Subdivisions of subcutaneous abdominal adipose tissue and insulin resistance

Different adipose depots: their role in the development of metabolic syndrome and mitochondrial response to hypolipidemic agents

Adipose tissue metabolism is closely linked to insulin resistance, and differential fat distributions are associated with disorders like hypertension, diabetes, and cardiovascular disease. Adipose tissues vary in their impact on metabolic risk due to diverse gene expression profiles, leading to differences in lipolysis and in the production and release of adipokines and cytokines, thereby affecting the function of other tissues. In this paper, the roles of the various adipose tissues in obesity are summarized, with particular focus on mitochondrial function. In addition, we discuss how a functionally mitochondrial-targeted compound, the modified fatty acid tetradecylthioacetic acid (TTA), can influence mitochondrial function and decrease the size of specific fat depots.

Strategies for reducing body fat mass: effects of liposuction and exercise on cardiovascular risk factors and adiposity

Liposuction is the most popular aesthetic surgery performed in Brazil and worldwide. Evidence showing that adipose tissue is a metabolically active tissue has led to the suggestion that liposuction could be a viable method for improving metabolic profile through the immediate loss of adipose tissue. However, the immediate liposuction-induced increase in the proportion of visceral to subcutaneous adipose tissue could be detrimental to metabolism, because a high proportion of visceral to subcutaneous adipose tissue is associated with risk factors for cardiovascular disease. The results of studies investigating the effects of liposuction on the metabolic profile are inconsistent, however, with most studies reporting either no change or improvements in one or more cardiovascular risk factors. In addition, animal studies have demonstrated a compensatory growth of intact adipose tissue in response to lipectomy, although studies with humans have reported inconsistent results. Exercise training improves insulin sensitivity, inflammatory balance, lipid oxidation, and adipose tissue distribution; increases or preserves the fat-free mass; and increases total energy expenditure. Thus, liposuction and exercise appear to directly affect metabolism in similar ways, which suggests a possible interaction between these two strategies. To our knowledge, no studies have reported the associated effects of liposuction and exercise in humans. Nonetheless, one could suggest that exercise training associated with liposuction could attenuate or even block the possible compensatory fat deposition in intact depots or regrowth of the fat mass and exert an additive or even a synergistic effect to liposuction on improving insulin sensitivity and the inflammatory balance, resulting in an improvement of cardiovascular risk factors. Consequently, one could suggest that liposuction and exercise appear to be safe and effective strategies for either the treatment of metabolic disorders or aesthetic purposes.

Ethnic-specific differences in abdominal subcutaneous adipose tissue compartments

South Asians have a higher prevalence of cardiovascular disease (CVD) than Europeans. Studies have identified distinct subcompartments of subcutaneous adipose tissue (SAT) that provide insight into the relationship between abdominal obesity and metabolic risk factors in different ethnic groups. Our objective was to determine the relationship between SAT compartments and fat-free mass (FFM) between South Asian and European cohorts, and between men and women. Healthy Europeans and South Asians (n = 408) were assessed for FFM via dual energy X-ray absorptiometry, and SAT areas by computed tomography (CT). SAT was subdivided into superficial subcutaneous abdominal adipose tissue (SSAT) and deep subcutaneous abdominal adipose tissue (DSAT). Linear regression analyses were performed using DSAT and SSAT as separate dependent variables and FFM and ethnicity as primary independent variables adjusting for age, gender, income, education, and smoking status. Results showed that South Asian men had significantly higher amounts of DSAT (median 187.65 cm(2) vs. 145.15 cm(2), P < 0.001), SSAT (median 92.0 cm(2) vs. 76.1 cm(2), P = 0.046), and body fat mass (BFM) (25.1 kg vs. 22.6 kg, P = 0.049) than European men. In a fully adjusted model, South Asians showed significantly greater DSAT at any FFM than Europeans. Women had more SSAT at any given FFM than men and less DSAT at any given FFM than men, irrespective of ethnic background. In conclusion, South Asians had more DSAT than Europeans and men had relatively more DSAT than women. These data suggest that specific fat depots are influenced by ethnicity and gender; therefore, could provide insight into the relationship between ethnicity, gender and subsequent risk for CVD.

Subepicardial adipose tissue thickness and its relation with anthropometric and clinical parameters in pubertal obese children

AIM

To determine the relation of echocardiographic subepicardial adipose tissue (SAT) thickness with anthropometric and clinical parameters in pubertal obese children.

SUBJECTS AND METHODS

A total of 52 obese pubertal subjects (13.1±1.56 yr, 27 male patients) and 39 age- and gender-matched lean pubertal subjects (13.0±1.28 yr, 16 male patients) were included in the study. Serum glucose, lipid profile, and insulin levels were measured during the fasting state. Each subject underwent a transthoracic echocardiography and the SAT thickness was measured during end-diastole from the parasternal long-axis views.

RESULTS

The obese pubertal subjects had significantly higher SAT, triceps skin fold (TSF) thickness (mm), waist (WC) and mid-arm circumference (MAC) values (cm) compared with lean pubertal subjects group (p<0.05). Correlation analysis showed that SAT thickness was significantly related with age, SD score-body mass index (SDS-BMI), BMI, WC, MAC, TSF, and homeostasis model assessment of insulin resistance (HOMA-IR) (p<0.05), whereas there was no significant relation of SAT with hip circumference and waist to hip ratio (p>0.05). As an optimal cut-off point, a SAT thickness of 5.25 mm determined IR with 92% sensitivity and 62.1% specificity.

CONCLUSIONS

Our study showed that SAT thickness in obese pubertal children shows a good correlation with age, SDS-BMI, BMI, WC, MAC, TSF, and HOMA-IR. In addition, our results suggest that SAT thickness might be used as a supportive data for risk stratification of metabolic syndrome in obese children.

Adiposity and β-cell function: relationships differ with ethnicity and age

The prevalence of type 2 diabetes is higher among African Americans (AA) vs. European Americans (EA), is highest at middle age, and is related to obesity. This study was conducted to test the hypothesis that the association of adiposity (percent body fat (%fat)) with indexes of insulin sensitivity (S(I)) and β-cell function would differ with ethnicity and age. Subjects were 168 healthy, normoglycemic AA and EA girls and women aged 7-12 years, 18-32 years, and 40-70 years. An intravenous glucose tolerance test (IVGTT) was used to assess indexes of insulin secretion and action: S(I), acute C-peptide secretion (X0); basal, first-phase, second-phase, and total β-cell responsivity to glucose (PhiB, Phi1, Phi2, and Phi(TOT), respectively); and the disposition index (DI = S(I) × Phi(TOT)). %Fat was assessed with dual energy X-ray absorptiometrys. Adiposity was significantly associated with S(I) among EA (-0.57, P < 0.001) but not AA (-0.20, P = 0.09). Adiposity appeared stimulatory to β-cell function in the two groups of younger subjects and in EA, but inhibitory in postmenopausal women, particularly AA postmenopausal women. Among AA postmenopausal women, %fat was inversely associated with Phi1 (r = -0.57, P < 0.05) and Phi(TOT) (r = -0.68, P < 0.01). These results suggest that the impact of adiposity on insulin secretion and action differs with age and ethnicity.

