Quantification of adipose tissue by MRI: relationship with anthropometric variables.

This study had two objectives: 1) to establish magnetic resonance imaging (MRI) as a tool for measuring total and regional adipose tissue (AT) distribution in humans and 2) to assess the relationship between selected anthropometric variables and MRI-measured AT. Twenty-seven healthy men varying in age [40.8 +/- 14.5 (SD) yr], body mass index (28.5 +/- 4.8), and waist-to-hip ratio (WHR, 0.96 +/- 0.07) participated in the study. Total AT volume was determined using a linear interpolation of AT areas obtained on consecutive slices (n = 41) taken from head to toe (10-mm thickness, 50-mm centers). The mean change for repeated measures of total AT volume was 2.9% (range 0.9-4.3%). Large interindividual differences were observed for total AT volume (6.9-59.3 liters), subcutaneous AT (6.3-49.8 liters), and visceral AT (0.5-8.5 liters). Visceral AT represented 18.3% of the total AT. The single best predictor of total adiposity was waist circumference (R2 = 0.92). For visceral AT volume, WHR was the strongest anthropometric correlate (r = 0.85, P less than 0.01). When controlled for age and adiposity, however, WHR explained only 12% of the variation in absolute visceral AT and less than 1% of the variation in visceral-to-subcutaneous ratio. Age was a better predictor of visceral-to-subcutaneous ratio than level of adiposity or WHR. The results of this study demonstrate that MRI offers a reliable measure of regional and total AT distribution in humans and, thus, is of value as a research tool.     

Regional skeletal muscle measurement: evaluation of new dual-energy X-ray absorptiometry model.

Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM) mass measurement methods remain limited. The aim of the present study was to develop a new dual-energy X-ray absorptiometry (DEXA) model for estimating regional adipose tissue-free skeletal muscle mass (AT-free SM). Relationships were derived from Reference Man data between tissue-system- level components (i.e., AT-free SM, AT, skeleton, and skin) and molecular-level components including fat-free soft tissue, fat, and bone mineral. The proposed DEXA-SM model was evaluated by multiscan computerized axial tomography (CT). Twenty-seven male subjects [age, 36 +/- 12 (SD) yr; body mass, 73.2 +/- 12.4 kg; 20 were healthy, and 7 had acquired immunodeficiency syndrome] completed DEXA and CT studies. Identical landmarks for DEXA and CT measurements were selected in three regions, including calves, thighs, and forearms. There was a strong correlation for AT-free SM estimates between the new DEXA and CT methods (e.g., sum of three regions, r = 0.86, P < 0.001). Regional AT-free SM measured in the 27 subjects by DEXA and CT, respectively, were 3.44 +/- 0.60 and 3. 47 +/- 0.55 kg (difference 0.9%, P > 0.05) for calves, 10.49 +/- 1. 77 and 10.05 +/- 1.79 kg (difference 4.4%, P < 0.05) for thighs, 1. 36 +/- 0.49 and 1.20 +/- 0.41 kg (difference 13.3%, P < 0.01) for forearms, and 15.29 +/- 2.33 and 14.72 +/- 2.33 kg (difference 3.9%, P < 0.05) for the sum all three regions. Although the suggested DEXA-SM model needs minor refinements, this is a promising in vivo approach for measurement of regional SM, because DEXA is widely available, relatively inexpensive, and radiation exposure is low.     

Abdominal fat distribution and peripheral and hepatic insulin resistance in type 2 diabetes mellitus

We examined the relationship between peripheral/hepatic insulin sensitivity and abdominal superficial/deep subcutaneous fat (SSF/DSF) and intra-abdominal visceral fat (VF) in patients with type 2 diabetes mellitus (T2DM). Sixty-two T2DM patients (36 males and 26 females, age = 55 +/- 3 yr, body mass index = 30 +/- 1 kg/m2) underwent a two-step euglycemic insulin clamp (40 and 160 mU. m(-2). min(-1)) with [3-3H]glucose. SSF, DSF, and VF areas were quantitated with magnetic resonance imaging at the L(4-5) level. Basal endogenous glucose production (EGP), hepatic insulin resistance index (basal EGP x FPI), and total glucose disposal (TGD) during the first and second insulin clamp steps were similar in male and female subjects. VF (159 +/- 9 vs. 143 +/- 9 cm2) and DSF (199 +/- 14 vs. 200 +/- 15 cm(2)) were not different in male and female subjects. SSF (104 +/- 8 vs. 223 +/- 15 cm2) was greater (P < 0.0001) in female vs. male subjects despite similar body mass index (31 +/- 1 vs. 30 +/- 1 kg/m2) and total body fat mass (31 +/- 2 vs. 33 +/- 2 kg). In male T2DM, TGD during the first insulin clamp step (1st TGD) correlated inversely with VF (r = -0.45, P < 0.01), DSF (r = -0.46, P < 0.01), and SSF (r = -0.39, P < 0.05). In males, VF (r = 0.37, P < 0.05), DSF (r = 0.49, P < 0.01), and SSF (r = 0.33, P < 0.05) were correlated positively with hepatic insulin resistance. In females, the first TGD (r = -0.45, P < 0.05) and hepatic insulin resistance (r = 0.49, P < 0.05) correlated with VF but not with DSF, SSF, or total subcutaneous fat area. We conclude that visceral adiposity is associated with both peripheral and hepatic insulin resistance, independent of gender, in T2DM. In male but not female T2DM, deep subcutaneous adipose tissue also is associated with peripheral and hepatic insulin resistance.     

