Visceral adipose tissue and markers of the insulin resistance syndrome in obese black and white teenagers

Fat Imaging via Magnetic Resonance Imaging (MRI) in Young Children (Ages 1-4 Years) without Sedation

Introduction

This pilot study developed techniques to perform Magnetic Resonance Imaging (MRI) of specific fat deposition in 18 children (age 18 months to 4 years).

Methods

The children engaged in a series of practice tests to become acclimated to the scanner noises, reduce claustrophobia, and rehearse holding still for a set time. The practice tests assessed if the child could remain still for two minutes while watching a video, first while lying on a blanket, second, on the blanket with headphones, and third, in the mock scanner. The children who passed the three practice tests were then scanned with a 3T Siemens Skyra magnet. Abdominal fat distribution (region of interest (ROI) from the top of the ileac crest to the bottom of the ribcage) volume was measured using 2-point DIXON technique. This region was chosen to give an indication of the body composition around the liver.

Results

Twelve out of eighteen participants successfully completed the actual MRI scan. Chi-squared test showed no significant difference between male and female pass-fail rates. The median age of completed scans was 36 months, whereas the median age for children unable to complete a scan was 28 months. The average total trunk fat was 240.9±85.2mL and the average total VAT was 37.7±25.9mLand liver fat was not quantifiable due to physiological motion. Several strategies (modeling, videos, and incentives) were identified to improve pediatric imaging in different age ranges.

Conclusion

Using an age-specific and tailored protocol, we were able to successfully use MRI for fat imaging in a majority of young children. Development of such protocols enables researchers to better understand the etiology of fat deposition in young children, which can be used to aid in the prevention and treatment of adiposity.

Visceral/epicardial adiposity in nonobese and apparently healthy young adults: association with the cardiometabolic profile

OBJECTIVE

We investigate associations of regional adipose tissues with cardiometabolic profile of nonobese and apparently healthy young adults.

METHODS

Four hundred twenty-five nonobese and apparently healthy individuals were assessed for blood pressure and fasting lipid profile, blood glucose and adiponectin. Subcutaneous abdominal adipose tissue (SAT) and ectopic fat depots (visceral abdominal adipose tissue [VAT], epicardial adipose tissue [EAT] and hepatic fat fraction [HFF]) were quantified by magnetic resonance imaging.

RESULTS

According to anthropometric measurements, blood pressure and blood markers, the population (18-35 years, 54% women) had a low cardiometabolic risk. Compared to women, men had more VAT, EAT and HFF, but less SAT. Regional adipose tissues were positively correlated with each other. VAT and EAT carried significant correlations with all markers of cardiometabolic risk, while SAT and HFF correlated variably with these markers. While taking into account age and gender, SAT, VAT and EAT were associated with most cardiometabolic markers, while HFF was only associated with total cholesterol/high-density lipoprotein ratio (TC/HDL-C) and triglycerides (TG). When comparing SAT, VAT and EAT head-to-head, VAT was the only adipose tissue location maintaining significant association with most markers of cardiometabolic risk. Greater VAT (≥50th percentile) was associated with a worse cardiometabolic profile, whether individuals were overweight or normal weight.

CONCLUSION

Even in nonobese and apparently healthy young women and men, accumulation of ectopic visceral adiposity in general, and of VAT in particular, is associated with a worse cardiometabolic profile whether individuals were overweight or normal weight.

Tanner Staging of Secondary Sexual Characteristics and Body Composition, Blood Pressure, and Insulin in Black Girls

OBJECTIVE

To assess Tanner staging (breast and pubic hair development) and its relationship to measures of body composition, blood pressure, and fasting insulin and glucose in young black girls.

RESEARCH METHODS AND PROCEDURES

Subjects were 138 black girls, 8 to 12 years of age, recruited from elementary schools in low socioeconomic status neighborhoods. Exclusion criteria included the presence of any acute/chronic medical conditions. Pubertal stages were assessed by one of two pediatricians and analyzed individually, as well as with a composite index (prepubertal, pubertal/premenarcheal, or pubertal/menarcheal). Glucose and insulin were measured after a 12-hour fast. Measures of body composition included height, weight, BMI, waist and hip circumferences, fat mass, fat-free soft tissue, bone mineral density (DXA), and visceral adipose tissue (magnetic resonance imaging). Resting systolic and diastolic blood pressure were measured by Dinamap.

RESULTS

With age in the model, breast development explained significant proportions of the variance in height, weight, fat-free soft tissue, bone mineral density, and insulin. Adding pubic hair development or menarche to those models did not significantly increase the proportion of variance that was explained by breast development. Furthermore, using a composite index of pubertal staging explained a smaller proportion of the variance compared with breast development alone.

DISCUSSION

Combined with age, breast development was a better predictor of body composition and fasting insulin than was pubic hair development or a composite index of pubertal staging.

Use of MRI and CT for fat imaging in children and youth: what have we learned about obesity, fat distribution and metabolic disease risk?

Childhood obesity is a matter of great concern for public health. Efforts have been made to understand its impact on health through advanced imaging techniques. An increasing number of studies focus on fat distribution and its associations with metabolic risk, in interaction with genetics, environment and ethnicity, in children. The present review is a qualitative synthesis of the existing literature on visceral and subcutaneous abdominal, intrahepatic and intramuscular fat. Our search revealed 80 original articles. Abdominal as well as ectopic fat depots are prevalent already in childhood and contribute to abnormal metabolic parameters, starting early in life. Visceral, hepatic and intramuscular fat seem to be interrelated but their patterns as well as their independent contribution on metabolic risk are not clear. Some ethnic-specific characteristics are also prevalent. These results encourage further research in childhood obesity by using imaging techniques such as magnetic resonance imaging and computed tomography. These imaging methods can provide a better understanding of fat distribution and its relationships with metabolic risk, compared to less detailed fat and obesity assessment. However, studies on bigger samples and with a prospective character are warranted.