Abdominal subcutaneous and visceral adipose tissue and insulin resistance in the Framingham heart study

Insulin resistance is associated with central obesity and an increased risk of cardiovascular disease. Our objective is to examine the association between abdominal subcutaneous (SAT) and visceral adipose tissue (VAT) and insulin resistance, to determine which fat depot is a stronger correlate of insulin resistance, and to assess whether there was an interaction between SAT, VAT, and age, sex, or BMI. Participants without diabetes from the Framingham Heart Study (FHS), who underwent multidetector computed tomography to assess SAT and VAT (n = 3,093; 48% women; mean age 50.4 years; mean BMI 27.6 kg/m(2)), were evaluated. Insulin resistance was measured using the homeostasis model and defined as HOMA(IR) ≥75th percentile. Logistic regression models, adjusted for age, sex, smoking, alcohol, menopausal status, and hormone replacement therapy use, were used to assess the association between fat measures and insulin resistance. The odds ratio (OR) for insulin resistance per standard deviation increase in SAT was 2.5 (95% confidence interval (CI): 2.2-2.7; P < 0.0001), whereas the OR for insulin resistance per standard deviation increase in VAT was 3.5 (95% CI: 3.1-3.9; P < 0.0001). Overall, VAT was a stronger correlate of insulin resistance than SAT (P < 0.0001 for SAT vs. VAT comparison). After adjustment for BMI, the OR of insulin resistance for VAT was 2.2 (95% CI: 1.9-2.5; P < 0.0001). We observed an interaction between VAT and BMI for insulin (P interaction = 0.0004), proinsulin (P interaction = 0.003), and HOMA(IR) (P interaction = 0.003), where VAT had a stronger association in obese individuals. In conclusion, SAT and VAT are both correlates of insulin resistance; however, VAT is a stronger correlate of insulin resistance than SAT.

IL-17 regulates adipogenesis, glucose homeostasis, and obesity

Inflammatory mediators have the potential to impact a surprising range of diseases, including obesity and its associated metabolic syndrome. In this paper, we show that the proinflammatory cytokine IL-17 inhibits adipogenesis, moderates adipose tissue (AT) accumulation, and regulates glucose metabolism in mice. IL-17 deficiency enhances diet-induced obesity in mice and accelerates AT accumulation even in mice fed a low-fat diet. In addition to potential systemic effects, IL-17 is expressed locally in AT by leukocytes, predominantly by γδ T cells. IL-17 suppresses adipocyte differentiation from mouse-derived 3T3-L1 preadipocytes in vitro, and inhibits expression of genes encoding proadipogenic transcription factors, adipokines, and molecules involved in lipid and glucose metabolism. IL-17 also acts on differentiated adipocytes, impairing glucose uptake, and young IL-17-deficient mice show enhanced glucose tolerance and insulin sensitivity. Our findings implicate IL-17 as a negative regulator of adipogenesis and glucose metabolism in mice, and show that it delays the development of obesity.

Coronary heart disease and body fat distribution

Larger waist circumference or waist-hip ratio, as crude indicators of visceral fat mass, are associated with adverse metabolic profile, but their role in predicting future coronary heart disease (CHD) events has been less investigated. Recent epidemiologic findings suggest that these simple and inexpensive measures of abdominal fat distribution predict CHD independently of body mass index, and, to a certain extent, cardiovascular disease risk factors. The magnitude and shape of the association between abdominal adiposity and CHD have been shown to vary with age, gender, and ethnicity. Studies have also suggested that lower body fat is associated with reduced CHD risk, although the clinical relevance for this finding needs further elucidation. Assessing body fat distribution may be useful for improving CHD risk assessment, although more studies are needed to assess consistency in CHD risk predictions across populations. A consensus is also needed to define the clinically relevant cut-off points for waist circumference or waist-hip ratio.

Visceral fat and adiponectin: associations with insulin resistance are tissue-specific in women

Body fatness and its distribution are strongly and independently associated with peripheral insulin action. However, these associations are limited in their ability to predict the independent nature of hepatic and peripheral insulin resistance, especially in obese women. To define the relationships more precisely between regional fat distribution and adiponectin, and hepatic and peripheral insulin resistance, we studied 22 obese (43 +/- 0.1%) women who underwent a dual-energy X-ray absorptiometry scan and a computed tomography scan at the L4-L5 level. An octreotide (60 ng x kg(-1) x min(-1)), glucagon (0.65 ng x kg(-1) x min(-1)), and two-step insulin (0.25 mU x kg(-1) x min(-1) and 1.0 mU x kg(-1) x min(-1)) infusion was performed to quantify insulin-mediated suppression of hepatic glucose production (SGP) and insulin-stimulated glucose disposal (ISGD) in a simultaneous fashion. Hepatic glucose production (HGP) was measured using a primed, constant infusion of [6,6(2)H(2)] glucose. Mean plasma insulin increased from 5.6 +/- 0.1 microU/mL at baseline to 15.1 +/- 1.5 microU/mL in the first stage, and to 80.7 +/- 0.5 microU/mL in the second stage. Although there was no significant relationship between visceral adipose tissue (VAT) and basal HGP (r = 0.34, p = 0.117), there was a significant inverse correlation (r = -0.67, p = 0.003) between VAT and SGP. There was a significant correlation (r = 0.55, p = 0.008) between adiponectin and ISGD. In conclusion, these data support: (1) the inability of basal glucose metabolism to accurately reflect hepatic insulin resistance, (2) the deleterious role of VAT in the development of insulin resistance in the liver, and (3) provide additional support for the positive influence of adiponectin against peripheral insulin resistance in obese, postmenopausal women.

Glucose metabolism and diet predict changes in adiposity and fat distribution in weight-reduced women

Among obesity-prone individuals, metabolic state may interact with diet in determining body composition. We tested the hypotheses that, among 103 weight-reduced women over 1 year, (i) insulin sensitivity would be positively associated with change in %fat; (ii) this association would be modulated by dietary glycemic load (GL); and (iii) changes in fat distribution would be related to indexes of glucose metabolism. Insulin sensitivity, glucose effectiveness, fasting and postchallenge insulin and glucose, and glucose tolerance were assessed during intravenous glucose tolerance test (IVGTT). Changes in %fat and fat distribution were examined using dual-energy X-ray absorptiometry and computed tomography. Dietary GL was assessed on 67 women using food records. On average, women showed a +5.3 +/- 3.0% change in %fat over 1 year, with the magnitude of this change being greater in relatively insulin sensitive women (+6.0 +/- 0.4%, mean +/- s.e.m.) than in relatively insulin resistant women (+4.4 +/- 0.4 kg; P < 0.05). Women who were relatively insulin sensitive and who consumed a higher GL diet showed a +6.8 +/- 0.7% change in %fat, which was greater than those who were less insulin sensitive, regardless of diet (P < 0.05), but did not differ from women who were relatively insulin sensitive and who consumed a lower GL diet (P = 0.105). Changes in intra-abdominal and deep subcutaneous abdominal fat were inversely associated with the postchallenge decline in serum glucose. In conclusion, greater insulin sensitivity may predispose to adiposity among weight reduced women, an effect that may be ameliorated by a lower GL diet. The potential association between indexes of glucose disposal and changes in fat distribution warrants further study.

The human visceral fat depot has a unique inflammatory profile

Obesity can be considered as a low-grade inflammatory condition, strongly linked to adverse metabolic outcomes. Obesity-associated adipose tissue inflammation is characterized by infiltration of macrophages and increased cytokine and chemokine production. The distribution of adipose tissue impacts the outcomes of obesity, with the accumulation of fat in visceral adipose tissue (VAT) and deep subcutaneous adipose tissue (SAT), but not superficial SAT, being linked to insulin resistance. We hypothesized that the inflammatory gene expression in deep SAT and VAT is higher than in superficial SAT. A total of 17 apparently healthy women (BMI: 29.3 +/- 5.5 kg/m2) were included in the study. Body fat (dual-energy X-ray absorptiometry) and distribution (computed tomography) were measured, and insulin sensitivity, blood lipids, and blood pressure were determined. Inflammation-related differences in gene expression(real-time PCR) from VAT, superficial and deep SAT biopsies were analyzed using univariate and multivariate data analyses. Using multivariate discrimination analysis, VAT appeared as a distinct depot in adipose tissue inflammation,while the SAT depots had a similar pattern, with respect to gene expression. A significantly elevated (P < 0.01)expression of the CC chemokine receptor 2 (CCR2) and macrophage migration inhibitory factor (MIF) in VAT contributed strongly to the discrimination. In conclusion, the human adipose tissue depots have unique inflammatory patterns, with CCR2 and MIF distinguishing between VAT and the SAT depots.

