Adolescence is a period with the secondary growth spur in the life cycle, during which the number of fat cells is actively increased and the body shape is changed due to hormonal action (Choi et al., 1997; Kim et al., 1998; Won et al., 2000), in addition to the development of reproductive functions. Thus proper nutritional management is very important because the development and maturity of physical, mental, and social health during this period directly influence the health status of adulthood (Edwards et al., 1964; Ryu, 1997; Yoon et al., 1992). Furthermore, this is the time when the value is firmly established, and the behavior for foods established in this period has been reported to significantly affect the food behavior after the adulthood (Ryu, 1997; Won et al., 2000).

Balanced meal through healthy and rational eating habits is very important in the growth, development and health improvement in humans, and this is not accomplished by appetite or food preference but can be accomplished by the practice of proper dietary habits on the basis of proper nutrition knowledge. The preference for eating habits or foods in humans is established by the influences from socioeconomic level of household, religion, tradition, regional characteristics, education level of parents, public media, and long-term education at home, school, and the society.

Adolescents have increased interests in their appearances due to psychological and social factors, and greatly influenced by various informative media and particularly peer groups. Recently, adolescents have recognized themselves with distorted perception depending on the subjective standard on the body image due to social pressure for slim and thin appearance, and tried reckless and unreal approaches for weight control. It has been reported that many adolescents have fear for obesity regardless of their body weights, and excessive concerns for obesity can induce underweight and be harmful to health (Lee et al., 1996; Must et al., 1992).

The growth rates of adolescents have been continuously increased around the world but the imbalance of undernutrition and overnutrition exists and thus the incidence of anemia due to malnutrition and the incidences of juvenile obesity, diabetes, and chronic diseases due to overnutrition have been increased (Epstein et al., 1985; Epstein et al., 1990; Gortmaker & Dietz, 1987). To solve these problems, as reported in previous studies (Her et al., 1999; Kang et al., 1997; Lee et al., 1997; Lee et al., 2000; Schwars, 1975; Sweeney, 1993), it is important to understand the optimal level of nutrition as healthy status that can lead productive life with socially and economically proper values. Also, it has been reported that the organized and scientific investigation for actual condition and the extension of positive and active nutrition education at the national level are imperative to minimize the presence of nutritionally vulnerable groups.

In advanced western countries since 1970s, the preference for thin physique has been excessively spread out in some groups with high interests in physical appearance, and the body image of an individual can affect the motive for weight control and thus poorly perceived body image can show improper weight control pattern (Kang et al., 1997; Must et al., 1992; Schwarz, 1975). Factors affecting distorted body image include gender, age, race, and body weight. Adolescence is a period when the interest for appearance, particularly body shape, is greatly increased and thus distorted body image and excessive obsession for dieting can affect nutritional intake and induce eating disorders not only to threaten health but also to cause mental and psychological complications. The degree of satisfaction for body shape and weight control in adolescents can affect their nutritional intake and food behavior and thus should be carefully handled along with food behavior and nutritional intake.

According to the studies reported in the USA (Schwarz, 1975; Sweeney et al., 1993), children who skipped their breakfast were much more aggressive than those who had breakfast, and the study by Ro (1998) reported that high school students with irregular daily meal patterns had poorer health status and lower academic achievements than those who had regular meals. In Korea, increased rate of eating out, fast-food consumption, and over consumption of sweets and carbonated beverages have increased the adolescent obese population, which has led to the incidence of chronic diseases such as diabetes, hypertension, and arteriosclerosis, and the adolescents want to become slim and the obese shape can be excluded in the peer group because of great interests in appearance and body weight, resulting in psychologically bad influence on character formation (Ro, 1998; Ro, 2000; You et al., 1997). As the preference for thin body shape has been increased in the society, the number of adolescents, while thinking they are obese or overweight, who are skipping meals or practicing irregular meals and unbalanced diet to recklessly reduce their body weights has been increased although the actual body weight is normal, and this situation can induce bad influence on health and lead to nutritional imbalance. Therefore, the necessity for proper recognition of one's own physique, desirable eating habits, and nutrition education is imperative to establish the proper food behavior during the period of adolescence. However, the importance of nutrition in adolescence with active physical and mental development should be emphasized. Thus, although the necessity for studies on nutritional knowledge, body image recognition, and food behavior in adolescents is urgent, actual studies for teens are greatly limited.

Good nutritional status in adolescents is decided by proper nutritional knowledge, eating habits, and food behavior, which plays an important role not only in the improvement of physical development but also in the maintenance of mental and emotional stabilization. On the other hand, if the growth and development is delayed and becomes difficult to recover because of malnutrition due to poor eating habits and food behavior during this period, balanced nutrition intake in adolescents should be emphasized to promote the most growth during adolescence. Therefore, it is considered that multi-faceted measures are imperatively needed to manage proper dietary life and to establish desirable eating habits in adolescents with nutritional imbalance.

