Relation between visceral fat and disease risk in children and adolescents

High visceral and low abdominal subcutaneous fat stores in the obese adolescent: a determinant of an adverse metabolic phenotype

OBJECTIVE

To explore whether an imbalance between the visceral and subcutaneous fat depots and a corresponding dysregulation of the adipokine milieu is associated with excessive accumulation of fat in the liver and muscle and ultimately with insulin resistance and the metabolic syndrome.

RESEARCH DESIGN AND METHODS

We stratified our multi-ethnic cohort of 118 obese adolescents into tertiles based on the proportion of abdominal fat in the visceral depot. Abdominal and liver fat were measured by magnetic resonance imaging and muscle lipid (intramyocellular lipid) by proton magnetic resonance spectroscopy.

RESULTS

There were no differences in age, BMI Z score, or fat-free mass across tertiles. However, as the proportion of visceral fat increased across tertiles, BMI and percentage of fat and subcutaneous fat decreased, while hepatic fat increased. In addition, there was an increase in 2-h glucose, insulin, c-peptide, triglyceride levels, and insulin resistance. Notably, both leptin and total adiponectin were significantly lower in tertile 3 than 1, while C-reactive protein and interleukin-6 were not different across tertiles. There was a significant increase in the odds ratio for the metabolic syndrome, with subjects in tertile 3 5.2 times more likely to have the metabolic syndrome than those in tertile 1.

CONCLUSIONS

Obese adolescents with a high proportion of visceral fat and relatively low abdominal subcutaneous fat have a phenotype reminiscent of partial lipodystrophy. These adolescents are not necessarily the most severely obese, yet they suffer from severe metabolic complications and are at a high risk of having the metabolic syndrome.

Gendered dimensions of obesity in childhood and adolescence

Background

The literature on childhood and adolescent obesity is vast. In addition to producing a general overview, this paper aims to highlight gender differences or similarities, an area which has tended not to be the principal focus of this literature.

Methods

Databases were searched using the terms 'obesity' and 'child', 'adolescent', 'teenager', 'youth', 'young people', 'sex', 'gender', 'masculine', 'feminine', 'male', 'female', 'boy' and 'girl' (or variations on these terms). In order to limit the potential literature, the main focus is on other reviews, both general and relating to specific aspects of obesity.

Results

The findings of genetic studies are similar for males and females, and differences in obesity rates as defined by body mass index are generally small and inconsistent. However, differences between males and females due to biology are evident in the patterning of body fat, the fat levels at which health risks become apparent, levels of resting energy expenditure and energy requirements, ability to engage in certain physical activities and the consequences of obesity for the female reproductive system. Differences due to society or culture include food choices and dietary concerns, overall physical activity levels, body satisfaction and the long-term psychosocial consequences of childhood and adolescent obesity.

Conclusion

This review suggests differences between males and females in exposure and vulnerability to obesogenic environments, the consequences of child and adolescent obesity, and responses to interventions for the condition. A clearer focus on gender differences is required among both researchers and policy makers within this field.

Comparison of low-dose CT and MR for measurement of intra-abdominal adipose tissue: a phantom and human study

RATIONALE AND OBJECTIVES

The aim of this study was to determine the accuracy and reproducibility of low-dose computed tomography (CT) and magnetic resonance (MR) for abdominal adipose tissue quantification on phantom and human studies.

MATERIALS AND METHODS

An adiposity phantom (with known internal/external oil volumes) was scanned at three different tube voltages (140, 120, and 90 kVp) using a 16-detector row CT scanner and was imaged using a T1-weighted spin echo MR sequence. For human studies, whole-volume coverage of the abdomen was obtained using CT (at 140 and 90 kVp) and T1-weighted spin echo MR imaging from five obese male volunteers (mean age, 40.6 years; mean body mass index, 30.2). The volumes of total, visceral, and subcutaneous adipose tissues (TAT, VAT, and SAT, respectively) were calculated independently by two radiologists for each CT scan and MR imaging using a computer-aided semiautomatic program.

RESULTS

The estimated radiation dose could be reduced by approximately 75% with a 90-kVp protocol as compared with the 140-kVp protocol. Phantom studies showed that there was no statistically significant difference between the four methods in estimating the percentage predicted of the true volumes (measurement errors <4% for all methods, P > .05). In human studies, we found no statistically significant difference between the three methods in TAT, VAT, and SAT volumes (P > .05). Inter- and intraobserver reproducibilities of the CT volume estimates using the 90-kVp protocol were better than those obtained from MR imaging (kappa > 0.9 versus 0.4-0.5; coefficient of variation < 1% versus 15-22%).

CONCLUSION

Low-dose CT provides accurate and reproducible measurement of abdominal adipose tissue volumes with a relevant dose reduction.

Overweight and cardiovascular risk factors in 4- to 18-year-olds

BACKGROUND

The objective of this study was to investigate the relationships between overweight and high waist circumference and cardiovascular risk factors in children.

MATERIAL AND METHODS

We carried out a secondary analysis of data from 1,944 participants of the 'National Diet and Nutrition Survey: young people aged 4-18 years'. Blood pressure and blood lipid levels were compared in overweight versus non-overweight and high versus low waist circumference groups. Overweight was defined using international cut-offs for body mass index. High waist circumference was defined as >or= 91st percentile of UK waist circumference charts. Analyses were done separately by sex and age group (4-10 and 11-18 years for overweight, and 11-17 years for waist circumference).

RESULTS

Overweight and high waist circumference were associated with increased systolic blood pressure, mean arterial pressure, low-density lipoprotein cholesterol (LDLC) and triacylglycerol, and decreased high-density lipoprotein cholesterol (HDLC). Those who were both overweight and had a high waist circumference had the highest blood pressure, plasma LDLC and triacylglycerol, and the lowest plasma HDLC.

CONCLUSION

Overweight and high waist circumference were associated with increased blood pressure and a less favourable lipid profile. Children who were both overweight and had a high waist circumference had the most unfavourable cardiovascular risk profile. Both measurements may be useful in identifying children with increased health risks.

[Waist circumference, dyslipidemia and hypertension in prepubertal children]

OBJECTIVE

To explore the relationship between anthropometric variables, lipid concentrations and blood pressure in a sample of prepubertal children and to asses the importance of waist circumference in identifying certain cardiovascular risk factors in this age group.

METHODS

A cross-sectional analysis of a random sample of prepubertal children aged 2 to 9 years old was performed. Height, weight, triceps skinfold, body mass index, waist circumference, and systolic and diastolic blood pressure were measured. Plasma levels of triglycerides, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and glucose were determined.

RESULTS

A total of 240 prepubertal children were studied. There were 123 (51.3 %) boys and 117 (48.8 %) girls. The prevalence of overweight, high blood pressure and insulin-resistance syndrome was 16.6 %, 3.7 % and 1.2 %, respectively. Triceps skinfold and fat mass were significantly higher in girls. There were no significant differences in lipid profiles between obese children and those with a healthy weight. Waist circumference had a positive and significant correlation with high-density lipoprotein cholesterol, systolic blood pressure, and diastolic blood pressure. Furthermore, waist circumference was also associated with a greater risk of elevated values of total cholesterol, triglycerides and hypertension.

CONCLUSION

Waist circumference may be a helpful parameter in identifying prepubertal children with an adverse lipid profile and hypertension.

Metabolic syndrome in youths

The metabolic syndrome (MetS), characterized by a clustering of cardiovascular disease and type 2 diabetes (T2DM) risk factors, has become prevalent in children and adolescents in recent years. However, the reported prevalence data on the MetS in youths has varied markedly, in large part, because of the disagreement among the variously proposed definitions of the MetS. Obesity is defined by using body mass index, waist circumference, or percent overweight, pointing to the need for standardized use of anthropometric variables to define obesity with a well-defined reference year for each ethnic population. In addition, slightly different cutoff values are used for triglycerides, high-density lipoprotein cholesterol, blood pressure, and fasting plasma glucose. Therefore, International Diabetes Federation recently proposed unified, easy-to-use criteria for diagnosing the MetS in youths. To provide insight into the mechanisms underlying the MetS in youths, the degree of insulin sensitivity/resistance and its correlation with the serum lipid and blood pressure levels have been evaluated. In addition, the serum levels of adipocytokines, such as adiponectin, leptin, tumor necrosis factor-alpha, resistin, interleukin-6, plasminogen activator inhibitor-1, and their correlation with childhood obesity have been extensively investigated. Recommendations for future research include exploring ways to assess visceral adiposity, to identify better biochemical markers for prediction of T2DM and disease progression, and to effectively intervene to prevent the MetS in youths.