Computed tomography-based validation of abdominal adiposity measurements from ultrasonography, dual-energy X-ray absorptiometry and anthropometry

Large-scale aetiological studies of obesity and its pathological consequences require accurate measurements of adipose mass, distribution and subtype. Here, we compared the validity of three abdominal obesity assessment methods (dual-energy X-ray absorptiometry (DXA), ultrasound and anthropometry) against the gold-standard method of computed tomography (CT) in twenty-nine non-diseased middle-aged men (BMI 26.5 (sd 3.1) kg/m(2)) and women (BMI 25.5 (sd 3.2) kg/m(2)). Assessments of adipose mass (kg) and distribution (total subcutaneous (TSAT), superficial subcutaneous (SSAT), deep subcutaneous (DSAT) and visceral (VAT)) were obtained. Spearman's correlations were performed adjusted for age and sex. VAT area that was assessed using ultrasound (r 0.79; P < 0.0001) and waist circumference (r 0.85; P < 0.0001) correlated highly with VAT from CT, as did BMI (r 0.67; P < 0.0001) and DXA (r 0.70; P < 0.0001). DXA (r 0.72; P = 0.0004), BMI (r 0.71; P = 0.0003), waist circumference (r 0.86; P < 0.0001) and ultrasound (r 0.52; P = 0.015) were less strongly correlated with CT TSAT. None of the comparison measures of DSAT was strongly correlated with CT DSAT (all r approximately 0.50; P < 0.02). BMI (r 0.76; P < 0.0001), waist circumference (r 0.65; P = 0.002) and DXA (r 0.75; P < 0.0001) were all fairly strongly correlated with the CT measure of SSAT, whereas ultrasound yielded a weaker yet statistically significant correlation (r 0.48; P = 0.03). Compared with CT, visceral and subcutaneous adiposity can be assessed with reasonable validity using waist circumference and BMI, respectively. Ultrasound or DXA does not generally provide substantially better measures of these traits. Highly valid assessments of DSAT do not appear to be possible with surrogate measures. These findings may help guide the selection of measures for epidemiological studies of obesity.

Visceral Adiposity Index: a reliable indicator of visceral fat function associated with cardiometabolic risk

OBJECTIVE

To individuate a novel sex-specific index, based on waist circumference, BMI, triglycerides, and HDL cholesterol, indirectly expressing visceral fat function.

RESEARCH DESIGN AND METHODS

Visceral adiposity index (VAI) was first modeled on 315 nonobese healthy subjects. Using two multiple logistic regression models, VAI was retrospectively validated in 1,498 primary care patients in comparison to classical cardio- and cerebrovascular risk factors.

RESULTS

All components of metabolic syndrome increased significantly across VAI quintiles. VAI was independently associated with both cardiovascular (odd ratio [OR] 2.45; 95% CI 1.52-3.95; P < 0.001) and cerebrovascular (1.63; 1.06-2.50; P = 0.025) events. VAI also showed significant inverse correlation with insulin sensitivity during euglycemic-hyperinsulinemic clamp in a subgroup of patients (R(s) = -0.721; P < 0.001). By contrast, no correlations were found for waist circumference and BMI.

CONCLUSIONS

Our study suggests VAI is a valuable indicator of "visceral adipose function" and insulin sensitivity, and its increase is strongly associated with cardiometabolic risk.

The effects of resistance training on metabolic health with weight regain

To determine whether resistance training effectively maintains improvements in cardiometabolic syndrome risk factors during weight regain, 9 individuals lost 4% to 6% of their body weight during an 8- to 12-week diet- and aerobic exercise-induced weight loss phase followed by a controlled weight regain phase (8-12 weeks), during which they regained approximately 50% of the lost weight while participating in a supervised resistance training program. Following weight loss (6.0%+/-0.3%), body mass index, body fat percentage, waist circumference, all abdominal adipose tissue depots, total cholesterol, low-density lipoprotein cholesterol, insulin, and homeostasis model assessment (HOMA) were significantly reduced, while quantitative insulin-sensitivity check index (QUICKI) and cardiorespiratory fitness (maximal oxygen consumption) significantly increased. During weight regain (48.3%+/-3.3% of lost weight), body fat percentage, waist circumference, and maximal oxygen consumption were maintained and muscular strength and lean body mass significantly increased. Abdominal adipose tissue depots, insulin, HOMA, and QUICKI did not significantly change after weight regain. Resistance training was effective in maintaining improvements in metabolic health during weight regain.

Metabolic changes following a 1-year diet and exercise intervention in patients with type 2 diabetes

OBJECTIVE

To characterize the relationships among long-term improvements in peripheral insulin sensitivity (glucose disposal rate [GDR]), fasting glucose, and free fatty acids (FFAs) and concomitant changes in weight and adipose tissue mass and distribution induced by lifestyle intervention in obese individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We measured GDR, fasting glucose, and FFAs during a euglycemic clamp and adipose tissue mass and distribution, organ fat, and adipocyte size by dual-energy X-ray absorptiometry, CT scan, and adipose tissue biopsy in 26 men and 32 women in the Look-AHEAD trial before and after 1 year of diet and exercise aimed at weight loss.

RESULTS

Weight and fasting glucose decreased significantly (P < 0.0001) and significantly more in men than in women (-12 vs. -8% and -16 vs. -7%, respectively; P < 0.05), while FFAs during hyperinsulinemia decreased and GDR increased significantly (P < 0.00001) and similarly in both sexes (-53 vs. -41% and 63 vs. 43%; P = NS). Men achieved a more favorable fat distribution by losing more from upper compared with lower and from deeper compared with superficial adipose tissue depots (P < 0.01). Decreases in weight and adipose tissue mass predicted improvements in GDR but not in fasting glucose or fasting FFAs; however, decreases in FFAs during hyperinsulinemia significantly determined GDR improvements. Hepatic fat was the only regional fat measure whose change contributed independently to changes in metabolic variables.

CONCLUSIONS

Patients with type 2 diabetes undergoing a 1-year lifestyle intervention had significant improvements in GDR, fasting glucose, FFAs and adipose tissue distribution. However, changes in overall weight (adipose tissue mass) and hepatic fat were the most important determinants of metabolic improvements.

Exercise and the metabolic syndrome with weight regain

Weight loss improves metabolic syndrome (MetS) factors, but risk may return with weight regain. This study was designed to determine if exercise training can maintain improvements in MetS risk factors during weight regain. In a randomized control trial,102 overweight or obese (body mass index 25.0-39.9 kg/m(2)) men and women (age 21-52 yr), with characteristics of the MetS, lost 10% of body weight with supervised walking/jogging at 60% of maximal oxygen consumption (Vo(2 max)) (-400 kcal/session), 5 days/wk, and caloric restriction (-600 kcal/day) over a 4- to 6-mo period. After weight loss, 77 remaining subjects underwent programmed weight regain (+50% of lost weight) for 4-6 mo with random assignment to two groups: no exercise (NoEX) or continued supervised exercise (EX). Blood pressure, regional fat, glucose homeostasis, lipids, and inflammatory markers were assessed at baseline, post-weight loss, and post-weight regain. Groups were compared by two-way repeated-measures ANOVA on the 67 subjects. After weight loss (9.7 +/- 0.2% of body weight), significant (P < 0.05) improvements were observed in almost all parameters assessed. Following weight regain (54.4 +/- 1.6% of lost weight), the NoEX group exhibited deterioration in most metabolic markers, while the EX group maintained improvements in Vo(2 max), blood pressures, glucose homeostasis, high- and low-density lipoprotein cholesterol (HDL-C and LDL-C), oxidized LDL, and other markers of inflammation, but did not maintain improvements in triglyceride and cholesterol concentrations or abdominal fat. Results of this design of controlled human weight regain suggest that aerobic exercise can counter the detrimental effects of partial weight regain on many markers of disease risk.