Ethnic and sex differences in body fat and visceral and subcutaneous adiposity in children and adolescents

Body fat and the specific depot where adipose tissue (AT) is stored can contribute to cardiometabolic health risks in children and adolescents. Imaging procedures including magnetic resonance imaging and computed tomography allow for the exploration of individual and group differences in pediatric adiposity. This review examines the variation in pediatric total body fat (TBF), visceral AT (VAT) and subcutaneous AT (SAT) due to age, sex, maturational status and ethnicity. TBF, VAT and SAT typically increase as a child ages, though different trends emerge. Girls tend to accumulate more TBF and SAT during and after puberty, depositing fat preferentially in the gynoid and extremity regions. In contrast, pubertal and postpubertal boys tend to deposit more fat in the abdominal region, particularly in the VAT depot. Sexual maturation significantly influences TBF, VAT and SAT. Ethnic differences in TBF are mixed. VAT tends to be higher in white and Hispanic youth, whereas SAT is typically higher in African American youth. Asian youth typically have less gynoid fat but more VAT than whites. Obesity per se may attenuate sex and ethnic differences. Particular health risks are associated with high amounts of TBF, VAT and SAT, including insulin resistance, hepatic steatosis, metabolic syndrome and hypertension. These risks are affected by genetic, biological and lifestyle factors including physical activity, nutrition and stress. Synthesizing evidence is difficult as there is no consistent methodology or definition to estimate and define depot-specific adiposity, and many analyses compare SAT and VAT without controlling for TBF. Future research should include longitudinal examinations of adiposity changes over time in representative samples of youth to make generalizations to the entire pediatric population and examine variation in organ-specific body fat.

The metabolically healthy but obese phenotype in African Americans

Obesity has become one of the leading public health concerns in the United States and worldwide. While obesity is associated with the metabolic syndrome, some obese individuals do not possess the constellation of the metabolic abnormalities and are referred to as metabolically healthy but obese (MHO) persons. Limited data exist on the prevalence and characteristics of the MHO in African Americans. The authors studied 126 obese African Americans and defined the MHO phenotype as an individual with a body mass index ≥30 kg/m(2) , high-density lipoprotein cholesterol ≥40 mg/dL, absence of type 2 diabetes mellitus, and absence of arterial hypertension. The correlates of the MHO phenotype with anthropometrical and metabolic indices were examined, as well as the effect of age on these correlates. Results showed that 36 (28.5%) of the individuals were identified with the MHO phenotype. Waist circumference (WC) and waist-to-hip ratio (WHR) were significantly lower (P<.05) in MHO than in non-MHO patients. While there were significant lower levels of low-density lipoprotein and triglycerides in MHO among patients younger than 40 years, the significance was lost among patients 40 years or older. This study indicates that increased WC and WHR may be early premetabolic syndrome markers in obese individuals and should warrant aggressive risk factor reduction therapy to prevent future development of related cardiovascular conditions.

Measurement site of visceral adipose tissue and prediction of metabolic syndrome in youth

OBJECTIVE

It is unknown whether measurement site of visceral adipose tissue (VAT) influences the relationship between VAT and associated health risk in youth and if so, whether ethnic differences exist in this relationship. We examined the influence of the measurement site of VAT on the relationships between VAT and metabolic syndrome (MetS) in African-American (AA) and American-White (AW) youth.

SUBJECTS

Healthy AA (n = 54) and AW (n = 54) children and adolescents (age: 8-18 yr; BMI: 15.3-42.5 kg/m(2)).

MEASUREMENTS

VAT mass was derived using a series of five transverse images measured by magnetic resonance imaging, extending from 5 cm below to 15 cm above L4-L5. MetS was defined using a modified IDF criteria.

RESULTS

In AA, VAT measure at 5 cm above L4-L5 (R(2) = 0.93) was most strongly (p < 0.05) correlated with VAT mass and was a significantly (p < 0.05) stronger correlate as compared to L4-L5 (R(2) = 0.84). In AW, VAT measures at 5 cm (R(2) = 0.93) and 10 cm (R(2) = 0.93) above L4-L5 were most strongly (p < 0.05) correlated with VAT mass; however, these were not stronger correlates as compared to L4-L5 (R(2) = 0.91). In AW, all VAT measures were significantly (p < 0.05) associated with an increased odds ratio (OR) for prevalent MetS, wherein the VAT mass [OR = 5.32(1.9-15.0)] and VAT at L4-L5[OR = 5.99(1.9-18.4)] were most strongly associated with MetS. In contrast, only VAT at 10 cm above L4-L5 [OR = 4.39 (1.1-18.1)] was significantly (p < 0.05) associated with MetS in AA.

CONCLUSION

In AA and AW youth, the measurement site for VAT has impact on the estimation of total VAT and the magnitude of the association with obesity-related health risks.

Lifestyle and socioeconomic-status modify the effects of ADRB2 and NOS3 on adiposity in European-American and African-American adolescents

The aim of the study is to investigate the influence of and interaction between lifestyle behaviors (diet and physical activity (PA)) and single-nucleotide polymorphisms (SNPs) in obesity-candidate genes (ADRB2, APOB and NOS3) on general and central adiposity. Six-hundred-and-twenty-one European-American (EA) and African-American (AA) youths aged 13-19 years were classified by ethnicity (49% AA), gender (45% male), and socioeconomic status (SES). PA and dietary intake with up to seven 24-h recalls were reported for all subjects. Percent body fat (%BF) was measured by dual-energy X-ray absorptiometry, visceral adipose tissue (VAT), and subcutaneous abdominal adipose tissue (SAAT) by magnetic resonance imaging. Reported energy intake (EI) and vigorous PA (VPA) were negative predictors of %BF and SAAT. Carriers of the NOS3 Asp298 allele had higher %BF only in the presence of an adverse environment (low SES). Compared to the most common NOS3 haplotype, homozygotes for haplotype A-non4r-Asp had 6.1% higher %BF. Significant interactions were revealed between the ADRB2 Arg16Gly SNP and VPA on VAT, SAAT and waist circumference (WC) such that Gly16 homozygotes may benefit less from increased VPA to reduce their weight. Genetic susceptibility to increased general and central adiposity is dependent on several factors, such as SES and vigorous exercise. Improved understanding of the joint effect of genes and lifestyle on adiposity will offer new insights into obesity and may provide new avenues for personalized prevention and treatment.

