Lifestyle factors associated with underweight among Japanese adolescents: a cross-sectional study

BACKGROUND Because underweight in adolescents poses several health problems, it is important to prevent it in adolescence. For the prevention of underweight, it is necessary to investigate risk factors, especially lifestyles, because these can be modified. However, a limited number of studies exist regarding lifestyle factors associated with underweight among adolescents. The present study aimed to investigate the relationship between lifestyle factors and underweight among Japanese adolescents. METHODS Study subjects comprised 2641 seventh-grade school children (age 12 or 13 years) from the town of Ina, Saitama Prefecture, Japan. Measurements of height and weight were made for each subject, while information regarding lifestyles of each subject was obtained using a self-administered questionnaire. Underweight was determined by the age- and sex-specific body mass index cut-off points. A logistic regression model was used to estimate the odds ratio (OR) and 95% confidence interval (95% CI) for underweight. RESULTS Adolescents who ate slowly were more likely to be underweight than those who did not eat slowly; the OR (95% CI) was 2.78 (1.77-4.39) in boys and 2.69 (1.81-3.98) in girls. Girls who did not exercise were more likely than those who exercised to be underweight (OR: 1.64, 95% CI: 1.07-2.51). CONCLUSIONS The present study showed that eating slowly and exercise were associated with underweight among Japanese adolescents. These results suggest that eating speed and exercise need to be considered in school health programs for healthy body weight.