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White adipose tissue is a highly plastic organ that is necessary to maintain whole-body energy homeostasis. The adipose tissue mass and changes in the fat mass or distribution are regulated by changes in the synthesis and breakdown (i.e., turnover) of adipose cells and triacylglycerols. Evidence suggests that the manner and magnitude of subcutaneous adipose tissue expansion (i.e., hypertrophy vs. hyperplasia) and turnover can influence metabolic health, as adipogenesis has been implicated in the pathogenesis of obesity and related diseases. Despite the potential role of adipose turnover in human health, there is a lack of knowledge about the in vivo kinetics of adipose cells. This is due, in part, to the slow turnover rate of the cells in adipose tissue and the practical complexity of directly labeling their metabolic precursors in vivo. Herein, we describe methods to measure in vivo adipose kinetics and turnover rates in humans through the consumption of deuterium ( 2 H)-labeled water. The incorporation of 2 H into the deoxyribonucleotide moieties of DNA in pre-adipocytes and adipocytes provides an accurate measure of cell formation and death (adipose turnover). Overall, this is an innovative approach to measuring in vivo adipose kinetics and represents a substantive departure from other in vitro assessments.

The extension of life span driven by 40% caloric restriction (CR) in rodents causes trade-offs in growth, reproduction, and immune defense that make it difficult to identify therapeutically relevant CR-mimetic targets. We report that about 14% CR for 2 years in healthy humans improved thymopoiesis and was correlated with mobilization of intrathymic ectopic lipid. CR-induced transcriptional reprogramming in adipose tissue implicated pathways regulating mitochondrial bioenergetics, anti-inflammatory responses, and longevity. Expression of the gene Pla2g7 encoding platelet activating factor acetyl hydrolase (PLA2G7) is inhibited in humans undergoing CR. Deletion of Pla2g7 in mice showed decreased thymic lipoatrophy, protection against age-related inflammation, lowered NLRP3 inflammasome activation, and improved metabolic health. Therefore, the reduction of PLA2G7 may mediate the immunometabolic effects of CR and could potentially be harnessed to lower inflammation and extend the health span.

Low total energy expenditure (TEE, MJ/d) has been a hypothesized risk factor for weight gain, but repeatability of TEE, a critical variable in longitudinal studies of energy balance, is understudied. We examine repeated doubly labeled water (DLW) measurements of TEE in 348 adults and 47 children from the IAEA DLW Database (mean ± SD time interval: 1.9 ± 2.9 y) to assess repeatability of TEE, and to examine if TEE adjusted for age, sex, fat-free mass, and fat mass is associated with changes in weight or body composition. Here, we report that repeatability of TEE is high for adults, but not children. Bivariate Bayesian mixed models show no among or within-individual correlation between body composition (fat mass or percentage) and unadjusted TEE in adults. For adults aged 20-60 y (N = 267; time interval: 7.4 ± 12.2 weeks), increases in adjusted TEE are associated with weight gain but not with changes in body composition; results are similar for subjects with intervals >4 weeks (N = 53; 29.1 ± 12.8 weeks). This suggests low TEE is not a risk factor for, and high TEE is not protective against, weight or body fat gain over the time intervals tested., (© 2022. The Author(s).)

Background: Physical activity may be a way to increase and maintain fat-free mass (FFM) in later life, similar to the prevention of fractures by increasing peak bone mass., Objectives: A study is presented of the association between FFM and physical activity in relation to age., Methods: In a cross-sectional study, FFM was analyzed in relation to physical activity in a large participant group as compiled in the International Atomic Energy Agency Doubly Labeled Water database. The database included 2000 participants, age 3-96 y, with measurements of total energy expenditure (TEE) and resting energy expenditure (REE) to allow calculation of physical activity level (PAL = TEE/REE), and calculation of FFM from isotope dilution., Results: PAL was a main determinant of body composition at all ages. Models with age, fat mass (FM), and PAL explained 76% and 85% of the variation in FFM in females and males < 18 y old, and 32% and 47% of the variation in FFM in females and males ≥ 18 y old, respectively. In participants < 18 y old, mean FM-adjusted FFM was 1.7 kg (95% CI: 0.1, 3.2 kg) and 3.4 kg (95% CI: 1.0, 5.6 kg) higher in a very active participant with PAL = 2.0 than in a sedentary participant with PAL = 1.5, for females and males, respectively. At age 18 y, height and FM-adjusted FFM was 3.6 kg (95% CI: 2.8, 4.4 kg) and 4.4 kg (95% CI: 3.2, 5.7 kg) higher, and at age 80 y 0.7 kg (95% CI: -0.2, 1.7 kg) and 1.0 kg (95% CI: -0.1, 2.1 kg) higher, in a participant with PAL = 2.0 than in a participant with PAL = 1.5, for females and males, respectively., Conclusions: If these associations are causal, they suggest physical activity is a major determinant of body composition as reflected in peak FFM, and that a physically active lifestyle can only partly protect against loss of FFM in aging adults., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.)

Objective: Eating earlier in the daytime to align with circadian rhythms in metabolism enhances weight loss. However, it is unknown whether these benefits are mediated through increased energy expenditure or decreased food intake. Therefore, this study performed the first randomized trial to determine how meal timing affects 24-hour energy metabolism when food intake and meal frequency are matched., Methods: Eleven adults with overweight practiced both early time-restricted feeding (eTRF) (eating from 8 am to 2 pm) and a control schedule (eating from 8 am to 8 pm) for 4 days each. On the fourth day, 24-hour energy expenditure and substrate oxidation were measured by whole-room indirect calorimetry, in conjunction with appetite and metabolic hormones., Results: eTRF did not affect 24-hour energy expenditure (Δ = 10 ± 16 kcal/d; P = 0.55). Despite the longer daily fast (intermittent fasting), eTRF decreased mean ghrelin levels by 32 ± 10 pg/mL (P = 0.006), made hunger more even-keeled (P = 0.006), and tended to increase fullness (P = 0.06-0.10) and decrease the desire to eat (P = 0.08). eTRF also increased metabolic flexibility (P = 0.0006) and decreased the 24-hour nonprotein respiratory quotient (Δ = -0.021 ± 0.010; P = 0.05)., Conclusions: Meal-timing interventions facilitate weight loss primarily by decreasing appetite rather than by increasing energy expenditure. eTRF may also increase fat loss by increasing fat oxidation., (© 2019 The Obesity Society.)

White adipose tissue is a highly plastic organ and is an important regulator of whole-body metabolism and energy balance. The magnitude of adipose tissue mass is determined by dynamic changes in the synthesis and breakdown (i.e. turnover) of adipocytes and triacylglycerols (TGs). Obesity is a disorder characterised by excessive adiposity and is a risk factor for diseases, including the metabolic syndrome and type 2 diabetes. Adipose tissue expansion is necessary to accommodate chronic excess energy intake and is characterised by enlargement of existing adipocytes (hypertrophy) and by increase in pre-adipocyte and adipocyte numbers (hyperplasia). Evidence suggests that the manner of subcutaneous adipose expansion can influence metabolic health, as impaired adipogenesis, namely restricted hyperplasia, may lead to ectopic lipid deposition in the liver and skeletal muscle, contributing to the pathogenesis of obesity-related disorders. Despite the plausible role of adipose turnover in human health and pathology, little is known about the in vivo kinetics of adipose tissue components (both adipose cells and TGs). This is due, in part, to the slow turnover rate of adipose tissue and the complexity of directly labelling pathway precursors. This review provides a brief summary of findings derived from in vitro techniques, as well as an overview of two in vivo methods that are being implemented to assess the turnover of adipose cells and TGs. Finally, the role of adipose tissue turnover in metabolic health and disease is discussed.

