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Indian Pediatr 2013;50:
832-833 |
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Relevance of Measuring Body Fat in Children
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Anju Seth
Department of Pediatrics, Lady Hardinge Medical
College, New Delhi, India.
Email: [email protected]
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T he adverse health consequences associated with
obesity are related to increase in body fat rather than body weight
per se. Thus, it stands to logic that measuring body fat would be a
better tool for identifying risk as compared to any indirect measures of
adiposity. Accurate measurement of body fat can be done by various
techniques like under-water weighing, dual energy X-ray
absorptiometry (DEXA), bioelectric impedance, etc. In recent times, DEXA
has emerged as a tool of choice for body composition studies. However,
use of these methods is largely restricted to research settings because
of their complexity and cost. In clinical setting, anthropometric
measurements such as skin fold thickness, waist circumference,
waist-stature or waist-hip ratio and various height and weight-based
indices like body mass index (BMI) are the common tools used to assess
adiposity and its related complications.
Body mass index has been validated as a simple, low
cost tool to assess body fatness for routine clinical evaluation in
children and adolescents [1], and is found to be strongly correlated
with adiposity [2]. Increasing BMI is also shown to be associated with
higher risk of metabolic complications [3]. However, BMI criteria for
obesity may not identify differences in body fat or their distribution
[4]. Thus, BMI is an appropriate screening test to identify children
requiring further evaluation and follow-up, though it may not be
diagnostic of the level of adiposity. Attempts have been made to link
percentage body fat (PBF) estimates derived by DEXA with BMI and
describe PBF values associated with BMI classification of over-weight
and obesity [1]. There are age-related and sex-related variations in PBF
and thus a single PBF value may not be suitable for classifying children
as over-weight or obese.
As an ethnic group, Asians tend to have a smaller
body size and a relative deficit of lean body mass as compared to
Europeans/Americans. Thus, at an equivalent body mass index (BMI), there
is a relative excess of body fat in Asians. They also tend to have a
more central rather than peripheral distribution of fat. These
differences in body composition are evident from childhood and become
more pronounced during adolescence. Shaw, et al. [4] from UK
demonstrated that from age of 5 years onwards, South Asian girls and
boys have higher PBF as compared to the White or African Caribbean
ethnic groups, the difference increasing with age. This relative excess
of adipose tissue at a given BMI makes Asians more predisposed to
metabolic complications like type 2 diabetes (T2DM), hypertension and
dyslipidemia [5]. These disorders also tend to occur a lower BMI in
Asians as compared to their Western counterparts [6]. Like the increase
in body fat, the risk of metabolic complications also starts becoming
evident from adolescence itself. In UK, the relative risk of developing
T2DM in childhood is reported to be 14 times greater in South Asian than
in White European children [7]. In another study from UK, children of
South Asian origin were reported to be more sensitive to adverse
metabolic effects of obesity than Caucasians [8], which also tend to
occur earlier in age in children of South Asian origin [9].
Though elevated body fat in Asian children and
adolescents residing in Europe and America has been well documented, the
study by Khadgawat, et al. [10] is the first large study from
India that has systematically measured PBF in children and adolescents
using DEXA. It brings out a few important points. Most importantly, it
shows that there is a high correlation between BMI and body fat in both
boys and girls (all boys: r = 0.76, P <0.0001; all girls
r = 0.81, P <0.0001). Thus, it reiterates, to the relief
of clinicians, that BMI, with all its limitations, remains a
valid tool for assessing obesity and its related complications in
clinical practice. Interestingly, the authors show that there was no
consistent relationship between BMI and PBF categories. Thus, 6.3%
children in normal BMI category showed moderate/excess body fat, 32% of
those in obese category by BMI showed normal/moderate body fat and 41%
of those in the over-weight category by BMI showed variation in either
direction. Overall, there was moderate agreement between BMI and PBF
categories and PBF seemed to pick up less children in higher categories
of adiposity as compared to BMI. Secondly, the study quantifies age-and
sex-related changes in PBF in children and adolescents and gives their
distribution in the study population. While likely to be of limited
clinical utility, the data will serve as a reference data for North
Indian children in research studies for intra-country and international
comparisons. Finally, it formally documents what studies from West have
been indicating- Indian boys and girls have higher PBF as compared to
American children. This difference is more obvious during adolescence
and in the higher centiles of PBF distribution. Stated simply, Indian
children, especially those who are obese and/or in adolescent age group,
have more PBF as compared to their American counterparts and are
therefore at a higher risk of obesity related metabolic complications.