Aging and regional differences in fat cell progenitors - a mini-review

Fat mass and fat tissue distribution change dramatically throughout life. In old age, fat becomes dysfunctional and is redistributed from subcutaneous to intra-abdominal visceral depots as well as other ectopic sites, including bone marrow, muscle and the liver. These changes are associated with increased risk of metabolic syndrome. Fat tissue is a nutrient storage, endocrine and immune organ that undergoes renewal throughout the lifespan. Preadipocytes, which account for 15-50% of cells in fat tissue, give rise to new fat cells. With aging, declines in preadipocyte proliferation and differentiation likely contribute to increased systemic exposure to lipotoxic free fatty acids. Age-related fat tissue inflammation is related to changes that occur in preadipocytes and macrophages in a fat depot-dependent manner. Fat tissue inflammation frequently leads to further reduction in adipogenesis with aging, more lipotoxicity and activation of cellular stress pathways that, in turn, exacerbate inflammatory responses of preadipocytes and immune cells, establishing self-perpetuating cycles that lead to systemic dysfunction. In this review, we will consider how inherent, age-related, depot-dependent alterations in preadipocyte function contribute to age-related fat tissue redistribution and metabolic dysfunction.

Dietary predictors of visceral adiposity in overweight young adults

The purpose of the present study was to determine the dietary predictors of visceral adipose tissue (VAT) area in overweight young adults. A total of 109 young adults (fifty males and fifty-nine females) ate ad libitum in a university cafeteria for 14 d. All food and beverages consumed in the cafeteria were measured using observer-recorded weighed plate waste. Food consumption outside the cafeteria (i.e. snacks) was assessed by multiple-pass 24 h recall procedures. VAT was determined using computed tomography. Stepwise regression demonstrated that the best predictor of visceral adiposity in women was total dietary fat (P <or= 0.05). In men, the model for predicting visceral adiposity included Ca and total dietary fat. We concluded that total dietary fat is the best predictor of VAT area in both men and women. While this relationship was independent in women, in men there was a synergistic relationship between dietary fat consumption and Ca consumption in predicting VAT.

Adipose tissue, metabolic syndrome and polycystic ovary syndrome: from pathophysiology to treatment

In the last few years, polycystic ovary syndrome (PCOS) has deserved major attention because it is linked to the same cluster of events that promote the metabolic syndrome. This review will point out the relationships between fat excess, insulin resistance and the metabolic syndrome. Adipocytes are actually considered as endocrine cells that synthesize and release molecules (adipokines) that play an endocrine/paracrine role, such as adiponectin, atrial natriuretic peptide, leptin, resistin, tumour necrosis factor alpha (TNFalpha). Metabolic syndrome is a chronic low-grade inflammatory condition in which adipokines play a major role. Isolated adipocytes from women with PCOS express higher mRNA concentrations of some adipokines involved in cardiovascular risk and insulin resistance. However, environmental factors and lifestyle play a major role in determining the appearance of the phenotypes of PCOS. In morbid obese women with PCOS, bariatric surgery decreases bodyweight and fat excess and reverses hyperandrogenism and sterility. In lean or overweight women with PCOS, changes in lifestyle in combination with drugs reducing visceral fat and insulin resistance reverse the symptoms and signs of PCOS. Promising treatments for PCOS seem to be insulin sensitizers such as metformin and glitazones.

Subcutaneous rather than visceral adipose tissue is associated with adiponectin levels and insulin resistance in young men

INTRODUCTION

Studies on the association between adiponectin, body composition, and insulin resistance (IR) have been conflicting.

AIM

Our aim was to evaluate the impact of body composition on adiponectin and IR determined by homeostasis model assessment (HOMA) in a population-based study on relatively healthy young men, minimizing the possible effects of age, obesity, and severe comorbidity. DESIGN, METHODS, AND SUBJECTS: A population-based, cross-sectional study of 783 men aged 20-29 yr, randomly drawn from the Danish Central Personal Registry. Adiponectin was assessed using an in-house assay, and IR was determined using HOMA. Central fat mass (CFM) and lower extremity fat mass (LEFM) was measured by dual-energy x-ray absorptiometry, and visceral adipose tissue (VAT), sc adipose tissue (SAT), and thigh fat area (TFA) were assessed by magnetic resonance imaging.

RESULTS

Using multiple linear regression analysis, adiponectin correlated negatively with CFM (r = -0.27; P < 0.001) and SAT (r = -0.20; P < 0.001) and positively with LEFM (r = 0.19; P < 0.001) and TFA (r = 0.18; P < 0.001), whereas VAT did not associate significantly. In multiple linear regression analysis, HOMA-IR (dependent variable), correlated significantly with CFM (r = 0.27; P < 0.001) and SAT (r = 0.15; P < 0.001), whereas LEFM, VAT, or TFA did not correlate. Adiponectin was an independent predictor of HOMA-IR in both analyses (r = -0.14; P < 0.001).

CONCLUSION

SAT rather than VAT was inversely associated with adiponectin levels, and, interestingly, fat on the lower extremities was positively associated with adiponectin. Focusing on insulin resistance, SAT rather than VAT and TFA independently predicted a higher HOMA-IR. The observation that adiponectin was independently associated with lower HOMA-IR must be repeated in other populations.

Subcutaneous adipose tissue topography and metabolic disturbances in polycystic ovary syndrome

OBJECTIVE

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder affecting women of reproductive age. Central obesity plays a major role in the pathophysiology of PCOS. However, there is little information on the impact of subcutaneous adipose tissue (SAT) on metabolic disturbances in PCOS. The aim of this study was to investigate whether SAT topography influences insulin resistance, impaired glucose tolerance and metabolic parameters in women with PCOS.

METHODS

36 women aged 16-41 years with PCOS and 87 healthy women aged 20-34 years were examined using lipometry, metabolic and hormonal measurements, oral glucose tolerance tests, hirsutism scores, and questionnaires. The homeostasis model assessment (HOMA) index was used for determination of insulin resistance.

RESULTS

SAT measurement points on the trunk showed significant positive correlation with the HOMA index. A negative correlation between calf SAT and the HOMA index was seen. Multiple regression analysis detected a positive association between the HOMA index and lower-abdomen SAT and upper-back SAT, whereas hip SAT showed a negative association with the HOMA index. In overweight/obese patients with PCOS, lower-abdomen and upper-back SAT showed significant positive correlations with insulin resistance. There was no correlation of SAT topography with insulin resistance in lean women with PCOS. Compared with PCOS women with normal glucose tolerance, patients with glucose intolerance had significantly increased trunk obesity and decreased leg fat. Increased SAT layers on the trunk were related to an unfavorable serum lipid profile, whereas increased leg fat correlated positively with HDL cholesterol.

CONCLUSIONS

Increased SAT layers on the trunk are associated with insulin resistance, impaired glucose tolerance and an unfavorable lipid profile in women suffering from PCOS. Increased thickness of leg SAT emerges as being protective against metabolic disturbances in PCOS.

Obesity, abdominal obesity, and insulin resistance

The correlation of body mass index (BMI) with both adiposity and risk for type 2 diabetes mellitus (DM) is positive. An elevated BMI is also associated with increased mortality from cardiovascular disease (CVD). However, for any given BMI measurement, some persons are at risk for type 2 DM and CVD, while others are not. This disparity of risk may relate to differences in age, fitness, and body composition, including body fat. Obesity- excess body fat- is associated with insulin resistance. Abdominal obesity, in particular, places people at higher risk for developing insulin resistance and, consequently, is associated with an increased risk for type 2 DM and CVD. The association between obesity and insulin resistance is largely due to changes in the function of adipose tissue, specifically, increased release of free fatty acids and abnormalities in adipokine secretion. The properties of visceral adipose tissue may cause these dysfunctions to become magnified. Weight loss has the potential to improve insulin sensitivity through alterations in adipose tissue function.

