Introduction

Globally, one in seven adolescents aged 10–19 years experiences mental health problems. If left unaddressed, these conditions may persist into adulthood, impairing both physical and mental health and reducing opportunities to achieve a better quality of life [1]. South Korea has the highest suicide rate among individuals aged 20 and older in the Organisation for Economic Co-operation and Development (OECD) member countries. Among youths aged 10–24 years, the OECD average suicide rate is 5.9 per 100,000, whereas Korea ranks second with a rate of 12.4 per 100,000, more than twice the OECD average [2]. Adolescence is a critical transitional period into adulthood [1], during which predispositions to mental health problems may emerge or intensify, potentially leading to suicidal behavior. As of 2022, suicide was the leading cause of death among Korean adolescents, accounting for 42.3% of all deaths. Its prevalence was more than three times higher than that of cancer (12.1%), which ranked second [2]. According to the 2024 White Paper on Suicide Prevention [2], the most frequently cited cause of adolescent suicide is psychological distress. Therefore, it is essential to examine suicide in close association with depression.

Depression is the leading cause of illness and disability among adolescents [1] and a major contributing factor to suicide [3]. Its prevalence has increased significantly in recent years [4], with a further increase observed in Korea following the COVID-19 pandemic [5]. Depression impairs school attendance and academic performance, intensifies social withdrawal, loneliness, and isolation [1], and increases the risk of suicide [3]. Therefore, addressing both depression and suicide should be a top priority in efforts to improve adolescent mental health.

The global prevalence of overweight and obesity among children and adolescents aged 5–19 years has increased sharply, rising from 8% in 1990 to 20% in 2022. Adolescent obesity has, in fact, quadrupled during this period [6]. A multinational study involving adolescents aged 13–17 years across 20 countries reported an overweight or obesity rate of 18.2% in the mid-2010s [7]. In Korea, as of 2023, 21% of adolescents—from the first year of middle school to the third year of high school—were classified as overweight or obese [8]. It is well established that being overweight or obese increases the risk of both immediate and long-term health problems. Adolescents with excess weight are more likely to develop severe obesity and noncommunicable diseases such as diabetes and cardio-cerebrovascular conditions [9]. They are also at heightened risk for psychosocial challenges. Obesity-related stigma and discrimination can have far-reaching negative effects on academic performance and overall quality of life [6].

Previous studies have consistently demonstrated a strong association between obesity and mental health problems, particularly depression and suicidal tendencies [10–12]. However, research focusing solely on the direct link between obesity and mental health may overlook critical underlying mechanisms, especially among adolescents. Adolescence is a critical stage of development, characterized by rapid physical changes [13] and increased attention to appearance [14]. During this period, being overweight or obese is closely linked to adolescents’ perceptions of their body image [13]. Body image is a multifaceted concept that encompasses individuals’ subjective perceptions and attitudes toward their own bodies [15]. IN 2023, 21.7% of Korean adolescents reported body image distortion—believing they were overweight or obese despite being underweight or of normal weight—a slight increase from the previous year [8]. Moreover, appearance has been reported as the most distressing concern among Korean teenagers [16]. Given prior evidence that distorted weight perception adversely affects adolescent mental health, including depression and suicidality [14,17–19], it is essential to investigate how both actual weight status and perceived weight influence psychological well-being.

To date, most studies on adolescent suicide have either focused exclusively on suicidal thoughts [18,20] or have examined suicidal thoughts, plans, and attempts as separate outcomes [10,17,21]. However, suicide is better understood as a behavioral continuum, ranging from ideation to planning and eventual attempts [22]. Accordingly, the present study aimed to clarify the relationship between weight perception and suicidality among adolescents with and without obesity, using an integrated definition of suicidality encompassing suicidal thoughts, plans, and attempts [5]. In addition, numerous studies have reported sex-based differences in the factors associated with obesity, weight perception, depression, and suicidality [5,17,18,20,21].

The present study aimed to investigate sex-based differences in the effects of weight perception on depression and suicidality among Korean adolescents, stratified by obesity status. It also sought to provide practical evidence to inform sex-specific intervention strategies for adolescent depression and suicide prevention.