Magnetic resonance imaging of abdominal adiposity in a large cohort of British children

OBJECTIVE

To describe abdominal adipose tissue distribution in a large sample of contemporary British children; to determine the influence of gender, stage of maturation and body mass index (BMI) on abdominal adipose tissue distribution; and to compare the ability of BMI and waist circumference to predict abdominal adipose tissue.

SUBJECTS AND METHODS

A total of 74 boys (mean age 13.4+/-0.4 years) and 96 girls (mean age 13.5+/-0.5 years) were selected from volunteer children enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). Height, weight and waist circumference were measured and BMI calculated. Stage of sexual maturation was available for 113 children using a self-report questionnaire based on Tanner's criteria. Magnetic resonance imaging was used to assess subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) volumes and patterning.

RESULTS

Boys had lower levels of IAAT (P=0.036) and SAAT (P=0.003) than girls. IAAT and SAAT were higher in overweight and obese boys and girls when compared with normal weight children (P<0.0001). This pattern was also reflected in waist circumference groups. Boys had higher IAAT/SAAT ratios than girls, indicating proportionately more adipose tissue deposited intra-abdominally (P=0.002). However, both boys and girls deposited less than 10% of their abdominal fat as internal adipose tissue. WC predicted 67.4% of the variance in IAAT (P<0.001), and BMI predicted 84.8% of the variance in SAAT (P<0.001). However, BMI as the best single predictor explained only 8.4% of the variance in the IAAT/SAAT ratio (P<0.001).

CONCLUSIONS

At this age and stage of sexual maturation, the amount of IAAT remains relatively small. WC and BMI offer a feasible alternative to the MRI estimation of IAAT and SAAT, respectively, in a population-based sample of boys and girls. International Journal of Obesity (2008) 32, 91-99; doi:10.1038/sj.ijo.0803780; published online 27 November 2007.

Measurement and definitions of obesity in childhood and adolescence: a field guide for the uninitiated

This paper aims to guide readers embarking on the complex literature in respect of childhood and adolescent obesity. It opens with a discussion of definitions of 'obesity' based on overall fat levels and the significance of fat distribution. This is followed by simple descriptions of the various techniques used to measure fat, including density-based, scanning, bioelectrical impedance and anthropometric methods. The paper then turns to 'overweight' and the measurement of weight in relation to height, particularly via body mass index (BMI). While it is a relatively simple measure and a valuable tool, BMI has several disadvantages, which are described. These include a lack of consensus on which values should be used to define 'overweight' or 'obese', with the result that the literature contains a confusing multiplicity of child and adolescent obesity rates.

Bone mineral content and body composition in overweight children and adolescents

The aim of this study was to analyze the bone mineral content (BMC) of the skeleton and the body composition in lean and fat masses in a population of young overweight subjects, before diet or medical intervention. A total of 496 white youths (298 females, 198 males) were studied. Their body mass index (BMI) values were 29.2+/-5.5 kg/m2 in females and 28.3+/-5.1 kg/m2 in males, corresponding to relative weights (wts) [actual wt, W, divided by the mean wt normal for height (ht), Wi] of 1.55+/-0.24 and 1.53+/-0.24, respectively. Whole-body dual-energy x-ray absorptiometry (DXA) scans were performed (Norland XR36 DXA system) to obtain the total BMC (BMCt), lean tissue mass (LTMt) and fat mass (FMt), as well as the values of the corresponding parameters in arms (a), legs (l), and abdomen (ab). The measured data were compared with theoretical values calculated for Wi. The differences with reference values in LTMt and FMt were sex dependent, and the accretion in FMt, greater in males than in females, yielded a similar FMt/LTMt ratio in both sexes. The wt corresponding to the BMC of the bearing skeleton, lower than the actual wt by about 20%, seemed a reasonable first step to consider in the wt management of these youths.

Sympathoadrenergic and metabolic factors are involved in ambulatory blood pressure rise in childhood obesity

We investigated in a young Italian obese population, the relationship between ambulatory BP (ABP) and several pathophysiological factors linking obesity to hypertension. A total of 89 obese children and adolescents underwent a 24-h ambulatory BP monitoring (ABPM) and an oral glucose tolerance test. The circulating levels of insulin, lipids, uric acid, C-reactive protein, interleukin-6, renin and aldosterone and the 24-h urinary levels of epinephrine, norepinephrine and albumin excretion rate were measured. Nine percent of subjects had daytime sustained hypertension (SH), 26% night-time hypertension and 11% a non-dipping pattern. SH subjects compared to those with sustained normotension (SN) were more obese (P<0.05), with a more frequent family history of hypertension (P<0.05), higher urinary catecholamine (P<0.05) and heart rate values (P<0.05) after adjustment for standard deviation score (SDS) of body mass index (BMI) and sex. Subjects with night-time hypertension compared to those with night-time normotension were more obese (P<0.0001), with a higher prevalence of impaired glucose tolerance (P<0.05) and metabolic syndrome (P<0.05) and higher 2-h glucose (P<0.05), uric acid (P<0.05) and triglycerides (P<0.05). In multivariate regression analysis, daytime systolic BP (SBP) remained independently correlated with urinary norepinephrine and SDS-BMI (P<0.05 for both), daytime diastolic BP (DBP) with waist circumference (P<0.05) and night-time SBP and DBP with SDS-BMI (P<0.01 for both). The risk of having systolic and diastolic hypertension increased with the increase in SDS-BMI and waist circumference, respectively. In conclusion, in our cohort of obese children and adolescents, daytime and night-time hypertension were associated with activation of the sympathoadrenal system and worst metabolic conditions, respectively.

New Insights into Body Composition and Health: Through Imaging Analysis: 2007 Ryley-Jeffs Memorial Lecture

From calipers to magnetic resonance imaging (MRI), we have come a long way in our ability to analyze body composition. Some historical milestones are a reminder that many concepts in muscle and fat metabolism, and their measurement, have stood the test of time. However, newer imaging technology has improved our understanding of population heterogeneity in body composition, and the potential health problems associated with certain body composition phenotypes. Imaging analyses, such as dual energy X-ray absorptiometry, computed tomography, and MRI, have provided detailed characterization of the type and amount of fat deposited centrally (abdominal adipose tissue), the trajectory of losses in muscle tissue (sarcopenia), and the combination of low muscle mass/high fat mass (sarcopenic obesity). The last is a new emerging health concern because the presence of these two disproportionate tissue depots may have an additive effect on increasing morbidity. Ongoing measurement of body composition is needed, and preliminary research suggests this may have important nutritional implications.

