baseline data from a total of three studies were included from the university of southern california ( usc ) center for transdisciplinary research on energetics and cancer ( trec ) . included were girls from the insulin resistance and declining physical activity levels in african american and latina girls study ( transitions ) ( 18 african american and 52 hispanic girls ) in tanner stages 1 and 2 . transitions is a longitudinal assessment of physical activity in african american and hispanic girls through adolescence . tanner stages 4 and 5 included the strength and nutrition outcomes in latino adolescents ( sano ) ( 53 hispanic girls ) and the strength and nutrition outcomes in african american youth ( stand ) ( 39 african american girls ) studies ( 11 ) . both studies examined the effect of a randomized control trial , including the combination of nutrition modification and strength training , on metabolic and adiposity parameters in overweight hispanic and african american teenagers . in total , the analysis included 149 female , overweight children and adolescents of hispanic ( n = 97 ) and african american ( n = 52 ) descent . both ethnicities were compared regarding the relationships of fasting measures of is with a more invasive measure of is ( fsivgtt ) in tanner stages 1 and 2 as well as in tanner stages 4 and 5 . tanner stages 1 and 2 were combined for the prepubertal and early puberty group , and tanner stages 4 and 5 were combined for the adolescent group . inclusion criteria for participants were hispanic or african american ethnicity , defined by all four grandparents being of hispanic or african american descent , and a bmi that was at or above the 85th percentile for age and sex ( 12 ) . participants were excluded from the study if they had diabetes , suffered from a major illness since birth , or had a condition known to affect body composition or is . written informed consent was obtained from parents and youth assent from participants . a pediatric health care provider conducted a medical history and physical examination and determined maturation using the criteria of tanner at every annual visit ( 13 ) . height was measured to the nearest 0.1 cm by a wall - mounted stadiometer , and weight was recorded to the nearest 0.1 kg by a balance beam medical scale . bmi and bmi percentiles for age and sex were determined based upon established centers for disease control normative curves using epi info 2000 , version 1.1 ( 14 ) . all girls participated in a fsivgtt , assessing is , acute insulin response ( air ) , and disposition index ( di ) . after a 12-h fasting period , intravenous catheters were placed in an anticubital vein in both arms . two fasting blood samples ( 15 and 5 min ) were followed by a 0.3 g / kg body weight intravenous glucose administration at time point 0 . at 20 min , insulin ( 0.02 units / kg body weight , humulin r ; blood samples were taken at 2 , 4 , 8 , 19 , 22 , 30 , 40 , 50 , 70 , 100 , and 180 min . is , air , and di as an indicator for -cell capacity were calculated with minmod millennium 2003 ( 15 ) . blood samples from the fsivgtt were centrifuged for 10 min at 2,500 rpm and plasma aliquots were frozen at 80c until further analysis . charles , mo ) ( intraassay coefficient of variation : 4.77% , interassay coefficient of variation : 9.11% ) . the assay is a double antibody sandwich elisa based on the capture of insulin to wells of a microtiter plate coated with monoclonal mouse anti - human insulin antibodies and the binding of a second biotinylated monoclonal mouse anti - human antibody to the captured insulin . glucose concentrations were measured with the glucose oxidase technique ( yellow springs instrument analyzer ; yis inc . , yellow springs , oh ) . body composition ( total body fat and total lean mass ) for all participants was determined with dual - energy x - ray absorptiometry using a hologic qdr 4500 w ( hologic , bedford , ma ) . abdominal fat ( visceral adipose tissue , subcutaneous adipose tissue , and hepatic fat fraction [ hff ] ) were assessed by magnetic resonance imaging using a general electric 1.5 tesla magnet ( waukesha , wi ) . multiple - slice axial tr 400/16 view of the abdomen at the level of the umbilicus was analyzed for volume of adipose tissue ( liter ) . fasting measures were calculated by taking the mean of the two fasting blood samples ( 15 and 5 ) for glucose and insulin of the fsivgtt . the following fasting indices were evaluated : descriptive statistics for all variables of interest were determined for