Dissatisfaction with body image among adolescent students: association with socio-demographic factors and nutritional status

1 Centro de Ciências da Saúde e do Esporte, Universidade do Estado de Santa Catarina. R. Pascoal Simone 358, Coqueiros. 88.080-350 Florianópolis SC Brasil. andreia.pelegrini@udesc.br 2 Universidade Estadual do Sudoeste da Bahia, Departamento de Saúde. Jequié, Bahia, Brasil. 3 Instituto Federal de Educação, Ciência e Tecnologia de Santa Catarina. Palhoça, Santa Catarina, Brasil. 4 Centro de Desportos, Universidade Federal de Santa Catarina. Dissatisfaction with body image among adolescent students: association with socio-demographic factors and nutritional status


Introduction
Body image is characterized by one's mental perception of measures, contours and shapes of the body and parts of it and feelings associated with these characteristics 1 . In addition, body image consists of a subjective component which refers to the individual's satisfaction with the size or specific parts of the body 2 .
Adolescence is a period characterized by important biological, physical, psychological and social changes 3 , and body image disturbance, especially due to dissatisfaction with one's own body, is frequently observed during this phase of life 4 . Body image dissatisfaction is influenced by numerous factors (family, friends, media, society), but the main pressure seems to come from the media and society by imposing a "thin-ideal" for female beauty and an athletic image for males 5 . This pressure is exerted on the whole population but adolescents are more vulnerable to it.
Studies regarding the perception of body image in adolescents have elicited marked interest over the last few years both at the national 6,7 and international level 8 . This interest is mainly due to the close relationship of body image dissatisfaction with psychological disorders and health-related risk behaviors 9 . In a recent study body image dissatisfaction was found to be the most important risk factor for manifestations of symptoms of anorexia nervosa in adolescents from a capital in the southern region of Brazil 10 . Evidence indicates that body image dissatisfaction is highly prevalent among adolescents 6,7 .
Numerous researches have been conducted on body image in adolescents 6-10 , however, there are no studies that verify the association of two different levels of body image dissatisfaction (desire to reduce and to increase body size) with sociodemographic factors (age, gender and economic status) and anthropometric indicators (body mass index and waist circumference). In this sense, this study may contribute to the advancement of knowledge in healthcare, especially for the health care of adolescents. Thus, the objective of the present study was to determine the prevalence of body image dissatisfaction and its association with sociodemographic factors and nutritional status in adolescents aged 14 to 19 years.