Weight loss increases cardiovagal baroreflex function in obese young and older men

We tested the hypothesis that reductions in total body and abdominal visceral fat with energy restriction would be associated with increases in cardiovagal baroreflex sensitivity (BRS) in overweight/obese older men. To address this, overweight/obese (25 < or = body mass index < or = 35 kg/m(2)) young (OB-Y, n = 10, age = 32.9 +/- 2.3 yr) and older (OB-O, n = 6, age = 60 +/- 2.7 yr) men underwent 3 mo of energy restriction at a level designed to reduce body weight by 5-10%. Cardiovagal BRS (modified Oxford technique), body composition (dual-energy X-ray absorptiometry), and abdominal fat distribution (computed tomography) were measured in the overweight/obese men before weight loss and after 4 wk of weight stability at their reduced weight and compared with a group of nonobese young men (NO-Y, n = 13, age = 21.1 +/- 1.0 yr). Before weight loss, cardiovagal BRS was approximately 35% and approximately 60% lower (P < 0.05) in the OB-Y and OB-O compared with NO-Y. Body weight (-7.8 +/- 1.1 vs. -7.3 +/- 0.7 kg), total fat mass (-4.1 +/- 1.0 vs. -4.4 +/- 0.8 kg), and abdominal visceral fat (-27.6 +/- 6.9 vs. -43.5 +/- 10.1 cm(2)) were reduced (all P < 0.05) after weight loss, but the magnitude of reduction did not differ (all P > 0.05) between OB-Y and OB-O, respectively. Cardiovagal BRS increased (11.5 +/- 1.9 vs. 18.5 +/- 2.6 ms/mmHg and 6.7 +/- 1.2 vs. 12.8 +/- 4.2 ms/mmHg) after weight loss (both P < 0.05) in OB-Y and OB-O, respectively. After weight loss, cardiovagal BRS in the obese/overweight young and older men was approximately 105% and approximately 73% (P > 0.05) of NO-Y (17.5 +/- 2.2 ms/mmHg). Therefore, the results of this study indicate that weight loss increases the sensitivity of the cardiovagal baroreflex in overweight/obese young and older men.     

Subcutaneous obesity is not associated with sympathetic neural activation

We tested the hypothesis that muscle sympathetic nerve activity (MSNA) would not differ in subcutaneously obese (SUBOB) and nonobese (NO) men with similar levels of abdominal visceral fat despite higher plasma leptin concentrations in the former. We further hypothesized that abdominal visceral fat would be the strongest body composition- or regional fat distribution-related correlate of MSNA among these individuals. To accomplish this, we measured MSNA (via microneurography), body composition (via dual-energy X-ray absorptiometry), and abdominal fat distribution (via computed tomography) in 15 NO (body mass index 0.05, respectively) despite approximately 2.6-fold higher (P < 0.05) plasma leptin concentration in the SUBOB men. Furthermore, abdominal visceral fat was the only body composition- or regional fat distribution-related correlate (r = 0.45; P < 0.05) of MSNA in the pooled sample. In addition, abdominal visceral fat was related to MSNA in NO (r = 0.58; P = 0.0239) but not SUBOB (r = 0.39; P = 0.3027) men. Taken together with our previous observations, our findings suggest that the relation between obesity and MSNA is phenotype dependent. The relation between abdominal visceral fat and MSNA was evident in NO but not in SUBOB men and at levels of abdominal visceral fat below the level typically associated with elevated cardiovascular and metabolic disease risk. Our observations do not support an obvious role for leptin in contributing to sympathetic neural activation in human obesity and, in turn, are inconsistent with the concept of selective leptin resistance.     

Lower limb skeletal muscle mass: development of dual-energy X-ray absorptiometry prediction model.

Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 +/- 16 (SD) yr, body mass index (BMI) 24.6 +/- 3.7 kg/m(2)]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R(2) = 0.89, P < 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXA-predicted SM mass were small (-0.006 +/- 1.07 and -0.016 +/- 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fat-free soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.     

Exercise-induced reversal of insulin resistance in obese elderly is associated with reduced visceral fat.