both ethnic groups . firstly , linear regression modeling was used to determine whether ethnicity or tanner stage significantly interact with the fasting measures . secondly , the relationship between is and fasting measures was assessed with partial pearson correlations , adjusted for age , fat mass , and fat - free mass ( ffm ) . a pediatric health care provider conducted a medical history and physical examination and determined maturation using the criteria of tanner at every annual visit ( 13 ) . height was measured to the nearest 0.1 cm by a wall - mounted stadiometer , and weight was recorded to the nearest 0.1 kg by a balance beam medical scale . bmi and bmi percentiles for age and sex were determined based upon established centers for disease control normative curves using epi info 2000 , version 1.1 ( 14 ) . all girls participated in a fsivgtt , assessing is , acute insulin response ( air ) , and disposition index ( di ) . after a 12-h fasting period , intravenous catheters were placed in an anticubital vein in both arms . two fasting blood samples ( 15 and 5 min ) were followed by a 0.3 g / kg body weight intravenous glucose administration at time point 0 . at 20 min , insulin ( 0.02 units / kg body weight , humulin r ; blood samples were taken at 2 , 4 , 8 , 19 , 22 , 30 , 40 , 50 , 70 , 100 , and 180 min . is , air , and di as an indicator for -cell capacity were calculated with minmod millennium 2003 ( 15 ) . blood samples from the fsivgtt were centrifuged for 10 min at 2,500 rpm and plasma aliquots were frozen at 80c until further analysis . charles , mo ) ( intraassay coefficient of variation : 4.77% , interassay coefficient of variation : 9.11% ) . the assay is a double antibody sandwich elisa based on the capture of insulin to wells of a microtiter plate coated with monoclonal mouse anti - human insulin antibodies and the binding of a second biotinylated monoclonal mouse anti - human antibody to the captured insulin . glucose concentrations were measured with the glucose oxidase technique ( yellow springs instrument analyzer ; yis inc . body composition ( total body fat and total lean mass ) for all participants was determined with dual - energy x - ray absorptiometry using a hologic qdr 4500 w ( hologic , bedford , ma ) . abdominal fat ( visceral adipose tissue , subcutaneous adipose tissue , and hepatic fat fraction [ hff ] ) were assessed by magnetic resonance imaging using a general electric 1.5 tesla magnet ( waukesha , wi ) . multiple - slice axial tr 400/16 view of the abdomen at the level of the umbilicus was analyzed for volume of adipose tissue ( liter ) . fasting measures were calculated by taking the mean of the two fasting blood samples ( 15 and 5 ) for glucose and insulin of the fsivgtt . the following fasting indices were evaluated : descriptive statistics for all variables of interest were determined for both ethnic groups . firstly , linear regression modeling was used to determine whether ethnicity or tanner stage significantly interact with the fasting measures . secondly , the relationship between is and fasting measures was assessed with partial pearson correlations , adjusted for age , fat mass , and fat - free mass ( ffm ) . all girls participated in a fsivgtt , assessing is , acute insulin response ( air ) , and disposition index ( di ) . after a 12-h fasting period two fasting blood samples ( 15 and 5 min ) were followed by a 0.3 g / kg body weight intravenous glucose administration at time point 0 . at 20 min , insulin ( 0.02 units / kg body weight , humulin r ; blood samples were taken at 2 , 4 , 8 , 19 , 22 , 30 , 40 , 50 , 70 , 100 , and 180 min . is , air , and di as an indicator for -cell capacity were calculated with minmod millennium 2003 ( 15 ) . blood samples from the fsivgtt were centrifuged for 10 min at 2,500 rpm and plasma aliquots were frozen at 80c until further analysis . charles , mo ) ( intraassay coefficient of variation : 4.77% , interassay coefficient of variation : 9.11% ) . the assay is a double antibody sandwich elisa based on the capture of insulin to wells of a microtiter plate coated with monoclonal mouse anti - human insulin antibodies and the binding of a second biotinylated monoclonal mouse anti - human antibody to the captured insulin . glucose concentrations were measured with the glucose oxidase technique ( yellow springs instrument analyzer ; yis inc . , yellow springs , oh ) . body composition ( total body fat and total lean mass ) for all participants was determined with dual - energy x - ray absorptiometry using