Effect of food restriction on adipose tissue in spontaneously diabetic Torii fatty rats

Spontaneously Diabetic Torii-fa/fa (SDT fatty) rat is a new model of obese type 2 diabetes. SDT fatty rat exhibits obesity associated with hyperphagia. In this study, SDT fatty rats were subjected to pair-feeding with SDT-+/+ (SDT) rats from 6 to 22 weeks of age. The ratio of visceral fat weight to subcutaneous fat weight (V/S) decreased at 12 weeks of age in the pair-feeding rats. The intraperitoneal fat weight such as epididymal and retroperitoneal fat weight decreased, whereas mesenteric fat weight had no change. Cell size of the epididymal fat in the pair-feeding rats tended to decrease. Glucose oxidation level in epididymal fat in the pair-feeding rats at 12 weeks of age was recovered to a similar level with that in SDT rats. These results indicated that SDT fatty rat is a useful model to evaluate the functional or the morphological features in adipose tissue and develop a novel drug for antiobesity.

Differential effects of abdominal adipose tissue distribution on insulin sensitivity in black and white South African women

Black South African women are more insulin resistant than BMI-matched white women. The objective of the study was to characterize the determinants of insulin sensitivity in black and white South African women matched for BMI. A total of 57 normal-weight (BMI 18-25 kg/m(2)) and obese (BMI > 30 kg/m(2)) black and white premenopausal South African women underwent the following measurements: body composition (dual-energy X-ray absorptiometry), body fat distribution (computerized tomography (CT)), insulin sensitivity (S(I), frequently sampled intravenous glucose tolerance test), dietary intake (food frequency questionnaire), physical activity (Global Physical Activity Questionnaire), and socioeconomic status (SES, demographic questionnaire). Black women were less insulin sensitive (4.4 +/- 0.8 vs. 9.5 +/- 0.8 and 3.0 +/- 0.8 vs. 6.0 +/- 0.8 x 10(-5)/min/(pmol/l), for normal-weight and obese women, respectively, P < 0.001), but had less visceral adipose tissue (VAT) (P = 0.051), more abdominal superficial subcutaneous adipose tissue (SAT) (P = 0.003), lower SES (P < 0.001), and higher dietary fat intake (P = 0.001) than white women matched for BMI. S(I) correlated with deep and superficial SAT in both black (R = -0.594, P = 0.002 and R = 0.495, P = 0.012) and white women (R = -0.554, P = 0.005 and R = -0.546, P = 0.004), but with VAT in white women only (R = -0.534, P = 0.005). In conclusion, body fat distribution is differentially associated with insulin sensitivity in black and white women. Therefore, the different abdominal fat depots may have varying metabolic consequences in women of different ethnic origins.

Gender differences in insulin resistance, body composition, and energy balance

BACKGROUND

Men and women differ substantially in regard to degrees of insulin resistance, body composition, and energy balance. Adipose tissue distribution, in particular the presence of elevated visceral and hepatic adiposity, plays a central role in the development of insulin resistance and obesity-related complications.

OBJECTIVE

This review summarizes published data on gender differences in insulin resistance, body composition, and energy balance, to provide insight into novel gender-specific avenues of research as well as gender-tailored treatments of insulin resistance, visceral adiposity, and obesity.

METHODS

English-language articles were identified from searches of the PubMed database through November 2008, and by reviewing the references cited in these reports. Searches included combinations of the following terms: gender, sex, insulin resistance, body composition, energy balance, and hepatic adipose tissue.

RESULTS

For a given body mass index, men were reported to have more lean mass, women to have higher adiposity. Men were also found to have more visceral and hepatic adipose tissue, whereas women had more peripheral or subcutaneous adipose tissue. These differences, as well as differences in sex hormones and adipokines, may contribute to a more insulin-sensitive environment in women than in men. When normalized to kilograms of lean body mass, men and women had similar resting energy expenditure, but physical energy expenditure was more closely related to percent body fat in men than in women.

CONCLUSION

Greater amounts of visceral and hepatic adipose tissue, in conjunction with the lack of a possible protective effect of estrogen, may be related to higher insulin resistance in men compared with women.

Abdominal subcutaneous adipose tissue: a protective fat depot?

OBJECTIVE

Obesity is associated with increased metabolic and cardiovascular risk. The ectopic fat hypothesis suggests that subcutaneous fat may be protective, but this theory has yet to be fully explored.

RESEARCH DESIGN AND METHODS

Participants from the Framingham Heart Study (n = 3,001, 48.5% women) were stratified by visceral adipose tissue (VAT) into sex-specific tertiles. Within these tertiles, age-adjusted abdominal subcutaneous adipose tissue (SAT) tertiles were examined in relation to cardiometabolic risk factors.

RESULTS

In the lowest VAT tertile, risk factor prevalence was low, although systolic blood pressure in women and rates of high triglycerides, impaired fasting glucose, hypertension, and the metabolic syndrome in men increased with increasing SAT tertile (all P < 0.04). In contrast, in the top VAT tertile, lower triglycerides were observed in men with increasing SAT (64.4% high triglycerides in SAT tertile 1 vs. 52.7% in SAT tertile 3, P = 0.03). Similar observations were made for women, although results were not statistically significant (50.6% high triglycerides in SAT tertile 1 vs. 41.0% in tertile 3, P = 0.10). Results in the highest VAT tertile were notable for a lack of increase in the prevalence of low HDL in men and women and in rates of impaired fasting glucose in men with increasing subcutaneous fat, despite sizable differences in BMI across SAT tertiles (27.1 to 36.3 kg/m(2)[women]; 28.1 to 35.7 kg/m(2)[men]).

CONCLUSIONS

Although adiposity increases the absolute risk of metabolic and cardiovascular disease, abdominal subcutaneous fat is not associated with a linear increase in the prevalence of all risk factors among the obese, most notably, high triglycerides.

Relation of abdominal fat depots to systemic markers of inflammation in type 2 diabetes

OBJECTIVE

Both visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) have been linked to systemic inflammation in nondiabetic cohorts. We examined the relationships between VAT and SAT and systemic inflammatory markers in a large well-characterized cohort of subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Three hundred eighty-two subjects with type 2 diabetes in the CHICAGO (Carotid Intima-Media Thickness in Atherosclerosis Using Pioglitazone) study cohort underwent abdominal computed tomography to determine SAT and VAT distribution. Fasting blood was obtained for measurement of inflammatory markers. The relationships between inflammatory markers and BMI, SAT, and VAT were examined using regression models adjusted for age, sex, diabetes treatment, duration of diabetes, smoking, statin use, and A1C.

RESULTS

VAT was positively related to CRP, monocyte chemoattractant protein (MCP), intracellular adhesion molecule (ICAM)-1, and plasminogen activator inhibitor type 1 (PAI-1) antigen before adjustment for BMI. After adjustment for BMI, the relationship to CRP was lost but positive associations with MCP (P < 0.01), PAI-1 (P < 0.0001), ICAM-1 (P < 0.01), and vascular cell adhesion molecule (P = 0.01) were evident. BMI was positively related to CRP (P < 0.0001) and IL-6 (P < 0.01) even after adjustment for VAT and SAT. SAT was not related to any inflammatory marker after adjustment for BMI.

CONCLUSIONS

In this large group of subjects with type 2 diabetes, BMI was most strongly associated with CRP and IL-6 levels. SAT was not associated with markers of systemic inflammation. The size of the VAT depot provided information additional to that provided by BMI regarding inflammatory markers that are strongly related to vascular wall remodeling and coagulation. Our findings suggest that adipose tissue distribution remains an important determinant of systemic inflammation in type 2 diabetes.

