Does the BMI reflect body fat in obese children and adolescents? A study using the TOBEC method

Abstract

OBJECTIVE: Due to the fact that obesity is de®ned as excess of body fat mass, we tested the hypothesis whether the body mass index (BMI) can be used as a valid measure for the detection of the degree of obesity in individual obese children and adolescents. METHODS: A total of 204 obese children and adolescents (105 boys, 99 girls) aged 6 ± 17 y, using total body electrical conductivity (TOBEC) for fat measurement, were included into this study.A multiple regression analysis was performed with percentage body fat (PBF) as dependent variable and BMI, age and sex as independent variables. First-and second-order interaction terms were also included. Since all interaction terms showed a signi®cant in¯uence on PBF, regression analysis was performed separately for boys and girls, dividing each group into two age subgroups (subjects younger than 10 y, and subjects 10 y or older). RESULTS: BMI and PBF were observed to be positively correlated (overall: r 0,65; P 0.0001; boys r 0.63 and girls: r 0.68). Through a multiple regression analysis 57% of the variance of PBF could be explained by the independent variables. In boys younger than 10 y 73% and in girls younger than 10 y 63% of the variance of PBF was explained by the BMI. In subjects 10 y or older the association was poor (boys: 27%; girls: 38%). It should be emphasized that there is a wide range in the relationship between PBF and BMI in the obese subjects. CONCLUSION: From these results we conclude that BMI might be a useful parameter for epidemiological studies: however in the individual pediatric patient, especially from 10 y onwards, it gives only a limited insight to the degree of obesity based on the de®nition.

Relation of BMI to fat and fat-free mass among children and adolescents

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21] For example, BMI was strongly associated with %body fat (r ¼ 0.83-0.94) among Pima Indian children (whose mean BMI was B5 kg/ m 2 higher than participants in the current study), 16 whereas a correlation of r ¼ 0.46 was observed among adolescent girls with anorexia nervosa (mean BMI ¼ 13.5 kg/m 2 ). 21 In agreement with the sex and age differences in body fatness, it has also been reported that the associations with BMI are stronger among females than among males, 4,10,11 and among 7-to 10-y-old boys than among 14-to 16-y-old boys.…”

“…BMI levels among adults are highly correlated with %body fat, and in combination with race, sex, and age, multiple R 2 -values of 0.7-0.8 have been reported. [4][5][6][7] Associations among children and adolescents have been more variable, [8][9][10][11][12][13][14][15][16][17][18][19][20][21] and relatively weak correlations (ro0.6) have been reported in several subgroups. 8,10,11,13,15,21 These weaker associations among children and adolescents may be attributable to the asynchronous changes that occur in the levels of fat mass and fat-free mass during growth.…”

Association of vitamin D with adiposity measures and other determinants in a cross-sectional study of Cypriot adolescents

“…BF% correlates well with BMI in children aged 6-9 years but exhibits a reduced degree of correlation with BMI in adolescents, in boys and at the extremes of BMI (15) . To date, only a handful of studies have investigated the nature of the association of both adiposity indices (BMI and BF%) with vitamin D in healthy adolescents across the whole spectrum of adiposity, with some however not adjusting for the effect of potential confounders (5,6,9) .…”

Prevalence of overweight and obesity in Irish school children, using four different definitions

“…Alternatively, body mass index (BMI) (weight/height 2 ) is a valid and reproducible method that is cheap and convenient for the assessment of weight status (where weight becomes a surrogate for body fatness) in epidemiological studies. BMI is commonly used in adults and more recently recommended for use in children and adolescents (Power et al, 1997;Bellizzi and Dietz, 1999;Dietz and Bellizzi, 1999;Bini et al, 2000;Reilly et al, 2000;Widhalm et al, 2001). However, the assessment of weight status in young people is more complex, when using BMI to assess adiposity in children and adolescents it is essential that age-and sex-specific BMI cutoffs be used to define overweight and obesity (Widhalm et al, 2001;Field et al, 2003).…”

“…BMI is commonly used in adults and more recently recommended for use in children and adolescents (Power et al, 1997;Bellizzi and Dietz, 1999;Dietz and Bellizzi, 1999;Bini et al, 2000;Reilly et al, 2000;Widhalm et al, 2001). However, the assessment of weight status in young people is more complex, when using BMI to assess adiposity in children and adolescents it is essential that age-and sex-specific BMI cutoffs be used to define overweight and obesity (Widhalm et al, 2001;Field et al, 2003). Given the economic, environmental, genetic and nutrition influences on body size, having growth standards that are nationally representative is an important consideration (Livingstone, 2000).…”