BMI: Does it really reflect body fat mass?

Abstract

To the Editor:There is general agreement that there is a real need for an appropriate definition of obesity in childhood and adolescence, from a practical, as well as from a scientific, point of view. There is a body of evidence that body mass index (BMI) is strongly associated with complications based on increased body fat in adulthood.1Guo SS Roche AF Chumlea WC Gardner JD Siervogel RM The predictive value of childhood body mass index values for overweight at age 35 y.Am J Clin Nutr. 1994; 59: 810-819PubMed Google Scholar, 2Vanltallie TB Predicting obesity in children.Nutr Rev. 1998; 56: 154-156Crossref PubMed Scopus (4) Google Scholar The use of BMI in the pediatric age group is age-dependent, and the significance of the association of BMI with total body fat (TBF) or percentage of body fat (PBF) is unclear.The data from 198 healthy, non-obese children and adolescents obtained by Pietrobelli et al3Pietrobelli A Faith MS Allison DB Gallagher D Chiumello G Heymsfield SB Body mass index as a measure of adiposity among children and adolescents: a validation study.J Pediatr. 1998; 132: 204-210Abstract Full Text Full Text PDF PubMed Scopus (702) Google Scholar indicate that there is a highly significant correlation between BMI and TBF/PBF; however, the individual range for a particular BMI is considerably wide. These outcomes underline the fact that the BMI does not seem to be a very good measure for the quantification of body fat mass, expressed by the PBF, of the individual young patient. In a previous study by Boot et al,4Boot AM Bouquet J de Ridder MAJ Krenning EP de Muinck Keizer-Schrama SMPF Determinants of body composition measured by dual-energy x-ray absorptiometry in Dutch children and adolescents.Am J Clin Nutr. 1997; 66: 232-238PubMed Google Scholar a correlation study between PBF/TBF measured by dual-energy x-ray absorptiometry and BMI (PBF: girls, r = 0.84; boys, r = 0.56; P < .0001; TBF: girls, r = 0.93; boys, r = .85; P < .0001) has already been presented without allowing a deeper insight into the results.Similar results have been reported by Schäfer et al5Schärfer F Georgi M Wühl E Schärer K Body mass index and percentage fat mass in healthy German school children and adolescents.Int J Obes. 1998; 22: 461-469Crossref Scopus (114) Google Scholar who calculated percent body fat by measuring skinfold thickness (girls, r = 0.84; boys, r = 0.58).We conducted a study using total body electrical conductivity (TOBEC) for the quantification of body fat in a group of 204 children and adolescents (99 girls and 105 boys) aged 6 to 17 years, who were referred to our clinic because of weight problems. For the TOBEC method, a high correlation with the dual-energy x-ray absorptiometry method (r = 0.948; P = .0001)6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google Scholar has been demonstrated. TOBEC has the advantage of not exposing the patient to radiation. The lowest BMI for each age group is set above the 85th percentile of the German Hebebrand BMI percentiles,7Hebebrand J Heseker H Himmelmann GW Schärfer H Remschmidt H Altersperzentilen für den Body-Mass-Index aus Daten der Nationalen Verzehrstudie einschließlich einer Übersicht zu relevanten Einflußfaktoren.Akt Ernähr Med. 1994; 19: 259-265Google Scholar and so the young patients must be defined as obese.Our results concerning the correlation of BMI with PBF were similar to those of Pietrobelli et al (r = 0.65; for girls, 0.68; for boys, 0.63; for all, P = .0001).By dividing the total of 204 children and adolescents into different BMI groups, a poor correlation with a significance of P = .002 was found for the group with the lowest BMI (mean BMI of 22.7) and the group with the highest BMI (mean BMI of 34.5; P = .0009). In the groups with BMI values in between, no significance and no correlation were detected. The curvilinear correlation, which starts inclining at a BMI of approximately 25 to 27, demonstrates that an increasing BMI is not necessarily linked to a higher PBF.By dividing the collective into age groups, the highest association between BMI and PBF was calculated for children aged 6 to 9 years (r = 0.79, P = .0001).The correlation decreased in the higher age groups without losing its significance. The data obtained should be seen as an addition to the results of the study by Pietrobelli et al.Confidence limits on the association of BMI with fatness are set, and interpretation should be made cautiously when comparing BMI values across different age groups or predicting a specific individual’s TBF or PBF.6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google ScholarThe available data do not show that the BMI adequately reflects body fat mass in children and adolescents with a higher degree of adiposity. To the Editor:There