appropriate health behaviors and decisions can take place.

With regards to adolescent health behaviors, as short sleep and poor sleep duration were associated with obesity relevant factors in adolescents (Chaput and Dutil, 2016). Previous studies provided evidence that starting school earlier had positive effects on adolescent health (Watson et al., 2017). Sedentary behavior is an example of physical inactivity that is also related to obesity.

However, this focus on obese and overweight adolescents overlooks those normal-weight adolescents who are also making weight loss efforts. For this reason, further research should be conducted in order to provide information about influential factors on sleeping, stress, depression, and the practice of sedentary behaviors. Therefore, this study aimed to analyze the body shape perception and health-related behavior of normal-weight Korean adolescents who account for more than 80% of all adolescents, and to verify the inadequate subjective body shape perception, weight control efforts, physical activity and mental health-related variables using the 10th KYRBWS data to provide information for the healthy and proper growth of adolescents.

Adolescence is a developmental period in which physical and mental growth occurs rapidly. Therefore, social, environmental, educational, and systematic health care is necessary for the healthy growth of adolescents (Bundy et al., 2018). In an ideal environment, adolescents who are underweight should be able to gain weight by taking in enough nutrition, adolescents of a normal weight should be able to maintain their healthy weight, and overweight or obese adolescents should be able to reach a normal weight. We have seen increasing trends in obesity, but in a 2015 US National Survey, a cohort study conducted on 12,275 Chinese American children and adolescents reported that the overall outbreak rate of overweight and obese adolescents had decreased from 24% in 2004 to 21% (Lau et al., 2019). Today, obesity rates are consistently controlled and mediated for adolescents around the world and in many ways, we have seen decreasing trends. It is a fact that more than 70% of adolescents are of normal weight. Thus, more studies should focus on the inappropriate weight control behavior of normal-weight adolescents. Generally, weight control can result in inappropriate efforts and results due to subjective perception of weight rather than objective, and so a health education and general environment should be provided to facilitate proper weight perception and judgment among adolescents. In 2013, Korean 4.4% middle and 7.1% high school obese students distortedly perceived overweight or obese themselves 59% middle and 71% high school students (Korean Ministry of Education, 2014). However, adolescents’ actual weight and their subjective body shape perception were shown to be different, thus providing evidence that normal-weight adolescents perceive themselves improperly and make unnecessary efforts to lose weight (Gaylis et al., 2019).

According to the subjective weight perception of normal adolescents perceived having obese and generally having weight control efforts, and perceived obese to control their weight. But in the previous study (World Health Organization, 2004), conformity between weight perception the same body image was very low in BMI normal group, which is different from the results of the present study.

Sixty min of physical activity per 1 day, 7 (5) days per 1 week, males and females perceived normal were practicing properly, and perceived in thin females were relatively less. Vigorous-intensity physical activity more than 3 times per 1 week, muscular strength exercise rate for more than 3 times per 1 week, regular physical activity rate, and sedentary behavior guidelines rate, were appeared only perceived normal males and female and perceived thin females practiced relatively less. The study shows that adolescents who perceived themselves normally were practicing physical activity properly and adolescents who perceived themselves as thin were not aware of the importance of physical activity for improving strength and body composition, confirming the need for the implementation of physical education (Song et al., 2019).