The storage of lipids in the form of triglycerides (TGs) and the de novo synthesis (lipogenesis) of fatty acids from nonlipid precursors [de novo lipogenesis (DNL)] are important functions of adipose tissue (AT) that influence whole-body metabolism. Yet, few studies have reported in vivo estimates of adipose lipid kinetics in humans. Fifty-two women with obesity (27 African-American and 25 Caucasian; 29.7 ± 5.5 years; BMI 32.2 ± 2.8 kg/m 2 ; 44.3 ± 4.0% body fat) were enrolled in the study. In vivo synthesis (or replacement) of TGs (f TG ) as well as the synthesis of the fatty acid, palmitate [a measure of adipose DNL (f DNL )], were assessed using an 8 week incorporation of deuterium into lipids (glycerol and palmitate moieties of TGs) in subcutaneous abdominal (scABD) and subcutaneous femoral (scFEM) AT. We report, for the first time, significant race differences in both TG synthesis and absolute DNL, with Caucasians having higher f TG and f DNL as compared with African-Americans. The DNL contribution to newly synthesized TG (corrected f DNL ) was not different between races. Interestingly, our findings also show that the scFEM adipose depot had higher TG replacement rates relative to the scABD. Finally, the replacement rate of TG (f TG ) was negatively correlated with changes in body weight over the 8 week labeling period. Our results provide the first evidence that in vivo TG replacement (synthesis and breakdown) rates differ by ethnicity. In addition, TG turnover varies by depot location in humans, implying an increased capacity for TG storage and higher lipolytic activity in the scFEM AT., (Copyright © 2018 by the American Society for Biochemistry and Molecular Biology, Inc.)

Context: Adipose tissue (AT) expansion occurs by hypertrophy and hyperplasia. Impaired hyperplasia, or adipogenesis, has been associated with obesity-related diseases., Objective: We examined how in vivo adipogenesis in the subcutaneous abdominal (scABD) and femoral (scFEM) depots (via 8-week incorporation of deuterium) correlates with markers of metabolic health., Design: Data from 52 women with obesity [27 black and 25 white; 29.7 ± 5.5 years; body mass index (BMI) 32.2 ± 2.8 kg/m2; 44.3% ± 4.0% body fat] were analyzed at Pennington Biomedical Research Center., Main Outcomes: A linear repeated measure model was used to assess the fraction of new adipose cells and the associated covariates. Akaike information criterion determined the covariates that best described the data. Simple associations were examined using Spearman's correlation., Results: The covariates that were associated with adipose kinetics included BMI, visceral AT/total abdominal AT (VAT/TAT) ratio, and the Matsuda index. Simple correlations demonstrated that adipocyte and preadipocyte formation in scABD (P = 0.02 and P = 0.16, trend, respectively) and scFEM (P = 0.01 and P = 0.24, trend, respectively) depots correlated positively with VAT/TAT. Preadipocyte and adipocyte formation in the scABD (P < 0.0001 and P = 0.02, respectively) and scFEM (P = 0.0001 and P = 0.003, respectively) was negatively associated with insulin sensitivity., Conclusions: Our results challenge the AT expandability hypothesis and suggest that higher in vivo adipose cell turnover is positively associated with BMI and VAT/TAT and negatively associated with insulin sensitivity, all correlates of impaired metabolic health., (Copyright © 2017 Endocrine Society)

Background: Calorie restriction (CR) retards aging and increases longevity in many animal models. However, it is unclear whether CR can be implemented in humans without adverse effects on body composition. Objective: We evaluated the effect of a 2-y CR regimen on body composition including the influence of sex and body mass index (BMI; in kg/m 2 ) among participants enrolled in CALERIE-2 (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy), a multicenter, randomized controlled trial. Design: Participants were 218 nonobese (BMI: 21.9-28.0) adults aged 21-51 y who were randomly assigned to 25% CR (CR, n = 143) or ad libitum control (AL, n = 75) in a 2:1 ratio. Measures at baseline and 12 and 24 mo included body weight, waist circumference, fat mass (FM), fat-free mass (FFM), and appendicular mass by dual-energy X-ray absorptiometry; activity-related energy expenditure (AREE) by doubly labeled water; and dietary protein intake by self-report. Values are expressed as means ± SDs. Results: The CR group achieved 11.9% ± 0.7% CR over 2-y and had significant decreases in weight (-7.6 ± 0.3 compared with 0.4 ± 0.5 kg), waist circumference (-6.2 ± 0.4 compared with 0.9 ± 0.5 cm), FM (-5.4 ± 0.3 compared with 0.5 ± 0.4 kg), and FFM (-2.0 ± 0.2 compared with -0.0 ± 0.2 kg) at 24 mo relative to the AL group (all between-group P < 0.001). Moreover, FFM as a percentage of body weight at 24 mo was higher, and percentage of FM was lower in the CR group than in the AL. AREE, but not protein intake, predicted preservation of FFM during CR ( P < 0.01). Men in the CR group lost significantly more trunk fat ( P = 0.03) and FFM expressed as a percentage of weight loss ( P < 0.001) than women in the CR group. Conclusions: Two years of CR had broadly favorable effects on both whole-body and regional adiposity that could facilitate health span in humans. The decrements in FFM were commensurate with the reduced body mass; although men in the CR group lost more FFM than the women did, the percentage of FFM in the men in the CR group was higher than at baseline. CALERIE was registered at clinicaltrials.gov as NCT00427193., (© 2017 American Society for Nutrition.)

Objective: Polycystic ovary syndrome (PCOS) is associated with reduced adipose tissue lipolysis that can be rescued by aerobic exercise. We aimed to identify differences in the gene expression of perilipins and associated targets in adipose tissue in women with PCOS before and after exercise., Design and Methods: We conducted a cross-sectional study in eight women with PCOS and eight women matched for BMI and age with normal cycles. Women with PCOS also completed a 16-week prospective aerobic exercise-training study. Abdominal subcutaneous adipose tissue biopsies were collected, and primary adipose-derived stromal/stem cell cultures were established from women with PCOS before 16 weeks of aerobic exercise training (n=5) and controls (n=5). Gene expression was measured using real-time PCR, in vitro lipolysis was measured using radiolabeled oleate, and perilipin 3 (PLIN3) protein content was measured by western blotting analysis., Results: The expression of PLIN1, PLIN3, and PLIN5, along with coatomers ARF1, ARFRP1, and βCOP was ∼ 80% lower in women with PCOS (all P<0.05). Following exercise training, PLIN3 was the only perilipin to increase significantly (P<0.05), along with coatomers ARF1, ARFRP1, βCOP, and SEC23A (all P<0.05). Furthermore, PLIN3 protein expression was undetectable in the cell cultures from women with PCOS vs controls. Following exercise training, in vitro adipose oleate oxidation, glycerol secretion, and PLIN3 protein expression were increased, along with reductions in triglyceride content and absence of large lipid droplet morphology., Conclusions: These findings suggest that PLIN3 and coatomer GTPases are important regulators of lipolysis and triglyceride storage in the adipose tissue of women with PCOS., (© 2015 European Society of Endocrinology.)