Independent effects of age-related changes in waist circumference and BMI z scores in predicting cardiovascular disease risk factors in a prospective cohort of adolescent females

BACKGROUND

Cross-sectional data indicate that central adiposity is associated with cardiovascular disease risk, independent of total adiposity. The use of longitudinal data to investigate the relation between changes in fat distribution and the emergence of risk factors is limited.

OBJECTIVE

We tested the hypothesis that age-related change in waist circumference (to reflect central adiposity) during adolescence is a significant predictor of longitudinal change in cardiovascular disease risk, after adjustment for change in body mass index (BMI) z score (to reflect total adiposity) in a cohort of postmenarcheal adolescent females. We also tested whether race modified this relation.

DESIGN

We analyzed publicly available data from the National Heart, Lung, and Blood Institute Growth and Health Study. Longitudinal regression models were fitted to investigate the independent effects of changes in waist circumference on cardiovascular disease risk factors.

RESULTS

Steeper age-related increases in waist circumference over time were associated with a greater increase in LDL-cholesterol concentrations, systolic blood pressure, diastolic blood pressure, and homeostasis model assessment of insulin resistance, after adjustment for BMI z score, in white but not in black females. Change in waist circumference was not a statistically significant predictor of age-related changes in HDL-cholesterol, triglyceride, insulin, and glucose concentrations, after adjustment for changes in BMI z score, in either white or black females.

CONCLUSIONS

Our research suggests that monitoring waist circumference in addition to BMI z score has the potential to identify adolescents at risk of the emergence of cardiovascular disease risk factors, at least in white females. The data also suggest that race may modify the relation between fat distribution pattern and cardiovascular disease risk factors.

Whole-body MRI and ethnic differences in adipose tissue and skeletal muscle distribution in overweight black and white adolescent boys

It is unclear whether ethnic differences exist in adipose tissue (AT) and skeletal muscle (SM) distribution in black and white youth. Investigation into the pattern of AT and SM distribution in black versus white youth may provide insight into the previously reported health disparities between these ethnicities. Therefore, we examined total and regional AT and SM in overweight black and white boys. The study sample included overweight black (n = 19) and white (n = 21) boys (11-18 yr, BMI ≥ 85th) whose body composition was evaluated using whole-body MRI. Despite similar age, Tanner stage, and BMI, black boys had significantly (P < .05) less visceral AT than white boys and more (P < .05) total and lower-body subcutaneous AT (SAT) in both absolute (kg) and relative (%) terms. There was a main effect (P < .05) of ethnicity on the relationship between total and regional AT, such that for a given amount of total body AT (kg), black boys had a greater (P < .05) lower-body SAT and less visceral AT than their white peers. For a given amount of total SM, black boys had more (P < .05) SM in the thigh. Compared with overweight white boys, overweight black boys have less visceral fat, more subcutaneous fat, and more thigh skeletal muscle.

Efficacy of increasing physical activity to reduce children's visceral fat: a pilot randomized controlled trial

OBJECTIVE

To examine whether differentially targeting physical activity within the context of pilot family-based pediatric weight control treatment results in differential change in abdominal fat, particularly visceral fat.

METHOD

Twenty-nine overweight children (>85(th) body mass index [BMI] percentile) and at least one participating parent were randomly assigned to one of two family-based behavioral weight management conditions that either targeted 1) primarily dietary change (STANDARD; n = 15) or 2) dietary plus physical activity change (ADDED; n = 14). Differences at post-treatment in overall child weight status (e.g., BMI), whole-body composition (measured by dual x-ray absorptiometry), and abdominal fat (measured by waist circumference and magnetic resonance imaging) were assessed using intent-to-treat analyses, as were post-treatment parent BMI and waist circumference. Child and parent physical activity and dietary behavior changes were also evaluated. Results. At post-treatment, overall child weight status, whole-body composition, and child dietary measures did not differ by condition. Children in the ADDED condition tended to have higher physical activity and lower visceral abdominal fat at post-treatment relative to children in the STANDARD condition.

CONCLUSIONS

Increasing physical activity may be important to optimize reductions in abdominal fat, especially visceral fat, among overweight children provided with family-based behavioral weight management treatment.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00359957.

Skeletal muscle lipid content and insulin sensitivity in black versus white obese adolescents: is there a race differential?

OBJECTIVE

We tested the hypothesis that skeletal muscle lipid content (SMLC) is higher in obese black adolescents compared with their white peers and assessed the relationship between SMLC and insulin sensitivity (IS).

METHODS

Subjects were healthy obese black (n = 42) and white (n = 38) adolescents. Measurements included an oral glucose tolerance test, IS by a 3-h hyperinsulinemic-euglycemic clamp, abdominal adipose tissue (AT) by magnetic resonance imaging and midthigh SMLC by computed tomography.

RESULTS

All measures of SMLC including intermuscular AT (IMAT), low-density muscle, and thigh sc AT increased (P < 0.05) with increasing total adiposity independent of race. For a given total body adiposity or thigh circumference, SMLC did not differ between black and white adolescents; however, for a given visceral adipose tissue, IMAT was higher in blacks. Consistent with prior observations, IS did not differ between black and white obese adolescents despite lower visceral fat in blacks. In whites, all markers of SMLC were associated (P < 0.05) with IS, whereas in blacks, only IMAT correlated (P < 0.05) with IS. However, in both races, these relationships did not remain significant after accounting for total fat (kilograms).

CONCLUSIONS

SMLC is not different between black and white obese adolescents who have similar total body adiposity but lower visceral fat in blacks. The lack of association between IS and SMLC after adjusting for total adiposity suggest that muscle fat does not make a unique contribution to IS in this group of obese adolescents regardless of race.