Stress perception was higher in males and females who perceived themselves as obese or thin. Compared to previous studies, adolescents stress was becoming obese (Chiang et al., 2019) and increasing the actual obesity is high (Hanlon et al., 2019) normal-weight perception, overweight perception, and underweight perception adolescents varied (Buscemi et al., 2018) and showed similar or different results from the reported as unrelated to personal BMI (Yayan and Çelebioğlu, 2018). Experiences of depression were more common in males who perceived themselves as thin and in females who perceived themselves as obese. We can deduct from this that males feel more depressed by a small body shape, and that females’ have a sensitive response to an increased body shape. Females experienced more stress and depression (Steadman et al., 2018) when they reported perceiving themselves as obese. Males, too, felt more depressed in instances where they perceived themselves as overweight or obese, and females felt less depressed in instances where they perceived themselves as underweight. This result matched or differed from the present study. With regards to subjective sleep fulfillment, males who perceived themselves as thin and females who perceived themselves as obese responded that they were not getting enough sleep. Most of the adolescents in this study did not experience enough sleep both subjectively and objectively (Heath et al., 2018). In South Korea, the United States, Japan, and China, a significant insufficiency in subjective sleep fulfillment was reported in Korean adolescents (National Youth Policy Institute, 2010). With regards to issues of mental health and weight due to insufficient sleep (Hayes et al., 2018). These results indicated that proper sleep management is needed since insufficient sleep gives rise to adolescent obesity. Subjective happiness perception was low in males and females who perceived themselves as obese. A study describes subjective health perception was high among males who perceived themselves as obese and relatively low among females who perceived themselves as thin, owing to the tendency to perceive obesity as being healthy and thin as being unhealthy. Females showed similar trends across those with both normal and abnormal perceptions of themselves (Choi and Kim, 2017) and subjective health perception was shown to affect the obesity level (Rey et al., 2017). Subjective weight perception and health behaviors in perceived thin, overweight perceiving changes in most countries (Choi and Kim, 2017) commonly 15-year-old adolescents of 33 European and North American countries from 2002 to 2014, but big changes and psychological dissatisfaction appeared in female adolescents of Scotland and Norway (Whitehead et al., 2018). In efforts control weight, the males who perceived themselves as normal showed fewer efforts. Perceived male in obese and female normal and obese showed more efforts for weight control, that they perceived the dangerous influence of obesity. The proportion of the normal-weight adolescents who perceived themselves as thin was high in males and the proportion who perceived themselves as fat was high in females (Choi and Kim, 2017). In efforts for weight control, the proportion of efforts to lose weight was higher in females than males, and the proportion of efforts to maintain weight in the normal-weight group was lower than in the overweight and obese groups (Buscemi et al., 2018). But the efforts for the weight that it was higher in abnormal perception group (Hawkins et al., 2018). In this study, the result partially matches with male and female adolescents, excluding obesity perception adolescents in males, are making a lot of efforts for weight control.

Through this study we analyzed the correlation between each variable concerning normal-weight perception and obesity perception based on the perceived thin, as a result, efforts for weight control were 0.7 times less in normal perceived males compared to males who perceived thin. Male obesity perceived and female normal and obesity perceived adolescents were trying to effort for weight control. Overall, this can be interpreted as demonstrative of the fact that the efforts for weight control were being made in the normal range.

Sixty minutes of physical activity 1 day, 7 (5) days per 1 week, in males, normal and obesity perceived adolescents practicing 0.8 times less physical activity. In perceived thin males and obese perceived females and normal adolescents practiced 1.0 times more physical activity. In vigorous intense physical activity for more than 3 times per 1 week, in perceived normal males and females and perceived obese females practiced normally, but in perceived obese males were practicing less. In other words, males who perceived themselves as obese were reluctant to engage in intense exercise for more than 3, 5, or 7 days per week, which further highlights the necessity for some kind of support or mediation in encouraging adolescents to participate in high-intensity physical activity efficiently. Males who perceived themselves as normal, and males and females who perceived themselves as obese were seen to practice muscular strengthening activities more than 3 times per week, but females who perceived themselves as normal practiced less. It can be deduced from this that females who perceive themselves to be of normal weight are reluctant to do exercises like strength training as such exercises are assumed to increase muscle volume and change the outward body shape. Both males and females who perceived themselves as normal or obese practiced more regular physical activity, understanding the importance of physical activity for health. Adolescents’ stress and depression both decreased when they received more physical education, but in the case of female adolescents, physical activity in physical education was practiced everyday life also had a negative impact (Daly-Smith et al., 2018). Regular physical activity has a positive impact on adolescent health, but female adolescents are reluctant to do intense physical activity or muscle strengthening exercises, and so ways to encourage their voluntary participation should be investigated. In terms of sedentary behavior, males and females who perceived themselves as normal and males who perceived themselves as obese exhibited more, but females who perceived themselves as obese exhibited less. Since adolescents in upper grades between 12 and 15 year-older who endure increasing class hours, sedentary time such as during school, after school, and at weekends (Harding et al., 2015) the practice of physical activity and the reduction of sedentary behavior are both known to positively impact the physical and mental health status of overweight and obese male adolescents (Bray et al., 2018). Ways of increasing activity and reducing sedentary behavior should therefore be discussed for adolescents.