Cardiovascular risk factor levels and their relationships with overweight and fat distribution in children: the Fleurbaix Laventie Ville Santé II study

This study aimed to document for the first time in a general population of French children the prevalence and levels of cardiovascular risk factors and to assess separately in boys and girls whether these risk factors were associated with fat mass distribution independently of subcutaneous overall adiposity. A cross-sectional analysis of baseline data from 452 children (235 boys and 217 girls) aged 8 to 17 years included in a 1999 population-based epidemiologic study (the Fleurbaix Laventie Ville Santé II study) was made. Overweight was defined according to the International Obesity Task Force references and the 90th percentiles of the French body mass index curves. The thresholds of parameters defining cardiovascular and metabolic risks were the 95th percentile of the Task Force Report on High Blood Pressure in Children and Adolescents for blood pressure and those of the American Academy of Pediatrics for lipids. Anthropometric and biological parameters were described by sex and according to overweight status. Partial correlations between cardiovascular risk factors and anthropometric measures of adiposity (body mass index, sum of 4 skinfold thicknesses, waist circumference, waist-to-height ratio) were calculated. Then, these correlations were additionally adjusted for the sum of 4 skinfold thicknesses. High plasma triglycerides, high insulin concentration, and low plasma high-density lipoprotein cholesterol (HDL-C) concentration were associated with all measures of adiposity (|r| > or = 0.20, P < .002). When obese children were excluded, overweight children already had high triglycerides and low HDL-C levels, respectively, 2 and 20 times more frequently than normal-weight children did. Among overweight children, 7.7% had at least 2 risk factors among high blood pressure, high plasma triglycerides or glucose, and low HDL-C concentration vs 0.25% among normal-weight children (P = .002). After adjusting for the sum of skinfolds, an independent association between the risk factors and waist circumference was found in girls. In conclusion, (a) modest excess weight is associated with increased levels of cardiovascular risk factors. (b) In girls, abdominal fat distribution is associated with cardiovascular risk factors, independently of overall adiposity. (c) International definition of abdominal obesity in children is required to standardize studies and to progress in the evaluation of childhood obesity and its consequences.

Body fat measurements in children as predictors for the metabolic syndrome: focus on waist circumference

The global epidemic of obesity in children will see a rise in the number of cases of metabolic syndrome, which is a clustering of CVD risk factors, including atherogenic levels of blood lipids, hyperinsulinaemia and raised blood pressure. Rather than excess general fatness (assessed by BMI), more specifically it is excess abdominal fatness, quantified by waist circumference measurement, which is a better measure of risk for these metabolic abnormalities in children of all ages. Insulin resistance, a consequence of excess visceral fat, is understood to be the driving force underpinning the metabolic syndrome. Consequently, assessment of abdominal fatness in children is proving to be more clinically useful. Waist circumference centile charts have now been developed for the UK and other paediatric populations to assist in this process. Furthermore, studies in the UK and elsewhere have shown that abdominal fatness has increased in infants, children and adolescents to a greater extent than overall fatness over the past 10-20 years, suggesting that obesity prevalence may be underestimated when based entirely on BMI. Additionally, ethnic differences in fat distribution have been demonstrated in children, with those from south Asian backgrounds having a greater abdominal distribution compared with Caucasian children and consequently having a much greater risk for type 2 diabetes. The information that can be provided by waist circumference measurement in children, as in adults, together with the recent changes in body fat distribution should provide the impetus for its measurement to be standardised and routinely taken in clinical and epidemiological settings.

Relationship between body composition and blood pressure in Bahraini adolescents

The objective of the present study was to examine the relationship between body composition and blood pressure (BP) in Bahraini adolescents. A sample of 504 Bahraini schoolchildren aged 12–17 years (249 boys and 255 girls) was selected using a multi-stage stratified sampling procedure. BP measurements were performed on the students. Anthropometric data including weight, height, waist circumference (WC), hip circumference, and triceps, subscapular and medial calf skinfold thicknesses were also collected. BMI, percentage body fat, waist:hip (WHR), and subscapular:triceps skinfold ratio were calculated. Mean systolic BP and mean diastolic BP were higher in males than in females. Weight and height in boys and weight only in girls were significantly associated with systolic BP independent of age or percentage fat. Nearly 14% of the adolescents were classified as having high BP. BMI and percentage body fat were significantly and positively associated with the risk of having high BP in the boys and girls. Adolescents with high WHR or WC, as indicators for central obesity, tended to have higher BP values. The results from the present study indicate that obesity influences the BP of Bahraini adolescents and that simple anthropometric measurements such as WHR and WC are useful in identifying children at risk of developing high BP. These findings together with the known tracking of BP from adolescence into adulthood underline the importance of establishing intervention programmes in order to prevent the development of childhood and adolescent obesity.

Total and intraabdominal fat distribution in preadolescents and adolescents: measurement with MR imaging

PURPOSE

To prospectively correlate single- and multisection magnetic resonance (MR) imaging measurements with clinical measurements for assessment of abdominal adipose tissue volumes in healthy (control subjects), overweight, and diabetic overweight preadolescents and adolescents.

MATERIALS AND METHODS

The study was approved by the institutional internal review board and was HIPAA compliant. Informed consent was obtained from parents, and assent was obtained from control subjects and patients. Thirty total study subjects (20 male, 10 female; age range, 10-18 years; mean, 14.5 years) underwent MR imaging, anthropometric measurement, and dual x-ray absorptiometry (DXA). A computer-assisted software program was used to quantify subcutaneous, visceral, and total abdominal adipose tissue volumes. Single-section measurements at disk space L4-L5 and whole-abdominal multisection measurements were compared, and each method was tested for correlations with anthropometric and DXA measurements with Spearman rho and Pearson correlation (r) coefficients. Single- and multisection image analyses required 5 and 25 minutes per subject, respectively.

RESULTS

There was a high degree of correlation between single- and multisection MR imaging methods for measurement of subcutaneous (r = 0.97), visceral (r = 0.96), and total abdominal fat (r = 0.97). MR imaging fat measurements strongly correlated with anthropometric measurements (rho correlation range, 0.81-0.96; P <or= .02), with overlapping 95% confidence intervals (CIs) for single- and multisection MR imaging correlations. MR imaging percentage of intraabdominal fat measurements (mean, 23%; 95% CI: 17%, 29%) highly correlated with DXA abdominal fat measurements (mean, 26%; 95% CI: 21%, 31%). Significant differences were found among healthy subjects, overweight patients, and diabetic overweight patients for total fat volumes (P < .001) but not for fat distribution patterns.

CONCLUSION

Single- and multisection MR imaging measurements for the quantitative assessment of abdominal adipose tissue strongly correlate with clinical and DXA fat measurements.

Dietary intake of 9–10-year-old and 11–12-year-old children in Liverpool

Objective:

To describe the eating habits of children in Liverpool and compare two age groups that bridge the transition from primary to secondary school.

Design:

Two cross-sectional studies carried out one year apart using a food intake questionnaire that records whether or not each child claims to have eaten specific marker foods on the previous day.

Setting:

Primary and secondary schools in Liverpool.

Subjects:

Six hundred and forty-nine children aged 11 or 12 years and 3556 children aged 9 or 10 years.

Results:

Fewer older children ate breakfast (68–82%), especially the girls, and not eating breakfast was associated with eating on the way to school in the younger children. More of the older girls ate nothing at breakfast or on the way to school. Overall, the less desirable foods were reported to have been eaten by more children, of both ages, than the more desirable foods. Fruit, however, was mentioned by most children (69–77%) but the next 10 foods mentioned by most children were all less desirable ones. Only 31% of primary and 21% of secondary children ate both fruit and vegetables but 23% of primary and 26% of secondary children ate neither fruit nor vegetables. Overall, more of the girls of both age groups claimed to have eaten foods that would normally be encouraged.

Conclusions:

Food choice changes appreciably between primary and secondary school and, in some key respects, for the worse. In particular, far more children of both age groups need to be eating fruit and vegetables every day.

Racial differences in the association of subcutaneous and visceral fat on bone mineral content in prepubertal children

Total fat mass plays a significant role in determining bone mass, but the specific role of central adiposity independent of total fat mass has not been widely studied. Prepubertal (Tanner 1) children (n = 181; 65 boys, 116 girls, 7.8 +/- 1.5 years), including 99 Caucasians and 82 African Americans from Birmingham, Alabama, participated in this study. Body composition, including total body and trunk fat mass, and bone mineral content (BMC) were measured using dual-energy X-ray absorptiometry. Subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) were determined by single-slice computed tomography (CT). After adjusting for gender, age, height, total fat, and lean mass, trunk weight was inversely correlated with BMC in Caucasians (r = -0.56, P < 0.0001) and in African Americans (r = -0.37, P < 0.05). In Caucasians, independent of gender, age, height, total fat, and lean mass, there was an inverse correlation between SAAT and BMC (r = -0.58, P < 0.0001) but no significant correlation between IAAT and BMC; in addition, SAAT explained 6% of the variance in BMC. In contrast, in African Americans, SAAT and BMC were not significantly correlated. However, while adjusting for gender, age, height, SAAT, total fat, and lean mass, an inverse association between IAAT and BMC was observed in African Americans (r = -0.50, P < 0.01); IAAT also explained 3% of the variance in BMC. These findings suggest that, in general, total abdominal weight is negatively associated with bone mass, but there appear to be racial differences with regard to the contributions of subcutaneous and visceral fat to BMC in prepubertal children.