FTO variant rs9939609 is associated with body mass index and waist circumference, but not with energy intake or physical activity in European- and African-American youth

Background

Genome-wide association studies found common variants in the fat mass and obesity-associated (FTO) gene associated with adiposity in Caucasians and Asians but the association was not confirmed in African populations. Association of FTO variants with insulin resistance and energy intake showed inconsistent results in previous studies. This study aimed to assess the influence of FTO variant rs9939609 on adiposity, insulin resistance, energy intake and physical activity in European - (EA) and African-American (AA) youth.

Methods

We conducted a cross-sectional study in EA and AA youths. One thousand, nine hundred and seventy-eight youths (48.2% EAs, 47.1% male, mean age 16.5 years) had measures of anthropometry. Percent body fat (%BF) was measured by dual-energy X-ray absorptiometry, visceral adipose tissue (VAT) and subcutaneous abdominal adipose tissue (SAAT) by magnetic resonance imaging. Energy intake and physical activity were based on self report from up to 7 24-hour recalls. Physical activity was also measured by accelerometry.

Results

FTO rs9939609 was significantly associated with body mass index (BMI) (P = 0.01), weight (P = 0.03) and waist circumference (P = 0.04), with per-allele effects of 0.4 kg/m², 1.3 kg and 0.8 cm, respectively. No significant association was found between rs9939609 and %BF, VAT, SAAT or insulin resistance (P > 0.05), or between rs9939609 and energy intake or vigorous physical activity (P > 0.05). No significant interactions of rs9939609 with ethnicity, gender, energy intake or physical activity were observed (P > 0.05).

Conclusions

The FTO variant rs9939609 is modestly associated with BMI and waist circumference, but not with energy intake or physical activity. Moreover, these effects were similar for EAs and AAs. Improved understanding of the effect of the FTO variant will offer new insights into the etiology of excess adiposity.

Common variants near melanocortin 4 receptor are associated with general and visceral adiposity in European- and African-American youth

OBJECTIVE

Recent genome-wide association studies found common variants near the melanocortin 4 receptor gene associated with obesity. This study aimed to assess the influence of the identified single nucleotide polymorphisms rs17782313 and rs17700633 on general and visceral adiposity in European- and African-American youth.

STUDY DESIGN

In 1890 youth (49.1% European-American, 45.6% male, mean age 16.7 years), we examined the associations of the rs17782313 and rs17700633 with anthropometry, percent body fat, visceral adipose tissue, and subcutaneous abdominal adipose tissue. Interaction of the single nucleotide polymorphisms with ethnicity or sex was investigated and haplotype analyses conducted.

RESULTS

Rs17782313 was significantly associated with weight (P = .02) and waist circumference (P = .03) in all subjects and with body mass index (P = .002) in females. In females rs17700633 was significantly associated with percent body fat (P = .001), visceral adipose tissue (P < .001), and subcutaneous abdominal adipose tissue (P < .001). Rs17700633 was significantly associated with fasting insulin and homeostasis model assessment, but the significance attenuated after adjustment for percent body fat. These findings were confirmed by haplotype analysis. No significant interactions of the variants with ethnicity were found for any of these phenotypes.

CONCLUSIONS

The relatively large effect of these common variants near melanocortin 4 receptor on general and visceral adiposity in childhood, especially in girls, could prove helpful in elucidating the molecular mechanisms underlying the development of obesity in early life.

Race and gender differences in the relationships between anthropometrics and abdominal fat in youth

OBJECTIVE

We examined the influence of race and gender on abdominal adipose tissue (AT) distribution for a given anthropometric measure including waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-height (W/Ht) in youth.

METHODS AND PROCEDURES

Subjects included healthy 62 black and 98 white youth. A single transverse image of the abdomen (L4-L5) was obtained using computed tomography.

RESULTS

For a given BMI, there was a significant (P<0.05) main effect of race and sex on the relationship between BMI and WC, such that boys and whites had a higher WC than girls and blacks. There was a significant (P<0.05) main effect and interaction effect of gender on the relationship between WC and visceral AT, such that boys had a higher visceral AT than girls, and the difference was magnified with increasing WC. For a given WC, black boys and girls had higher abdominal subcutaneous AT (SAT) than white peers, wherein the magnitude of the difference is increased with increasing WC. For a given W/Ht, black boys had significantly (P<0.05) lower visceral AT than white boys, but with no difference in girls. Black boys and girls had higher SAT than white peers, wherein the magnitude of the difference is increased with increasing W/Ht.

DISCUSSION

Our findings demonstrate a significant race and gender differential in the abdominal AT distribution for a given BMI, WC, WHR, and W/Ht. Future studies should take these differences into consideration when developing race- and gender-specific anthropometric cut-offs for obesity and obesity-related health risks in youth.

Epidemiology of paediatric metabolic syndrome and type 2 diabetes mellitus

The epidemic in childhood obesity is a driving force behind the increase in paediatric metabolic syndrome, a collection of abnormalities that is associated in adults with increased risk for cardiovascular disease and type 2 diabetes mellitus. Although there is no clear consensus about the paediatric definition for metabolic syndrome, the prevalence of this syndrome is clearly rising. Children with metabolic syndrome are at increased risk for metabolic syndrome in adulthood. A late consequence of metabolic syndrome is type 2 diabetes, which increasingly affects adolescents. The rise in metabolic syndrome and type 2 diabetes in children is almost sure to lead to an increase in associated complications in young adulthood, including early cardiovascular disease. This epidemic will bear fruit in forthcoming decades, putting further stress on the healthcare system and probably leading to increased morbidity and a shorter lifespan for future generations.

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.

General and visceral adiposity in black and white adolescents and their relation with reported physical activity and diet

BACKGROUND

Excess body fat accumulation may begin in youth and is linked with increased risk of cardiovascular disease. Examination of physical activity (PA) and diet behaviours predictive of adiposity may help target efforts to reduce chronic disease risk.

OBJECTIVE

We hypothesized that energy intake (EI) from fat, vigorous PA (VPA), and their interaction would predict body fat percentage (%BF) and visceral adipose tissue (VAT) in youth and that sedentary behaviours and intake of dairy, fruit, vegetable and whole grain foods would be related to adiposity.

DESIGN

A cross-sectional, observational study of reported PA and diet behaviours and objective adiposity measures.

