Concordância e associação entre imagem corporal e índice de massa corporal em adolescentes

Abstract

Body image is one of the themes included in the risk factors surveillance systems directed to adolescents both in national and international levels. The aim of this study is to examine the agreement between different indicators of body image and between each one with nutritional status and the association of those indicators with BMI among adolescent students in public and private schools in the city of Rio de Janeiro. 152 students from a random sample of nine public and private schools in the city of Rio de Janeiro were studied. Data collection occurred in three phases: a first visit to the school for the students to fill in a questionnaire on Personal Digital Assistant (PDA) and answer about the first scale of silhouettes (ES_A); two telephone interviews in different days, for the student to answer questions about his/her opinion about his/her body (OpC) and his/her weight (OpP); and a second visit to the school for anthropometric measurements and application of the second scale of silhouettes (ES_B). Body Mass Index [BMI, weight (kg) / height (m2)] was examined both as nutritional status (EN), according to the criterion proposed by the World Health Organization, and as a continuous variable (raw and as z-score). For the analysis of agreement between the variables of interest (OpC, OpP, ES_A, ES_B and EN), we used the quadratic weighted kappa statistic. To examine the association between indicators of body image and BMI we calculated the median, mean, standard deviation and confidence interval of 95% (IC 95%) of BMI for each category of body image variables studied. The statistical significance of differences was examined by comparing the IC 95%, considering statistically different estimates those which confidence intervals did not overlap. The results were stratified by sex, type of school (public or private) and by sex and type of school simultaneously. Linear regressions were also conducted controlling for student s age and sex and for type of school where each student was enrolled. The agreement between the different variables of body image was, in general, from reasonable to good and, between these variables and EN the agreement was, in general, from regular to reasonable. Best results were observed between boys and between students from private schools. All variables of body image showed good discriminatory power for BMI when this last was analyzed as a continuous variable. This result remained after controlling for potential confounders. OpC seems to be better than OpP to compose the list of variables in a risk factors surveillance system directed to teenagers