a hologic qdr 4500 w ( hologic , bedford , ma ) . abdominal fat ( visceral adipose tissue , subcutaneous adipose tissue , and hepatic fat fraction [ hff ] ) were assessed by magnetic resonance imaging using a general electric 1.5 tesla magnet ( waukesha , wi ) . multiple - slice axial tr 400/16 view of the abdomen at the level of the umbilicus was analyzed for volume of adipose tissue ( liter ) . fasting measures were calculated by taking the mean of the two fasting blood samples ( 15 and 5 ) for glucose and insulin of the fsivgtt . firstly , linear regression modeling was used to determine whether ethnicity or tanner stage significantly interact with the fasting measures . secondly , the relationship between is and fasting measures was assessed with partial pearson correlations , adjusted for age , fat mass , and fat - free mass ( ffm ) . linear regression models testing the relationship of ethnicity and tanner stage with fasting measures showed a significant interaction of tanner stage with fasting insulin (  = 1.19 ; p < 0.01 ) and homa (  = 1.12 ; p < 0.01 ) on the relationship with is . therefore , tanner stages were separated into tanner stages 1 and 2 versus tanner stages 4 and 5 and were tested separately for further analysis . no significant interaction of ethnicity with either fasting measure ( fasting insulin [  = 0.24 ; p > 0.05 ] and homa [  = 0.29 ; p > 0.05 ] ) was observed in tanner stages 1 and 2 . we did find a significant interaction of ethnicity with both fasting insulin (  = 1.59 ; p < 0.01 ) and homa (  = 1.36 ; p < 0.05 ) , testing the relationship of fasting measures with is in tanner stages 4 and 5 . consequently , this led to a separate analysis of ethnicities in that group of participants . characteristics for participants from both ethnicities in tanner stages 1 and 2 as well as tanner stages 4 and 5 are summarized in table 1 . in tanner stages 1 and 2 , african american girls had more ffm and less visceral adipose tissue compared with hispanic girls . african american girls were not more insulin resistant according to is and homa , but they had a higher di compared with hispanic girls . in tanner stages 4 and 5 , african american girls weighed more and had a higher ffm compared with hispanic girls . participants characteristics separated by tanner stage sat , subcutaneous adipose tissue ; vat , visceral adipose tissue . figure 1 shows the relationship of is with fasting measures for both ethnicities . in partial correlations adjusting for age , fat , and ffm , is was significantly correlated with fasting insulin ( r = 0.67 ; p < 0.01 ) and homa ( r = 0.66 ; p < 0.01 ) for all participants . relationship of fasting insulin ( a ) and homa ( b ) with is in tanner stages 1 and 2 . figure 2 shows the relationship of is and fasting measures for both ethnicities , adjusted for age , fat mass , and ffm . for african american girls , fasting insulin ( r = 0.55 ; p < 0.01 ) and homa ( r = 0.47 ; p < 0.01 ) were significantly associated with is . however , in hispanic girls , none of the fasting measures were associated with is ( fasting insulin : r = 0.09 , p = 0.55 ; homa : r = 0.12 , p = 0.45 ) . relationship of fasting insulin ( a ) and homa ( b ) with is in tanner stages 4 and 5 . for african american girls , fasting insulin was associated with total fat mass ( r = 0.68 ; p < 0.01 ) , total lean mass ( r = 0.74 ; p < 0.01 ) , and fasting glucose ( r = 0.53 ; p < 0.01 ) . in hispanic girls , fasting insulin was associated with total fat mass ( r = 0.35 ; p < 0.01 ) , total lean mass ( r = 0.42 ; p < 0.01 ) , but was unrelated to fasting glucose . fasting insulin was associated with hff in both african american ( r = 0.58 ; p < 0.01 ) and hispanic girls ( r = 0.45 ; p < 0.01 ) . figure 1 shows the relationship of is with fasting measures for both ethnicities . in partial correlations adjusting for age , fat , and ffm , is was significantly correlated with fasting insulin ( r = 0.67 ; p < 0.01 ) and homa ( r = 0.66 ; p < 0.01 ) for all participants . relationship of fasting insulin ( a ) and homa ( b ) with is in tanner stages 1 and 2 . figure 2 shows the relationship of is and fasting measures for both ethnicities , adjusted for age , fat mass , and ffm . for african american girls , fasting insulin ( r = 0.55 ; p < 0.01 ) and homa ( r = 0.47 ; p < 0.01 ) were significantly associated with is . however , in hispanic girls , none of the fasting measures were associated with is ( fasting insulin : r = 0.09 , p = 0.55 ; homa : r = 0.12 , p = 0.45 ) . relationship of