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the obesity epidemic is affecting all age groups and could decrease prospects for an active life expectancy .
the prevalence of overweight among children and adolescents in the india has doubled from 11.7% to 22.1% from 2006 to 2011 . although the body mass index ( bmi ) is widely used as a surrogate measure of adiposity , it is a measure of excess weight relative to height , rather than excess body fat .
the interpretation of bmi among children and adolescents is further complicated by the changes that occur in weight , height , and body composition during growth .
bmi levels among adults are highly correlated with the percentage of body fat among various race , sex , and age .
these weaker associations among children and adolescents may be attributable to the asynchronous changes that occur in the levels of fat mass ( fm ) and lean mass ( lm ) during growth .
it is suggested that the  obesity paradox  is merely based on the inadequacy of bmi to differentiate between lm and fm . against the background of obesity
, it is perceived that adipose tissue is a plain risk factor and lm is the protective element .
it is argued that the favorable impact of elevated bmi results from the beneficial effects of lean tissue , overriding the adverse effects of excess body fat .
however , the association of obesity and lm has not been studied well in literature .
hence , we designed this cross - sectional population - based study to ( i ) evaluate the relationship between bmi categories and lm and ( ii ) to analyze the effect of regional obesity ( subcutaneous and visceral ) on total lm ( tlm ) in children and adolescents .
adolescents were recruited from different schools in the city of new delhi as a part of the project to generate normative data for bmd .
there were 1829 apparently healthy children and adolescents who underwent health examination ( clinical , biochemical , and densitometric ) on a voluntary basis .
the data on lm and fm and its distribution were available from 1403 children and adolescents for the present study .
children and adolescents with clinically overt hepatic , renal , neoplastic , gastrointestinal , dermatological , endocrine , and systemic infective disorders , steroid intake , or alcoholism were excluded .
demographic , anthropometric , and clinical data were ascertained , and a detailed physical examination was conducted .
this study was conducted according to the guidelines laid down in the declaration of helsinki , and all procedures involving the children and adolescents were approved by the institutional ethics committee of the institute of nuclear medicine and allied sciences .
administrative approval was taken from the school authorities , written informed consent from parents / guardians , while verbal assent was taken from the children who participated in the study .
height was measured to the nearest 0.1 cm using a portable wall - mounted stadiometer ( 200 cm/78 inches ) model ws045 ( narang medical limited , new delhi , india ) with the participant standing straight with head held in the frankfurt horizontal plane .
weight , without shoes and while wearing light clothes , was measured to the nearest 0.1 kg , using an electronic scale ( equinox digital weighing machine , model eb6171 , equinox overseas private limited , new delhi , india ) .
the study population was divided according to bmi - based criteria proposed by cole et al . as normal , overweight , and obese .
pubertal staging was carried out by trained professionals of the same sex based on tanner criteria .
testicular volume was determined by comparative palpation with prader orchidometer ( pharmacia and upjohn , uppsala , sweden ) .
stage 1 ( prepubertal ) included participants with testicular volume < 4 ml , stage 2 ( early puberty ) 
volume 4 but 8 ml , stage 3  volume 10 but 15 , and stage 4 ( fully mature )  testicular volume > 15 ml . a testicular volume of 4 ml or greater was considered as the onset of puberty .
if there was a discrepancy in the testicular volumes of two sides , the larger one was taken as the final volume .
lm was measured using the prodigy oracle ( ge lunar corp . , madison , wi ) according to a standard protocol .
instrument variation was determined regularly using a phantom supplied by the manufacturer , and the mean coefficient of variation was < 0.5% . for in vivo measurements ,
instrument variation was determined by measuring total fm and regional fm in twenty healthy adults twice , and the mean coefficient of variation was < 0.5% .
leg and arm fat - to - total fat ratio ( latr ) was considered as indicative of subcutaneous fat and trunk fat - to - total fat ratio ( ttr ) was indicative of visceral fat .
interquartile range for latr and ttr was 0.05 and 0.06 and 0.06 and 0.08 for girls and boys , respectively .
appendicular skeletal muscle mass index ( asmi ) was calculated by lm at arms and leg in kilogram divided by square of height in meters .
statistical analysis was carried out using spss software version 20.0 ( chicago , il , usa ) .
data were presented as mean  standard deviation or number ( % ) unless specified .
one - way analysis of variance was used to test the differences between bmi groups .
post hoc analysis was used to compare the significance level between two groups within each parameter .
mean age of the study participants was 13.2  2.7 years ( boys - 13.0  2.7 ; girls - 13.4  2.8 years ) .
nearly , 79.5% of the children and adolescents were normal weight , 16.0% were overweight , and 4.5% were obese .
age and pubertal status were comparable in all groups in both genders [ table 1 ] .