Objective: The presence of large subcutaneous adipocytes in obesity has been proposed to be linked with insulin resistance and type 2 diabetes through the "adipose tissue expandability" hypothesis, which holds that large adipocytes have a limited capacity for expansion, forcing lipids to be stored in nonadipose ectopic depots (skeletal muscle, liver), where they interfere with insulin signaling. This hypothesis has, however, been largely formulated by cross-sectional findings and to date has not been prospectively demonstrated in the development of insulin resistance in humans., Research Design and Methods: Twenty-nine men (26.8 ± 5.4 years old; BMI 25.5 ± 2.3 kg/m(2)) were fed 40% more than their baseline requirement for 8 weeks. Before and after overfeeding, insulin sensitivity was determined using a two-step hyperinsulinemic-euglycemic clamp. Intrahepatic lipid (IHL) and intramyocellular lipid (IMCL) were measured by (1)H-MRS and abdominal fat by MRI. Subcutaneous abdominal adipose and skeletal muscle tissues were collected to measure adipocyte size and markers of tissue inflammation., Results: Subjects gained 7.6 ± 2.1 kg (55% fat) and insulin sensitivity decreased 18% (P < 0.001) after overfeeding. IHL increased 46% from 1.5% to 2.2% (P = 0.002); however, IMCL did not change. There was no association between adipocyte size and ectopic lipid accumulation. Despite similar weight gain, subjects with smaller fat cells at baseline had a greater decrease in insulin sensitivity, which was linked with upregulated skeletal muscle tissue inflammation., Conclusions: In experimental substantial weight gain, the presence of larger adipocytes did not promote ectopic lipid accumulation. In contrast, smaller fat cells were associated with a worsened metabolic response to overfeeding., (© 2014 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Context: In animal models of obesity, chronic inflammation and dysregulated extracellular matrix remodeling in adipose tissue leads to insulin resistance. Whether similar pathophysiology occurs in humans is not clear., Objective: The aim of this study was to test whether 10% weight gain induced by overfeeding triggers inflammation and extracellular matrix remodeling (gene expression, protein, histology) in skeletal muscle and sc adipose tissue in humans. We also investigated whether such remodeling was associated with an impaired metabolic response (hyperinsulinemic-euglycemic clamp)., Design, Setting, Participants, and Intervention: Twenty-nine free-living males were fed 40% over their baseline energy requirements for 8 weeks., Results: Ten percent body weight gain prompted dramatic up-regulation of a repertoire of extracellular matrix remodeling genes in muscle and to a lesser degree in adipose tissue. The amount of extracellular matrix genes in the muscle were directly associated with the amount of lean tissue deposited during overfeeding. Despite weight gain and impaired insulin sensitivity, there was no change in local adipose tissue or systemic inflammation, but there was a slight increase in skeletal muscle inflammation., Conclusion: We propose that skeletal muscle extracellular matrix remodeling is another feature of the pathogenic milieu associated with energy excess and obesity, which, if disrupted, may contribute to the development of metabolic dysfunction.

Context: Adipose tissue is a highly active endocrine organ that secretes many factors that affect other tissues and whole-body metabolism. Adipocytes are responsive to several glycoprotein 130 (gp130) cytokines, some of which have been targeted as potential antiobesity therapeutics., Objective: Oncostatin M (OSM) is a gp130 family member known to inhibit adipocyte differentiation in vitro, but its effects on other adipocyte properties are not characterized. The expression of OSM in white adipose tissue (WAT) has not been evaluated in the context of obesity. Thus, our objective was to examine the expression of adipose tissue OSM in obese animals and humans., Design: OSM expression was examined in adipose tissues from mice with diet-induced and genetic obesity and in obese humans as well as in fractionated adipose tissue from mice. Murine adipocytes were used to examine OSM receptor expression and the effects of OSM on adipocytes, including the secretion of factors such as plasminogen activator inhibitor 1 and IL-6, which are implicated in metabolic diseases., Results: OSM expression is increased in rodent and human obesity/type 2 diabetes mellitus. In humans, OSM levels correlate with body weight and insulin and are inversely correlated with glucose disposal rate as measured by hyperinsulinemic-euglycemic clamp. OSM is not produced from the adipocytes in WAT but derives from cells in the stromovascular fraction, including F4/80(+) macrophages. The specific receptor of OSM, OSM receptor-β, is expressed in adipocytes and adipose tissue and increased in both rodent models of obesity examined. OSM acts on adipocytes to induce the expression and secretion of plasminogen activator inhibitor 1 and IL-6., Conclusions: These data indicate that WAT macrophages are a source of OSM and that OSM levels are significantly induced in murine and human obesity/type 2 diabetes mellitus. These studies suggest that OSM produced from immune cells in WAT acts in a paracrine manner on adipocytes to promote a proinflammatory phenotype in adipose tissue.

Objective: To develop a new geometrical index that combines height, waist circumference (WC), and hip circumference (HC) and relate this index to total and visceral body fat., Design and Methods: Subject data were pooled from three databases that contained demographic, anthropometric, dual energy X-ray absorptiometry (DXA) measured fat mass, and magnetic resonance imaging measured visceral adipose tissue (VAT) volume. Two elliptical models of the human body were developed. Body roundness was calculated from the model using a well-established constant arising from the theory. Regression models based on eccentricity and other variables were used to predict %body fat and %VAT., Results: A body roundness index (BRI) was derived to quantify the individual body shape in a height-independent manner. Body roundness slightly improved predictions of %body fat and %VAT compared to the traditional metrics of body mass index (BMI), WC, or HC. On this basis, healthy body roundness ranges were established. An automated graphical program simulating study results was placed at http://www.pbrc.edu/bodyroundness., Conclusion: BRI, a new shape measure, is a predictor of %body fat and %VAT and can be applied as a visual tool for health status evaluations., (Copyright © 2013 The Obesity Society.)

Objective: The overexpression of the adipose gene (adp/WDTC1) in mice inhibits lipid accumulation and improves the metabolic profile. Subcutaneous fat adp expression in humans and its relation to metabolic parameters was evaluated., Design and Methods: Abdominal subcutaneous fat adp expression, insulin sensitivity (clamp), and respiratory quotient (RQ; indirect calorimetry) were assessed in: 36 obese and 56 BMI-, race-, and sex-matched type 2 diabetic volunteers (Look AHEAD Adipose Ancillary Study); 37 nondiabetic Pima Indians including obese (n = 18) and nonobese (n = 19) subjects and; 62 nonobese nondiabetic subjects at the Pennington Center in the ADAPT study., Results: In the Look AHEAD Study, adp expression normalized for cyclophilin B was higher in males versus females (1.27 ± 0.06 vs. 1.11 ± 0.04; P < 0.01) but not after controlling for body fat. Adp expression was not influenced by the presence of diabetes but was related to body fat (r = -0.23; P = 0.03), insulin sensitivity (r = 0.23; P = 0.03) and fasting/insulin-stimulated RQ (r = 0.31 and 0.33; P < 0.01). In Pima Indians, adp expression was also higher in males versus females (1.00 ± 0.05 vs. 0.77 ± 0.05; P = 0.02) and higher in nonobese versus obese (1.02 ± 0.05 vs. 0.80 ± 0.06; P = 0.03). In the ADAPT study, there was no difference in adp expression between males and females., Conclusion: Consistent with animal studies, our results suggest that high adp expression in human adipose tissue is associated with lower adiposity and enhanced glucose utilization., (Copyright © 2013 The Obesity Society.)

