Prevalence and sociodemographic trends of weight misperception in Korean adolescents

Rapid physical and emotional growth occurs during youth. Adolescence is one of the most important periods for adapting to body change and establishing an ideal body image. Body change is an important and sensitive concern for adolescents, and the values and self-conception established at this time affect various aspects of the entire life [1, 2].

People tend to regard low weight as normal and prefer a thin body type [1]. Dissatisfaction with one’s body shape and extreme dieting have become common because the trend in public opinion and mass media is to lay emphasis on slimness and appearance [3‐5]. Under this influence, an adolescent whose ego is not established recognizes a thin body shape as the standard of beauty, and this attitude distorts the perception of and increases dissatisfaction with their body shape [6], causing bad eating habits and excessive reduction in body weight [3, 7‐9].

Misperception of the ideal body shape threatens the physical and mental health of adolescents during growth. Obese, normal, and even underweight individuals may try immoderate weight control measures and experience depression [8, 10‐14] that extends even into the early adult period [15]. Misperception of body shape is therefore a serious public health problem and negatively affects the future as well as present physical and mental health in adolescents.

Known differences exist between male and female students in perception of body shape. While female students tend to overestimate their weight, male students tend to underestimate their weight [1, 14, 16‐23]. Female students also have more interest in body weight [7, 18] and control their body weight more aggressively than do male students [3, 17, 19, 24]. Furthermore, male students tend to underestimate their body weight even though their weight is normal, because they have more interest in increasing muscle mass [25].

In Western countries, many studies have been conducted on current attitudes and sociodemographic factors that contribute to misperception of body shape in order to provide a basis for effective adolescent weight control programs [9, 18, 26‐29]. However, Korean studies on misperception of body shape in adolescents examined mainly the relationship between perception of body shape and eating habits, self-esteem, and depression [1, 14, 20, 30‐35], ignoring factors affecting discordance. The adolescents who regarded their body shape as normal or thin even though they were overweight or obese had a lower participation rate in weight control programs, because they lacked the need of weight control [18, 36]. Nevertheless, subjects in most domestic studies were overweight/obese adolescents; adolescents who underestimated their weight were rarely included. It was also difficult to generalize the findings because most domestic studies included adolescents living in a single specific region [1, 20, 30, 34].

The present study aimed to identify the factors affecting misperception of body shape in adolescents underestimating and overestimating their body weight and to provide evidence for future obesity-management policies and interventions. Specifically, we addressed (1) the present condition of misperception by comparing perception of body shape and weight status, and (2) sociodemographic characteristics affecting discordance between perception of body shape and weight status (overestimation and underestimation).

The perception of body weight by adolescents affects eating habits, eating behavior, and weight control [9]. Misperception of body shape is important because it negatively affects future as well as present physical and mental health, such as occurrence of depression in young adulthood [8, 10‐15]. This study examined sociodemographic factors affecting misperception of body shape in Korean adolescents using data from the entire country, and attempted to provide basic information for future policies and education on adolescent obesity.

Only 50.7% of adolescents in our study correctly recognized their body weight. This value was lower than the 56.7–77.7% reported in other domestic studies [1, 14, 20] and the 70.1–77.7% suggested by studies from Western countries such as the United States and Australia [17, 18, 36, 38]. Differences in subject characteristics, including height and weight, may account for these disparate results. Generally, in surveys including height and weight, BMI tends to be lower than the actual value because people report greater height and lower weight [18, 39]. Thus, in a study using the survey, the accuracy of weight perception is lowered by large difference between actual BMI and weight perception; therefore, the study using the survey would have lower accuracy of weight perception than that of other studies using actual measurements. Compared with American, Chinese, and Japanese adolescents, Korean adolescents are more sensitive to appearance, have more interest in weight control, and exhibit more weight-related behavior [40].

This result indicated that because of different cultural pressures, Korean adolescents are facing social environments that could predispose them to higher rates of weight misconception. Furthermore, well-designed studies are necessary to solve this issue in Korean adolescents. It is also interesting that compared with Western students, Eastern students had a higher misperception of body shape. Zhang et al. [26] reported that compared to American adolescents, adolescents in Hong Kong, Macau, and Taipei had a higher rate of body shape misperception, and that the perception of body shape is affected by sociocultural factors such as region and race [17, 18, 26, 41‐43]. Additional studies are required to include Korean adolescents as well as Western students from the Americas and Europe.