basic characteristics of the population asmi , tlm , and its regional distribution were higher in overweight and obese compared to normal weight children and adolescents , but were comparable between overweight and obese boys ( lm : p = 0.828 ; asmi : p = 0.982 ) and girls ( lm : p = 0.268 ; asmi : p = 0.096 ) [ table 2 ] .
tlm per unit of fat ( tlm / tf ratio ) showed a significant decrease from normal weight group to obese group , but was comparable between overweight and obese groups , even after adjustment with age , height , and sms in both genders [ table 3 ] .
lean mass according to weight categories among boys and girls total lean mass versus total fat ratio in weight categories according to interaction with age , height , and sexual maturity score unadjusted tlm decreased with the quartiles of latr ( subcutaneous fat ) and increased with the quartiles of ttr ( visceral fat ) in both gender . however , when adjusted for age and sms , the same pattern persisted among boys , but the pattern of tlm became nonsignificant with latr in girls [ table 4 ] .
effect of subcutaneous fat ( leg arm fat - to - total fat ratio ) and visceral fat ( trunk - to - total fat ratio ) on total lean mass *
in the present study , we observed that tlm and regional lm were more in overweight and obese categories when compared to the normal weight category , but were comparable between overweight and obese category .
consistent with this , we expect that lm should show a similar pattern of increase .
surprisingly , tlm / tf decreased after adjustment with age , height , and sms in both genders .
this suggests that overweight and obese children and adolescents have lower tlm / tf when compared to normal bmi category .
studies have shown that lm is increased when weight gain is observed in early childhood , but fm increases when weight gain is seen in late childhood . hence , weight gain in later childhood will have relatively lower lm when compared to early childhood .
physical activity increases lm and decreases fm with decreasing weight and obesity in children and adolescents . pharmacological therapy ( sibutramine )
hence , an increase in the physical activity is the best mode of therapy to achieve weight loss .
increase in lm may help in improving the health status by decreasing obesity while a decrease in lm is associated with an adverse outcome .
the relationship between regional lean and fm was influenced by age and gender . with an increasing adiposity , skeletal muscle
to adipose tissue ratio declined faster at the trunk in men and at the extremities in women .
we observed a negative effect of subcutaneous fat and a positive effect of visceral fat on lm which was influenced by age and pubertal status in girls , indicating the importance of pubertal status for the effect .
a study has shown that the change in the pattern of subcutaneous fat distribution could be due to a varied response of different sites toward the loss of subcutaneous fat due to increased levels of activity .
furthermore , increase in physical activity will result in a decrease in subcutaneous fat and increase in lm , and this can explain the inverse relationship .
visceral fat due to its gravitational effect will put physical strain on appendicular system and will increase tlm .
the main limitation of the study was the absence of longitudinal data , which could have assessed the change in bmi categories and its effect on lm .
another limitation was the absence of measurement of adipokines and myokines , which could have highlighted the mechanism of association between body fat and lm .
however , the strength of the study attributes to the large sample size from healthy indian population .
obese children and adolescents have higher lm than normal weight children , but when calculated as per the unit of fm , they have lower lm . subcutaneous fat had a negative impact and visceral fat had a positive impact on tlm which is influenced by age and pubertal status .
background : the association of obesity and lean mass ( lm ) has not been examined well in children and adolescents , and it remains controversial.objective:the objective of this study was to evaluate the relationship of body mass index ( bmi ) categories and regional obesity with total and regional lm in children and adolescents.methods:a total of 1408 children and adolescents ( boys 58.9% ; girls 41.1% ) divided according to bmi ( normal weight 79.5% , overweight 16.0% , and obese 4.5% ) were included in this cross - sectional study . 
 total and regional lm and fat mass were measured by dxa . 
 leg and arm fat - to - total fat ratio ( latr ) indicative of subcutaneous fat and trunk fat - to - total fat ratio ( ttr ) , an indicator of visceral fat , were calculated.results:mean age of the study population was 13.2  2.7 years ( boys - 13.0  2.7 ; girls - 13.4  2.8 years ) . 
 total lm ( tlm ) and its regional distribution were higher in overweight and obese groups when compared with those with normal bmi in both genders . 
 tlm was comparable between overweight and obese in both genders . 
 tlm per unit of fat progressively decreased from normal to obese categories . 
 the difference in lm per unit fat between bmi categories persisted after adjustment for age , height , and sexual maturity score . 
 tlm increased across the quartiles of ttr , but decreased with an increment in subcutaneous fat ( quartiles of latr).conclusions : obese children and adolescents apparently have higher lm than normal bmi children , but have lower lm per unit of fat . 
 subcutaneous fat had a negative impact and visceral fat had a positive impact on tlm .