Materials and methods

Results

Characteristics of study participants and main variables

The characteristics of participants and major variables according to sex are presented in Table 1.

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Table 1. Characteristics of the participants (N = 51,462).

https://doi.org/10.1371/journal.pone.0328549.t001

BMI-based obese adolescents comprised a higher proportion of male participants (22.5%) than that of female participants (17.4%). The rate of underweight perception was higher among male participants (32.4%) than among female participants (23.3%); however, the rate of overweight perception was higher among female participants (37.3%) than among male participants (36.0%).

The risk of depression or suicidality was higher among female participants (30.7% and 18.2%, respectively) than among male participants (21.3% and 10.7%, respectively).

Differences in participants’ characteristics according to mental health

Table 2 shows the sex-based differences in participants’ characteristics according to depression.

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Table 2. Sex-based differences in the characteristics of participants with and without depression (N = 51,462).

https://doi.org/10.1371/journal.pone.0328549.t002

Among male participants, significant differences in the presence or absence of depression were observed according to economic status, academic performance, parental education level, current smoking status, current drinking status, and weight perception. In contrast, among female participants, significant differences in the presence or absence of depression were observed according to school level, school location, economic status, academic performance, parental education level, current smoking status, current drinking status, and weight perception.

Table 3 shows the sex-based differences in participants’ characteristics according to suicidality.

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Table 3. Sex-based differences in the characteristics of participants with and without suicidality (N = 51,462).

https://doi.org/10.1371/journal.pone.0328549.t003

Among male participants, significant differences in the presence or absence of suicidality were observed according to school level, economic status, academic performance, current smoking status, current drinking status, BMI, and weight perception. In contrast, among female participants, significant differences were observed in the presence or absence of suicidality according to school level, economic status, academic performance, parental education level, current smoking status, current drinking status, BMI, and weight perception.

Odds ratio of mental health according to BMI and weight perception

Table 4 shows odds ratio of depression and suicidality according to BMI and weight perception stratified by sex.

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Table 4. Adjusted OR (95% CI) for mental health based on BMI and weight perception categories stratified by sex (N = 51,462).

https://doi.org/10.1371/journal.pone.0328549.t004

Among male adolescents with obesity, weight perception was not identified as a risk factor for depression; however, among female adolescents, the odds ratio of depression decreased by 0.250 times (95% confidence interval [CI] 0.068–0.916) for normal weight perception and 0.247 times (95% CI 0.070–0.873) for overweight perception compared to that for underweight perception, which served as the reference group.

In contrast, among male adolescents without obesity, the odds ratio of depression decreased by 0.853 times (95% CI 0.790–0.922) for normal weight perception compared to that for the underweight perception. Among female adolescents without obesity, the odds ratio of depression decreased by 0.858 times (95% CI 0.798–0.922) for normal weight perception compared to the underweight perception. However, among female adolescents without obesity, the odds ratio of depression increased by 1.106 times (95% CI 1.020–1.199) for overweight perception compared to that for underweight perception.

Among male adolescents with obesity, the odds ratio of suicidality decreased by 0.427 times (95% CI 0.193–0.944) for normal weight perception and 0.432 times (95% CI 0.205–0.909) for overweight perception compared to that for underweight perception. Among female adolescents with obesity, the odds ratio of suicidality decreased by 0.165 times (95% CI 0.046–0.598) for normal weight perception and 0.213 times (95% CI 0.062–0.730) for overweight perception compared to that for underweight perception.

In contrast, among male adolescents without obesity, the odds ratio of suicidality decreased by 0.871 times (95% CI 0.785–0.966) for normal weight perception compared to that for underweight perception. Among female adolescents without obesity, the odds ratio of suicidality decreased by 0.832 times (95% CI 0.761–0.910) for normal weight perception compared to that for underweight perception; however, it increased by 1.295 times (95% CI 1.176–1.427) for overweight perception.

Discussion

The present study revealed that sex-based differences were evident in terms of obesity, weight perception, depression, and suicidal tendencies among Korean adolescents.