fasting insulin ( a ) and homa ( b ) with is in tanner stages 4 and 5 . for african american girls , fasting insulin was associated with total fat mass ( r = 0.68 ; p < 0.01 ) , total lean mass ( r = 0.74 ; p < 0.01 ) , and fasting glucose ( r = 0.53 ; p < 0.01 ) . in hispanic girls , fasting insulin was associated with total fat mass ( r = 0.35 ; p < 0.01 ) , total lean mass ( r = 0.42 ; p < 0.01 ) , but was unrelated to fasting glucose . fasting insulin was associated with hff in both african american ( r = 0.58 ; p < 0.01 ) and hispanic girls ( r = 0.45 ; p < 0.01 ) . the aim of this study was to examine the relationship of fasting plasma markers of is with is derived from a more invasive measure ( fsivgtt ) in ethnic minority girls . our results show that fasting indicators of is were modestly associated with is derived from the fsivgtt in prepubertal and early puberty girls , independent of ethnicity . in postpubertal adolescents however , fasting indicators were associated with is in african american girls , but not in hispanic girls . insulin sensitive tissues include muscle , liver , adipose tissue , and the brain ( 16 ) . because fasting measures primarily reflect insulin suppression of hepatic glucose production , they are mostly thought to represent hepatic is , whereas more invasive measures are thought to be more indicative of whole - body is ( 17 ) . the observation that hff is related to both fasting measures and is in early tanner stages suggests a significant contribution of hepatic is to overall is in prepurbertal and early puberty . in the adolescent group , hff was related to both fasting insulin and is in the african american girls , but only to fasting insulin in the hispanic girls . the difference in the relative contribution of hepatic is to whole - body is in more advanced tanner stages may explain the missing association of fasting measures with is in hispanic girls . the ethnic specific difference in the relationship of fasting measures with whole - body is is in accordance with other studies showing a better reflection of body is by fasting measures in african american women compared with non - hispanic white women ( 9 ) . our results suggest that ethnicity is an important component in determining the clinical utility of fasting measures as less invasive surrogates for is . the current study extends the comparison between fasting measures of is and is published by alvarez et al . ( 9 ) between non - hispanic white and african americans to the hispanic ethnicity . in addition to ethnicity , our results do demonstrate the importance of pubertal stage in the association of fasting measures with is . even though other publications find the relationship between fasting insulin and is to be independent of tanner stage ( 18 ) , the frequent finding of a significant effect of puberty on is ( 19 ) may contribute to the findings in this article . other work has discussed how the relationship of si and fasting measures may depend on specific characterizations of the group investigated , including ethnicity ( 9 ) , weight status ( 20 ) , or health status ( 21 ) . our results underline that not only weight status , but also ethnicity and pubertal status play an important role for the relationship of is and fasting measures of is . several measures based on fasting insulin and glucose in children and adolescents have been investigated regarding their pros and cons as surrogate measures for is ( 10 ) . fasting insulin concentrations can be highly variable because of serum half - life , cyclicity , and rapid responsiveness to hormonal and metabolic milieu ( 21 ) . to account for variability ( 22 ) , we found reliable correlations and consider the results acceptable . fasting measures including homa - ir are based on the assumption of a linear relationship between glucose and insulin concentrations . a linear relationship can be observed with normal glucose tolerance , but not in participants with impaired fasting glucose ( ifg ) or impaired glucose tolerance ( igt ) ( 17 ) . fasting insulin and fasting glucose were correlated for both ethnicities in tanner stages 1 and 2 , but only in african american girls in tanner stages 4 and 5 . the lack of relationship between fasting insulin and fasting glucose in late pubertal hispanic girls may be an explanation for our discrepancy in the relationship of is and fasting measures . the mismatch between fasting insulin and glucose may well be because of the higher hff in the hispanic group . with a  test , we examined whether the hispanic