Impact of abdominal fat and insulin resistance on arterial hypertension in non-obese women

OBJECTIVE: To evaluate the impact of abdominal fat and insulin resistance on arterial hypertension of non-obese women. METHODS:Thirty-five non-obese women (NO), age 35-68 years were studied, and divided into two groups according to the presence of hypertension (BP > 140 x 90 mmHg) ( HT = hypertensive; NT = normotensive). Leptin measurement and oral glucose tolerance test (OGTT) to assess insulin were performed in these patients. A CT-scan was used to evaluate visceral (VF) and subcutaneous abdominal fat (SCF). The Central fat distribution index (CDI) was proposed to evaluate the impact of subcutaneous abdominal fat on central fat distribution in hypertensive patients. RESULTS: When compared to NT-NO (n = 17) group, HT-NO (n = 18) showed higher blood pressure levels (systolic and diastolic), greater VF area (84.40 ± 55.70 versus 37.50 ± 23.00 cm²; p = 0.036), greater SCF area (174.30 ± 83.00 versus 79.80 ± 27.40 cm²; p = 0.030), higher HOMAr index (1.59 ± 0.72 versus 0.93 ± 0.48 mmol.mU/L²; p = 0.006), higher CDI index (12.67 ± 7.04 versus 6.19 ± 2.57 cm²/kg) and higher leptin level (19.1 ± 9.6 versus 7.4 ± 3.5 ng/mL; p = 0.028). CONCLUSIONS: Arterial hypertension in non-obese women is associated with insulin resistance, central fat distribution and higher leptin levels.

Insulin sensitivity in African-American and white women: association with inflammation

Whether the contribution of inflammation to risk for chronic metabolic disease differs with ethnicity is not known. The objective of this study was to determine: (i) whether ethnic differences exist in markers of inflammation and (ii) whether lower insulin sensitivity among African Americans vs. whites is due to greater inflammatory status. Subjects were African-American (n = 108) and white (n = 105) women, BMI 27-30 kg/m(2). Insulin sensitivity was assessed with intravenous glucose tolerance test and minimal modeling; fat distribution with computed tomography; body composition with dual-energy X-ray absorptiometry; markers of inflammation (tumor necrosis factor (TNF)-alpha, soluble tumor necrosis factor receptor (sTNFR)-1, sTNFR-2, C-reactive protein (CRP), and interleukin (IL)-6) with enzyme-linked immunosorbent assay (ELISA). Whites had greater intra-abdominal adipose tissue (IAAT), insulin sensitivity, and concentrations of TNF-alpha, sTNFR-1, and sTNFR-2 than African Americans. Greater TNF-alpha in whites vs. African Americans was attributed to greater IAAT in whites. Among whites, but not African Americans, CRP was independently and inversely associated with insulin sensitivity, after adjusting for IAAT (r = -0.29 P < 0.05, and r = -0.13 P = 0.53, respectively). Insulin sensitivity remained lower in African Americans after adjusting for CRP (P < 0.001). In conclusion, greater IAAT among whites may be associated with greater inflammation. Insulin sensitivity was lower among African Americans, independent of obesity, fat distribution, and inflammation.

Sagittal abdominal diameter is more predictive of cardiovascular risk than abdominal fat compartments in severe obesity

OBJECTIVE

To compare the predictive role of abdominal fat distribution by computed tomography (CT) with that of total abdominal fat by sagittal abdominal diameter (SAD) on cardiovascular risk in severe obesity.

DESIGN

A cross-sectional, clinical study.

SUBJECTS

64 males and 64 females, aged 42+/-15 years (mean+/-s.d.; range 18-75 years), BMI (kg/m(2)) 41.7+/-5.3 (30.2-57.6).

MEASUREMENTS

Blood glucose, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides (TGLs), insulin (IRI), insulin resistance (HOMA-IR), slice areas (cm(2)) of total (tSAT), superficial (sSAT) and deep subcutaneous adipose tissue (dSAT), visceral adipose tissue (VAT) and SAD (mm) by CT.

RESULTS

The sSAT depot was negatively associated with blood glucose, HOMA-IR, LDL cholesterol and TGLs, whereas dSAT was negatively associated with HDL cholesterol. VAT was associated with blood glucose and HOMA-IR, whereas SAD was associated with all variables evaluated. In males, VAT was associated with blood glucose (r(2)=0.12, P<0.01), SAD was associated with blood glucose (r(2)=0.67, P<0.01), IRI (r(2)=0.65, P<0.05), and HOMA-IR (r(2)=0.67, P<0.01). In females, sSAT was negatively associated with blood glucose (r(2)=0.63, P<0.05), whereas VAT was associated positively with blood glucose (r(2)=0.21, P< 0.001), total cholesterol (r(2)=0.16, P<0.01), LDL cholesterol (r(2)=0.20, P<0.001) and TGLs (r(2)=0.12, P<0.01). SAD was associated positively with IRI (r(2)=0.52, P<0.05), HOMA-IR (r(2)=0.53, P<0.05), total cholesterol (r(2)=0.52, P<0.05), LDL cholesterol (r(2)=0.54, P<0.01), TGLs (r(2)=0.52, P<0.05) and negatively to HDL cholesterol (r(2)=0.51, P<0.001).

CONCLUSION

When compared with CT-based measures of abdominal fat compartments, SAD is a more predictive indicator of cardiovascular risk in severe obesity.

Short-term metabolic and cardiovascular effects of metformin in markedly obese adolescents with normal glucose tolerance

OBJECTIVE

Although metformin (MET) is an insulin sensitizer currently used as an adjunct to the treatment of some of the complications of childhood obesity besides type 2 diabetes mellitus, few studies have comprehensively examined its metabolic and clinical effects in obese children with normal glucose tolerance (NGT).

METHODS

We therefore conducted a 4-month double-blind clinical trial in 28 obese [mean body mass index (BMI): 40.3 +/- 5.7 kg/m(2)], insulin-resistant [homeostasis model assessment - insulin resistance: 7.6 +/- 2.8 and whole body insulin sensitivity index (WBISI): 1.5 +/- 0.7] adolescents (age 15.0 +/- 1.3 yr) randomized to MET (n = 15, dose 1500 mg daily) or placebo (n = 13).

RESULTS

The treatment with MET was well tolerated. MET treatment was associated with a decreased BMI (p = 0.02) as well as with a reduction in subcutaneous fat (p = 0.03), particularly the deep subcutaneous fat (p = 0.04) as assessed by magnetic resonance imaging. Postintervention, the MET group had a 35% improvement in insulin sensitivity (WBISI) compared with the placebo group (p = 0.008). However, significance was lost with adjustments for differences in baseline insulin sensitivity (p = 0.09). While there was no change in inflammatory cytokines or lipid parameters, cardiovascular function as assessed by heart rate recovery after exercise improved with MET and worsened in placebo (p = 0.03).

CONCLUSION

Short-term use of MET is well tolerated by obese children with NGT and has a beneficial effect on BMI and autonomic control of the heart as well as a trend toward improved insulin sensitivity. Thus, long-term treatment with MET may provide a means to ameliorate the cardio-metabolic consequences of adolescent obesity.

New computed tomography-derived indices to predict cardiovascular and insulin-resistance risks in overweight/obese patients

OBJECTIVE

To determine whether a series of new computed tomography (CT)-derived indices are better diagnostic criteria than the classical CT-derived measurements. A second objective is to propose specific or sensitive threshold values of the most accurate criteria for the occurrence of metabolic disturbances.

SUBJECTS/METHODS

Anthropometric measurements and CT scans were performed in 74 obese subjects. Fat thicknesses, diameters, diagonals and areas were determined. Plasma lipids, insulin, glucose and fat cell size were analyzed. A multivariate regression analysis was performed to determine the most accurate predictor index for metabolic alterations explaining the highest percentage of variance.

RESULTS

All the new indices were highly correlated with body mass index, percentage of fat and fat cell size. Subcutaneous thicknesses were greater in women, while internal-coronal and sagittal diameters, visceral adipose tissue (VAT) and internal circumference area were greater in men (P<0.001). Those observations were reinforced by the adipocyte size in both fat depots. Subcutaneous parameters showed the strongest correlation with metabolic alterations, being positively associated with metabolic risk in women and negatively in men. Multivariate regression analysis showed that the best predictor index was the superficial subcutaneous adipose tissue (SSAT) and its relation to visceral area (SSAT/VAT), explaining 42% of total variance for high-density lipoprotein-cholesterol in men and 26% for homeostasis model assessment in women. After receiver operating characteristic-curves analysis, three threshold values for both sexes were proposed to select the most appropriate depending on the clinical situation.

