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International Journal of Obesity (2004) 28, S54–S58 & 2004 Nature Publishing Group All rights reserved 0307-0565/04 $30.00 Body composition in adolescents: measurements andmetabolic aspects G Rodrı´guez1*, LA Moreno2, MG Blay3, VA Blay3, JM Garagorri1, A Sarrı´a1 and M Bueno1 1Department of Pediatrics, University of Zaragoza, Zaragoza, Spain; 2University School of Health Sciences, University ofZaragoza, Zaragoza, Spain; and 3Endocrinology Unit, Military Hospital of Zaragoza, Zaragoza, Spain INTRODUCTION: Adolescence is a decisive period in human life in which important body composition changes occur. Increaseof total body mass and its relative distribution are mainly related to gender and pubertal development.
OBJECTIVE: This review explores the specific measurements that may be used in this age group to assess excess body fat and todefine obesity and overweight.
RESULTS: Identification of subjects at risk for adiposity requires simple anthropometric cutoffs for the screening of overweightand obesity. In this context, BMI criterion is the most frequently used but, in spite of its high sensitivity and specificity, animportant number of adolescents classified as overweight or obese do not have really high adiposity (32.1% of females and 42%of males). Excess total body fat and intra-abdominal visceral fat are related to metabolic abnormalities that increase the risk ofcardiovascular diseases. Waist circumference seems to be the best simple anthropometric predictor for the screening of themetabolic syndrome in children and adolescents.
CONCLUSIONS: Early identification of adolescents at risk for adiposity and its related metabolic complications requires reliable,simple and specific measures of excess body fat for this age group.
International Journal of Obesity (2004) 28, S54–S58. doi:10.1038/sj.ijo.0802805 Keywords: body composition; adolescents; metabolic syndrome leg-to-trunk length ratio. Sex differences in fat mass are Adolescence is a decisive period in human life due to the apparent even long before puberty tends to start.2,3 multiple changes that take place between childhood and These body composition and psycho-sociological changes adulthood. Puberty is the main neuro-hormonal determi- determine nutritional requirements, and eating and physical nant of both physiological and psychological changes, activity behavior modifications. Sometimes, characteristic although other social and behavior factors must be con- adolescent behavior patterns produce both energy balance and nutritional status disturbances. Therefore, obesity, Adolescence is characterized by a global acceleration of anorexia nervosa, bulimia or dislipidemia are important growth and maturation, with differential changes between alterations that commonly appear during adolescence and both sexes. Annual height velocity, weight gain, fat-free mass persist frequently into adulthood.4,5 With reference to and bone mineral content increase during this period in all obesity, the assessment of body composition is useful for adolescents, but the onset of puberty generally begins earlier the screening of excess body fat and its related metabolic in females than in males.1,2 The amount of fat mass in complications. Reliable measurements of body fatness and adolescent girls is usually higher than in boys. In girls, its distribution pattern are necessary in epidemiological, independently of the chronological age, pubertal develop- clinical and population studies, and in the management of ment is associated with an increase of body fat.2 However, the characteristic body composition pattern that appears inadolescent boys is a decrease of body fat, higher picks ofheight velocity and an increase of both shoulder span and Body composition measurementsMany reference methods are able to estimate body composi-tion accurately at the individual level. Multicompartment *Correspondence: Dr G Rodrı´guez, Departamento de Pediatrı´a, Facultad models, underwater weighing, air displacement plethysmo- de Medicina, C/ Domingo Miral, s/n, 50009 Zaragoza, Spain.
E-mail: [email protected] graphy, labeled water techniques and dual-energy X-ray Body composition in adolescentsG Rodrı´guez et al absorptiometry (DXA) are the most reliable methods to Skinfold thickness and other anthropometric measures are obtain accurate measures of total body fat.6,7 Computed often used as ‘field’ methods to predict total body fat in tomography and magnetic resonance imaging have been adolescents, either at population or at individual level.10–14 also shown to provide information about body fat distribu- Skinfold thickness measurements are able to predict body tion.8 Nowadays, reference methods are still not enough fatness better than BMI because subcutaneous fat (40–60% of suitable for field and clinical use. Therefore, anthropometry total body fat) can be directly measured with a calliper.12 and bioelectrical impedance are the most widely used Anthropometry may also give interesting information about methods when population size is big, whether no economic how body fat is distributed. The waist-to-hip circumference resources are available or when a quick measure is required.