girls in tanner stages 4 and 5 presented with higher frequency of ifg or igt . ifg and igt were classified according to the revised criteria of the world health organization ( 23 ) . the frequency of both ifg and igt was not different between ethnicities and thus can not explain our findings . it remains to be tested , if our results hold , if both sexes are taken into consideration . in our adolescent participants , hff was significantly higher in hispanic compared with african american girls , which may possibly contribute to the disruption of a relationship between fasting measures and is in that ethnicity . hepatic fat is associated with visceral fat and insulin resistance , especially in hispanic adolescents ( 24,25 ) . the individual fat depots in hispanics are only related to fasting measures , but not is , suggesting that the relative contribution of hepatic insulin resistance to overall insulin resistance in hispanic girls is regulated differently compared with african american girls . the results suggest that is and fasting measures equally reflect overall is in african american girls independent of tanner stage . different compensatory mechanisms for overall insulin resistance between the ethnicities may also play a role in the explanation for the different relationship of fasting measures and is in late puberty between ethnicities ( 5 ) . in association with the significant difference in hff between the ethnicities , one would expect differences in fasting insulin and glucose concentrations as well . while fasting insulin concentrations were not different between the ethnicities , fasting glucose was significantly higher in hispanic girls . the limited power of fasting insulin to suppress hepatic glucose output also supports the idea of more hepatic insulin resistance in the hispanic girls . the progressive failure of the -cell to adjust to the increased insulin demands is evident in the significantly lower -cell capacity ( di ) in hispanic girls . a limitation of this study is that we have no data on is derived from a glucose clamp in our group of participants . however , the fsivgtt , especially the current protocol including insulin administration , was shown to produce results equivalent to the euglycemic glucose clamp in nondiabetic normal weight and obese adults ( 7 ) . furthermore , the fsivgtt was shown to be a reliable measure in children , even in a modified shortened form ( 18 ) . in summary , the current study delivers evidence for the clinical value of fasting measures of is in prepubertal or early puberty african american and hispanic girls . more invasive measures are necessary postpuberty to obtain an accurate estimation of is  at least in hispanic girls . our results do emphasize the importance of ethnicity and tanner stage as factors to consider when determining the clinical usefulness of fasting measures as an indicator for is .
objectiveto examine the relationship of fasting indicators of insulin sensitivity with a more invasive measure of insulin sensitivity ( frequently sampled intravenous glucose tolerance test [ fsivgtt ] ) and the effect of tanner stage and ethnicity on that relationship.research design and methodsdata were analyzed from 149 overweight girls ( 97 hispanic and 52 african american ) who were either in the early stages of maturation defined by tanner stages 1 or 2 ( 52 hispanic and 18 african american ) or in the later stages of maturation defined by tanner stages 4 and 5 ( 45 hispanic and 34 african american ) . 
 fasting indicators of insulin sensitivity ( is ) included fasting insulin and glucose and the homeostasis model assessment of insulin resistance ( homa - ir ) . 
 is was derived from an fsivgtt with minimal modeling.resultsin tanner stages 1 and 2 , all fasting indicators were significantly associated with is : ( fasting insulin : r = 0.67 , p < 0.01 ; homa : r = 0.66 , p < 0.01 ) with no significant influence of ethnicity on these relationships 
 . in tanner stages 4 and 5 , however , all fasting indicators were associated with is in african american girls ( fasting insulin : r = 0.55 , p < 0.01 ; homa : r = 0.47 , p < 0.01 ) , but none of the indicators were significantly associated with is in hispanic girls.conclusionsfasting indicators were reflective of is for girls in tanner stages 1 and 2 , regardless of ethnicity and may provide a clinical measure of future risk for type 2 diabetes . in the latter stages of maturation 
 , however , more invasive measures are warranted to adequately determine is in clinical practice .