CONCLUSION

For the first time, we have described SSAT and the SSAT/VAT ratio as important indices in obesity-related disturbances.

Independent and opposite associations of hip and waist circumference with metabolic syndrome components and with inflammatory and atherothrombotic risk factors in overweight and obese women

Recent studies have shown independent and opposite associations of hip circumference (HC) and waist circumference (WC) with glucose intolerance, insulin resistance, and type 2 diabetes mellitus. However, no studies have simultaneously considered the independent contributions of both markers to metabolic proinflammatory and atherosclerotic risk factors. In this study, we examine the independent associations of WC and HC with metabolic syndrome and with proinflammatory and atherothrombotic features. Independent associations of thigh muscle and adipose tissue (AT) compartments with metabolic features were also studied. Abdominal and thigh muscle and AT distributions were assessed by computed tomography in 140 overweight and obese women (mean +/- SD: age, 38.3 +/- 0.5 years; body mass index, 30.4 +/- 0.3 kg/m(2)). Blood lipids and inflammatory and atherothrombotic markers were measured. For a given WC, a larger HC was inversely associated with fasting insulin (beta = -0.288, P = .008), hemoglobin A(1c) (beta = -0.246, P = .041), and plasminogen activator inhibitor-1 concentrations (beta = -0.241, P = .023). Contrarily, WC was related with an unfavorable metabolic profile. For a given WC, higher total thigh AT and total thigh subcutaneous AT masses were associated with lower hemoglobin A(1c) (beta = -0.244, P = .049; beta = -0.233, P = .049) and low-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (beta = -0.252, P = .040; beta = -0.245, P = .037). In addition, total thigh AT was related with leptin (beta = 0.310, P = .012), whereas total thigh subcutaneous AT revealed opposite associations with fasting insulin concentrations (beta = -0.239, P = .034). Total thigh muscular tissue mass was related with lower plasminogen activator inhibitor-1 (beta = -0.164, P = .049) and fibrinogen concentrations (beta = -0.222, P = .018). In conclusion, HC revealed independent and opposite associations with insulin resistance and atherothrombotic disturbances. Contrarily, a larger WC predicted an increased metabolic risk. These contrasting effects in diabetogenic and atherothrombotic disturbances were, respectively, mediated by gluteofemoral AT and thigh muscle tissue. Besides body mass index and WC screening relevance, HC can contribute to additionally predict health risk in overweight and obese women.

Distribution of subcutaneous fat predicts insulin action in obesity in sex-specific manner

The pattern of adipose tissue (AT) distribution is an important predictor of metabolic risk. The aim of this study was to analyze the association of peripheral (insulin-mediated glucose disposal--M) and hepatic (suppression of endogenous glucose production--EGP) insulin action with abdominal (subcutaneous abdominal AT-SAAT intraabdominal AT-IAAT) and thigh AT depots in obese individuals. Fifty-seven Pima Indians with normal glucose tolerance underwent magnetic resonance imaging (MRI) and euglycemic-hyperinsulinemic clamp. M was negatively related to intraperitoneal IAAT (P = 0.02) and deep SAAT (P = 0.03). Suppression of EGP was negatively related to total (P < 0.05) or deep SAAT (P < 0.05 and P = 0.01, respectively), and total or intraperitoneal IAAT (P = 0.009 and P = 0.002, respectively). A significant interaction with sex was found in the association between superficial SAAT and M, so that in women, but not men, M negatively correlated with superficial SAAT (P = 0.02). In stepwise regression analysis, both M (r2 = 0.09) and EGP suppression (r2 = 0.17) were associated only with intraperitoneal IAAT in the whole group. In the sex-specific analysis (because of the significant interaction), lower M was associated with higher deep SAAT (r2 = 0.15) in combination with lower superficial SAAT (r2 = 0.09) in men, and with higher superficial SAAT (r2 = 0.29) in combination with lower thigh subcutaneous AT (r2 = 0.16) in women. Although intraperitoneal IAAT and deep SAAT were major predictors of peripheral and hepatic insulin action in obese Pima Indians, the largest variance in M rate was explained in a sex-specific manner by relative size of subcutaneous AT depots.

Insulin resistance: the link between obesity and cardiovascular disease

Insulin-mediated glucose disposal varies at least sixfold in apparently healthy individuals. The adverse effect of decreases in the level of physical fitness on insulin sensitivity is comparable to the untoward impact of excess adiposity, with each accounting for approximately 25% of the variability of insulin action. It is the loss of insulin sensitivity that explains why obese individuals are more likely to develop cardiovascular disease, but not all overweight/obese individuals are insulin resistant. At a clinical level, it is important to identify those overweight individuals who are also insulin resistant and to initiate the most intensive therapeutic effort in this subgroup. Finally, it appears that the adverse impact of overall obesity, as estimated by body mass index, is comparable to that of abdominal obesity, as quantified by waist circumference.

Subcutaneous abdominal adipose tissue subcompartments: potential role in rosiglitazone effects

Abdominal visceral tissue (VAT) and subcutaneous adipose tissue (SAT), comprised of superficial-SAT (sSAT) and deep-SAT (dSAT), are metabolically distinct. The antidiabetic agents thiazolidinediones (TZDs), in addition to their insulin-sensitizing effects, redistribute SAT suggesting that TZD action involves adipose tissue depot-specific regulation. We investigated the expression of proteins key to adipocyte metabolism on differentiated first passage (P1) preadipocytes treated with rosiglitazone, to establish a role for the diverse depots of abdominal adipose tissue in the insulin-sensitizing effects of TZDs. Adipocytes and preadipocytes were isolated from sSAT, dSAT, and VAT samples obtained from eight normal subjects. Preadipocytes (P1) left untreated (U) or treated with a classic differentiation cocktail (DI) including rosiglitazone (DIR) for 9 days were evaluated for strata-specific differences in differentiation including peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and lipoprotein lipase (LPL) expression, insulin sensitivity via adiponectin and glucose transport-4 (GLUT4), glucocorticoid metabolism with 11 beta-hydroxysteroid dehydrogenase type-1 (11 beta HSD1), and alterations in the adipokine leptin. While depot-specific differences were absent with the classic differentiation cocktail, with rosiglitazone sSAT had the most potent response followed by dSAT, whereas VAT was resistant to differentiation. With rosiglitazone, universal strata effects were observed for PPAR-gamma, LPL, and leptin, with VAT in all cases expressing significantly lower basal expression levels. Clear dSAT-specific changes were observed with decreased intracellular GLUT4. Specific sSAT alterations included decreased 11 beta HSD1 whereas secreted adiponectin was potently upregulated in sSAT with respect to dSAT and VAT. Overall, the subcompartments of SAT, sSAT, and dSAT, appear to participate in the metabolic changes that arise with rosiglitazone administration.