Recent trends in waist circumference and waist-height ratio among US children and adolescents

OBJECTIVES

Abdominal obesity may be a better predictor than overall obesity for the risk of cardiovascular disease and type 2 diabetes. Waist circumference and waist-height ratio are 2 simple, yet effective, surrogate measures of abdominal obesity. We sought to examine the recent trends in mean waist circumference and waist-height ratio and prevalence of abdominal obesity among children and adolescents aged 2 to 19 years in the United States.

METHODS

Representative samples of the civilian, noninstitutionalized US population from the National Health and Nutrition Examination Survey conducted during 4 time periods, 1988-1994 (ie, National Health and Nutrition Examination Survey III), 1999-2000, 2001-2002, and 2003-2004, were examined to estimate the mean waist circumference and waist-height ratio of boys and girls in 4 different age groups. Data from the 3 most recent National Health and Nutrition Examination Surveys were combined to establish a National Health and Nutrition Examination Survey 1999-2004 category.

RESULTS

Categorized by age group, the unadjusted mean waist circumference for boys increased between National Health and Nutrition Examination Survey III and National Health and Nutrition Examination Survey 1999-2004 from 50.7 cm (aged 2-5 years), 61.9 cm (aged 6-11 years), 76.8 cm (aged 12-17 years), and 81.3 cm (aged 18-19 years) to 51.9, 64.5, 79.8, and 86.6 cm, respectively. During the same time periods and within the same age groups, the unadjusted mean waist circumference for girls increased from 51.0, 61.7, 75.0, and 77.7 cm to 51.8, 64.7, 78.9, and 83.9 cm, respectively. The relative change in waist-height ratio was similar to waist circumference at each age group for both boys and girls. Using the 90th percentile values of waist circumference for gender and age, the prevalence of abdominal obesity increased by 65.4% (from 10.5% to 17.4%) and 69.4% (from 10.5% to 17.8%) for boys and girls, respectively.

CONCLUSIONS

Mean waist circumference and waist-height ratio and the prevalence of abdominal obesity among US children and adolescents greatly increased between 1988-1994 and 1999-2004.

Serum phospholipid fatty acids, adipose tissue, and metabolic markers in obese adolescents

OBJECTIVE

Fatty acid (FA) composition has a role in adipogenesis. The objective was to study serum phospholipid (PL) FAs in adolescents and their relation to abdominal adipose tissue (AT) compartments and metabolic markers.

RESEARCH METHODS AND PROCEDURES

Abdominal AT was measured by magnetic resonance imaging and FA pattern was determined in serum PL of 10 obese adolescents (5 females), median age 12.0 years (range, 10.4 to 16.4) and BMI 30.7 (26.8 to 40.4), and 15 lean control subjects (9 females), median age 12.6 years (range, 11.3 to 15.4), and BMI 19.5 (17.1 to 23.4).

RESULTS

Obese adolescents had relatively higher levels of saturated FA (SFA) and nervonic acid compared with controls. Serum PL concentration of n-3 polyunsaturated fatty acids (PUFA) was lower in the obese vs. lean females (p = 0.01), including docosahexaenoic acid (DHA) (p = 0.01). The ratios of arachidonic acid to DHA and total n-6/n-3 FA were increased in obese children (p = 0.02 and 0.01, respectively). n-3 PUFAs were inversely correlated to all subcutaneous AT compartments except visceral AT. The homeostasis model assessment index of beta-cell function related inversely to DHA concentration (p = 0.03). All changes were more marked in the females.

DISCUSSION

Serum FA pattern in obese adolescents differed significantly from that in age-matched lean controls, reflecting a decrease in n-3 PUFA, especially DHA, and an increase in SFA. The subcutaneous AT, but not visceral AT, correlated to the changes in PUFA and SFA, suggesting an abnormal essential FA metabolism in obese adolescents.

Pediatric nonalcoholic fatty liver disease: a critical appraisal of current data and implications for future research

Although population prevalence is very difficult to establish, nonalcoholic fatty liver disease (NAFLD) is probably the most common cause of liver disease in the preadolescent and adolescent age groups. There seems to be an increase in the prevalence of NAFLD, likely related to the dramatic rise in the incidence of obesity during the past 3 decades. Despite an increase in public awareness, overweight/obesity and related conditions, such as NAFLD, remain underdiagnosed by health care providers. Accurate diagnosis and staging of nonalcoholic steatohepatitis (NASH) requires liver biopsy. The development of noninvasive surrogate markers and the advancements in imaging technology will aid in the screening of large populations at risk for NAFLD. Two distinct histological patterns of NASH have been identified in the pediatric population, and discrete clinical and demographic features are observed in children with these 2 patterns. The propensity for NASH to develop in obese, insulin-resistant pubertal boys of Hispanic ethnicity or a non-Hispanic white race may provide clues to the pathogenesis of NAFLD in children. The natural history of pediatric NASH has yet to be defined, but most biopsies in this age group demonstrate some degree of fibrosis. In addition, cirrhosis can be observed in children as young as 10 years. While the optimal treatment of pediatric NAFLD has yet to be determined, lifestyle modification through diet and exercise should be attempted in children diagnosed with NAFLD. A large, multicenter trial of vitamin E and metformin is underway as part of the NASH clinical research network.

Prevention and treatment of type 2 diabetes in youth

Parallel to the increase in obesity worldwide, there has been a rise in the prevalence of type 2 diabetes mellitus (T2DM) in children and adolescents. The etiology of T2DM in youth, similar to adults, is multifactorial including genetic and environmental factors, among them obesity, sedentary lifestyle, family history of the disease, high-risk ethnicity and insulin resistance phenotype playing major roles. Treatment of T2DM should not have a glucocentric approach; it should rather target improving glycemia, dyslipidemia, hypertension, weight management and the prevention of short- and long-term complications. Prevention strategies, especially in high-risk groups, should focus on environmental change involving participation of families, schools, the food and entertainment industries and governmental agencies. Presently, limited pharmacotherapeutic options need to be expanded both for childhood T2DM and obesity. The coming decades will prove very challenging for healthcare providers battling socioeconomic waves conducive to obesity and T2DM. Evidence-based research and clinical experience in pediatrics, possibly modeled after adult trials, need to be developed if this public health threat is to be contained.

Crossvalidation of anthropometry against magnetic resonance imaging for the assessment of visceral and subcutaneous adipose tissue in children

BACKGROUND

The study of the relationship between anthropometry and visceral adipose tissue (VAT) is of great interest because VAT is associated with many risk factors for noncommunicable diseases and anthropometry is easy to perform in clinical practice. The studies hitherto available for children have, however, been performed on small sample sizes.

DESIGN

Pooling of the data of studies published from 1992 to 2004 as indexed on Medline.

AIMS

To assess the relationship between anthropometry and VAT and subcutaneous adipose tissue (SAT) as measured by magnetic resonance imaging (MRI) in children and to analyze the effect of age, gender, pubertal status and ethnicity.

SUBJECTS AND METHODS

Eligible subjects were 7-16 year-old, with availability of VAT and SAT, gender, ethnicity, body mass index (BMI) and waist circumference (WC). A total of 497 subjects were collected from seven different investigators and 407 of them (178 Caucasians and 229 Hispanics) were analyzed.