Context: The link between weight gain and cardiovascular risk characterized with circadian blood pressure variability [CBPV] and endothelial function [EF] is unexplored., Objective: To prospectively demonstrate weight gain in healthy adults, increases body fat [BF], enlarges waist circumference [WC], expands visceral adipose tissue [VAT], exacerbates systemic inflammation [sIF], worsens insulin resistance [IR] and enhances functional cardiovascular disease [CVD] risk., Design, Setting and Participants: Healthy men [n=11] and women [n=3] provided initial and eight-week post-caloric excess anthropometric and fasting laboratory measures. Functional CVD risk assessments: CBPV and resting EF were also obtained with 7-day automatic ambulatory BP monitoring and increased test finger peripheral arterial tone [PAT] relative to control [reported as relative hyperemia index (RHI)], respectively., Intervention: After determining individualized mean energy requirements for weight maintenance over 7-days, each participant received a personalized over feeding prescription (1.4 times; 41% carbohydrate, 44% fat, and 15% protein) for 8-weeks., Results: mean (SEM). Participants increased body weight [BW; +7.4(0.1) kg]*, body mass index [BMI; +2.5(0.2) kg/m²]*, BF [+2.0(0.01)%]*, WC [+8.2(1.0) cm]*, and VAT [+0.2(0.03) L]* and intrahepatic lipid [IHL + 0.0004(0.002) L] :*all p < 0.01. Increased subcutaneous adipose cell size [+0.3(0.01) ρL; p = 0.02] accompanied significant sIF [hs-CRP + 0.4(0.09) mg/dL; p = 0.04; leptin 6.63 ng/ml; p = 0.0008] and IR [fasting plasma glucose; [FPG] +7.0(0.6) mg/dL;p = 0.01, fasting insulin; [FI] +5.7(1.4) uIU/ml; p = 0.001, HOMA-IR +1.6(0.5); p = 0.02]. Abn CBPV {systolic [+5.4(0.8); p = 0.002, diastolic [+1.7(0.1); p = 0.07 and pulse pressure [PP] [+3.5(0.4); p = 0.003 mm Hg} or elevated heart rate [HR] [+4.9(0.5) bpm; p = 0.003] ensued. Resting RHI declined by 0.47(0.004) from initial 2.24(0.09) to 1.77(0.1); p = 0.001, indicating endothelial dysfunction [ED]., Conclusions: Controlled caloric excess in healthy human adults over only 8-weeks significantly increased BF, VAT, sIF [hs-CRP], IR [FPG, FI, HOMA-IR] and functional CVD risk [measured as abnormal circadian blood pressure variability and impaired resting endothelial function].

Context: Aging is associated with insulin resistance and unfavorable changes in body composition including increased fat accumulation, particularly in visceral and ectopic depots. Recent studies suggest that skeletal muscle mitochondrial activity may underlie some age-associated metabolic abnormalities., Objective: Our objective was to measure mitochondrial capacity and coupling of the vastus lateralis muscle in elderly and young adults using novel in vivo approaches and relate mitochondrial activity to metabolic characteristics., Design: This was a cross-sectional study., Participants and Intervention: Fourteen sedentary young (seven males and seven females, 20-34 yr of age) and 15 sedentary elderly (seven males and eight females, 70-84 yr of age) nonobese subjects selected for similar body weight underwent measures of body composition by magnetic resonance imaging and dual-energy x-ray absorptiometry, oral glucose tolerance, and in vivo mitochondrial activity by (31)P magnetic resonance and optical spectroscopy. Muscle biopsy was carried out in the same muscle to measure mitochondrial content, antioxidant activity, fiber type, and markers of mitochondrial biogenesis., Results: Elderly volunteers had reduced mitochondrial capacity (P = 0.05) and a trend for decreased coupling efficiency (P = 0.08) despite similar mitochondrial content and fiber type distribution. This was accompanied by greater whole-body oxidative stress (P = 0.007), less skeletal muscle mass (P < 0.001), more adipose tissue in all depots (P ≤ 0.002) except intramyocellular (P = 0.72), and lower glucose tolerance (P = 0.07)., Conclusions: Elderly adults show evidence of altered mitochondrial activity along with increased adiposity, oxidative stress, and reduced glucose tolerance, independent of obesity. We propose that mild uncoupling may be induced secondary to age-associated oxidative stress as a mechanism to dissipate the proton-motive force and protect against further reactive oxygen species production and damage.

The purpose of this study was to examine sex and race differences in the relationship between anthropometric measurements and adiposity in white and African-American (AA) adults. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas were measured with computed tomography (CT). Fat mass (FM) was measured with dual-energy-X-ray absorptiometry (DXA). Correlation coefficients were used to assess the relationship of waist circumference (WC) and BMI to VAT, SAT, and FM within sex-by-race groups. General linear models were used to compare relationships between WC or BMI, and adiposity across sex and race, within age groups (18-39 and 40-64 years). The sample included 1,667 adults (men: 489 white; 120 AA; women: 666 white, 392 AA). WC and BMI correlations were highest for FM and SAT compared to VAT. Women had higher FM levels than men regardless of WC, but the sex difference in FM was attenuated in younger AA adults with a high BMI. For a given level of WC or BMI, women had higher levels of SAT than men; however, significant interactions indicated that the relationship was not consistent across all levels of BMI and WC. Sex and race differences in VAT varied significantly with WC and BMI. In general, white adults had higher levels of VAT than AA adults at higher levels of BMI and WC. Sex differences, and in some instances race differences, in the relationships between anthropometry and fat-specific depots demonstrate that these characteristics need to be considered when predicting adiposity from WC or BMI.

Context: Adipose tissue in obese individuals is characterized by reduced capillary density and reduced oxygenation., Objective: Our objective was to test whether hypoxia is associated with reduced antilipolytic effect of insulin., Participants, Design, and Setting: Twenty-one lean and obese individuals participated in this cross-sectional study at a university-based clinical research center., Intervention: In all subjects, in situ adipose tissue (AT) oxygenation [AT oxygen partial pressure (ATpO2)] was measured with a Clark electrode, insulin sensitivity as well as basal and insulin-suppressed lipolysis (continuous infusion of (2H5)glycerol) were measured during a euglycemic-hyperinsulinemic clamp, and abdominal sc AT biopsies were collected to assess fat cell size (Coulter counting of osmium-fixed cells), capillary density (by staining of histological sections), and gene expression (by quantitative RT-PCR)., Main Outcome Measure: In situ ATpO2 was evaluated., Results: The ability of insulin to suppress lipolysis (percent) was positively correlated with insulin sensitivity (r=0.43; P<0.05), ATpO2 (r=0.44; P<0.05), vascular endothelial growth factor mRNA (r=0.73; P<0.01), and capillary density (r=0.75; P<0.01)., Conclusion: These results indicate that low capillary density and ATpO2 in AT are potentially upstream causes of AT dysfunction.

Objectives: Basic science studies show that the extracellular matrix of adipose tissue, mainly represented by collagen VI, is dysfunctional in obesity and contributes to the development of the metabolic syndrome. We hypothesized in humans that increased collagen VI alpha3-subunit (COL6A3) mRNA is associated with adipose tissue macrophage chemotaxis and inflammation and that weight gain is accompanied by changes in the expression of COL6A3., Research Design and Methods: Adipose tissue biopsies were obtained from a cross-sectional study (n = 109), an overfeeding study (n = 9), and a pioglitazone treatment study (n = 14). Adipose tissue gene expression was measured by quantitative RT-PCR, immunohistochemistry, and adipocyte sizing by fixation with osmium and Coulter counting. Body composition was measured by dual-energy x-ray absorptiometry and visceral adipose tissue by computed tomography. Patients with high or low COL6A3 mRNA were compared by one-way ANOVA., Results: In humans, immunohistochemistry revealed that COL6 is present in adipose tissue extracellular matrix. COL6A3 mRNA is correlated with body mass index (r = 0.60, P < 0.0001) and fat mass (r = 0.41, P < 0.0001). COL6A3 expression was similar in obese vs. type 2 diabetes patients. Obese subjects with high COL6A3 mRNA had greater visceral adipose tissue mass (P < 0.05), lower size of small and medium adipocytes (P < 0.05), more CD68+ and CD163/MAC2+ macrophages, and increased macrophage inflammatory protein-1alpha and macrophage chemoattractant protein-1alpha mRNA (P < 0.05). Eight weeks of overfeeding increased body weight and COL6A3 mRNA (P < 0.05). Pioglitazone decreased COL6A3 mRNA, and the change was inversely proportional to baseline COL6A3 mRNA (r = -0.95, P < 0.0001)., Conclusion: These results are consistent with basic science data, suggesting that COL6A3 might contribute to adipose tissue inflammation.