Our findings that male students tend to underestimate their body weight and female students tend to overestimate their body weight are consistent with findings of previous studies [1, 14, 16‐23]. While 29.5% of female students overestimated their weight, only 19.7% underestimated their weight. Overestimation promotes weight control by causing dissatisfaction with body shape [3, 6‐9, 44]. However, it tends to quickly reduce body weight by unhealthy weight control behavior such as drug usage, fasting, smoking, and single-food diets [3, 7, 18, 35, 45]. Previous studies showed that 13.5–22.9% of Korean adolescents trying to control body weight showed unhealthy weight control behavior, a higher level than that found in China, the Americas, and Japan [39, 40]. This suggests that intensive management is required for adolescents who overestimate their weight.

In contrast, male students showed higher rate of underestimation (33.2%) compared with overestimation (17.9%). This rate is higher than the 9.8% reported by Park in American adolescents [18]. Previous studies on perception of body shape focused on adolescents overestimating their weight [1, 8, 21, 28, 36]. The present study suggests that adolescents underestimating their body weight also require attention and study. Weight control is motivated by self-perception of body shape and not true weight [3]; these adolescents have lower motivation, resulting in many problems such as ineffectiveness of preventive interventions for obesity and eating disorder behaviors [6, 18].

Actual weight was the most important factor affecting misperception. Interestingly, adolescents who had a normal weight had a higher misperception rate than did overweight/obese adolescents. The misperception rate was 32.8-times higher in normal weight students compared with obese students, implying that normal weight students as well as obese students should be considered in weight control programs.

Future obesity intervention programs should include normal-weight adolescents having different subjective perceptions of body shape. In addition, obesity policies for adolescents should include monitoring the subjective perception of body shape as well as actual BMI.

The lower the SES, the higher is the misperception of body shape in adolescents. This suggests that adolescents at a lower SES level should be the subjects of obesity programs, because the obesity rate is high in this group [25]. Class does not affect discordance in total student analysis, but female high school students showed higher misperception than their middle school counterparts. This result corresponds to results of previous studies [18, 30]. High school female students show a higher diet stress than do middle school females [46]. This is thought to represent higher interest in body shape in high school students, because they have a shorter time for adjusting to social interactions such as finding employment or entering a university/college.

This study has several limitations. First, we could determine interrelationships alone and not cause and effect because this was a retrospective and cross-sectional study. Second, the height and weight were self-reported, which limits accuracy. In general, compared with male students, female students tend to report lower height and weight than the actual value [47]. This tendency may account for the different results between male and female students. However, studies based on large samples actually use self-reported height and weight; furthermore, actual height and weight were assumed to be recorded as this study also was a self-reported survey performed using a computer. In addition, a previous study suggested that little discrepancy was found between self-reported and measured BMI in Asian adolescents [48]. Nevertheless, in future large studies, height and weight should be directly measured to improve assessment of weight perception. Third, factors affecting misperception of weight were limited to sociodemographic variables, limiting the evaluation of overall factors. Future studies should include physical and mental variables. In spite of these limitations, the findings of this study are significant because notional data representing the entire Korean adolescent population were investigated for the first time, and the discordance between perception of body shape and actual weight was determined by examining both overestimation and underestimation. In addition, the results of this study can facilitate selection of subjects for adolescent obesity programs by proposing that both BMI-based weight status and subjective perception of body shape should be monitored and reflected.

In conclusion, 50.7% of Korean adolescents correctly recognized their body shape, while 33.2% of male students underestimated and 29.6% of female students overestimated their weight. In the overall analysis of adolescents, gender, socioeconomic status, and BMI-based weight status affected misperception of body shape. Class was an additional factor in case of female students. An effective obesity program should monitor and reflect both BMI-based weight status and subjective perception of body shape in adolescents who underestimate or overestimate their weight.