Thus, the study was performed in middle school students resided in San Francisco to investigate how they recognized their body image by gender and by race, and whether they had weight control experience, and their food behavior were examined and compared by gender and by race. Through the results of this study, the basic data will be provided for the comparative analysis with students in Korea in the future.

We evaluated height, weight, and BMI and self-estimation on their physique to investigate the degree of recognition of body image by sex and by race. It showed that there was no significant difference by sex in their self-estimation on their physique. However there was a significant difference by race (p<0.05), and in case of Asian, 20.0% was considered as underweight and in case of Hispanic, none was considered as underweight, and in case of White, 7.5% was considered as underweight, showing significant differences. This showed the same tendency as actual physical indexes (p<0.05). Also, the ratio of being recognized as more than overweight was 17.3% in Asian, 23.3% in Hispanic, and 13.4% in White students.

These results were consistent with other previous studies in Korea. In studies with teenagers in Korea (Kim & Moon, 2001; Ro, 2000), about half of female students wanted to be slightly underweight, and considerable number of female students recognized themselves as obese despite that they were not obese. In addition, in the study of recognition for physical status in middle school students, higher ratio of students answered as slightly obese, and female students recognized themselves as more obese compared to male students and most female students preferred underweight. It is considered that this phenomenon can promote weight reduction in the process of copying popular celebrities appeared in TV commercials and broadcasting, resulting in negative influence on food behaviors of growing adolescents.

Recently, young women and adolescents in our society tend to reduce their body weights recklessly with wrong perception that thinner is more beautiful. Also, many adolescents have wrong body image and poor eating habits with the obsession to appearance and bodyweight without knowing the standard of normal weight (Ryu, 1997). Therefore, eating disorders such as anorexia and bulimia in this age group have been gradually increased (Kang & Paik, 1988; Kim & Moon, 2001; Kim et al., 2000). This phenomenon shows that wrong perception for desirable body shape has greatly influenced food behavior or eating habits, and weight control.

Overweight and obesity have been recognized as common nutritional problems in the western society (Sweeney et al., 1993), and the frequency for overweight has been greatly increased along with changes in the lifestyle due to improved economic standard in Korea (Yoon et al., 1992). Moreover, the age when the obesity develops has been gradually lowered and the incidence of childhood obesity has been increased (Woo et al., 1986). Childhood obesity has high incidence in infancy and school children, and particularly pre-adolescence and adolescence, and 60~80% of childhood obesity has been led to adult obesity, and 1/3 of adult obesity has been reported as being developed between school children and adolescence, suggesting the importance of health management (Must et al., 1992). In particular, adolescence is not only a period of rapid growth and development but also a period with changes in the body shape due to hormonal action, and thus health management is very important. However in our country, factors leading to obesity include overeating due to psychological instability and the lack of exercise due to excessive school works (Lee et al., 1998).

Adolescence is a period of rapid physical, physiological, and emotional changes, when dietary habits are established and those established dietary habits are fixed. Also, this is a period when adolescents become more interested in their appearance due to psychological and social factors, and when undesirable food behavior such as unbalanced diet, skipping meals, imbalanced food intake, and preference for instant foods tend to appear (Kwon et al., 2001; Lee et al., 1998). In addition, in case of adolescents in these days who sensitively receive the influence of information media and advertisements, it is greatly concerned that they become interested in their appearance and try wrong approach in the aspect of body weight and body shape to cause malnutrition. Thus the health problems of adolescents nowadays have undernutrition along with overnutrition coexisted.

In summary, there was a significant difference by race (p<0.05) in their self-estimation on their physique (p<0.05). This showed the same tendency as actual physical indexes (p<0.05). The analysis for dieting experience and its frequency showed significant differences by sex and by race. In case of female students, the ratio of dieting experience was 63.3%, and 49.3% of white students and 63.3% of hispanic students experienced dieting, and 27.4% of students of other races experienced more than 3 times of dieting. The analysis of food behavior perceived by body image showed that the group perceived itself as obese consumed more fast food but had low scores in 'vegetables' intake, with frequent intake of 'soda' and tendency to 'overeat'. Also, the tendency for 'balanced life' was significantly lower and for skipping breakfast was significantly higher.

Adolescents in these days who are influenced by advanced western countries can complain about their rapidly changing bodies, and at the same time, want to become their perfect peers or cultural icons because they are affected by external factors (Kim et al., 1997). Adolescents in Korea, as well as those in advanced western countries, prefer and copy the appearance in the frame of mass media, and try to change their appearance and to manipulate their food behavior, and respond impulsively to the propaganda of commercial advertisement.

Therefore, the results of this study suggest that nutritional management which is different from that for adults should be provided considering that the adolescence is a period with rapid growth compared to other life cycle, and particularly in case of female students, it is necessary to correct distorted viewpoint for obesity and to establish positive attitude. Thus it is suggested that the development of effective nutritional education program for middle school students is needed to help them recognize desirable body weight and establish proper eating habits and food behavior through proper nutritional education.