is general agreement that there is a real need for an appropriate definition of obesity in childhood and adolescence, from a practical, as well as from a scientific, point of view. There is a body of evidence that body mass index (BMI) is strongly associated with complications based on increased body fat in adulthood.1Guo SS Roche AF Chumlea WC Gardner JD Siervogel RM The predictive value of childhood body mass index values for overweight at age 35 y.Am J Clin Nutr. 1994; 59: 810-819PubMed Google Scholar, 2Vanltallie TB Predicting obesity in children.Nutr Rev. 1998; 56: 154-156Crossref PubMed Scopus (4) Google Scholar The use of BMI in the pediatric age group is age-dependent, and the significance of the association of BMI with total body fat (TBF) or percentage of body fat (PBF) is unclear.The data from 198 healthy, non-obese children and adolescents obtained by Pietrobelli et al3Pietrobelli A Faith MS Allison DB Gallagher D Chiumello G Heymsfield SB Body mass index as a measure of adiposity among children and adolescents: a validation study.J Pediatr. 1998; 132: 204-210Abstract Full Text Full Text PDF PubMed Scopus (702) Google Scholar indicate that there is a highly significant correlation between BMI and TBF/PBF; however, the individual range for a particular BMI is considerably wide. These outcomes underline the fact that the BMI does not seem to be a very good measure for the quantification of body fat mass, expressed by the PBF, of the individual young patient. In a previous study by Boot et al,4Boot AM Bouquet J de Ridder MAJ Krenning EP de Muinck Keizer-Schrama SMPF Determinants of body composition measured by dual-energy x-ray absorptiometry in Dutch children and adolescents.Am J Clin Nutr. 1997; 66: 232-238PubMed Google Scholar a correlation study between PBF/TBF measured by dual-energy x-ray absorptiometry and BMI (PBF: girls, r = 0.84; boys, r = 0.56; P < .0001; TBF: girls, r = 0.93; boys, r = .85; P < .0001) has already been presented without allowing a deeper insight into the results.Similar results have been reported by Schäfer et al5Schärfer F Georgi M Wühl E Schärer K Body mass index and percentage fat mass in healthy German school children and adolescents.Int J Obes. 1998; 22: 461-469Crossref Scopus (114) Google Scholar who calculated percent body fat by measuring skinfold thickness (girls, r = 0.84; boys, r = 0.58).We conducted a study using total body electrical conductivity (TOBEC) for the quantification of body fat in a group of 204 children and adolescents (99 girls and 105 boys) aged 6 to 17 years, who were referred to our clinic because of weight problems. For the TOBEC method, a high correlation with the dual-energy x-ray absorptiometry method (r = 0.948; P = .0001)6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google Scholar has been demonstrated. TOBEC has the advantage of not exposing the patient to radiation. The lowest BMI for each age group is set above the 85th percentile of the German Hebebrand BMI percentiles,7Hebebrand J Heseker H Himmelmann GW Schärfer H Remschmidt H Altersperzentilen für den Body-Mass-Index aus Daten der Nationalen Verzehrstudie einschließlich einer Übersicht zu relevanten Einflußfaktoren.Akt Ernähr Med. 1994; 19: 259-265Google Scholar and so the young patients must be defined as obese.Our results concerning the correlation of BMI with PBF were similar to those of Pietrobelli et al (r = 0.65; for girls, 0.68; for boys, 0.63; for all, P = .0001).By dividing the total of 204 children and adolescents into different BMI groups, a poor correlation with a significance of P = .002 was found for the group with the lowest BMI (mean BMI of 22.7) and the group with the highest BMI (mean BMI of 34.5; P = .0009). In the groups with BMI values in between, no significance and no correlation were detected. The curvilinear correlation, which starts inclining at a BMI of approximately 25 to 27, demonstrates that an increasing BMI is not necessarily linked to a higher PBF.By dividing the collective into age groups, the highest association between BMI and PBF was calculated for children aged 6 to 9 years (r = 0.79, P = .0001).The correlation decreased in the higher age groups without losing its significance. The data obtained should be seen as an addition to the results of the study by Pietrobelli et al.Confidence limits on the association of BMI with fatness are set, and interpretation should be made cautiously when comparing BMI values across different age groups or predicting a specific individual’s TBF or PBF.6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google ScholarThe available data do not show that the BMI adequately reflects body fat mass in children and adolescents with a higher degree of adiposity. There is general agreement that there is a real need for an appropriate definition