Assessment of individual changes in body fatness in boys during early pubertal period

BACKGROUND: In order to know whether the changes in indexes of overweight, body mass index (BMI; kg/m2) and percentage of overweight (POW) (%), really represent the tendency toward obesity, we examined longitudinal individual changes in these indexes, and the change in body composition in boys during early pubertal period. METHODS: The subjects were 50 school boys who lived in Shizuoka, Japan. Standing height and weight were measured, and BMI and POW were obtained. Body fat percentage (BF%), fat mass (FM) and lean body mass (LBM) were estimated by bioelectrical impedance method. The influence of predictive variables (LBM, FM) on the changes in BMI and POW was investigated by multiple regression analysis. We examined the 3-year changes in BMI, POW and predictive variables in each individual, from 9 to 12 years of age. RESULTS: The mean change of BMI was 1.7 +/- 0.3 (mean +/- SEM) kg/m2 and that of POW was 2.2 +/- 1.9%. The influence of predictive variables on the changes in BMI and POW was determined. The variance of the change in POW could be explained by that in FM (r(2) = 0.737, P < 0.0001), while the change in BMI was influenced by both LBM and FM (r2 = 0.891, P < 0.0001). CONCLUSIONS: Based on the definition of obesity, POW is the better index of body fatness to assess its individual change for boys during early pubertal period, because the index independent from the change in LBM is supposed to be the appropriate index for obesity in practical use.