SUBJECTS

Six-hundred sixty-one healthy black and white adolescents aged 14-18 years.

MEASUREMENTS

Diet by 24-h recalls using Nutrition Data Systems for Research (Minneapolis, MN, USA), VPA by previous day physical activity recalls (PAR), and %BF with dual-energy X-ray absorptiometry. VAT by magnetic resonance imaging for 434 subjects.

RESULTS

Reported EI and VPA were positively correlated with each other and were negative predictors of %BF. Time spent watching television or movies and %EI from protein were positive predictors of %BF. Adjusted for EI, none of the independent variables predictive of %BF retained their significance. %BF and VAT were highly correlated (r=0.73, P<0.0001). EI was the sole and negative predictor of VAT.

CONCLUSIONS

Higher energy 'throughput', not energy restriction, characterize leaner youths. Youths should be advised to engage in VPA so that they can eat sufficient calories to obtain the nutrients required for optimal health while remaining lean.

Markers of insulin resistance are associated with fatness and fitness in school-aged children: the European Youth Heart Study

AIMS/HYPOTHESIS

Our aim was to examine the association between markers of insulin resistance and: (1) body fat and waist circumference, taking into account cardiorespiratory fitness in school-aged children; and (2) cardiorespiratory fitness at differing levels of body fat and waist circumference.

SUBJECTS AND METHODS

This was a cross-sectional study of 873 children aged 9.6 +/- 0.4 years from Estonia and Sweden. Weight, height and waist circumference were measured. Body fat was expressed as the sum of five skinfold thicknesses. Cardiorespiratory fitness was estimated by a maximal cycle-ergometer test. The studied markers of insulin resistance were fasting insulin and glucose, and homeostasis model assessment (HOMA).

RESULTS

HOMA and fasting insulin were positively associated with body fat and waist circumference after adjusting for cardiorespiratory fitness, age, pubertal status and study location. HOMA and fasting insulin were negatively associated with cardiorespiratory fitness in children in the third (highest) tertile of body fat and waist circumference after controlling for sex, age, pubertal status and study location. Fasting glucose was negatively associated with cardiorespiratory fitness in children in the third (highest) tertile of waist circumference, but it was not associated when body fat was taken into account.

CONCLUSIONS/INTERPRETATION

In school-aged children, HOMA and fasting insulin are significantly associated with body fat and waist circumference. In addition, cardiorespiratory fitness explains a significant proportion of the HOMA and fasting insulin variance in those children with high levels of body fat and waist circumference. The findings suggest that the deleterious consequences ascribed to high fatness could be counteracted by having high levels of cardiorespiratory fitness.

Relationship of visceral adiposity to cardiovascular disease risk factors in black and white teens

OBJECTIVE

We tested the hypothesis that visceral adiposity, compared with general adiposity, would explain more of the variance in cardiovascular disease (CVD) risk factors.

RESEARCH METHOD AND PROCEDURES

Subjects were 464 adolescents (238 black and 205 girls). Adiposity measures included visceral adipose tissue (VAT; magnetic resonance imaging), percent body fat (%BF; DXA), BMI, and waist girth (anthropometry). CVD risk factors were fasting insulin, fibrinogen, total to high-density lipoprotein-cholesterol ratio, triglycerides (TGs), systolic blood pressure, and left ventricular mass indexed to height2.7.

RESULTS

After adjustment for age, race, and sex, all adiposity indices explained significant proportions of the variance in all of the CVD risk factors; %BF tended to explain more variance than VAT. Regression models that included both %BF and VAT found that both indices explained independent proportions of the variance only for total to high-density lipoprotein-cholesterol ratio. For TGs, the model that included both %BF and VAT found that only VAT was significant. For systolic blood pressure and left ventricular mass indexed to height2.7, anthropometric measures explained more of the variance than VAT and %BF.

DISCUSSION

The hypothesis that visceral adiposity would explain more variance in CVD risk than general adiposity was not supported in this relatively large sample of black and white adolescents. Only for TGs did it seem that VAT was more influential than %BF. Perhaps the deleterious effect of visceral adiposity becomes greater later in life as it increases in proportion to general adiposity.

Anthropometric Determinants of a Clustering of Lipid-Related Metabolic Risk Factors in Overweight and Non-Overweight Adolescents – Influence of Cardiorespiratory Fitness

BACKGROUND/AIMS

To explore in adolescents the associations between simple anthropometric variables with a continuously distributed summary score for lipid-related metabolic risk in both overweight and non-overweight adolescents, and to test whether these associations are modified by the level of cardiorespiratory fitness.

METHODS

Cardiorespiratory fitness, BMI, skinfold thicknesses, body circumferences, and a continuously distributed clustering of lipid- related metabolic risk (calculated from LDL and HDL cholesterol, triglycerides, and glucose) were measured in 524 adolescents (265 males, 259 females, 15.3 +/- 1.4 years) from the cross-sectional multicentric AVENA study. Participants were classified as overweight (including obesity) or non-overweight.

RESULTS

Most anthropometric parameters were univariately related to the continuous lipid-related metabolic risk. However, after multicollinear analysis and generalized linear modelling, suprailiac skinfold thickness in males (p < 0.001, explained variance 12.2%) and waist-to-height ratio in females (p < 0.001, explained variance 10.0%) were the best determinants of the continuous metabolic risk score, after adjustment for age, sexual maturation, and economic status. These associations were slightly weakened in overweight males (p = 0.034) and females (p = 0.087), and did not interact with cardiorespiratory fitness.

CONCLUSION

Our data emphasize the usefulness of suprailiac skinfold thickness in males and waist-to-height ratio in females as simple anthropometric measurements associated to an overall lipid-related metabolic risk, mainly in non-overweight adolescents and regardless their cardiorespiratory status.