RESULTS

Despite ethnic differences in MRI data, BMI, WC and age, no difference in VAT was found between Caucasians and Hispanics after correction for SAT and BMI. Univariate regression analysis identified WC as the best single predictor of VAT (64.8% of variance) and BMI of SAT (88.9% of variance). The contribution of ethnicity and gender to the unexplained variance of the VAT-WC relationship was low (< or =3%) but significant (P < or =0.002). The different laboratories explained a low (< or =4.8%) but significant (P < 0.0001) portion of the unexplained variance of the VAT-WC and SAT-BMI relationships. Prediction equations for VAT (VAT (cm(2)) = 1.1 x WC (cm)-52.9) and SAT (SAT (cm(2)) = 23.2 x BMI (kg/m(2))-329) were developed on a randomly chosen half of the population and crossvalidated in the remaining half. The pure error of the estimate was 13 cm(2) for VAT and 57 cm(2) for SAT.

CONCLUSIONS

WC can be considered a good predictor of VAT as well as BMI of SAT. The importance of ethnicity and gender on VAT estimation is not negligible.

Growth curves of anthropometric indices in a general population of French children and comparison with reference data

BACKGROUND

The description of growth patterns of the different anthropometric measurements mainly used in epidemiological studies is useful to better understand the development of obesity in children and its consequences.

OBJECTIVE

Our aim was to establish growth curves of anthropometric indices in a general population of French children born during the 1980s and to compare them with the French reference curves based on children born in the 1950s.

DESIGN

As part of the Fleurbaix Laventie Ville Santé Studies I and II (FLVS), 441 girls and 467 boys were examined at least twice between 1993 and 2001. Height, weight and four skinfold thicknesses were measured. Body mass index (BMI), sum of peripheral and truncal skinfolds and truncal-to-peripheral ratio were calculated. Mean growth curves from ages 5 to 17 years were assessed for these indices, calculating means and 95% confidence interval per 1 year age group and by gender.

RESULTS

Trajectories with age differed importantly according to the index considered; BMI was the one with the smallest difference between genders and the most linear shape with age. From the age of 5 years and after, the FLVS children were on average taller and had a higher subcutaneous adiposity than children born 30 years earlier. Truncal-to-peripheral ratio was higher in our population; this difference became more marked with puberty in girls.

DISCUSSION

This study suggests the existence of a secular trend towards a precocious accelerated growth, and a more truncal adiposity distribution, especially in girls. It is a disquieting trend considering its expected consequences on adult health.

Changes in body weight and fat mass of men and women in the first year of college: A study of the "freshman 15"

Students entering their first year of college are faced with many stresses and changes, including changes in eating and exercise behavior. A common but often undocumented myth among college students is that there is a high risk of gaining 15 pounds of weight during freshman year. The objective of this study was to measure changes in body weight and percentage of body fat among first-year college students. Using a digital scale with bio-electrical impedance, the authors measured height, weight, and percentage of body fat for a sample of students who volunteered to be weighed during a health assessment in the university dining halls. The authors sent e-mails inviting those same students to complete a second measurement in February of the academic year. Sixty-seven of the 217 students who volunteered for the health assessment agreed to undergo a second set of measurements in the spring. The mean change in body weight was 2.86 pounds (1.3 kg, SD = 4.0 kg), and the mean change in percentage of body fat was 0.7% (SD = 4.0%). For those students who gained weight only, the mean increase in body weight (as measured by body mass index, weight divided by height in kg/m2) was 6.82 pounds (3.1 +/- 2.4 kg) and percentage of body fat was 0.9 +/- 3.8%. The authors found that the first year of college is a period in which weight and fat gain may occur. The exact causes behind these changes are unclear and warrant further research to plan or improve intervention and prevention.

Physical activity, cardiovascular fitness, and insulin sensitivity among U.S. adolescents: the National Health and Nutrition Examination Survey, 1999-2002

OBJECTIVE

The purpose of this study was to examine the association of physical activity and cardiovascular fitness (CVF) with insulin sensitivity in a nationally representative sample of U.S. youth.

RESEARCH DESIGN AND METHODS

The study included 1,783 U.S. adolescents (11% Mexican American, 14% non-Hispanic black, 63% non-Hispanic white, and 12% other) aged 12-19 years who were examined in the 1999-2002 National Health and Nutrition Examination Survey. Physical activity was assessed by questionnaire and expressed in units of MET hours per week. Predicted maximal oxygen uptake (Vo(2max), expressed in milliliters per kilogram of body weight per minute), a measure of CVF, was determined by a submaximal multistage treadmill test. Insulin sensitivity was defined by the Quantitative Insulin Sensitivity Check Index.

RESULTS

Boys were more likely than girls to be highly active (>or=30 MET h/week; 51 vs. 37%, P < 0.001) and had higher levels of CVF (mean Vo(2max) 47 vs. 39 ml x kg(-1) x min(-1), P < 0.001). Sex-specific multiple regression models controlled for age, race/ethnicity, and BMI showed that in boys, high levels of physical activity and high levels of CVF were significantly and positively associated with insulin sensitivity (beta = 0.84, P < 0.001 and beta = 0.82, P = 0.01, respectively). Among girls, insulin sensitivity was not significantly associated with physical activity or with CVF but was inversely and significantly associated with BMI.

CONCLUSIONS

Increasing physical activity and CVF may have an independent effect of improving insulin sensitivity among boys. For girls, the primary role of physical activity may be in weight maintenance.

Vascular risks and management of obesity in children and adolescents

Childhood obesity has reached epidemic proportions in many countries. Pediatric obesity is associated with the development of cardiovascular (CV) risk factors including type 2 diabetes, hypertension, dyslipidemia, and the metabolic syndrome. It is also associated with an increased risk of CV disease (CVD) in adulthood. Moreover, obesity and CVD risk factors in obese youth tend to track into adulthood, further increasing the risk of adult CVD. Consequently, the treatment and prevention of childhood overweight and obesity has become a public health priority. Proper nutrition and increased physical activity are the main focus of these efforts; however, few studies have shown positive results. Treatment options for obesity in youth also include pharmacotherapy and surgery. While pharmacotherapy appears promising, additional evidence is needed, especially with respect to the long-term impact, before it becomes a widespread treatment option in the pediatric population.

Early programming of body composition and fat distribution in adolescents

Size at birth and early postnatal growth are determinants of adult height and BMI. The aim of this study was to evaluate the effect of birth weight on body composition and fat distribution in a group of Spanish adolescents. Current body composition was assessed by both skinfold thickness and dual X-ray absorptiometry in 234 adolescents born at term (140 girls and 94 boys), now aged 13-18 y and living in the city of Zaragoza. Relative fat distribution was estimated using the ratio of the subscapular to triceps skinfolds (S:T). Birth weight and gestational age were assessed by a questionnaire. Birth weight was inversely associated with the S:T ratio (P < 0.05) in boys and directly associated with bone mass (P < 0.01) and fat-free mass (P < 0.05) in girls. This association was independent of factors such as age, Tanner stage, gestational age, socioeconomic status, physical activity, and height. In conclusion, our data support the hypothesis that impaired fetal growth, measured by birth weight, may be related to central fat distribution in boys and decreased bone and fat-free mass in girls.

Percentile distribution of the waist circumference among Mexican pre-adolescents of a primary school in Mexico City

AIM

The aim of this study is to describe the percentile distribution of the waist circumference in Mexican pre-pubertal children living in an urban, middle-income area.

METHODS

Children, aged 6-10, from a primary school, located in a middle-income area in Mexico City were included (n=833). Anthropometric measurements were made in the case of all children by using standardized procedures.

RESULTS

The prevalence of obesity and overweight was greater among boys (p<0.001). Of them, 30 were obese (7.2%) and 47 were overweight (11.4%). Girls had a prevalence of obesity of 2.8% and of overweight of 8.8%. Boys had greater waist circumference than girls (p<0.001). This observation was independent from differences in age or body mass index (BMI). The distribution of the waist circumference was shifted towards higher values among boys. The values corresponding to the 85th percentile ranged, in boys aged 6-10, between 62.9 and 85.9 cm. By contrast, for girls, those values were 66.8 and 72.08 cm, respectively. A receiver-operator curve was constructed in order to identify the waist circumference most likely to be associated with a BMI of > 85th percentile. We found that age- and sex-specific cut-off points are required for the detection of central adiposity in children aged 6-10.