Concerning reported perceptions of stress and experiences of depression, stress was high in female adolescents who had normal weight but perceived themselves as obese. A study which emphasized the importance of mental health surveyed, using psychosocial approaches, overweight and obese children and adolescents over a 2-year period and presented evidence to demonstrate that the likelihood of becoming overweight or obese in adulthood was increased (Quek et al., 2017). Overall, this study compared to adolescents who perceive themselves as thin, adolescents who see themselves as fat experience a lower quality of mental health (Whitehead et al., 2018). A study related to subjective body shape perception (Choi and Choi, 2016) showed that a group with mental health issues made more efforts to lose weight (Chu et al., 2019) as well. In other words, the degree to which inappropriate body perception is increasing stress perception and experience of depression (Neumark-Sztainer et al., 2000) stands to support the importance of mental health promotion. With regards to subjective sleep fulfillment, females who perceived themselves as obese did not report satisfactory amounts of sleep. Continually insufficient sleep among adolescents can lead to harmful behavior for inappropriate health promotion (Bansil et al., 2011). In the United States, research showed the impact of abnormal sleep patterns on the mental health of 13- to 18-year-old adolescents (Zhang et al., 2017). This evidence supports the result of this study that deciphered a relation between perceptions of abnormal weight and mental health. The National Youth Policy Institute (2010) reported physical activity participation as being associated with subjective sleep satisfaction (Lang et al., 2019). Thus, appropriate methods should be suggested to improve the Korean adolescent lifestyle, which is limited in the education environment, in order to improve their sleeping patterns.

In subjective happiness perception, males and females who perceived themselves as normal felt happier and males and females who perceived themselves as obese males and females felt less happy. In Scotland from 1990 to 2014, the subjective weight perception of 12- to 14-year-old male and female adolescents was almost negligible. But to compare adolescents perceived weight normally, confidence and happiness decreased in perceived overweight adolescents (Whitehead et al., 2018). In Korea, compared to adolescents perceived weight normally, happiness was lower in perceived overweight (OR, 0.889) and usual stress was 1.0 times higher (Kim et al., 2018). This result reaffirmed that obesity misperception harms adolescent happiness and that normal and proper weight and body shape perception is important. Subjective health perception in males was 1.2 times higher in perceived normal and 1.9 times higher in perceived obese. In females, it was 1.6 times higher in perceived normal and 2.1 times higher in perceived obese. This result explains that male and female normal perceived obesity appeared positively higher, which is similar to a research that adolescents’ BMI and body weight perception associated negative with body weight perception (Heshmat et al., 2015).

In conclusion, to analyze adolescent health behavior that perceived normal weight is very important social-scientific approach to healthy growth. In other words, abnormally perceiving weight and body shape behavior harms adolescent physical and mental health, implying a need for health education and mediation. Thus, further studies should proceed to focus on appropriate efforts for weight control related to adolescent mental health promotion, the effects of reduction in depression and stress perception through physical activity (Witherspoon et al., 2013), and effective ways to improve sleep satisfaction, subjective health perception, and happiness. In this respect, the results of this research verified the evidence related to the health behavior of Korean normal-weight adolescents as it was analyzed in KYRBWS, which is a resource that can represent the characteristics of Korean adolescents, and thus can be used as informative data for adolescent appropriate behavior for the health promotion.