Utility of Different Measures of Body Fat Distribution in Children and Adolescents
Stephen R. Daniels,
Philip R. Khoury and
John A. Morrison
From the Division of Cardiology, Department of Pediatrics, University of Cincinnati College of Medicine, and the Children's Hospital Medical Center, Cincinnati, OH.
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ABSTRACT
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The distribution of body fat has been shown to be an important determinant of cardiovascular disease risk. The purpose of this study was to evaluate which method of evaluating body fat distribution compares most favorably with dual-energy x-ray absorptiometry. The study included 201 children and adolescents aged 717 years who were recruited from Cincinnati, Ohio, schools in 19921993. The strongest correlate of fat distribution was waist circumference (r = 0.80). Age was a more important determinant of fat distribution than was pubertal maturation. There was a greater relative deposition of central body fat with increasing age. Multiple regression analysis demonstrated that waist circumference was the best simple measure of fat distribution, since it was least affected by gender, race, and overall adiposity. Waist circumference is easy to determine and is a useful measure of fat distribution for children and adolescents.
adipose tissue; anthropometry; body constitution; body mass index; child
Abbreviations:
DEXA, dual-energy x-ray absorptiometry.
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INTRODUCTION
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Obesity is becoming an increasing problem for children and adults in the United States (1
). The sequelae of obesity include cardiovascular disease, diabetes mellitus, sleep and respiratory problems, and psychological difficulties (2
). Research on the distribution of body fat has shown that for both adults and children, a more central distribution of fat is associated with type 2 (non-insulin-dependent) diabetes mellitus, a worse cardiovascular disease risk profile, and other adverse outcomes (3



8
).
Clinicians and investigators have used a variety of measurements, including waist circumference, the ratio of waist circumference to hip circumference, and the ratio of truncal skinfold thickness to peripheral skinfold thickness, as an approximation of the distribution of body fat. These methods have not been extensively studied in children. The method which provides the most useful measure of fat distribution remains to be determined. Dual-energy x-ray absorptiometry (DEXA) has been shown to be a reliable and accurate method of measuring fat mass (9



14
). Because DEXA provides body composition measures by body segment, it can be used to measure fat in different regions of the body (12
). Therefore, DEXA provides a useful comparison method with which to assess the utility of circumference and skinfold measures in the evaluation of body fat distribution.
The purpose of this study was to evaluate which methods for determining the distribution of fat compare favorably with DEXA and to investigate whether these measures are representative of the distribution of body fatness independent of age, race, gender, and sexual maturation in children and adolescents.
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MATERIALS AND METHODS
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This study included 201 subjects ranging in age from 7 years to 17 years. There were 44 Black females, 52 White females, 54 Black males, and 51 White males. The subjects were healthy children and adolescents recruited in 19921993 from local schools in Cincinnati, Ohio. The study was approved by the institutional review board of the Children's Hospital Medical Center (Cincinnati). Subjects were studied after signed informed consent had been obtained.
Anthropometry
The methods of anthropometric measurement were identical to those used in the National Heart, Lung, and Blood Institute Growth and Health Study (13
). Measurements were made with the children wearing their underwear and a T-shirt provided for them by the investigators. Height was measured using a stadiometer while the subjects stood wearing socks and with their heads in the Frankfort horizontal plane. Weight was measured with an electronic scale. All measurements were taken twice. A third measurement was taken if the first two differed by more than 0.5 cm (height) or 0.3 kg (weight).
Circumferences were measured with a fiberglass tape using the methods of Cameron (14
). The plane of the tape was perpendicular to the long axis of the body and parallel to the floor. Waist circumference was measured at the level of the umbilicus and the superior iliac crest. The measurement was made at the end of a normal expiration while the subject stood upright, with feet together and arms hanging freely at the sides. Hip circumference was measured at the maximum point below the waist, without compressing the skin.
Skinfold thicknesses were measured at the triceps, suprailiac, and subscapular sites using Holtain calipers (Pfister Import-Export, Inc., Carlstadt, New Jersey). All measurements were made on the right side of the subject. The fold of skin to be measured was firmly grasped and then raised with no muscle included. The calipers were then placed below the thumb and finger, and the grip on the calipers was released, allowing the spring to compress the skinfold. Persons making the measurements underwent an extensive training and certification program as part of the National Heart, Lung, and Blood Institute Growth and Health Study. Measurements were taken twice and were repeated if the first two measurements differed by more than 1.0 mm. The mean of the two measurements was used in the analysis. For the purposes of analysis, two approaches to determining fat distribution by skinfold thickness were utilized. The first approach was to divide the subscapular skinfold by the triceps skinfold. The second approach took the sum of the subscapular and suprailiac skinfolds and divided that sum by the triceps skinfold measurement.