CONCLUSIONS

The percentile distribution of the waist circumference in Mexican pre-pubertal children living in urban, middle-income areas is described in this study. Moreover, included are the cut-off points most likely to be associated with increased adiposity. This information can be used for defining abdominal obesity in paediatric populations.

Adipose tissue and metabolic effects: new insight into measurements

BACKGROUND

Epidemiologic evidence supports the theory that the relation between obesity and disease risk begins early in life, and those risk factors for disease track, or remain at a similar level, with advancing age, growth, and development. The fat tissue, once considered as a depot for energy substrate, is a metabolically active tissue. The fat cells produce agents that regulate a host of physiological processes directly related to carbohydrate and fat metabolism and the development of cardiovascular disease and type 2 diabetes.

AIM

To discuss fat tissue, and fat distribution in relation to body composition measurements, with particular emphasis on imaging techniques (ie, dual energy X-ray absorptiometry (DXA), computed tomography (CT), and magnetic resonance imaging (MRI)) and its relationship with metabolic and cardiovascular heath variables mediated by the metabolic characteristics of the adipose tissue.

DISCUSSION

In sum, the medical and physiological health complications of childhood obesity are well documented. Imaging methods are considered the most accurate means available for in vivo quantification at the tissue-organ level and the methods of choice for calibration of field methods designed to measure adipose tissue.

Antiretroviral Therapy in HIV-Infected Children: The Metabolic Cost of Improved Survival

Although highly active antiretroviral therapy (HAART) has positively altered the morality rates in HIV-infected children, these drugs have the potential to cause significant morbidity. These drugs cause changes in fat distribution, lipid profiles, glucose, homeostasis, and bone turnover. The direct relationship between duration of drug exposure and increased risk of cardiovascular disease is particularly concerning for HIV-infected infants and children, who likely will have longer cumulative exposure to HAART. It is unclear whether the metabolic effects of decades of exposure would be reversible with cessation of therapy. The benefits of HAART in HIV infection are indisputable, but the impetus to find a cure or design more tolerable therapy is clear. Infarction may replace infection as the major cause of morbidity and mortality from HIV.

Dysmetabolic syndrome in childhood and adolescence

The dysmetabolic syndrome, consisting of dyslipidaemia, hypertension, hyperinsulinaemia and central obesity, has been well recognized as a major risk for cardiovascular disease in adults. Although the clustering of cardiovascular risk factors has also been identified in childhood, the occurrence of full-blown dysmetabolic syndrome at younger ages has only recently been investigated. In this article we attempted an overview of the data for children and adolescents, focused on the mechanisms and natural history of the disease, the prevalence among paediatric populations, the assessment and the treatment approaches.

CONCLUSION

There is substantial evidence that the dysmetabolic syndrome has its origins in childhood. In the face of the epidemic increase of obesity in children and adolescents, the development of effective screening and preventive strategies would be a major challenge for paediatricians.

Effects of recombinant growth hormone on visceral fat accumulation: pilot study in human immunodeficiency virus-infected adolescents

CONTEXT

Recombinant human GH (rhGH) reduces excess accumulation of intraabdominal adipose tissue (IAT) in lipodystrophic HIV-infected adults, whereas data in pediatric patients are lacking.

OBJECTIVE

The objective of this study was to assess the efficacy of rhGH treatment on lipodystrophy in HIV-infected adolescents.

DESIGN

The study is a prospective, 24-wk open-label study of rhGH.

SETTING

The study was conducted at a referral center for pediatric HIV infection.

PATIENTS AND OTHER PARTICIPANTS

Eight HIV-infected adolescents (ages, 13.7-18.5 yr), with abnormal IAT accumulation (>41 cm(2) at L4-magnetic resonance imaging) and 97 healthy controls (HC) (ages, 9.5-19.9 yr) were enrolled.

INTERVENTION

rhGH was given by sc injection at a daily dose of 0.028 mg/kg.

MAIN OUTCOME MEASURES

The main outcome was change in IAT at L4-magnetic resonance imaging. Body composition by dual-energy x-ray absorptiometry, glucose and lipid metabolism, and IGF-I changes were also evaluated.

RESULTS

All patients completed the study period; none of them showed adverse event, and no change in the daily dose of rhGH was required. The treatment was associated with a mean height increase of 2.4 cm. From baseline to wk 24, IAT area decreased significantly by a median of 34.5% (-19.2 to -70%). Fat mass decreased significantly in patients, compared with HC, with a median loss of total, trunk, and arm and leg fat mass of 10.4, 10.9, 12.7, and 5.4%, respectively. Total, arm, and leg lean masses increased significantly, compared with HC. IGF-I increased significantly, but supraphysiological values of mild degree (2-23% over the upper normal limit) were detected in only nine of 24 samples. No significant effects on glucose metabolism, triglyceride, and cholesterol levels were observed.

CONCLUSIONS

Our data showed that rhGH 0.028 mg/kg daily for 24 wk in HIV-infected adolescents reduces IAT, trunk, and also limb fat and increases lean mass. Overall, short-term rhGH is well tolerated and is not associated with a worsening of glucose and lipid metabolism.

Combined influence of body mass index and waist circumference on coronary artery disease risk factors among children and adolescents

OBJECTIVES

In adult populations, it is recognized widely that waist circumference (WC) predicts health risk beyond that predicted by BMI alone; current recommendations for adults are that a combination of BMI and WC be used to classify obesity-related health risk. For children and adolescents, however, little is known about the combined influence of BMI and WC on health outcomes. The objectives of this study were to determine whether BMI and WC predict coronary artery disease (CAD) risk factors independently for children and adolescents and to assess the clinical utility of using WC in combination with BMI to identify CAD risk.

METHODS

Subjects included 2597 black and white, 5- to 18-year-old, male and female youths. Outcome measures included 7 CAD risk factors. In the first analysis step, BMI and WC were used as continuous variables to predict CAD risk factors. In the second analysis step, participants were placed into normal-weight, overweight, and obese BMI categories and, within each BMI category, CAD risk factors were compared for groups with low and high WC values.

RESULTS

When BMI and WC were included in the same regression model to predict CAD risk factors, the added variance above that predicted by BMI or WC alone was minimal, which indicated that BMI and WC did not have independent effects on the risk factors. For example, for systolic blood pressure, BMI alone explained 7.3% of the variance, WC alone explained 7.7% of the variance, and the combination of BMI and WC explained 8.1% of the variance. When BMI and WC values were categorized with a threshold approach, WC provided information on CAD risk beyond that provided by BMI alone, particularly when the categories were used to predict elevated CAD risk factor levels. For instance, in the overweight BMI category, the high-WC group was approximately 2 times more likely to have high triglyceride levels, high insulin levels, and the metabolic syndrome, compared with the low-WC group.

CONCLUSION

These findings provide some evidence that a combination of BMI and WC should be used in clinical settings to evaluate the presence of elevated health risk among children and adolescents.

Longitudinal changes in activity patterns, physical capacities, energy expenditure, and body composition in severely obese adolescents during a multidisciplinary weight-reduction program

OBJECTIVE

To determine the longitudinal changes in body composition, physical capacities, and time and energy expenditure (EE) devoted to various activities in the course of a 9-month weight-reduction period.

DESIGN

Longitudinal, clinical intervention including lifestyle education, moderate energy restriction, progressive training, and psychological follow-up.

SUBJECTS

A total of 27 (13 boys and 14 girls) severely obese adolescents (mean BMI: 33.9 kg/m2; 41.5% fat mass (FM)), aged 12-16 y.

MEASUREMENTS

Before the beginning and after the weight-reduction program, body composition was assessed by dual-energy X-ray absorptiometry (DXA), physical capacities by multistage treadmill test, and EE both by whole-body calorimetry and in free-living conditions using the heart rate-recording method. During 8 months of the weight-reduction period, type and duration of each activity were recorded using a daily controlled activity diary.