Methods
Data from the project "Risk factors for atherosclerosis in adolescents", coordinated by mem-bers of the Sports Center of the Federal University of Santa Catarina, in partnership with the Town Hall of Três de Maio, Rio Grande do Sul, Brazil, were used. A school-based cross-sectional epidemiological study was conducted in the urban zone of the town of Três de Maio, with data being collected between June and July 2006. The project was approved by the Ethics Committee on Human Research of the Federal University of Santa Catarina (protocol 41/2006), and the adolescents or responsible persons (in the case of minors) signed a free informed consent form.
Três de Maio is located in the northwestern region of the State of Rio Grande do Sul and belongs to the microregion of Santa Rosa. The estimated population is 24,136 inhabitants and the territorial area comprises 424.2 km 2 . The human development index is 0.83 11 , corresponding to high development according to the United Nations Development Programme 12 .
The sample size was calculated considering a population of 1642 adolescents of both genders ranging in age from 14 to 19 years, who were regularly enrolled in public and private middle schools (last year, eighth grade), high schools and technical courses. A probabilistic sample stratified according to gender and proxy of economic status was established using the following parameters: 95% confidence interval (95% CI), tolerable sample error of 3.5%, prevalence of sedentarism of 40%, and design effect of 1.2 13 . The minimum sample size calculated was 624 adolescents.
Sampling was performed in two steps: i) stratification according to gender and a proxy of socioeconomic status; ii) drawing lots. In the latter case, participants were systematically selected from two lists of each school (one for each gender) according to the age group of the study. To guarantee the randomness of the sample the students were divided according to alphabetical order. The selection interval was established by dividing the total number of students on the list by the number of adolescents that should represent the school in the sample. This selection criterion permitted recomposition of the sample since in the case of absence from class on two consecutive days, lack of participation in the two sampling phases, refusal, transfer or school evasion another student was selected from the list according to the preestablished systematic sampling strategy. The final sample consisted of 660 adolescents (317 boys and 343 girls), 5.5% more than the calculated expected minimum sample size, in view of possible predicted blanks in the responses that would impair analysis of the variables studied.
Demographic data including age, gender and economic status were collected. The socioeconomic status of the family was classified using the Brazilian Economic Classification Criterion (divided into five levels from A to E, in decreasing order) 14 . The adolescents responded to this question at home together with the parents or responsible persons.
Data regarding body image perception were obtained using the figure rating scale proposed by Stunkard et al. 15 and validated for the Brazilian population 16 . The set of silhouettes was shown to the subjects and the following questions were then asked: Which silhouette (current) best represents your current physical appearance? Which silhouette (ideal) would you like to have? Body image dissatisfaction was analyzed based on the discordance between the current and ideal silhouette and the subjects were classified as satisfied and dissatisfied. Next, subjects with body dissatisfaction were dichotomized into those who wished to increase their body size (dissatisfaction due to thinness) and those who wished to reduce their body size (dissatisfaction due to excess weight).
After the questionnaire was filled out, body weight and height were measured 17 . Nutritional status was evaluated based on body mass index (BMI = weight/height 2 ). The cut-off values for gender and age suggested by the International Obesity Task Force were used for the classification of BMI 18 . Waist circumference was measured using an anthropometric fiber glass tape (Mabbis ® ) midway between the lowest rib and iliac crest 19 , and was classified as normal or increased according to the cut-off values recommended by Katzmarzyk 20 .
Statistical analysis included the calculation of means, standard deviations and distribution of frequencies. The Student t-test for independent samples was used to evaluate differences in current and ideal silhouettes between genders. Nominal and ordinal variables were dichotomized or grouped into strata: gender (male, female), age group (14, 15, 16, 17 and 18 + 19 years), socioeconomic status (A + B, C, D + E), waist circumference (normal and increased), and nutritional status [eutrophic and excess weight (overweight + obesity)]. A frequency table (absolute and relative) was constructed to describe the distribution of categorical variables in the sample as a whole and according to gender. Frequencies were compared using the chi-square test.
The overall prevalence of body image dissatisfaction and the prevalence according to gender were calculated. Differences in prevalence were determined using a test for the comparison of two proportions. Since the dependent variable (perception of body image) consisted of three categories (satisfied, desire to reduce and desire to increase), multinomial logistic regression was used to estimate the association between body image dissatisfaction and the independent variables (gender, age group, socioeconomic status, nutritional status and waist circumference). The category "satisfied" was used as a reference. In all tests, the level of significance was set at 5% (p < 0.05 or 95% IC). Statistical analysis was performed using the SPSS ® version 13.0 and Med-Calc version 9.3.3.0 programs.

Results
The mean score for ideal figure rating was higher among adolescent boys (3.73 ± 0.93) than girls (2.68 ± 0.68, p < 0.001). In contrast, no significant difference between genders was observed in the perception of current body silhouette (boys: 3.66 ± 1.38; girls: 3.54 ± 1.31, p = 0.278). Table 1 shows the distribution of the variables analyzed according to gender. Significant differences between genders were only observed for the proportions of the different categories of age and waist circumference.
The distribution of the adolescents according to body image dissatisfaction and gender is shown in Figure 1. The percentage of dissatisfied subjects was higher among adolescent girls (p < 0.05) ( Figure 1A). When the group of dissatisfied subjects was divided according to the desire to change body size ( Figure 1B), the desire to reduce body size predominated among girls, whereas the wish to increase it was higher among boys, with significant differences between genders. Table 2 shows the results of multiple regression analysis for the association between body image dissatisfaction (desire to increase and desire to reduce body size) and the independent variables (gender, age, socioeconomic status, waist circumference and nutritional status). The desire to reduce body size was positively associated with female gender, increased waist circumference and excess weight. The desire to increase body size was negatively associated with female gender and increased waist circumference, and was positively associated with ages 16, 17 and 18 + 19 years.