Human adenovirus Ad-36 is causatively and correlatively linked with animal and human obesity, respectively. Ad-36 enhances differentiation of rodent preadipocytes, but its effect on adipogenesis in humans is unknown. To indirectly assess the role of Ad-36-induced adipogenesis in human obesity, the effect of the virus on commitment, differentiation, and lipid accumulation was investigated in vitro in primary human adipose-derived stem/stromal cells (hASC). Ad-36 infected hASC in a time- and dose-dependent manner. Even in the presence of osteogenic media, Ad-36-infected hASC showed significantly greater lipid accumulation, suggestive of their commitment to the adipocyte lineage. Even in the absence of adipogenic inducers, Ad-36 significantly increased hASC differentiation, as indicated by a time-dependent expression of genes within the adipogenic cascade-CCAAT/Enhancer binding protein-beta, peroxisome proliferator-activated receptor-gamma, and fatty acid-binding protein-and consequentially increased lipid accumulation in a time- and viral dose-dependent manner. Induction of hASC to the adipocyte state by Ad-36 was further supported by increased expression of lipoprotein lipase and the accumulation of its extracellular fraction. hASC from subjects harboring Ad-36 DNA in their adipose tissue due to natural infection had significantly greater ability to differentiate compared with Ad-36 DNA-negative counterparts, which offers a proof of concept. Thus, Ad-36 has the potential to induce adipogenesis in hASC, which may contribute to adiposity induced by the virus.

Adipose tissue has proven to serve as an abundant, accessible, and rich source of adult stem cells with multipotent properties suitable for tissue engineering and regenerative medical applications. Here, we describe a detailed method for the isolation and expansion of adipose-derived stem cells (ASCs). We present a large scale procedure suitable for processing >100 mL volumes of lipoaspirate tissue specimens and a small scale procedure suitable for processing adipose tissue biopsy specimens of < 0.5 g. Although we have focused on the isolation of ASCs from human adipose tissue, the procedure can be applied to adipose tissues from other species with minimal modifications.

Objective: Our objective was to delineate the potential role of adipogenesis in insulin resistance and type 2 diabetes. Obesity is characterized by an increase in adipose tissue mass resulting from enlargement of existing fat cells (hypertrophy) and/or from increased number of adipocytes (hyperplasia). The inability of the adipose tissue to recruit new fat cells may cause ectopic fat deposition and insulin resistance., Research Methods and Procedures: We examined the expression of candidate genes involved in adipocyte proliferation and/or differentiation [CCAAT/enhancer-binding protein (C/EBP) alpha, C/EBPdelta, GATA domain-binding protein 3 (GATA3), C/EBPbeta, peroxisome proliferator-activated receptor (PPAR) gamma2, signal transducer and activator of transcription 5A (STAT5A), Wnt-10b, tumor necrosis factor alpha, sterol regulatory element-binding protein 1c (SREBP1c), 11 beta-hydroxysteroid dehydrogenase, PPARG angiopoietin-related protein (PGAR), insulin-like growth factor 1, PPARgamma coactivator 1alpha, PPARgamma coactivator 1beta, and PPARdelta] in subcutaneous adipose tissue from 42 obese individuals with type 2 diabetes and 25 non-diabetic subjects matched for age and obesity., Results: Insulin sensitivity was measured by a 3-hour 80 mU/m2 per minute hyperinsulinemic glucose clamp (100 mg/dL). As expected, subjects with type 2 diabetes had lower glucose disposal (4.9 +/- 1.9 vs. 7.5 +/- 2.8 mg/min per kilogram fat-free mass; p < 0.001) and larger fat cells (0.90 +/- 0.26 vs. 0.78 +/- 0.17 microm; p = 0.04) as compared with obese control subjects. Three genes (SREBP1c, p < 0.01; STAT5A, p = 0.02; and PPARgamma2, p = 0.02) had significantly lower expression in obese type 2 diabetics, whereas C/EBPbeta only tended to be lower (p = 0.07)., Discussion: This cross-sectional study supports the hypothesis that impaired expression of adipogenic genes may result in impaired adipogenesis, potentially leading to larger fat cells in subcutaneous adipose tissue and insulin resistance.

Objective: The purpose of this article was to determine the relationships among total body fat, visceral adipose tissue (VAT), fat cell size (FCS), ectopic fat deposition in liver (intrahepatic lipid [IHL]) and muscle (intramyocellular lipid [IMCL]), and insulin sensitivity index (S(i)) in healthy overweight, glucose-tolerant subjects and the effects of calorie restriction by diet alone or in conjunction with exercise on these variables., Research Design and Methods: Forty-eight overweight volunteers were randomly assigned to four groups: control (100% of energy requirements), 25% calorie restriction (CR), 12.5% calorie restriction +12.5% energy expenditure through structured exercise (CREX), or 15% weight loss by a low-calorie diet followed by weight maintenance for 6 months (LCD). Weight, percent body fat, VAT, IMCL, IHL, FCS, and S(i) were assessed at baseline and month 6., Results: At baseline, FCS was related to VAT and IHL (P < 0.05) but not to IMCL. FCS was also the strongest determinant of S(i) (P < 0.01). Weight loss at month 6 was 1 +/- 1% (control, mean +/- SE), 10 +/- 1% (CR), 10 +/- 1% (CREX), and 14 +/- 1% (LCD). VAT, FCS, percent body fat, and IHL were reduced in the three intervention groups (P < 0.01), but IMCL was unchanged. S(i) was increased at month 6 (P = 0.05) in the CREX (37 +/- 18%) and LCD (70 +/- 34%) groups (P < 0.05) and tended to increase in the CR group (40 +/- 20%, P = 0.08). Together the improvements in S(i) were related to loss in weight, fat mass, and VAT, but not IHL, IMCL, or FCS., Conclusions: Large adipocytes lead to lipid deposition in visceral and hepatic tissues, promoting insulin resistance. Calorie restriction by diet alone or with exercise reverses this trend.

Objective: To test the hypothesis that low adiponectin is associated with low fat oxidation in humans., Research Methods and Procedures: We measured plasma adiponectin concentrations in 75 healthy, nondiabetic Pima Indians (age, 28 +/- 7 years; 55 men and 20 women; body fat, 29.7 +/- 7.5%) and 18 whites [(age, 33 +/- 8 years; 14 men and 4 women; body fat, 28.2 +/- 10.8% (means +/- SD)] whose body composition was measured by DXA and 24-hour energy expenditure (24-hour EE) by a respiratory chamber. Respiratory quotient (an estimate of whole-body carbohydrate/lipid oxidation rate) was calculated over 24 hours (24-hour RQ)., Results: Before correlational analyses, waist-to-thigh ratio (WTR) and percentage of body fat (PFAT) were adjusted for age, sex, and race; 24-hour EE was adjusted for fat mass and fat-free mass, and 24-hour RQ were adjusted for energy balance. Plasma adiponectin concentrations were negatively correlated with WTR (r = -0.42, p < 0.0001) and PFAT (r = -0.46, p < 0.0001). There was no correlation between plasma adiponectin concentrations and 24-hour RQ, (r = 0.09, p = 0.36) before or after adjustment for PFAT (r = 0.001, p = 0.99, respectively, partial correlation), and no correlation was found between plasma adiponectin concentrations and 24-hour EE (r = -0.12, p = 0.27)., Discussion: Our cross-sectional data do not suggest physiological concentrations of fasting plasma adiponectin play a role in the regulation of whole-body fat oxidation or energy expenditure in resting conditions. Whether administration of adiponectin to individuals with low levels of this hormone will increase their fat oxidation rates/energy expenditure remains to be established.