of obesity in childhood and adolescence, from a practical, as well as from a scientific, point of view. There is a body of evidence that body mass index (BMI) is strongly associated with complications based on increased body fat in adulthood.1Guo SS Roche AF Chumlea WC Gardner JD Siervogel RM The predictive value of childhood body mass index values for overweight at age 35 y.Am J Clin Nutr. 1994; 59: 810-819PubMed Google Scholar, 2Vanltallie TB Predicting obesity in children.Nutr Rev. 1998; 56: 154-156Crossref PubMed Scopus (4) Google Scholar The use of BMI in the pediatric age group is age-dependent, and the significance of the association of BMI with total body fat (TBF) or percentage of body fat (PBF) is unclear. The data from 198 healthy, non-obese children and adolescents obtained by Pietrobelli et al3Pietrobelli A Faith MS Allison DB Gallagher D Chiumello G Heymsfield SB Body mass index as a measure of adiposity among children and adolescents: a validation study.J Pediatr. 1998; 132: 204-210Abstract Full Text Full Text PDF PubMed Scopus (702) Google Scholar indicate that there is a highly significant correlation between BMI and TBF/PBF; however, the individual range for a particular BMI is considerably wide. These outcomes underline the fact that the BMI does not seem to be a very good measure for the quantification of body fat mass, expressed by the PBF, of the individual young patient. In a previous study by Boot et al,4Boot AM Bouquet J de Ridder MAJ Krenning EP de Muinck Keizer-Schrama SMPF Determinants of body composition measured by dual-energy x-ray absorptiometry in Dutch children and adolescents.Am J Clin Nutr. 1997; 66: 232-238PubMed Google Scholar a correlation study between PBF/TBF measured by dual-energy x-ray absorptiometry and BMI (PBF: girls, r = 0.84; boys, r = 0.56; P < .0001; TBF: girls, r = 0.93; boys, r = .85; P < .0001) has already been presented without allowing a deeper insight into the results. Similar results have been reported by Schäfer et al5Schärfer F Georgi M Wühl E Schärer K Body mass index and percentage fat mass in healthy German school children and adolescents.Int J Obes. 1998; 22: 461-469Crossref Scopus (114) Google Scholar who calculated percent body fat by measuring skinfold thickness (girls, r = 0.84; boys, r = 0.58). We conducted a study using total body electrical conductivity (TOBEC) for the quantification of body fat in a group of 204 children and adolescents (99 girls and 105 boys) aged 6 to 17 years, who were referred to our clinic because of weight problems. For the TOBEC method, a high correlation with the dual-energy x-ray absorptiometry method (r = 0.948; P = .0001)6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google Scholar has been demonstrated. TOBEC has the advantage of not exposing the patient to radiation. The lowest BMI for each age group is set above the 85th percentile of the German Hebebrand BMI percentiles,7Hebebrand J Heseker H Himmelmann GW Schärfer H Remschmidt H Altersperzentilen für den Body-Mass-Index aus Daten der Nationalen Verzehrstudie einschließlich einer Übersicht zu relevanten Einflußfaktoren.Akt Ernähr Med. 1994; 19: 259-265Google Scholar and so the young patients must be defined as obese. Our results concerning the correlation of BMI with PBF were similar to those of Pietrobelli et al (r = 0.65; for girls, 0.68; for boys, 0.63; for all, P = .0001). By dividing the total of 204 children and adolescents into different BMI groups, a poor correlation with a significance of P = .002 was found for the group with the lowest BMI (mean BMI of 22.7) and the group with the highest BMI (mean BMI of 34.5; P = .0009). In the groups with BMI values in between, no significance and no correlation were detected. The curvilinear correlation, which starts inclining at a BMI of approximately 25 to 27, demonstrates that an increasing BMI is not necessarily linked to a higher PBF. By dividing the collective into age groups, the highest association between BMI and PBF was calculated for children aged 6 to 9 years (r = 0.79, P = .0001). The correlation decreased in the higher age groups without losing its significance. The data obtained should be seen as an addition to the results of the study by Pietrobelli et al. Confidence limits on the association of BMI with fatness are set, and interpretation should be made cautiously when comparing BMI values across different age groups or predicting a specific individual’s TBF or PBF.6Ellis KJ Measuring body fatness in children and young adults: comparison of bioelectrical impedance analysis, total body electrical conductivity, and dual-energy x-ray absorptiometry.Int J Obes. 1996; 20: 866-873Google Scholar The available data do not show that the BMI adequately reflects body fat mass in children and adolescents with a higher degree of adiposity.