While definitely a cause for concern, one should keep
in mind that this work has been done in North Indian affluent school
children. This group had a higher prevalence of overweight and obesity
than the country on the whole. In India, where obesity is still a
phenomenon predominantly restricted to the urban affluent, findings of
this work may be applicable to other children from similar background;
populations where obesity/overweight prevalence is lower may not show
similarly high PBF. In fact, they have found lower PBF than that in
American children in the lower centiles, thereby indicating that thinner
Indian children may actually have less PBF as compared to their Western
counterparts [10].
So what is the clinical relevance of this
documentation of increased body fat in Indian children? Few studies till
now have directly assessed magnitude of health risk associated with
excess body fat in children [11,12] and it is not known as yet if
measurement of PBF is superior to BMI in determining health risks. Till
this risk is quantified, BMI firmly retains its position as a valuable
clinical tool for pediatric practice.
Competing interest: None stated; Funding:
Nil.
References
1. Taylor RW, Jones IE, Williams SM, Goulding A. Body
fat percentages measured by dual-energy X-ray absorptiometry
corresponding to recently recommended body mass index cutoffs for
overweight and obesity in children and adolescents aged 3-18 y. Am J
Clin Nutr. 2002;76:1416-21.
2. Ellis KJ, Abrams SA, Wong WW. Monitoring childhood
obesity: assessment of the weight/height2 index. Am J Epidemiol.
1999;150:939-46.
3. Steinberger J, Jacobs DR, Raatz S, Moran A, Hong
CP, Sinaiko AR. Comparison of body fatness measurements by BMI and
skinfolds vs dual energy X-ray absorptiometry and their relation
to cardiovascular risk factors in adolescents. Int J Obes (Lond).
2005:29; 1346-52.
4. Shaw NJ, Crabtree NJ, Kibirige MS, Fordham JN.
Ethnic and gender differences in body fat in British school children as
measured by DXA. Arch Dis Child. 2007;92:872-5.
5. Jafar TH, Chaturvedi N, Pappas G. Prevalence of
overweight and obesity and their association with hypertension and
diabetes mellitus in an Indo-Asian population. Can Med Assoc J.
2006;175:1071-7.
6. Oh SW, Shin S-A, Yun YH, Yoo T, Huh BY. Cut-off
point of BMI and obesity-related comorbidities and mortality in
middle-aged Koreans. Obesity Res. 2004;12:2031-40.
7. Ehtisham S, Hattersley AT, Dunger DB, Barrett TG;
British Society for Paediatric Endocrinology and Diabetes Clinical
Trials Group. First UK survey of paediatric Type 2 diabetes and MODY.
Arch Dis Child. 2004;89:526-9.
8. Whincup PH, Gilg JA, Papacosta O, Seymour C,
Miller GJ, Alberti KG, et al. Early evidence of ethnic
differences in cardiovascular risk: cross sectional comparison of
British South Asian and white children. BMJ. 2002;324:1-6.
9. Bhardwaj S, Misra A, Khurana L, Gulati S, Shah P,
Vikram NK. Childhood obesity in Asian Indians: a burgeoning cause of
insulin resistance, diabetes and sub-clinical inflammation. Asia Pac J
Clin Nutr. 2008;17:172-75.
10. Khadgawat R, Marwaha RK, Tandon N, Mehan N,
Upadhyay AD, Sastry A, et al. Reference intervals of percentage
body fat in apparently healthy North-Indian school children and
adolescents. Indian Pediatr. 2013;50.859-66.
11. Dwyer T, Blizzard CL. Defining obesity in
children by biological endpoint rather than population distribution. Int
J Obes Relat Metab Disord. 1996;20:472-80.
12. Washino K, Takada H, Nagashima M, Iwata H.
Significance of the atherosclerogenic index and body fat in children as
markers for future, potential coronary heart disease. Pediatr Int.
1999;41:260-5.
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