Body mass index is widely used as a measure of adiposity in adults, but its use in children and adolescents is controversial. We assessed body mass index as a measure of adiposity in children and adolescents between the ages of 5 and 20 yr examined as part of the NIH survey of health in the Pima Indian population. Body mass index (measured in 985 subjects and analyzed in 3 age groups: 5-9, 10-14, and 15-19 yr, in both sexes) was compared cross-sectionally to percent fat and fat mass derived from dual energy x-ray absorptiometry and to fasting and 2-h plasma glucose, systolic and diastolic blood pressures, cholesterol, high density lipoprotein cholesterol, fasting insulin, and triglycerides. Body mass index was strongly correlated in all age groups to both percent fat (r = 0.83-0.94; for each group, P < 0.0001) and fat mass (r = 0.96-0.98; P < 0.0001). The relationship of body mass index to percent fat was different in males and females; differences were more marked in older age groups. Body mass index, percent fat, and fat mass showed similar degrees of correlation to metabolic measures in childhood. Body mass index is strongly associated with measures of adiposity derived from dual energy x-ray absorptiometry. Both measures show similar associations with cardiovascular risk factors in Pima Indian children.

Objective: To evaluate the feasibility of using deuterated water and isotope ratio mass spectrometry to measure de novo fatty acid synthesis in adipose tissue, and to compare this parameter in obese and lean women., Subjects: Six lean and six obese premenopausal Caucasian women in the main study and three obese Pima Indians in a pilot study., Measurements: Deuterated water was administered orally twice daily for 14 days to create stable deuterium enrichment in body water, during which series of blood samples were collected to measure body water deuterium enrichment and deuterium incorporation into plasma total Triacylglycerol (TG) fatty acids and total cholesterol. Subcutaneous fat at different sites were sampled at the beginning and the end of deuterium administration to measure deuterium incorporation into TG fatty acids., Results: Fractional de novo synthesis rate of TG fatty acids in adipose tissue was 0. 014+/-0.005 and 0.014+/-0.007% in lean and obese Caucasian women, corresponding to 2+/-0.7 and 5.6+/-3.2 g (P=0.3) of fatty acids synthesized daily, respectively. Plasma TG fatty acids and cholesterol synthesis rates were comparable to those reported previously. A pilot study showed that de novo lipid synthesis in adipose tissue of obese Pima Indians was also quantitatively minor., Conclusion: Human adipose tissue, like the liver, does not make a major contribution to whole body lipogenesis under eucaloric conditions. A combination of deuterated water and isotope ratio mass spectrometry is a useful research tool for studying accumulation of de novo synthesized lipids in human adipose tissue.

Objective: A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post-obese adults (2 males and 6 females; 48.9 +/- 12.2 years; body mass index [BMI]: 24.5 +/- 1.0 kg/m2; body fat 33 +/- 5%; mean +/- SD) who lost 27.1 +/- 21.3 kg (16 to 79 kg) and had maintained this weight loss for > or =2 months (2 to 9 months) to eight age- and BMI-matched control never-obese subjects (1 male and 7 females; 49.1 +/- 5.2 years; BMI 24.4 +/- 1.0 kg/m2; body fat 33 +/- 7%)., Research Methods and Procedures: Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10-hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48-hour period in free living conditions., Results: After adjustment for fat mass and fat-free mass, post-obese subjects had, compared with controls, similar levels of physical activity (4185 +/- 205 vs. 4295 +/- 204 counts) and similar RMR (1383 +/- 268 vs. 1430 +/- 104 kcal/day) but higher RQ (0.86 +/- 0.04 vs. 0.81 +/- 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat-free mass, was lower in post-obese than in control subjects (4.5 +/- 2.1 vs. 11.6 +/- 7.9 ng/mL, p < 0.05)., Discussion: The low fat oxidation and low plasma leptin concentrations observed in post-obese individuals may, in part, explain their propensity to relapse.

We have screened a subtracted cDNA library in order to identify differentially expressed genes in omental adipose tissue of human patients with Type 2 diabetes. One clone (#1738) showed a marked reduction in omental adipose tissue from patients with Type 2 diabetes. Sequencing and BLAST analysis revealed clone #1738 was the adipocyte-specific secreted protein gene apM1 (synonyms ACRP30, AdipoQ, GBP28). Consistent with the murine orthologue, apM1 mRNA was expressed in cultured human adipocytes and not in preadipocytes. Using RT-PCR we confirmed that apM1 mRNA levels were significantly reduced in omental adipose tissue of obese patients with Type 2 diabetes compared with lean and obese normoglycemic subjects. Although less pronounced, apM1 mRNA levels were reduced in subcutaneous adipose tissue of Type 2 diabetic patients. Whereas the biological function of apM1 is presently unknown, the tissue specific expression, structural similarities to TNFalpha, and the dysregulated expression observed in obese Type 2 diabetic patients suggest that this factor may play a role in the pathogenesis of insulin resistance and Type 2 diabetes.

Pima Indians are insulin resistant and hyperinsulinaemic compared with Caucasians. We investigated whether abdominal fat distribution was different between Pimas and Caucasians and whether differences in the amount of visceral fat explained metabolic differences between the groups. Total body fat (absorptiometry) and abdominal fat distribution at L4-L5 (magnetic resonance imaging) were compared in 20 Pima Indians (10 men/10 women) and 20 age-, sex- and BMI-matched Caucasians. Insulin action was measured as glucose disposal during a two-step hyperinsulinaemic-euglycaemic glucose clamp and insulin secretion was assessed in response to oral and intravenous glucose tolerance tests. By design, percent body fat was similar in Pimas and Caucasians. Abdominal visceral and subcutaneous adipose tissue areas were also similar in the two groups (151+/-16 vs 139+/-15 cm2 and 489+/-61 vs 441+/-7 cm2 respectively). Plasma insulin concentrations were higher in Pimas than Caucasians in the fasting state (27+/-6 vs 11+/-2 mU/ml; p < 0.01) and after a 75-g oral glucose load (area under the curve 19975+/-2626 vs 9293+/-1847 mU x l(-1) x 180 min(-1); p < 0.005). Glucose disposal was lower in Pimas than Caucasians during both steps of the clamp and negatively correlated (after adjustment for percent body fat and sex) with visceral adipose tissue in Caucasians (partial r = -0.51, p = 0.03), but not in Pima Indians (r = -0.03, p = 0.92). Insulin secretion was not related to visceral fat independently of percent body fat in either group. We conclude that a relative increase in visceral fat does not explain insulin resistance and hyperinsulinaemia in Pima Indians.