Elevated total and central adiposity and low physical activity are associated with insulin resistance in children

The aim of this study was 2-fold: (1) to examine insulin resistance, blood lipid levels, and inflammatory markers in 9- to 11.5-year-old obese and lean children and (2) to identify factors that influence insulin resistance in this cohort of youths. Body mass index, skinfold thickness, waist circumference, physical activity (4-day triaxial accelerometer), cardiorespiratory fitness (submaximal bicycle ergometer test), and dietary intake (3-day food records) were evaluated in 27 obese and 27 lean boys and girls. Fasting blood samples were analyzed for insulin, glucose, lipids and lipoproteins, C-reactive protein (CRP), interleukin 6, soluble intercellular adhesion molecule, and soluble vascular cell adhesion molecule. Homeostasis model assessment (HOMA) was used to evaluate insulin resistance (HOMA-IR). Obese children presented higher HOMA-IR, CRP, and blood lipid levels (all P < .01) compared with lean children. Total body fat and waist circumference were positively associated with fasting insulin (r > or = 0.51), HOMA-IR (r > or = 0.56), CRP (r > or = 0.51), and blood triacylglycerol (r > or = 0.38), and were inversely correlated with high-density lipoprotein cholesterol (r > or = -0.39; all P < .01). Cardiorespiratory fitness was inversely associated with HOMA-IR (r = -0.24; P < .05), but this association disappeared when adjusted for age, sex, and fat mass. Waist circumference and total daily physical activity explained 49% of the variance in HOMA-IR in these children. In conclusion, these findings suggest that total and central adiposity are positively associated and physical activity is negatively associated with insulin resistance in children. Interventions to improve glucose metabolism in youth should target at reducing total body and abdominal fat and increasing physical activity. The lack of association between inflammatory markers and HOMA-IR suggests that obesity may precede the elevation of these markers in the evolution of insulin resistance in youth.

Computed tomography scans of intra-abdominal fat, anthropometric measurements, and 3 nonobese metabolic risk factors

The present cross-sectional study of 46 adult Danish white men and women aimed to evaluate association between intra-abdominal obesity, 4 anthropometric measurements of obesity, and combinations of 3 nonobese metabolic risk factors: systolic blood pressure of 130 mm Hg or higher, serum triglyceride concentration of more than 1.7 mmol/L, and fasting capillary blood glucose concentration of 5.6 mmol/L or more. For 80% of the subjects, intra-abdominal fat on a computed tomography scan of the abdomen using a cutoff limit of more than 144 cm(2) gave a correct classification of combinations of at least 2 of the 3 metabolic risk factors. Body mass index and waist circumference were better markers of intra-abdominal obesity than waist-to-hip ratio in receiver operating characteristic analyses (P = .0035). Body mass index of more than 26 kg/m(2) and waist circumference of more than 0.92 m classified 76% and 74% of the subjects correctly regarding combinations of the 3 nonobese metabolic risk factors. Intra-abdominal obesity was significantly stronger associated with the combinations than a raised waist-to-hip ratio (P = .016). Both body mass index and waist circumference may be used as markers of intra-abdominal obesity, whereas waist-to-hip ratio was significantly inferior. Correspondingly, both body mass index and waist circumference were better than waist-to-hip ratio to indicate combinations of the 3 nonobese metabolic risk factors.

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.

Aerobic physical fitness in relation to blood lipids and fasting glycaemia in adolescents: influence of weight status

BACKGROUND AND AIMS

We explored the associations between aerobic physical fitness with blood lipids and a composite index of blood lipids and fasting glycaemia in adolescents, analysing possible interactions with weight status.

METHODS AND RESULTS

Body mass index and aerobic physical fitness was measured in 2090 adolescents (1034 males and 1056 females) 13-18.5 years by using the 20-m shuttle run test. Plasma glucose, total, high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol, triglycerides, apolipoprotein (apo) A-I, apo B-100 and lipoprotein(a) [Lp(a)] were measured in 460 of the 2090 subjects. After adjustment for confounding factors, a continuously distributed summary score for blood lipids and fasting glycaemia was significantly related to aerobic fitness in males (P=0.018) and females (P=0.045, from the 2nd to the 4th quartile of aerobic fitness). After adjustment for gender, age, sexual maturation and economic status, aerobic fitness was related to the composite index of blood lipids and glycaemia in both overweight and non-overweight adolescents (P< 0.05). However, for the same level of aerobic fitness, the composite index of blood lipids and glycaemia was significantly higher in overweight adolescents (P=0.001). After setting the minimal aerobic fitness standards to present a healthy lipid profile, about 50% of males did not reach such values.

CONCLUSION

Our data suggest that both aerobic fitness and weight management are associated with a composite index of blood lipids and glycaemia in adolescents. Our study also provides the minimal levels of aerobic physical fitness associated with a favourable lipid profile in male adolescents, a new tool which should be adopted by schools as "aerobic fitness standards".

Birth weight, puberty, and systolic blood pressure in children and adolescents: a longitudinal analysis

We examined the association between birth weight and systolic blood pressure (SBP) from pre-puberty to late puberty in a cohort of American children. Ninety-eight children aged 4-12 years at baseline were followed annually for 2-6 years with at least two Tanner stages. Annual measures included SBP, age, gender, race, birth weight, Tanner stage, and body composition using dual-energy X-ray absorptiometry and computed tomography. Birth weight was inversely correlated with SBP in pre-pubertal children (r=-0.23, P<0.05), especially in white children. SBP persisted at a higher level from pre-puberty through late puberty among children with low birth weight (<2500 g). However, SBP significantly increased from pre-puberty to early or late puberty among children with high birth weight (>or=4000 g). After adjusting for visceral fat, one unit change of birth weight category was associated with a 2.6 mm Hg reduction in SBP (P<0.05), but this association was attenuated as puberty progressed. The changes in SBP across puberty followed different trajectories in children with low vs high birth weight. Attenuation in the association between birth weight and SBP from pre-puberty to late puberty may be influenced by sexual maturation.

Central adiposity is associated with cardiovascular reactivity to stress in adolescents

The current study examined the association between central adiposity, measured by waist circumference, and cardiovascular reactivity to stress among 106 White and 105 Black adolescents, approximately 50% of whom were girls. Participants engaged in 4 laboratory tasks while cardiovascular reactivity measures were taken. Independent of body mass index, race, and gender, participants with a greater waist circumference exhibited greater systolic blood pressure reactivity and diastolic blood pressure reactivity (boys only). Race did not affect the results. Results from the present study suggest that central adiposity is associated with blood pressure reactivity early in life, especially in adolescent boys.