ratio, waist circumference alone and the subscapular-to- One of the major priorities for obesity research is the triceps ratio are all positively related to a more centralized improvement of early identification of populations at risk for pattern of body fat distribution.13,14 Waist circumference, overweight and its associated alterations among different which is an indirect measure of abdominal fat, seems to be a age-groups, especially with a better characterization of the good anthropometric predictor for the screening of the relationship between simple measures and metabolic com- metabolic syndrome in children.14 As well as its advantages, plications.9 It must be taken into account in further studies anthropometry has many drawbacks associated with factors that adolescence is a particular period of life in which body that can affect its accuracy and precision: nonstandardized composition change dramatically when puberty appears methodology, technical and measurement limitations, selec- and, therefore, the amount of body fatness and its distribu- tion of adequate fat mass prediction equations for each age tion pattern may be more strongly related to gender and group, and measurement discrepancies between methods.10 pubertal development stage than to age. As an example ofthis fact, data from the AVENA Study (Alimentacio´n yValoracio´n del Estado Nutricional en Adolescentes) showed that the sum of four skinfolds did not significantly change Obesity is more than an excessive deposition of fat in the with age; however, when Tanner pubertal stage was con- body. Excess body fat is associated with adverse metabolic sidered, a significant decrease in males and a significant complications, as well as with significant short- and long- increase in females were observe (Figure 1).10,11 term physical and psychosocial problems that must be The body mass index (BMI; weight (kg)/height (m2)) is included in the same concept.9,15 Therefore, in order to accepted as the standard index for the definition of over- manage this enormous problem and its consequences, weight and obesity, and its ability for the screening of excess objective and standard parameters of body fatness are body fat in adolescents is discussed later in this review.
required for the screening of obesity. It is obvious that body Figure 1 Sum of four skinfolds (biceps þ triceps þ subscapular þ suprailiac skinfold thicknesses) in male and female adolescents in each age group and Tannerpuberty stage. Data from 1870 adolescents (843 females and 1027 males); the AVENA (Alimentacio´n y Valoracio´n del Estado Nutricional en Adolescentes)multicentre cross-sectional survey.10,25 fat cutoff values determined by reference methods are the evaluate the nutritional status, dietary and leisure time best criterion for overweight and obesity definition.
habits, and physical activity and fitness of a representative The definition of excess body fat is somewhat arbitrary sample of Spanish adolescents from five cities (Granada, even if total body fat mass or body fat mass percentage Madrid, Murcia, Santander and Zaragoza).
(%FM) is known. Nowadays, there is no consensus about In a group of 280 adolescents from the city of Zaragoza, %FM cutoffs for obesity in adolescents. Especially in aged 13.0–17.9 y (167 females and 113 males), we have this period, the level of adiposity may vary widely in relation measured %FM by DXA. Obesity status was defined by IOTF with age, gender and pubertal development. In the absence cutoff values and subjects were therefore classified into three of clear cutoff points, the most consistent %FM values for groups: normal-weight, overweight and obese.20 Correla- the definition of excess body fat in female adolescents range tions between %FM and BMI were strongly positive in both between 30 and 35%.16–19 Contrary to females, adiposity sexes: 0.73 in males and 0.82 in females (Po0.0001). Male in male adolescents decreases with age and sexual develop- and female adolescents classified as normal-weight, over- ment.18 Therefore, %FM cutoffs selected for excess body weight and obese were distributed according to their %FM fat in males are 25–30% for adolescents aged 10–15 y, values (Figures 2 and 3). The 85th percentile of the %FM and 20–25% when subjects up to the age of 18 y are distribution in each sex group was considered as cutoff point for excess adiposity (Z30% in males and Z35% in females).
BMI is the parameter most frequently used for the In total, 94% of males and 84% of females with high screening of excess body fat because it is easy to determine adiposity were correctly identified by BMI (sensitivity or and it tends to correlate well with body fat. BMI cutoff values true-positive rate), and 88% of males and 93% of females generally accepted for the definition of overweight and without high adiposity were also correctly classified (speci- obesity in adults are 425 and 430 kg/m2, respectively. In ficity or true-negative rate). Among those adolescents children and adolescents, based on BMI centile curves, considered as overweight or obese by BMI cutoffs, only International Obesity Task Force (IOTF) BMI cutoff points 67.9% of females and 58.0% of males had really excess have been recently proposed for each half-year of age, which correspond to the adult BMI values of 25 and 30 kg/m2 at the Therefore, BMI cutoffs are a good criterion for the screen- age of 18 y.20 This standard international definition allows the screening of adolescent overweight and obesity world- high sensitivity and specificity, but an important percentage of subjects classified as overweight or obese did nothave really excess adiposity. In a similar study performedby Taylor et al,17 in subjects aged 8.5–15.5 y, 86% of bothmales and females with high adiposity (%FM Z25% in males Is the BMI suitable for the screening of obesity in and Z35% in females) were correctly identified by BMI Although correlation between BMI and body fatnessis generally strong, it is higher in prepubertal childrencompared with pubertal adolescents, and it is also higherin female than in male children.12,21–23 The use of BMIto identify children with excess adiposity during the pubertaldevelopment has an important limitation; it has been shownthat BMI increases in adolescents from both sexes areprimarily determined by increases in fat-free mass ratherthan may erroneously classify some adolescents without over-weight as subjects with excess adiposity. In spite of thisfact, Sardinha et al19 have observed that BMI is ableto identify effectively children with excess body fataged 10–15 y (areas under ROC curve for BMI: 0.89–0.95 inboys and 0.61–0.97 in girls), as well as Sarrı´a et al25 inboys aged 7–16 y (area under the ROC curve for age-adjustedBMI: 0.86).