A high 24-h respiratory quotient (RQ), i.e., low fat oxidation, predicts weight gain. To determine whether impaired fat mobilization (lipolysis) may contribute to weight gain, we studied the relation between lipolytic response to nonselective beta-adrenergic stimulation and RQ measured in a respiratory chamber in 21 males (11 Caucasians, 10 Pima Indians; age 32 +/- 5 yr, weight 93 +/- 24 kg, body fat 30 +/- 8%; means +/- SD) and 23 females (10 Caucasians, 13 Pima Indians; age 32 +/- 9 yr, weight 95 +/- 26 kg, body fat 44 +/- 8%). Lipolytic response was assessed as the relative increase in dialysate glycerol concentration (% above baseline) when isoproterenol (1 micromol/l) was added to the perfusate of a microdialysis probe inserted in the abdominal subcutaneous adipose tissue. In males, but not in females, basal RQ measured during sleep from 0500 to 0630 and adjusted for waist circumference was negatively correlated to lipolytic response (r = -0.66, P = 0.001). The results suggest that in males, impaired beta-adrenergic-mediated lipolysis may contribute to low rates of fat oxidation, a condition known to predispose to weight gain.

The white blood cell (WBC) count is correlated to the amount of body fat in humans, but the mechanism for this association is unknown. Leptin, a 16 kD protein produced in adipocytes, circulates in humans in direct proportion to the amount and percentage of body fat. Recent evidence suggests that leptin and the leptin receptor are part of a novel pathway which stimulates haemopoiesis. This study was designed to test whether fasting plasma leptin concentrations contribute to the relationship between the WBC count and body fat. 117 Pima Indians with a wide range in body composition were studied. The WBC count was positively correlated with percentage of body fat (r = 0.44, P = 0.0001) and fasting plasma leptin concentration (r = 0.38, P = 0.0001). In multiple regression analyses, age, gender and percent body fat were significant independent determinants of the WBC count. After controlling for age and gender, percent body fat accounted for 23% of the variance in the WBC count (partial r = 0.48, P = 0.0001). In similar models which also included plasma leptin concentration, percent body fat remained significantly related to the WBC count. but only accounted for 7% of its variance (partial r = 0.27, P = 0.003). Based on these results, and the demonstration that leptin directly effects the stimulation of proliferation of haemopoietic stem cells in vitro, we hypothesize that the relation of the WBC count to percent body fat may be mediated, in part, through the effect of leptin.

Leptin is believed to play a role in the regulation of energy balance, but little is known about factors influencing plasma leptin concentrations. To determine the effect of short-term changes in energy balance, we measured plasma leptin concentrations as well as plasma glucose, insulin, triglyceride, nonesterified fatty acid concentrations, and metabolic rate in response to a standard test meal followed by a 24-h fast in 21 healthy Pima Indians. Plasma leptin concentrations decreased by 8% (P < 0.05) 2-4 h after the test meal. They returned to baseline 6-12 h after the subjects ate, then subsequently decreased, and, by the end of the fast, were an average of 37% below baseline (P < 0.0001). Changes in plasma leptin concentrations did not correlate with changes in plasma glucose, insulin, triglyceride, or nonesterified fatty acid concentrations or with changes in metabolic rate. The results of this study indicate that plasma leptin concentrations decrease in response to short-term energy restriction. These changes were not due to changes in glucose, insulin, triglycerides, or nonesterified fatty acids, nor did they relate to changes in metabolic rate. The decrease in plasma leptin concentrations with fasting may be an important homeostatic response to an energy deficit, stimulating food intake and thus restoring energy balance.

To investigate the possible role of impaired sympathetic nervous system and/or adrenal medullary function in the etiology of human obesity, we studied 64 Pima Indian men (28 +/- 6 years, 101 +/- 25 kg, 34 +/- 9% body fat, mean +/- SD) in whom sympathoadrenal function was estimated at baseline by measurements of 24-hour urinary norepinephrine (NE) and epinephrine (Epi) excretion rates under weight-maintenance conditions. Body weight, body composition (hydrodensitometry), and body fat distribution (waist-to-thigh circumference ratio, W/T) were measured at baseline and follow-up. Follow-up data were available on 44 subjects who gained on average 8.4 +/- 9.5 kg over 3.3 +/- 2.1 years. In these subjects, baseline NE excretion rate, adjusted for its determinants (i.e., fat free mass, fat mass, and W/T), correlated negatively with bodyweight gain (r = -0.38; p = 0.009). Baseline Epi excretion rate correlated negatively with changes in W/T (r = -0.44; p = 0.003). In conclusion, our data show for the first time that a flow sympathetic nervous system activity is associated with body weight gain in humans. Also, a low activity of the adrenal medulla is associated with the development of central adiposity.

A Trp64Arg variant in the human beta 3-adrenoceptor is associated with earlier onset of non-insulin-dependent diabetes mellitus and obesity in several populations. The present study investigated in vivo lipolysis in individuals homozygous for the 'variant' allele coding for arginine (Arg) in position 64 of the beta 3-adrenoceptor or homozygous for the 'wild type' tryptophan (Trp) allele. Subjects were 25 healthy, non-diabetic Pima Indians, 8 Arg (2 males, 6 females; aged 34 +/- 9 years, BMI 36.2 +/- 7.7 kg/m2, 43 +/- 11% body fat [mean +/- SD]), and 17 Trp (9 males, 8 females; aged 30 +/- 5 years, BMI 30.4 +/- 6.1 kg/m2, 39 +/- 9% body fat). After an overnight fast, a microdialysis probe was inserted in the subcutaneous adipose tissue and perfused with Ringer's solution. Dialysate was collected in 10-min fractions during a 30-min baseline and during 40 min with isoproterenol, a non-selective beta-adrenergic agonist, added to the perfusate (1 mumol/l). Changes in rate of lipolysis were assessed as changes in dialysate glycerol concentration. The relative changes in dialysate glycerol concentrations in response to isoproterenol, expressed as percent over baseline, were similar in the two groups (i.e. 63 +/- 30 and 74 +/- 28% in the Arg and Trp subjects, respectively). The results were also similar in the two groups after adjustment for sex and percentage of body fat. No differential effect of isoproterenol on blood flow was demonstrated between the two groups (assessed by the ethanol dilution technique). These results are consistent with in vitro studies showing no functional effect of the beta 3-adrenoceptor variant, and/or indicate that the beta 3-adrenoceptor is not very important for subcutaneous adipose tissue lipolysis.

On the basis of accumulating evidence that obesity has a substantial genetic component, a genomewide search for linkages of DNA markers to percent body fat is ongoing in Pima Indians, a population with a very high prevalence of obesity. An initial screen of the genome (>600 markers in 874 individuals) has been completed using highly polymorphic markers (mean heterozygosity = .67). Reported here are the sib-pair linkage results for percent body fat (277 siblings), the best available indicator of overall obesity. Single-marker linkages to percent body fat were evaluated by sib-pair analysis for quantitative traits. From these analyses, the best evidence of genes influencing body fat came from markers at chromosome 11q21-q22 and 3p24.2-p22 (P = .001; LOD = 2.0). Regions flanking these markers were further investigated by multipoint linkage. The evidence for linkage at 11q21-q22 increased to P = .0002 (LOD = 2.8), peaking between markers D11S2000 and D11S2366. Evidence for linkage at 3p24.2-p22 did not change. No association was detected for any marker in the region. Although several genes are known in the 11q21-q22 region, none have been implicated as candidate genes for obesity.