Our findings align with previous research showing that adolescents face increasing risks of both obesity and mental health problems, including depression and suicidality. For example, national trends in South Korea demonstrate that obesity rates among adolescents have doubled over the past decade, especially among male adolescents [8,20]. Simultaneously, the prevalence of depression and suicidality has risen significantly, with female adolescents exhibiting greater overall vulnerability [4,5]. Although the prevalence of these mental health issues is generally higher among female adolescents, increasing attention is being paid to psychosocial risks among males as well [3].

In this context, our study highlights the complex associations between actual weight status, weight perception, and psychological outcomes. Among adolescents without obesity, those who perceived themselves as overweight were at increased risk of both depression and suicidality, an association that was particularly pronounced among females. In contrast, among male adolescents without obesity, weight perception was not significantly associated with either depression or suicidality. These sex-based differences suggest that body image and self-perception, rather than objective weight status alone, are critical in understanding adolescent mental health and developing targeted interventions.

Obesity is influenced by multidimensional factors, including physiological factors, such as sex hormones and genes, as well as lifestyle, such as food preferences and physical activity, or sociocultural factors [24]. In particular, after puberty, adolescents experience rapid changes in fat distribution and body composition due to the influence of sex hormones [24] and are influenced by sociocultural ideal body stereotypes and weight stigma, often shaped by sex-specific double standards. The mesomorph body type for male individuals and thin body type for female individuals are considered ideal body types, and both male and female adolescents internalize these standards without critical thinking [25]. A total of 81.8% of adolescents with obesity reported experiencing weight-related stigma, with female individuals being 2.6 times more likely to encounter such stigma than male individuals [26].

Unlike actual weight status, differences were found in weight perception. The rate of underweight perception was higher among male participants than among female participants and that of overweight perception was higher among female participants than among male participants. These findings align with those of previous studies, which reported that men underestimate their weight and women overestimate their weight [18,21,27,28]. Kim [29] stated that sex and age are the most critical causal factors related to weight evaluation and pointed out that young female individuals overestimate their weight due to heightened sensitivity to their appearance and social expectations regarding their physique. Recent findings [25] also indicate that this weight misperception is not limited to young female individuals, and young male individuals underestimate weight for the same reason. Interestingly, these trends in weight perception are observed across both eastern and western countries [21,27,29,30]. However, it is interesting to note that although Korea’s obesity rate is not high compared to the western countries [31], weight perception closely aligns with the Westernized typicality.

Sources of pressure regarding weight or body shape include society, parents, schools, peers, and mass media [24,26]. For example, parents are more likely to underestimate their children’s weight if their children are overweight or obese, and the risk of underestimating their children’s weight is higher for sons than for daughters [32]. Li, et al. [33] reported that underweight recognition by parents or grandparents is the most powerful predictor of overweight or obesity in children, with boys being more prone than girls to having their weight underestimated. Additionally, recent studies have reported that the discrepancy between objective and subjective weight status, caused by the internalization of unrealistic body ideals through media, increases the likelihood of body dissatisfaction or eating disorders [34,35]. The influence of media ideal internalization through negative physical self on social appearance anxiety is greater in girls than in boys [36]. In conclusion, a sex-based difference exists in the intensity of pressure on weight or body shape, with the acceptable range for male individuals being broader than that for female individuals.

This study showed that the rate of depression is higher among female participants than among male participants, supporting previous research findings [4]. The frequency or severity of depressive symptoms was also higher in girls than in boys [5]. In general, the sex-related gap in depression begins to appear in early adolescence, with several factors contributing to girls’ higher vulnerability to depression. These factors include (1) biological vulnerabilities such as genes, puberty timing, and puberty hormones; (2) affective vulnerability such as temperament; and (3) cognitive vulnerability such as rumination, objectified body consciousness, and a negative cognitive style. In other words, stress or negative life events play an important role in sex-based differences in biological, physical, and psychological changes accompanying puberty, along with the contribution of sociocultural factors such as gender inequality [37].