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DEXA
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DEXA is a method of assessing total and regional body composition. This method measures fat mass, lean mass, and bone mineral density using two x-ray beams that traverse the body. The energy is then collected by a detector after it has been attenuated by the bone and soft tissue through which it has passed. The number of photons per unit of area is corrected for soft tissue by linear, two-dimensional interpolation. The values are summed to estimate total bone mineral content. Soft tissue is resolved using mass attenuation coefficients from tissue equivalent standards for fat and fat-free tissue. DEXA has been shown to provide accurate and precise measurements of total body and regional fat mass. DEXA has been validated in children and adults against hydrodensitometry, which has been considered the standard for measurement of fat mass (11
).
For evaluation of regional fat distribution, subjects were scanned using a Hologic QDR-1000/W whole body scanner (Hologic, Inc., Waltham, Massachusetts). For data interpretation, body composition is divided into bone mass and soft tissue mass. Soft tissue mass can then be divided into fat mass and lean body mass. Fat mass was determined in the waist region, the subscapular region, the hip region, and the thigh region. Each of the four regions was of identical height. Region height was defined by anatomic bony landmarks. This allows standardization from subject to subject. The height of a region was one third of the distance between the top of the iliac crest and the knee joint. The waist region was placed on top of the iliac crest, and the subscapular region was placed on top of the waist region. The hip region was placed at midpelvis, with the thigh region placed just below the hip region. The fat mass ratio (fat distribution by DEXA) was calculated as the fat mass in the waist and subscapular regions divided by the fat mass in the hip and thigh regions.
Sexual maturation
Pubertal staging was determined by physical assessment. Boys were examined by male study personnel, and girls were examined by females. For boys, the maturation assessment included pubic hair stage as defined by Marshall and Tanner (15
) and determination of testicular volume by means of an orchidometer. Pubertal staging was accomplished using the criteria of Biro et al. (16
) on a scale of 1 to 4. Maturation staging for girls utilized criteria which incorporated assessment of pubic hair and areolar development (
). These criteria were based on staging principles developed by Tanner (17
) and were modified for use in girls of all ethnic groups and body habitus. The method results in staging on a scale of 1 to 3, where 1 is prepubertal, 2 is pubertal but premenarcheal, and 3 is postmenarcheal (18
).
Data analysis
Data were analyzed using SAS statistical programs (SAS Institute, Cary, North Carolina). Mean values between ethnic groups and between genders were compared using Student's t test. Pearson correlation coefficients were used to evaluate the relations between measures of body fat distribution and fat distribution by DEXA. Multiple linear regression was used to investigate the effects of age, sexual maturation, gender, and ethnicity on the relations of waist circumference, waist:hip circumference ratio, and skinfold ratio with body fat distribution by DEXA. In these regression models, the fat distribution measured by DEXA was used as the dependent variable. A p value less than 0.05 was considered to indicate statistical significance. For the purposes of regression analysis, females were coded as 0 and males as 1; Blacks were coded as 0 and Whites as 1.
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RESULTS
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The characteristics of the study population are presented in table 1. There were no significant differences in age by gender or race. There were significant differences by gender or ethnic group for height and body mass index (weight (kg)/height (m)2). White males were significantly taller than White females (p = 0.01), and Black males were taller than Black females (p = 0.06). Black females had greater body mass indices than White females (p = 0.03), and Black males had greater body mass indices than White males (p = 0.013).
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TABLE 1. Characteristics of schoolchildren aged 717 years in a study of measures of body fat distribution, Cincinnati, Ohio, 19921993
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The correlation coefficients for the relations of fat distribution by DEXA with age, maturation stage, and anthropometric variables are presented in table 2. The strongest correlations with fat distribution were those of waist circumference and subscapular skinfold thickness (r = 0.80). This was true for boys as well as girls and for both Black and White subjects. Suprailiac skinfold thickness also provided a good correlation with fat distribution by DEXA. These skinfold measurements provided the highest correlation for girls (r = 0.85).
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TABLE 2. Pearson coefficients for correlations of age, pubertal stage, and anthropometric indices with fat distribution assessed by dual-energy x-ray absorptiometry in children aged 717 years, Cincinnati, Ohio, 19921993
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To evaluate whether the relation of fat distribution with the various anthropometric measures was independent of age or maturation stage, we performed multiple regression analysis. In this analysis, fat distribution by DEXA was the dependent variable, with the anthropometric measure of interest (e.g., waist:hip ratio) and either age or maturation stage being used as the independent variables. These analyses were performed separately for each race/gender group (table 3).
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TABLE 3. Results of model fitting* for fat distribution assessed by dual-energy x-ray absorptiometry, using age and simple measures, for children aged 717 years, Cincinnati, Ohio, 19921993
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Age was a significant independent variable in many of the models, but maturation stage was not significant in any of the models. This suggests that age is a more important determinant of the relation of fat distribution to the anthropometric variables than is pubertal maturation. The regression coefficient for age was usually positive. This suggests that there was a greater relative deposition of central body fat with increasing age after data were controlled for the anthropometric measure. However, age was not a significant independent variable for boys when the waist measurement was used, and it was not significant for girls when the subscapular:triceps skinfold ratio was considered. Age was not a significant independent variable for any of the race/gender groups when the (subscapular + suprailiac):triceps skinfold ratio was used.