Regional body fat distribution and metabolic profile in postmenopausal women

The aim of the study was to examine how body fat distribution variables were associated with metabolic parameters in a sample of 113 postmenopausal women not receiving hormone therapy (56.9 +/- 4.4 years, 28.4 +/- 5.1 kg/m(2)). Body fat distribution variables (visceral adipose tissue [AT], subcutaneous AT, and total midthigh AT) were measured using computed tomography; body fat mass was assessed by hydrostatic weighing; insulin sensitivity was determined with the euglycemic-hyperinsulinemic clamp; fasting plasma glucose (FPG) and 2-hour plasma glucose (2hPG) concentrations were measured by a 75-g oral glucose load; and (high-sensitivity) C-reactive protein (hs-CRP) was measured using a highly sensitive assay. After controlling for fat mass, visceral AT was positively associated with plasma triglyceride, hs-CRP, FPG, and 2hPG, and negatively associated with high-density lipoprotein cholesterol (HDL-C) and insulin sensitivity. Total midthigh AT was negatively associated with apolipoprotein B, FPG, and 2hPG, and positively associated with insulin sensitivity. Stepwise multiple regression analyses including abdominal visceral AT, subcutaneous AT and total midthigh AT as independent variables showed that abdominal visceral AT best predicted the variance in plasma triglyceride, HDL-C, low-density lipoprotein peak particle size, hs-CRP, FPG, 2hPG, and insulin sensitivity. Abdominal subcutaneous AT was a significant predictor of only insulin sensitivity, whereas total midthigh AT predicted HDL-C, low-density lipoprotein peak particle size, and apolipoprotein B. These multivariate analyses also indicated that total midthigh AT was favorably related to these outcomes, whereas abdominal visceral AT and subcutaneous AT were unfavorably related. These results confirmed that abdominal visceral fat is a critical correlate of metabolic parameters in postmenopausal women. In addition, a higher proportion of AT located in the total midthigh depot is associated with a favorable metabolic profile.

Relationship of abdominal visceral and subcutaneous adipose tissue with lipoprotein particle number and size in type 2 diabetes

OBJECTIVE

Insulin resistance and type 2 diabetes are associated with an atherogenic lipoprotein profile. We examined the role of visceral and subcutaneous fat depots, independent of BMI, on the dyslipidemia associated with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 382 subjects with type 2 diabetes underwent abdominal computed tomography to evaluate subcutaneous (SAT) and visceral adipose tissue (VAT) distribution and had anthropometric measurements to determine BMI and waist and hip circumference. Fasting blood was obtained for lipoprotein particle number and size using nuclear magnetic resonance spectroscopy. The relationship of lipoprotein particle number and size with BMI, SAT, and VAT was examined using multivariable regression models adjusted for age, sex, diabetes therapy, duration of diabetes, smoking, statin use, and A1C levels. The relation of VAT to lipoprotein particle number and size was further evaluated after the addition of BMI, BMI plus SAT, or BMI plus homeostatis is model assessment of insulin resistance (HOMA-IR) to the model.

RESULTS

VAT was positively related to VLDL particle number (P < 0.0001), LDL particle number (P < 0.01), and VLDL size (P < 0.0001) and negatively related to LDL size (P < 0.0001) and HDL size (P < 0.0001). These relationships remained unchanged after addition of BMI and SAT to the model. After addition of HOMA-IR, VAT remained positively related to VLDL particle number (P < 0.0001) and size (P < 0.01) and negatively related to LDL and HDL particle size (P < 0.0001 for both comparisons). Neither BMI nor SAT was independently related to lipoprotein parameters.

CONCLUSIONS

In patients with type 2 diabetes, higher VAT independent of BMI was associated with higher VLDL and LDL particle number, larger VLDL particles, and smaller LDL and HDL particles. This lipoprotein pattern has been associated with increased risk for atherosclerosis and cardiovascular disease.

Impact of hormone replacement therapy on exercise training-induced improvements in insulin action in sedentary overweight adults

Exercise training (ET) and hormone replacement therapy (HRT) are both recognized influences on insulin action, but the influence of HRT on responses to ET has not been examined. To determine if HRT use provided additive benefits for the response of insulin action to ET, we evaluated the impact of HRT use on changes in insulin during the course of a randomized, controlled, aerobic ET intervention. Subjects at baseline were sedentary, dyslipidemic, and overweight. These individuals were randomized to 6 months of one of 3 aerobic ET interventions or continued physical inactivity. In 206 subjects, an insulin sensitivity index (S(I)) was obtained with a frequently sampled intravenous glucose tolerance test pre- and post-ET. Baseline and postintervention fitness, regional adiposity, general adiposity, skeletal muscle biochemistry and histology, and serum lipoproteins were measured as other putative mediators influencing insulin action. Two-way analyses of variance were used to determine if sex or HRT use influenced responses to exercise training. Linear modeling was used to determine if predictors for response in S(I) differed by sex or HRT use(.) Women who used HRT (HRT+) demonstrated significantly greater improvements in S(I) with ET than women not using HRT (HRT-). In those HRT+ women, plasma triglyceride change best correlated with change in S(I). For HRT- women, capillary density change and, for men, subcutaneous adiposity change best correlated with change in S(I). In summary, in an ET intervention, HRT use appears to be associated with more robust responses in insulin action. Furthermore, relationships between ET-induced changes in insulin action and potential mediators of change in insulin action are different for men, and for women on or off HRT. These findings have implications for the relative utility of ET for improving insulin action in middle-aged men and women, particularly in the setting of differences in HRT use.

Early childhood predictors of adult body composition

Intra-uterine life has been identified as a possible critical period for the development of obesity risk in both adults and children; others have highlighted the importance of growth and nutrition in the first few years. It is suggested that fetal growth, as assessed by birth weight, may programme lean body mass later in life. Children who are born small for gestational age also have a predisposition to accumulating fat mass, particularly intra-abdominal fat. It is not yet clear whether this predisposition is due to their prenatal growth restraint, their rapid postnatal catch-up growth or a combination of both. Recently, genetic and heritable factors have been shown to contribute to both rapid postnatal growth and childhood obesity risk in children and adults. Future studies should explore their timing of action and potential interactions with markers of antenatal growth restraint.

Contribution of the lean body mass to insulin resistance in postmenopausal women with visceral obesity: a Monet study

Some insulin-resistant obese postmenopausal (PM) women are characterized by an android body fat distribution type and higher levels of lean body mass (LBM) compared to insulin-sensitive obese PM women. This study investigates the independent contribution of LBM to the detrimental effect of visceral fat (VF) levels on the metabolic profile. One hundred and three PM women (age: 58.0+/-4.9 years) were studied and categorized in four groups on the basis of their VF (higher vs. lower) and lean BMI (LBMI=LBM (kg)/height (m2); higher vs. lower). Measures included: fasting lipids, glucose homeostasis (by euglycemic/hyperinsulinemic clamp technique and 2-h oral glucose tolerance test (OGTT)), C-reactive protein (CRP) levels, fat distribution (by computed tomography (CT) scan), and body composition (by dual-energy X-ray absorptiometry). Women in the higher VF/higher LBMI group had lower glucose disposal and higher plasma insulin levels compared to the other groups. They also had higher plasma CRP levels than the women in the lower VF/lower LBMI group. VF was independently associated with insulin levels, measures of glucose disposal, and CRP levels (P<0.05). LBMI was also independently associated with insulin levels, glucose disposal, and CRP levels (P<0.05). Finally, significant interactions were observed between LBMI and VF levels for insulin levels during the OGTT and measures of glucose disposal (P<0.05). In conclusion, VF and LBMI are both independently associated with alterations in glucose homeostasis and CRP levels. The contribution of VF to insulin resistance seems to be exacerbated by increased LBM in PM women.

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.

Fatty acid composition of adipose tissue and blood in humans and its use as a biomarker of dietary intake

Accurate assessment of fat intake is essential to examine the relationships between diet and disease risk but the process of estimating individual intakes of fat quality by dietary assessment is difficult. Tissue and blood fatty acids, because they are mainly derived from the diet, have been used as biomarkers of dietary intake for a number of years. We review evidence from a wide variety of cross-sectional and intervention studies and summarise typical values for fatty acid composition in adipose tissue and blood lipids and changes that can be expected in response to varying dietary intake. Studies in which dietary intake was strictly controlled confirm that fatty acid biomarkers can complement dietary assessment methodologies and have the potential to be used more quantitatively. Factors affecting adipose tissue and blood lipid composition are discussed, such as the physical properties of triacylglycerol, total dietary fat intake and endogenous fatty acid synthesis. The relationship between plasma lipoprotein concentrations and total plasma fatty acid composition, and the use of fatty acid ratios as indices of enzyme activity are also addressed.

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.