The prevalence of suicidality was higher among female participants than among male participants. Since the inception of the KYRBS in 2005, female participants have consistently exhibited higher suicidality rates than those of male participants [5]. These results are similar to those of previous studies conducted abroad [38,39]. According to a statistical analysis report on the causes of death, a sex-based gap was noted in the number of suicides that led to death. In 2016, 455 boys (61.2%) and 289 (38.8%) girls committed suicide, showing a large difference in the numbers between them; however, in 2019, the numbers had nearly equalized to 455 (51.9%) and 421 (48.1%) in boys and girls, respectively. Notably, the number of suicides among female adolescents has increased significantly in recent years [40]. Miranda-Mendizabal, et al. [39] identified eating disorders, dating violence, depression symptoms, and interpersonal problems as risk factors for suicidality among female individuals and conduct disorders and peer suicidality as risk factors for suicidality among male individuals. To fully understand the causes of mental health problems, a multidimensional approach, including genetic, biological, psychological, emotional, cognitive, and behavioral factors, as well as interaction experiences with the environment to which the individual belongs, is necessary [40]. Hence, follow-up studies should be aim to specifically identify the mechanism and the risk factors affecting sex-based differences in suicidality to prevent suicide in adolescents.

Another major finding of the present study was that, unlike male adolescents without obesity, in female adolescents without obesity, weight overestimation was as risk factor for poor mental health. Regardless of BMI, an association exists between overweight perception and mental health deterioration [17]. Furthermore, social body comparison or internalization plays a more decisive role than BMI in female adolescents’ body satisfaction and body image concerns [13]. Considering these factors, it can be inferred that weight perception, rather than the actual weight itself, is an important predictor of mental health promotion, especially for female adolescents. The seriousness of distorted weight perception lies in its potential to cause inappropriate or unnecessary risks not only in lifestyle choices or weight control strategy selection but also in social relations [19,21,25,30]. The “Thomas theorem,” a sociological argument, has repeatedly emphasized that perception (i.e., weight perception) can be more consequential than objective facts (i.e., BMI), which may lead to significant consequences such as physical and sociopsychological risks [41].

In modern society, the socio-cultural standardized body type ideals tend to favor “slender” or “thin” women and “muscular” men [25,34]. These ideals, set as a social norm, create pressure on individuals, causing them to compare their body type with others and experience greater discrepancies between their actual and perceived body types [13]. The seriousness of the problem is that such a social environment not only induces negative emotions and behaviors toward one’s own body image but also causes stigma and bias against other people’s body image. Female individuals are at a higher risk of experiencing or internalizing weight stigma than male individuals [26]. This is in line with the findings of previous studies, in which even female participants with normal weight or underweight are not free from weight stigma and bias and are forced to have emotional cognitions, such as a negative self-perception or loss of self-esteem [36,42]. Moreover, considering that the prevalence of overweight or obesity in Korea is not as severe as in the western countries [31], the increase in psychological risks such as depression and suicidal tendencies due to overestimation of weight in female adolescents without obesity, revealed in this study, suggests that lookism in Korea is not only prevalent but also exacerbates sex-based imbalance. Therefore, to protect mental health, education on subjective weight perception as well as actual BMI should be provided to all adolescents, and careful attention should be paid to sex-based differences inherent in obesity or weight perception.

Conclusions

This study investigated sex-based differences in the associations between weight perception, BMI, and psychological outcomes among Korean adolescents. The findings revealed that distorted weight perception was significantly associated with depression and suicidality, particularly among female adolescents without obesity. In contrast, these associations were not significant among male adolescents without obesity. These findings highlight the distinct psychological mechanisms through which subjective and objective weight factors interact to adolescent mental health.

In light of these findings, it is essential that mental health interventions address not only objective measures such as BMI but also adolescents’ subjective perceptions of their weight. Programs aimed at improving body image awareness, reducing stigma, and providing psychological support should be designed with sensitivity to sex-specific differences. School-based screenings and mental health curricula should incorporate assessments of both actual weight status and body image perception, with particular attention to female adolescents who may be more vulnerable to the internalization of distorted body ideals. The development of sex-informed public health strategies can help promote improved psychological well-being and reduce the risk of depression and suicidality among adolescents.