RESULTS

One boy resigned after 5 months. Body weight (BW) and FM decreased (-19 and -42%, respectively, P<0.001) both in boys and in girls, but fat-free mass (FFM) decreased only in girls (-6%, P<0.001). VO2max (l/min) did not vary significantly, but strength and fitness were improved (P<0.001). Time and EE spent at sedentary activities decreased significantly (P<0.001) to the benefit of moderate (recreational) activities and total physical activities (P<0.001) at the institution during the weekdays, and at home during the weekends and holidays.

CONCLUSION

The great BW and FM losses, preservation of FFM, and improvement of physical capacities of obese adolescents obtained under experimental conditions were associated with increases in leisure physical activities in free-living conditions at the expense of sleep and sedentary activities.

MRI of Fat Distribution in a Mouse Model of Lysosomal Acid Lipase Deficiency

OBJECTIVE

We assessed the use of MRI in the evaluation of abdominal fat distribution in a lysosomal acid lipase (LAL)-deficient mouse model.

MATERIALS AND METHODS

LAL-deficient mice are born with a normal fat distribution but over time deplete the fat stores in the subcutaneous and retroperitoneal tissues and accumulate fat in the liver, spleen, and bowel. Four MRI studies of LAL-deficient mice and control mice were obtained with 3-T T1-weighted spin-echo images and volume segmentation processing to create parameters for the study of fat distribution: intraabdominal adipose tissue-subcutaneous adipose tissue (IAT/SAT) ratio, liver volume, reproductive fat, and retroperitoneal fat. MRI adiposity parameters in LAL-deficient mice were compared with those in control mice. Adiposity volumes calculated on MRI were compared with those calculated at autopsy.

RESULTS

Statistically significant differences were found between LAL-deficient and control mice for IAT/SAT ratio (p=0.0336), liver volume (p=0.0336), and reproductive fat (p=0.0336), and a statistically significant trend was found for retroperitoneal fat (p=0.0514). No statistically significant difference was found between adiposity volumes calculated on MRI and adiposity volumes found at autopsy (all p >0.2).

CONCLUSION

Use of an in vivo model showed MRI techniques to be accurate in predicting visceral adiposity. LAL-deficient mice provided a unique model showing a pattern of adipose distribution that is markedly different from that in control mice, and MRI may provide a means of evaluating therapeutic interventions sequentially.

Comparison of visceral adipose tissue mass in adult African Americans and whites

OBJECTIVE

Previous studies have reported racial differences in the amount of visceral adipose tissue (VAT), a risk factor for metabolic diseases. These results are equivocal and have not controlled for hormonal influences on VAT mass. This study was designed to measure the extent to which race is associated with VAT, controlling for total adipose tissue (TAT) mass and testosterone.

RESEARCH METHODS AND PROCEDURES

Using a cross-sectional study design, we measured TAT mass using DXA, VAT and subcutaneous adipose tissue mass using magnetic resonance imaging, and sex hormones using radioimmunoassay in 224 African-American and white men and women.

RESULTS

White men had increased VAT mass, even when controlling for TAT and age, compared with African-American men. White women also had a higher VAT mass compared with African-American women, but only when controlling for TAT and age. When multiple linear regression was used to evaluate the racial differences in VAT mass in a subset of subjects (n=80), controlling for sex hormones, it was found that white men, but not women, had increased VAT mass compared with their African-American counterparts.

DISCUSSION

Based on the results of this study, we conclude that, when controlling for TAT, sex hormone levels, and age, white men, but not women, have more VAT mass than African-American men and women. Additional studies are needed to explore possible environmental and genetic influences on fat distribution relative to race and sex.

Leptin and the metabolic syndrome in Korean adolescents: factor analysis

BACKGROUND

The objectives of this study were to evaluate the relationships of leptin with the metabolic syndrome and to examine leptin's role in clustering of the metabolic components among Korean adolescents.

METHODS

A cross sectional study was carried out in 68 male and 80 female adolescents aged 13-18 years in an urban area of South Korea. Anthropometric variables were measured and blood pressure, fasting plasma glucose, low-density lipoprotein cholesterol, triglyceride, high-density lipoprotein cholesterol, and serum leptin were obtained.

RESULTS

As more metabolic components were clustered, body mass index, body fat, waist circumference, and serum leptin levels were significantly increased. Principal components factor analysis revealed three factors in males and females that explained 70% and 65%, respectively, of the observed variance of the 10 measured variables. These were obesity-leptin-lipid factor, blood pressure factor, and glucose-cholesterol factor in males and obesity-leptin-glucose factor, blood pressure factor, and cholesterol factor in females. Leptin loaded on only one factor in both genders.

CONCLUSION

Leptin did not appear to have a major role linking various components of the metabolic syndrome, even though it was strongly associated with obesity indices. Gender difference of linking of leptin with glucose or lipid was observed. There seems to be more than one pathophysiological mechanism which might underlie full expression of the metabolic syndrome among Korean adolescents.

Trends in waist circumferences in young British children: a comparative study

OBJECTIVE

To compare waist circumference (a measure of central fatness) and body mass index (BMI, a measure of general fatness) between a contemporary cohort and similar aged British children measured in 1987.

DESIGN

: Comparative study of two cohorts. The first was a cross-sectional survey and the second an ongoing longitudinal survey.

SETTING

: The cross-sectional study was conducted throughout Great Britain during 1987. The ongoing longitudinal study was conducted in the Avon region between 1995 and 1998.

PARTICIPANTS

A total of 1821 children were measured in the cross-sectional study, and around 1000 children were measured in the longitudinal study. Ages ranged between 2 and 5 y.

MAIN OUTCOME MEASURES

Waist circumference, height, weight and BMI. Values were expressed as mean+/-s.d. Age-related measures were compared.

RESULTS

At equivalent ages, mean waist circumference values were greater in the contemporary children, compared with children measured in the earlier cross-sectional study in 1987 (P<0.05). Although boys from the contemporary cohort had the larger absolute waist circumference measurements, the absolute and percentage differences in waist circumference between the cohorts were greater for the girls. Mean BMI values were slightly but significantly higher in the contemporary children compared with children measured in the earlier cross-sectional study (P<0.05). The proportional increase in waist circumference for each age-sex group generally exceeded the proportional increase in BMI.

CONCLUSION

These results suggest that central fatness in young British children has increased over the period of 1987-97 to a greater extent than general fatness. This should be of concern since evidence associates greater central adiposity with adverse levels of cardiovascular risk factors in children. Furthermore, the study highlights important shortcomings of the BMI measurement, in that it provides no information on body fat distribution and can mask true obesity-related risk in children.

Adolescent Obesity: Current Trends in Identification and Management

PURPOSE

To discuss the prevalence, identification, and clinical manifestations of adolescent obesity for the advanced practice nurse in primary care.

DATA SOURCES

Selected research and clinical articles.

CONCLUSIONS

Adolescent obesity has been historically attributed to inappropriate diet and exercise; however, recent research also attributes adolescent obesity to genetic factors and metabolic dysfunction. If left untreated, adolescent obesity may result in the metabolic complications of dyslipidemia, hypertension, cardiovascular disease, and early onset of type 2 diabetes.

IMPLICATIONS FOR PRACTICE

Practitioners should focus on using the new body mass index (BMI) national guidelines for early identification of obesity. Essential to the management of this condition are education, parental involvement, behavior modification, and psychological support.

Waist circumference percentiles in nationally representative samples of African-American, European-American, and Mexican-American children and adolescents

OBJECTIVE

To describe and provide estimates of the distribution of waist circumference (WC) according to percentiles in African-, European-, and Mexican-American children, and to test for group differences at different percentiles.

STUDY DESIGN

Cross-sectional data from the Third National Health and Nutrition Examination Survey (NHANES III) were examined. The sample evaluated included 9713 nonpregnant persons 2 to 18 years of age with measured values of WCs. Age-, sex-, and ethnicity-specific percentiles were estimated via percentile regression.

RESULTS

WC measurements increased in a monotonic fashion across ages but at nonconstant rates and in a manner that varied across age and sex. At higher percentiles of the distribution, estimates of WC differ between Mexican-American (MA) and European-American (EA) and between African-American (AA) and European-American (EA), and, in some cases, exceeded the adult cutoff value for obesity-related disease risk at as early as 13 years of age.