Body mass index and high-density lipoproteins in Cherokee Indian children and adolescents

Native Americans are predisposed to insulin resistance and associated cardiovascular risk. Therefore, we studied whether BMI (body mass index) in a population of Cherokee children and adolescents is associated with HDL-C (HDL cholesterol), and the HDL particles Lp (lipoprotein) A-I and LpA-I:A-II. Subjects were grouped by BMI Z score quartiles within three gender-specific age brackets (5-9, 10-14, and 15-19 y) to examine for trends in lipoprotein and HOMA-IR (homeostasis index insulin resistance) values associated with adiposity and age. HDL-C decreased by BMI Z score quartiles in all three age groups for both genders. HDL-C, LpA-I, and LpA-I:A-II decreased with age in boys but not girls. Log HOMA-IR increased by BMI Z score quartiles in all three age groups for both genders. Linear regression modeling showed BMI Z score, triglyceride, and age to be associated with HDL-C, whereas HOMA-IR was associated with LpA-I:A-II but not with HDL-C or LpA-I. When waist circumference was substituted for BMI Z score in the same models, it was associated with HDL-C and both lipoprotein particles. In conclusion, adiposity is more associated with HDL-C lowering than with declines in the lipoprotein particles. HOMA-IR is less associated with HDL-C but may selectively influence LpA-I:A-II. Greater decreases in HDL-C, LpA-I, and LpA-I:A-II with age in boys is attributed to gender-specific hormonal changes. The early onset of HDL lowering in these Native American children and adolescents, particularly boys, warrants intervention strategies to prevent obesity and associated cardiovascular risk.

Relations of fatness and fitness to fasting insulin in black and white adolescents

OBJECTIVE

To determine in black and white youths the degree to which fatness and cardiovascular fitness (CVF) explained independent proportions of the variance in fasting insulin concentrations.

STUDY DESIGN

Youths 14 to 18 years of age (n = 278) were studied. Insulin was measured after a 12-hour fast. Percent body fat (%BF) was measured with dual-energy x-ray absorptiometry. CVF was determined with a multistage treadmill test.

RESULTS

Girls had higher %BF and lower CVF than boys. Whites were higher in CVF than blacks. There was a race by sex interaction for fasting insulin concentration, such that black girls had the highest and white girls had the lowest concentrations. When %BF and CVF was controlled statistically, this interaction was no longer significant. Multiple regression models that controlled for race, sex, and their interaction showed that (1) both higher %BF and lower CVF were significantly associated with higher insulin concentrations; (2) there were significant interactions with sex, such that the deleterious effects of low CVF and high %BF were greater in boys than in girls; (3) there was a significant CVF-%BF interaction, such that youths who were both fit and lean had especially low insulin concentrations; and (4) sex-specific regressions showed that both %BF and CVF explained significant independent proportion of the insulin variance for the boys but that only %BF did so for the girls.

CONCLUSIONS

Interventions to prevent hyperinsulinemia in youths should be designed both to minimize fatness and maximize CVF.

Childhood obesity in Canada: a review of prevalence estimates and risk factors for cardiovascular diseases and type 2 diabetes

Childhood obesity in Canada has become increasingly prevalent over the past 2 decades. Despite inconsistencies regarding different anthropometric indicators, cut-offs, and reference populations, both regional and national investigations have revealed high numbers of overweight and obese children and adolescents. A number of risk factors and health consequences have been associated with increased levels of body fatness in youth. Specifically, risk factors for cardiovascular diseases (CVD) and type 2 diabetes are known to develop early in life and tend to emerge in clusters among overweight youngsters. Unhealthy lifestyle behaviours (i.e., physical inactivity), a genetic disposition, and a centralized body fat distribution, all contribute to increased risk. In order to prevent future generations of children from experiencing increased morbidity and mortality as overweight and obese adults, coordinated efforts at all levels (family, school, community, and government) must be established with a long-term commitment to promote healthy nutrition and physical activity behaviours in our youth.

Physical training improves insulin resistance syndrome markers in obese adolescents

INTRODUCTION

The purpose of this study was to test the hypothesis that physical training (PT), especially high-intensity PT, would have a favorable effect on components of the insulin resistance syndrome (IRS) in obese adolescents.

METHODS

Obese 13- to 16-yr-olds (N = 80) were randomly assigned to one of the following 8-month interventions; 1) lifestyle education (LSE)-alone every 2 wk, 2) LSE+moderate-intensity PT, and 3) LSE+high-intensity PT. PT was offered 5 d x wk(-1). Plasma triacylglycerol (TAG), total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), very low-density lipoprotein cholesterol (VLDLC), low-density lipoprotein cholesterol (LDLC), low-density lipoprotein (low density lipoprotein (LDL)) particle size, apolipoproteins AI and B, glucose, insulin, and blood pressure were measured with standardized methods.

RESULTS

The intent-to-treat analyses for all subjects who completed pre- and post-tests regardless of their adherence to the interventions showed that the LSE+high-intensity PT group had more favorable changes than the LSE-alone group in TAG level (P = 0.012), TC/HDLC (P = 0.013), and diastolic blood pressure (P = 0.031). For efficacy analyses, all PT subjects who attended at least 2 d x wk(-1) (40%) were combined into one group (LSE+PT) and compared with the LSE-alone group. These two-group analyses showed significant interactions (P < 0.001) between baseline values and group membership for deltaTAG, deltaVLDLC, and deltaTC/HDLC, such that subjects who had the least favorable baseline values showed the most beneficial impact of the PT. Of particular interest was a favorable effect of the PT on LDL particle size.

CONCLUSION

PT, especially high-intensity PT, had a favorable effect on several IRS markers in obese adolescents.

Relations of adiposity and effects of training on the left ventricle in obese youths

PURPOSE

1) To determine the relations of left ventricular (LV) structure and function to total body composition, visceral adipose tissue (VAT), and hemodynamics in obese children; 2) to determine the effects of 4-month of physical training (PT) on LV structure and function and hemodynamics; and 3) to explore determinants of individual variability in response to PT.