The next step was to add gender to the regression models, including the anthropometric variables and age as independent variables. This was done to determine whether the relations between fat distribution and the anthropometric variables differed in boys and girls. The results of these analyses are presented in table 4. Gender was an important variable for Black subjects when waist:hip ratio was the measure of fat distribution. Gender was significant for Whites when waist circumference was considered. Gender was significant for both Whites and Blacks when (subscapular + suprailiac):triceps skinfold ratio was the measure of fat distribution. Gender was not significant when subscapular:triceps skinfold ratio was considered. The regression coefficients for gender were all negative, except in the regression for waist:hip ratio. A negative regression coefficient means that for a similar waist circumference or (subscapular + suprailiac):triceps skinfold thickness ratio, girls have a higher central body fat distribution than boys.
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TABLE 4. Results of model fitting* for fat distribution assessed by dual-energy x-ray absorptiometry versus simple measures, by age and gender, for children aged 717 years, Cincinnati, Ohio, 19921993
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The next step was to add race and percentage of body fat to the multiple regression model, explaining the variance of the fat mass ratio by DEXA. These results are presented in table 5. Race was a significant independent variable only in the regression model for waist:hip ratio. Percentage of body fat was a significant independent variable in the regression models for both skinfold measurements and for waist:hip ratio, but not for waist circumference.
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TABLE 5. Results of model fitting* for fat distribution assessed by dual-energy x-ray absorptiometry versus anthropometric measures, by age, race, gender, and age, for children aged 717 years, Cincinnati, Ohio, 19921993
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Waist circumference was least affected by gender, race, and the overall measure of adiposity. The multiple R2 for the model with waist circumference was 0.66similar to that for the other models, which included additional variables.
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DISCUSSION
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Epidemiologic studies have increasingly emphasized the importance of body fat distribution in determining cardiovascular risk status. A more central deposition of fat has been shown to be associated with higher blood pressure, less favorable lipid and lipoprotein levels, and increased left ventricular mass index (8
). For this reason, it is important to find simple, useful measures of fat distribution for future studies and for possible use in clinical settings as physicians make decisions about the evaluation and treatment of obesity.
A number of measures have been suggested as appropriate for evaluating fat distribution. It is important to have a measure that is relatively easy to use and that can be applied in clinical and research settings. However, the use of measures such as the waist:hip and skinfold thickness ratios assumes that these measures represent the distribution of fat independent of age, race, and gender. This would mean that individuals with a certain anthropometric measure of fat distribution would have the same degree of fat distribution regardless of their age, race, or gender. Goodman-Gruen and Barrett-Connor (19
) have shown systematic differences in the relation of these measures to fat distribution by age and gender in an elderly population. To our knowledge, these questions have not been systematically evaluated in children and adolescents.
We found that the relations between anthropometric measures and body fat distribution are all dependent on age. In addition, some of the measures are also dependent on gender, race, or percentage of body fat. The implication of these analyses is that investigators and clinicians must use caution if these measures are employed to compare fat distributions between gender or ethnic groups.
These results suggest that waist circumference may be the most useful measure of fat distribution in comparison with determination of fat distribution by DEXA. These results are consistent with results from other studies carried out in adults. Pouliot et al. (20
) examined anthropometric correlates of abdominal visceral adipose tissue in men and women. They found that waist circumference and abdominal sagittal diameter were better correlates of visceral adipose tissue measured by computed tomography scan than the commonly used waist:hip ratio. In women, they also found waist circumference to be more closely related to triglyceride, high density lipoprotein cholesterol, and fasting insulin and glucose levels than the waist:hip ratio. They suggested greater use of the waist circumference measure in practice. Studies of this sort would be difficult to conduct in children, since use of computed tomography scanning in normal children and adolescents might not be ethically acceptable.
The skinfold thickness ratios also provided good explanation of the variance of body fat distribution as measured by DEXA. However, both skinfold thickness ratios had percentage of body fat as a significant independent variable in the regression model, and the first skinfold thickness ratio (subscapular:triceps) also had gender in the model. The decision regarding which simple anthropometric measure to use to evaluate the distribution of fat in practice will require investigators to consider a number of factors, including the correlation with measures such as DEXA, the ability to accurately characterize the distribution of body fat independent of other factors, such as race and gender, and the ease of use in a practical research setting.
Our findings indicate that there are important factors to consider when using anthropometric measures of fat distribution, particularly when an objective is to make comparisons by race or gender. It appears that waist circumference may be a more useful measure, since it is not related to race or gender. However, it is still important to consider the age of the subject when waist circumference is used as a measure of fat distribution in children and adolescents.
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ACKNOWLEDGMENTS
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This study was supported in part by grant RR 08084 from the National Institutes of Health.
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NOTES
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Reprint requests to Dr. Stephen R. Daniels, Division of Cardiology, Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229 (e-mail: sdaniels{at}chmcc.org).
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Received for publication August 11, 1999.
Accepted for publication January 13, 2000.