CONCLUSION

Age-, sex-, and ethnicity-specific WC percentiles are available for US children and adolescents and can be used as an assessment tool that could impact public health recommendations. Results suggest concern with respect to high WC values among certain ethnic groups.

Self-perception of physical competences in preadolescent overweight Chinese children

OBJECTIVE

To compare self-perceptions of physical competences in overweight and in normal weight preadolescent Chinese children.

DESIGN

Cross-sectional study.

SETTING

Three primary schools and a university hospital in Hong Kong.

SUBJECTS

A total of 634 children, comprising 558 (462 normal weight, 96 overweight) aged 8-12 y randomly sampled from three primary schools, and 76 similar age overweight children recruited from the community for a diet and exercise intervention programme.

MEASUREMENTS

Height, weight and percentage body fat were measured. Self-perceptions of physical competences were determined by Physical Self-Descriptive Questionnaire (PSDQ). Corresponding actual physical competences were measured by physical fitness tests.

RESULTS

Overweight children perceived themselves to have significantly more body fat than normal weight children, with poorer appearance, sports competence, endurance, coordination, flexibility, overall physical self-concept and self-esteem, but to be no less healthy, no less physically active and no less strong. Overweight children performed less well than normal weight children in measures of endurance, coordination and flexibility but better in strength. Poor self-perception of physical competences appeared only partly related to deficiencies in actual physical competences.

CONCLUSION

Overweight children have poorer self-perception of their physical competences but do not perceive themselves to be less strong, healthy or physically active than normal weight children. Exercise programmes for overweight children could be more effective if designed with the knowledge of these self-perceptions.

Responses of lipolysis and salivary cortisol to food intake and physical activity in lean and obese children

This investigation was conducted to determine whether there were differences in lipolytic responses to feeding and physical activity between lean (LN) and obese (OB) children, and if these responses were related to cortisol. Fourteen LN and 11 OB children participated in this study of abdominal lipolysis and salivary cortisol response to breakfast and lunch with an intervening exercise session. Calculated fasting glycerol release was lower in OB than LN (0.645 +/- 0.06 vs. 0.942 +/- 0.11 micromol/ml; P < 0.05). Fasting adipose tissue nutritive flow was lower in OB than in LN subjects, but responses to feeding and exercise were not different. Breakfast elicited a decrease in interstitial glycerol concentration in LN (-33%; P < 0.05), but not in OB (-5%), children, although decreases in glycerol concentration in response to lunch were similar (LN, -41%; OB, -36%). An interaction was evident in the salivary cortisol response to breakfast (LN, no change; OB, increase) and exercise (LN, no change; OB, decrease), but there were no group differences in response to lunch. Alterations in salivary cortisol and lipolysis were not related. These data suggest that salivary cortisol and lipolytic responses are not necessarily linked, but are altered in obesity. Furthermore, prior exercise may improve the antilipolytic response to a meal in OB children.

Regular participation in sports is associated with enhanced physical fitness and lower fat mass in prepubertal boys

OBJECTIVE

To study the effect of physical activity on whole body fat (BF), its regional deposition and the influence of body fatness on physical performance in prepubertal children.

DESIGN

Cross-sectional study.

SUBJECTS

A total of 114 boys (9.4+/-1.5 y, Tanner I-II), randomly sampled from the population of Gran Canaria (Spain), 63 of them physically active (PA, at least 3 h per week during the previous year) and 51 nonphysically active (non-PA).

MEASUREMENTS

Body composition (DXA), anthropometric variables (body circumferences and skinfolds) and physical fitness were determined in all subjects.

RESULTS

The PA obtained better results in maximal oxygen uptake, isometric leg extension force, vertical jump (muscular power), and 300 m (anaerobic capacity) and 30 m running tests (speed) than the non-PA. A lower percentage of body fat (% BF) (4 U less, P<0.05), whole BF mass (36% less, P<0.05) and regional fat mass (28, 25, and 30% less in the trunk, legs and arms, respectively, all P<0.05) was observed in the PA compared to the non-PA. The waist and hip circumferences correlated more closely with both the fat mass accumulated in the trunk region and the % BF (r=0.81-0.95, P<0.001) than the waist-to-hip ratio (WHR). The WHR correlated with the percentage of the whole fat mass accumulated in the trunk (PFT) (r=0.52-0.53, P<0.001). In both groups, the PFT increased curvilinearly with the % BF, regardless of the level of physical activity. ANCOVA analysis revealed that total and regional fat masses explained less than 40% of the difference in performance between the PA and non-PA group. The mean speed in the 30 m running test (V30), combined with the height and whole body mass, has predictive value for the BF mass (R=0.98, P<0.001). The % BF may be estimated from the body mass index (BMI) and V30 (% BF=8.09+2.44.BMI (kg m(-2))-5.8.V30 (m s(-1)), R=0.94, P<0.001) in prepubertal boys.

CONCLUSIONS

Regular participation in at least 3 h per week of sports activities and competitions on top of the compulsory physical education program is associated with increased physical fitness, lower whole body and trunkal fat mass in prepubertal boys.

Race/ethnic issues in obesity and obesity-related comorbidities

The prevalence of obesity is increasing among all age and racial groups in the United States. There is, however, a disproportionate rise in the prevalence of obesity among African-Americans and Hispanic/Mexican Americans. Obesity is a major contributor to the insulin resistant syndrome (IRS), a condition of multiple metabolic abnormalities that is a precursor to type 2 diabetes, and confers a high risk for cardiovascular events. The estimated prevalence of IRS is also greater in Mexican Americans and African-Americans than in Caucasians. The IRS is identifiable in children, and as with adults, there are racial differences in its expression even at a young age. The obesity-associated diseases, including diabetes and hypertension, are found at higher rates within the minority races compared with Caucasians. However, there are differences, in that obesity-related hypertension occurs at higher rates among African-Americans, and obesity-related diabetes occurs at higher rates among Mexican Americans. Race/ethnic differences in lifestyle behaviors and economic disadvantage may account for some of the race disparity in obesity-related diseases and disease outcomes. Environmental factors, however, do not explain all of the race disparity in disease expression, indicating that there are genetic/molecular factors that are operational as well.

Insulin sensitivity, cardiorespiratory fitness, and physical activity in overweight Hispanic youth

OBJECTIVE

To determine whether cardiorespiratory fitness and/or physical activity (PA) were related to measures of insulin sensitivity and secretion independent of body composition in overweight Hispanic children.

RESEARCH METHODS AND PROCEDURES

Ninety-five Hispanic children (n = 55 boys; n = 40 girls; 8 to 13 years old) participated in this investigation. The frequently sampled intravenous glucose tolerance test was used to determine the insulin sensitivity index (SI), the acute insulin response, and the disposition index. Cardiorespiratory fitness [maximal oxygen uptake (VO(2max))] was evaluated using a treadmill protocol, and PA was determined by an interviewer-administered questionnaire. Body composition was measured using DXA.

RESULTS

Unadjusted correlations indicated that VO(2max) (milliliters of O(2) per minute) was negatively related to SI (r = -0.46, p < 0.05) and disposition index (r = -0.31, p < 0.05) and positively associated with fasting insulin (r = 0.29, p < 0.05), but these relationships were no longer significant once gender, Tanner stage, fat mass, and soft lean tissue mass were included as covariates (all p > 0.05). Multivariate linear regression analysis showed that body fat mass explained 53% of the variance in SI and that VO(2max) (milliliters of O(2) per minute) was not independently related to SI. Cardiorespiratory fitness was positively related to both fat mass (r = 0.43, p < 0.001) and soft lean tissue mass (r = 0.89, p < 0.001). PA was not related to any measure of insulin sensitivity and secretion.

DISCUSSION

Cardiorespiratory fitness, as determined by VO(2max) (milliliters of O(2) per minute), was not independently related to insulin sensitivity or secretion, suggesting that VO(2max) influences insulin dynamics indirectly through fat mass.