Discussion
The prevalence of body image dissatisfaction was high among adolescents from Três de Maio, Rio Grande do Sul (71.4%), demonstrating that the frequency of body dissatisfaction is high even among adolescents from small towns. The prevalence of body image dissatisfaction among adolescents observed in the present study was higher than that reported by Pelegrini et al. 6 (56.7%) and Petroski et al. 7 (60.4%). These rates suggest that body dissatisfaction should be regarded an important public-health problem and should be included in the list of adolescent health issues, since this behavior can cause eating disorders (bulimia, anorexia), low self-esteem, and health-related risk attitudes and behaviors such as acceptance of poorly planned diets, exercise dependence and  The present findings demonstrated a higher prevalence of body image dissatisfaction among adolescent girls, in agreement with Petroski et al. 7 . According to Williams et al. 23 , females are generally more concerned about their body image, presenting greater dissatisfaction and weight gain concerns and preferring thin beauty ideals. Similarly, Gualdi-Russo et al. 24 and Knauss et al. 8 found a greater body image dissatisfaction in young and adolescent girls.
Adolescent girls generally desired to reduce their body silhouette, whereas the desire to increase it predominated among boys. Similar results have been reported in the national 7 and international 21,25 literature, suggesting that in females body image dissatisfaction is more related to the desire to be thin, whereas in males body dissatisfaction is associated with the desire to gain muscle mass. One possible explanation for the differences in the presentation of body image dissatisfaction between genders might be a greater sociocultural Desire to increase Desire to reduce emphasis on physical attractiveness of adolescents in western societies, since internalization of a thin ideal (among girls) or athletic body (among boys) has been identified as a key component in the development of body dissatisfaction 25 . However, this internalization, which is mainly influenced by the media, is not always reachable 26 , a fact resulting in dissatisfaction and low self-esteem.
In the present study, increased waist circumference and inadequate nutritional status (overweight or obesity) were the strongest predictors of body dissatisfaction due to excess weight (desire to reduce body size). Thus, an elevated BMI and body fat distribution seem to be the main determinants of body dissatisfaction in adolescents. Other studies have shown a greater desire to reduce body size among adolescent girls with excess weight 7 . In general, the literature has shown that nutritional status, evaluated based on BMI, is not a consistent predictor of body dissatisfaction 27 . Regarding body fat distribution (waist circumference), we found no studies investigating its association with body dissatisfaction.
On the other hand, body dissatisfaction due to the desire to increase body size was negatively associated with increased waist circumference but not with excess weight. In addition, greater dissatisfaction due to thinness was observed among older adolescents, a finding suggesting that excessive concern with self-image tends to aggravate with age. However, the supposed risk of body dissatisfaction in older adolescents without excess abdominal fat is believed to be related to the fact that thin adolescents, especially boys, desire a more athletic and muscular body, but not a fatter one 21 . This fact might be related to both the need for self-affirmation among peers and the imposition of this beauty pattern by the media and society 5 .
The fact that body image dissatisfaction was not associated with socioeconomic status indicates that the risks of this outcome were the same for adolescents of high, middle and low social classes irrespective of gender, age, body fat distribution and nutritional status, demonstrating that body image dissatisfaction is a problem affecting adolescents of all social classes. Some authors support the view that the media, especially television, has been the major disseminator of these ideals 28 .
The limitations of the present study are related to its cross-sectional cohort design, which does not permit the identification of a causal relationship between the variables analyzed and the use of an instrument (figure rating scale) for the determination of body image perception. Although this scale is easily and rapidly applied and has been widely used over the last years 6,29 , the silhouette drawings are directly related to two-dimensional linear shapes which may lead to failures in total body presentation, fat mass distribution and other aspects of body composition that are important for the formation of a body image 30 . The advantages of the present study include the fact that the sample is representative of students from public and private schools in Três de Maio, Rio Grande do Sul. In addition, this is the first Brazilian study associating two different levels of body dissatisfaction (desire to increase and desire to reduce body size) with sociodemographic factors, nutritional status and body fat distribution.

Conclusions
The present results led us to conclude that: i) the prevalence of body image dissatisfaction is high among adolescents from the town of Três de Maio, especially among girls; ii) body dissatisfaction manifests differently in boys and girls; iii) increased abdominal fat, excess weight and female gender were predictors of body dissatisfaction due to excess weight (desire to reduce body size) and male gender and advanced age were predictors of body dissatisfaction due to thinness (desire to increase body size). In view of these conclusions, it is of fundamental importance that the school alerts adolescents to the risks of aggressive attitudes and behaviors aimed at weight loss or gain in muscle mass. Multidisciplinary interventions at school promoting healthy eating habits, physical activity and changes in body image concepts should be encouraged.