METHODS

Measurements included LV structure/function with echocardiography, total body composition with dual-energy x-ray absorptiometry, VAT with magnetic resonance imaging (MRI), and resting and exercising hemodynamics with a Dinamap monitor and Doppler-echocardiography. Youths were randomly assigned to engage in PT for the first or second 4-month periods of the 8-month intervention period.

RESULTS

Correlation and regression at baseline showed that elevated LV mass was associated with excess general and visceral adiposity, and elevated cardiac output. Although the PT had favorable effects on percent body fat and VAT, no significant changes were found in LV or hemodynamic variables. Over the 4-month period of the PT intervention, those who increased the most in VAT tended to increase the most in LV mass.

CONCLUSION

General and visceral adiposity were associated with elevated LV mass. However, no evidence was provided that 4 months of PT had a significant effect on LV or hemodynamic variables.

Obesigenic families: parents' physical activity and dietary intake patterns predict girls' risk of overweight

OBJECTIVE

To determine whether obesigenic families can be identified based on mothers' and fathers' dietary and activity patterns.

METHODS

A total of 197 girls and their parents were assessed when girls were 5 y old; 192 families were reassessed when girls were 7 y old. Measures of parents' physical activity and dietary intake were obtained and entered into a cluster analysis to assess whether distinct family clusters could be identified. Girls' skinfold thickness and body mass index (BMI) were also assessed and were used to examine the predictive validity of the clusters.

RESULTS

Obesigenic and a non-obesigenic family clusters were identified. Mothers and fathers in the obesigenic cluster reported high levels of dietary intake and low levels of physical activity, while mothers and fathers in the non-obesigenic cluster reported low levels of dietary intake and high levels of activity. Girls from families in the obesigenic cluster had significantly higher BMI and skinfold thickness values at age 7 and showed significantly greater increases in BMI and skinfold thickness from ages 5 to 7 y than girls from non-obesigenic families; differences were reduced but not eliminated after controlling for parents' BMI.

CONCLUSIONS

Obesigenic families, defined in terms of parents' activity and dietary patterns, can be used predict children's risk of obesity.

Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents

BACKGROUND

Little is known about how the intensity of exercise influences cardiovascular fitness and body composition, especially in obese adolescents.

OBJECTIVE

Our goal was to determine the effects of physical training intensity on the cardiovascular fitness, percentage of body fat (%BF), and visceral adipose tissue (VAT) of obese adolescents.

DESIGN

Obese 13-16-y-olds (n = 80) were assigned to 1) biweekly lifestyle education (LSE), 2) LSE + moderate-intensity physical training, or 3) LSE + high-intensity physical training. The intervention lasted 8 mo. Physical training was offered 5 d/wk, and the target energy expenditure for all subjects in physical training groups was 1047 kJ (250 kcal)/session. Cardiovascular fitness was measured with a multistage treadmill test, %BF with dual-energy X-ray absorptiometry, and VAT with magnetic resonance imaging.

RESULTS

The increase in cardiovascular fitness in the high-intensity physical training group, but not in the moderate-intensity group, was significantly greater than that in the LSE alone group (P = 0.009); no other comparisons of the 3 groups were significant. Compared with the LSE alone group, a group composed of subjects in both physical training groups combined who attended training sessions >or=2 d/wk showed favorable changes in cardiovascular fitness (P < 0.001), %BF (P = 0.001), and VAT (P = 0.029). We found no evidence that the high-intensity physical training was more effective than the moderate-intensity physical training in enhancing body composition.

CONCLUSIONS

The cardiovascular fitness of obese adolescents was significantly improved by physical training, especially high-intensity physical training. The physical training also reduced both visceral and total-body adiposity, but there was no clear effect of the intensity of physical training.

Left ventricular structure and function in obese adolescents: relations to cardiovascular fitness, percent body fat, and visceral adiposity, and effects of physical training

OBJECTIVE

Little is known about the relations of fitness and fatness to left ventricular structure and function in obese adolescents. This project had 2 purposes: 1) to determine the correlations of cardiovascular fitness and adiposity to left ventricular parameters in obese adolescents; and 2) to see the effect of 8 months of physical training (PT) at low and high intensities.

DESIGN

Obese 13- to 16-year-olds (N = 81) were tested at baseline and then randomly assigned to lifestyle education (LSE) alone, LSE plus moderate-intensity PT, or LSE plus high-intensity PT. Follow-up testing was conducted 8 months later. Because no significant differences were found between moderate-intensity and high-intensity PT, the groups were combined to form a LSE + PT group.

INTERVENTION

Eight months of PT, offered 5 days per week with the target energy expenditure for all PT participants being 250 kcal/session, and LSE every 2 weeks. Outcome Measures. Left ventricular mass divided by height to the 2.7th power (LVM/Ht(2.7)), midwall fractional shortening (MFS), and relative wall thickness (RWT) were measured using M-mode echocardiography. Cardiovascular fitness was measured by a maximal multistage treadmill test; percent body fat (%BF) with dual-energy radiograph absorptiometry; and visceral adipose tissue (VAT) with magnetic resonance imaging.

RESULTS

At baseline, high levels of VAT were associated with higher RWT (r = 0.30) and lesser MFS (r = -0.29). Compared with the LSE-alone group, the LSE + PT group significantly improved in cardiovascular fitness and decreased in %BF and VAT. However, there were no significant differences between groups on changes in LVM/Ht(2.7), MFS, or RWT. Individual changes in cardiovascular fitness, %BF, and VAT did not correlate significantly with interindividual changes in left ventricular structure and function.

CONCLUSIONS

High levels of VAT were associated with unfavorable left ventricular structure and function. However, no evidence was provided that an 8-month PT program, which improved cardiovascular fitness and reduced general and visceral adiposity, improved left ventricular structure and function. Future studies consisting of longer training programs and/or greater weight reductions are needed to see whether the adverse left ventricular effects of obesity can be ameliorated by exercise training.