Our group has also studied the ability of BMI for the screening of overweight and obesity in adolescents. Dataconcerning the relationship between BMI and adiposity are Figure 2 Number of male adolescents classified using BMI criterion asnormal-weight, overweight and obese, and distributed according to their part of results obtained from the AVENA (Alimentacio´n y body fat percentage measured by dual-energy X-ray absorptiometry. Doted Valoracio´n del Estado Nutricional en Adolescentes) multi- line is the 85th percentile of the body fat percentage distribution considered center cross-sectional survey.10,11 This study was designed to Body composition in adolescentsG Rodrı´guez et al normal. They concluded that, independently of the amountof fat mass, intra-abdominal fat accumulation was stronglyrelated to insulin resistance and hyperglycemia in obeseadolescents.
Other metabolic abnormalities, associated with excess adiposity and implicated in cardiovascular morbidity andmortality, have also shown direct relations with central fatdistribution in children and adolescents: greater plasmahemostatic factor concentrations;30 increased intramyo-cellular lipid content;28 low HDL-cholesterol and highLDL-cholesterol, ApoA1/ApoB and triglycerides plasmalevels;26,31,32 and hypertension.26,31,32 Metabolic syndromeis characterized in childhood and adolescence by a clusteringof several independent cardiovascular risk factors,26,33 whichappears in 8.9% of obese children (defined by the simulta-neous presence of four risk factors).27 The role of differentvariables of metabolic syndrome that are highly interrelated, Figure 3 Number of female adolescents classified using BMI criterion as including parameters of body fat distribution, has been normal-weight, overweight and obese, and distributed according to their analyzed in obese and nonobese children and a set of body fat percentage measured by dual-energy X-ray absorptiometry. Doted composite factors unrelated to each other have been line is the 85th percentile of the body fat percentage distribution consideredas cutoff point for high adiposity.
obtained to explain the multifaceted nature of this syn-drome.26,33 Moreno et al,26 after a varimax rotation analysis,showed that waist circumference is one of the most Body fat distribution and metabolic complications important determinants of metabolic syndrome in child- The last point of this review explores the importance of hood and adolescence. Waist circumference, BMI, systolic body fat distribution for the screening of the metabolic and diastolic blood pressure, trunk-to-total skinfolds (%), syndrome in obese children and adolescents. Obesity, and plasma levels of fasting insulin, glucose, tryglicerides, especially central body fatness, is associated with dyslipide- leptin, HDL-cholesterol and uric acid; associated in four composite factors, explained 74.18 and 72.16% of the and impaired glucose tolerance/type 2 diabetes. This cluster metabolic syndrome variance in obese and in nonobese of metabolic abnormalities that already appears in obese children and adolescents increases the risk of cardiovasculardiseases.14,26,27 Obese children and adolescents with impaired glucose tolerance have peripheral insulin resistance and insulin The major conclusions of this review are the followings: secretion abnormalities that cause major defects in lipidand carbohydrate metabolism. Early in the natural history (1) Body composition change dramatically during adoles- of type 2 diabetes in obese young people, insulin resistance cence. Gender and pubertal development differences as prediabetes status is related to an increased visceral related to body composition must be considered in this fat more than to excess body fat.28 Freedman et al29 showed relative short period of human life.
a positive relation of central adiposity measured by circum- (2) Early identification of adolescents at risk for obesity and ferences and skinfold thickness to lipid and insulin its related metabolic complications requires reliable, concentrations in children and adolescents. Waist circum- simple and specific measures of excess body fat for this ference seems to be the best simple anthropometric predictor for the screening of the metabolic syndrome in children.14 (3) International Obesity Task Force BMI cutoffs20 may be Waist circumference may be used as an index of abdominal used for the screening of excess body fat in adolescents adiposity, which is the sum of visceral and subcutaneous due to its high sensitivity and specificity, but an fat at this level. In a recent study, Weiss et al28 have important percentage of subjects classified as overweight measured abdominal fat partitioning by nuclear magnetic or obese did not have really excess adiposity.
resonance into two groups of obese adolescents, one (4) In adolescents, excess body fat and, specifically, in- with impaired glucose tolerance and the other with creased intra-abdominal visceral fat are related to normal tolerance, both with similar ages, sex distribution dyslipidemia, hypertension, insulin resistance and im- and degree of obesity. Adolescents with impaired glucose tolerance had more abdominal visceral fat, less abdominal (5) Waist circumference seems to be the best simple subcutaneous fat and, therefore, greater visceral-to-subcuta- anthropometric predictor for the screening of the neous fat ratio than those whose glucose tolerance was metabolic syndrome in children and adolescents.
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