Muscle sympathetic nerve activity (MSNA) has been correlated with percent body fat (%BF) in males. Because MSNA is typically lower and %BF higher in females, we tested whether this relationship could be generalized to females. Because abdominal-visceral body fat in men may be responsible for elevated sympathetic activity, we hypothesized that an estimate [waist-to-thigh ratio (W/T)] would correlate positively with MSNA in both genders and account for higher MSNA in males. Microneurography, hydrodensitometry, and W/T measures were obtained in 14 males and 14 females with a large range of %BF and W/T. Regression analyses revealed positive correlations between MSNA and %BF in males (r = 0.55, P = 0.04) and in females (r = 0.63, P = 0.02), with no difference in the slopes of the regression lines but a higher intercept in males (P < 0.01). When genders were pooled, MSNA and W/T were correlated (r = 0.68, P < 0.0001); this positive correlation was also found in males (r = 0.57, P = 0.04) but not as strongly in females (r = 0.49, P = 0.07). Forward stepwise multiple-regression analysis using %BF, W/T, gender, and age indicated that W/T was the primary factor related to MSNA (R2 = 0.46); the other factors were not independent predictors. It is concluded that %BF is related to MSNA in both males and females but that the regression line is shifted downward in females because of lower levels of MSNA. W/T is a better correlate of MSNA than %BF and partially explains the higher MSNA in males. These findings may be relevant to the cardiovascular and metabolic disease risk associated with abdominal obesity.

To assess the role of fasting plasma non-esterified fatty acids (NEFA) in the development of non-insulin-dependent diabetes mellitus (NIDDM), data were analysed from annual examinations of 190 non-diabetic Pima Indians. Glucose tolerance was measured by a 75-g oral glucose tolerance test, insulin action by a euglycaemic hyperinsulinaemic (40 mU x m-2 x min-1) clamp and in vitro lipolysis using isolated abdominal fat cells. After a mean follow-up period of 4.0 +/- 2.4 years (mean +/- SD), 47 subjects developed NIDDM. Risk factors for NIDDM were estimated by proportional-hazards analysis and risk ratios (RR) with 95% confidence intervals (95% CI) calculated at the 90th and 10th percentile of the predictor variables. A large average fat-cell volume was predictive of NIDDM (RR=2.4; 95% CI=1.2-4.8) independent of age, sex, percent body and body fat distribution. A high fasting plasma NEFA concentration was also a risk factor for NIDDM (RR=2.3; 95% CI=1.1-4.7) independent of sex, percent body fat, waist/thigh ratio, insulin-mediated glucose uptake and fasting triglyceride concentration. We conclude that large fat cells and the resulting increased plasma NEFA concentrations are risk factors for the development of NIDDM.

Objective: Upper body obesity seems to be associated with a better prognosis for weight loss than does lower body obesity. However, the impact of body fat distribution on energy metabolism is not clear., Subjects: One hundred fifteen non-diabetic obese Caucasians (64 males and 51 females) and 108 Caucasian lean controls (82 males and 26 females) were studied., Methods: Body composition was assessed by hydrodensitometry and body fat distribution was estimated by the waist-to-thigh circumference ratio (W/T). Values of 24-hour energy expenditure (24h-EE), basal metabolic rate (BMR), sleeping metabolic rate (SMR) and respiratory quotient (RQ) were measured in a respiration chamber., Results: BMR, adjusted for differences in fat-free mass, fat mass, age and sex, correlated with W/T in obese males (r = 0.40; p < 0.01), but not in obese females. Obese male subjects with upper body obesity had BMR significantly higher than those with lower body obesity (2189 +/- 268 vs 1974 +/- 141 kcal/day; p < 0.01), independently of differences in fat-free mass, fat mass and age. No correlations were found between W/T and adjusted 24h-EE, SMR or RQ in all examined groups., Conclusion: These findings indicate that in obese males, upper body obesity is associated with increased metabolic rate, possibly related to higher levels of lipid turnover in visceral fat.

Adipsin, which is identical to complement factor D, is synthesized by fat cells, circulates in the bloodstream and is profoundly deficient in mice with genetic and hypothalamic obesity. With the recent cloning of human adipsin, a quantitative human immunoassay has been developed. In the present study, we measured adipsin blood concentrations in humans with increased and decreased adipose stores as well as adipsin secretion by adipose tissue obtained from lean and obese individuals. The results demonstrate that adipsin is released by human adipose tissue fragments as has previously been shown in mice, and that, in contrast to obese mice, blood adipsin concentrations were not reduced in the obese humans tested in this study. We also observed that blood adipsin concentrations can vary as a function of feeding or adiposity, in that they tend to be mildly elevated in obese individuals or mildly reduced in individuals with total lipo-atrophy, cachexia related to AIDS and anorexia nervosa. Thus, the circulating concentration of adipsin tends to correlate positively with degree of adiposity. Clearly, no deficiency in blood adipsin concentrations or adipsin secretion by adipose tissue was observed in the obese individuals studied.

Carbohydrate intake stimulates sympathetic nervous system activity in lean subjects, whereas in obese subjects, the results have been inconsistent. The aim of this study was to directly measure sympathetic neural outflow to skeletal muscle in response to a 75-g oral glucose tolerance test (OGTT) in 15 Pima Indian and 16 Caucasian men, matched for body fat and age, but covering a large range of body weight (57-113 kg) and body fat (4-41%). Fasting muscle sympathetic nerve activity (MSNA) correlated positively with body fat (r = 0.73; P = 0.001) in Caucasians but not in Pima Indians, whereas the increase in MSNA during the OGTT correlated negatively with the percentage of body fat (r = -0.38, P = 0.03) independently of race. In each subject, the increase in MSNA over time correlated positively with the increase in plasma insulin levels, but the slopes of these relationships were inversely related to the percentage of body fat (r = -0.52, P = 0.003) independently of race. In conclusion, obesity is associated with a higher fasting sympathetic neural outflow to muscle but a blunted increase in response to an oral glucose load despite a larger increase in plasma insulin levels. This blunted response may represent another feature of the obesity/insulin resistance syndrome.

Studies have been conducted on various metabolic characteristics of lean and obese Pima Indians, including studies of fat-cell morphology, glucose transport, and lipolysis; lipoprotein lipase activities; sodium-potassium ATPase in red cells, adipocytes, and fibroblasts; lipids and lipoprotein metabolism; fatty acid metabolism; and sterol balance. Insulin concentrations, insulin binding, insulin action on glucose disposal, fatty acid metabolism, and islet function were compared in lean and obese individuals, and the relationship between insulin resistance and muscle morphology was explored. To explore potential abnormalities in energy balance, calorie intake and gastric emptying were compared in lean and obese Pimas and measurements of energy expenditure were performed. The data suggest that there are multiple metabolic differences that accompany obesity in Native Americans. A lower metabolic rate was a determinant of future weight gain, and abnormalities in use of free fatty acids and cell insulin action were suggested, which emphasize the need for further studies in these areas.

To assess the validity of bioelectrical resistance (BR) in an obese population, body composition was determined by both hydrostatic weighing and by BR in 156 Pima Indian volunteers representing a wide range of body weight (46.1-202.6 kg) and body composition (11-52% fat). A predictive equation was derived by use of data on height, BR, weight, age, and sex from 130 randomly selected volunteers and was applied to the remaining 26 volunteers. When compared with the manufacturer's software, the new equation increased correlations with hydrostatic weighing for predicting percent body fat and fat-free mass (FFM) from 0.70 to 0.92 and 0.79 to 0.97, respectively. The manufacturer's software underestimated FFM by 5.3 +/- 8.6 kg (P less than 0.05) when compared with FFM derived from hydrostatic weighing whereas the new equation improved the accuracy to -0.1 +/- 3.3 kg (NS). There were no significant effects of fluid intake (700 mL) or breakfast consumption on body composition as determined by BR. BR represents a simple and accurate way to assess body composition in Pima Indians with our newly derived equation.