[The association between lifestyle and body proportion in primary school children].

OBJECTIVES

To investigate the association between lifestyle and body proportion in children.

METHODS

The subjects were 499 students at "B" primary school, located in "A" prefecture. Data were obtained by analyzing the results of routine health checkups carried out in the fiscal year 2007 by using self-reported questionnaires on lifestyle. For the analysis of body proportion, the degree of obesity (overweight degree) divided by sex, age, and body height was calculated using a standard weight-based criterion; values greater than +20% indicated an inclination toward obesity, and values smaller than -20% indicated a tendency toward underweight. To analyze the relation between body proportion and lifestyle, binomial logistic regression analysis was performed using body proportion ("normal group" and "obesity inclination/underweight group") as the dependent variable and lifestyle as the independent variable. In addition, lifestyle factors common to and unrelated to both the obesity-inclined and the underweight groups were examined.

RESULTS

Comparison between the incidences of children with an inclination toward either obesity or underweight with national averages in the same fiscal year revealed that the overall inclination toward obesity was high in boys. Among other factors, influence by lifestyle habits such as insufficient chewing and the habit of watching TV for long periods was suggested. The incidence of children tending toward underweight or obesity was high among boys in the fourth and fifth grades and in girls in the fifth grade. Logistic regression analysis showed that the occurrence of unhealthy lifestyle habits such as "insufficient chewing" (2.1 times the number of those who chew well; P = 0.016) and "TV watching for more than 2 hours per day" (1.9 times the number of those who do not watch TV for more than 2 hours per day; P = 0.071) were highly correlated with the incidence of underweight or obesity. In addition, when we categorized the relationship between lifestyle and body proportion into 3 types ("tendency to underweight", "normal," and "obesity inclination"), we found a high incidence of the unhealthy lifestyle factor "insufficient chewing" in the groups that tended toward underweight or obesity and "TV watching for more than 2 hours per day" in the group that was inclined toward obesity.

CONCLUSION

When considering lifestyle issues, children inclined toward being either obese or underweight are often perceived to be contradictory to their external appearance. However, the results of the present study suggest that children with a tendency to be underweight and those with an inclination toward obesity share several lifestyle habits such as insufficient chewing.