Exercise improves glucose metabolism and delays the onset and/or reverses insulin resistance in the elderly by an unknown mechanism. In the present study, we examined the effects of exercise training on glucose metabolism, abdominal adiposity, and adipocytokines in obese elderly. Sixteen obese men and women (age = 63 +/- 1 yr, body mass index = 33.2 +/- 1.4 kg/m2) participated in a 12-wk supervised exercise program (5 days/wk, 60 min/day, treadmill/cycle ergometry at 85% of heart rate maximum). Visceral fat (VF), subcutaneous fat, and total abdominal fat were measured by computed tomography. Fat mass and fat-free mass were assessed by hydrostatic weighing. An oral glucose tolerance test was used to determine changes in insulin resistance. Exercise training increased maximal oxygen consumption (21.3 +/- 0.8 vs. 24.3 +/- 1.0 ml.kg(-1).min(-1), P < 0.0001), decreased body weight (P < 0.0001) and fat mass (P < 0.001), while fat-free mass was not altered (P > 0.05). VF (176 +/- 20 vs. 136 +/- 17 cm2, P < 0.0001), subcutaneous fat (351 +/- 34 vs. 305 +/- 28 cm2, P < 0.03), and total abdominal fat (525 +/- 40 vs. 443 +/- 34 cm2, P < 0.003) were reduced through training. Circulating leptin was lower (P < 0.003) after training, but total adiponectin and tumor necrosis factor-alpha remained unchanged. Insulin resistance was reversed by exercise (40.1 +/- 7.7 vs. 27.6 +/- 5.6 units, P < 0.01) and correlated with changes in VF (r = 0.66, P < 0.01) and maximal oxygen consumption (r = -0.48, P < 0.05) but not adipocytokines. VF loss after aerobic exercise training improves glucose metabolism and is associated with the reversal of insulin resistance in older obese men and women.     

Meal-related increases in vascular reactivity are impaired in older and diabetic adults: insights into roles of aging and insulin in vascular flow

A fatty meal induces vasodilatation (of both resting and stimulated forearm flow) in healthy young adults, an effect most likely mediated by the vasodilator actions of insulin. We therefore hypothesized that an impaired meal-related vascular response might be an in vivo marker of vascular insulin resistance, related to the presence of diabetes and/or higher age. Postprandial vascular responses were assessed in three groups of subjects: 15 Type 2 diabetic subjects (age 58 +/- 8 yr), 15 age-, gender-, and body mass index (BMI)-matched older control subjects (age 57 +/- 9 yr), and 15 healthy young control subjects (age 33 +/- 7 yr). Studies were carried out before and 3 and 6 h after a standardized high-fat meal (1,030 kcal, 61 g fat). Forearm microvascular flows were measured by strain gauge plethysmography and large-artery function by ultrasound. Resting blood flow and hyperemic area under curve (AUC) flow were not significantly different in diabetic subjects (resting 117 +/- 42% and AUC 134 +/- 46% of premeal values) compared with age-matched controls (resting 131 +/- 39% and AUC 134 +/- 47%); however, the response in diabetic subjects was blunted compared with young controls (resting 171 +/- 67% and AUC 173 +/- 99% of premeal values; P = 0.02 and P = 0.18, respectively). On multiple regression analysis, we found that increasing age (but not BMI or diabetes) was significantly associated with impaired postprandial vascular responses (resting: r = -0.4, P = 0.002; AUC: r = -0.4, P = 0.006). Therefore, meal ingestion results in impaired vasodilator responses in older nondiabetic and diabetic adults, related to aging rather than insulin resistance.     

Pre-heparin plasma lipoprotein lipase mass: correlation with intra-abdominal visceral fat accumulation.

OBJECTIVE: To determine how lipoprotein lipase mass in the pre-heparin plasma is affected by body fat distribution, which is known to be closely related to lipid disorder, either directly or through insulin resistance. SUBJECTS: A total of 57 subjects consisting of 50 hyperlipidemic and 7 normolipidemic subjects (age 54 +/- IIy; 31 men, 26 women; body mass index 24+/- 2.5 kg/m2; serum total cholesterol 6.4+/-1.5 mmol/l; triglycerides, 2.4 +/- 1.7 mmol/l; HDL-cholesterol 1.3 +/- 0.5 mmol/l) were enrolled. MEASUREMENTS: We investigated the correlation between pre-heparin plasma LPL mass and intra-abdominal visceral fat area (or subcutaneous fat area) evaluated by computed tomography, and serum lipids and lipoproteins. RESULTS: Pre-heparin plasma LPL mass correlated inversely against intra-abdominal visceral fat area (r = - 0.51, p < 0.0001) and body mass index (r = - 0.46, p = 0.0003), but did not show any significant correlation with subcutaneous fat area. Pre-heparin plasma LPL mass had a positive correlation with serum high density lipoprotein cholesterol (r = 0.45, p = 0.0004) and a negative correlation against serum triglycerides (r = - 0.48, p = 0.0002). CONCLUSIONS: Pre-heparin plasma LPL mass is closely associated with intra-abdominal fat distribution, and the measurement of its value gives useful information concerning metabolic disorder.     

Plasma adiponectin concentration in healthy pre- and postmenopausal women: relationship with body composition, bone mineral, and metabolic variables

The aim of the current investigation was to determine the possible relationships of fasting adiponectin level with body composition, bone mineral, insulin sensitivity, leptin, and cardiorespiratory fitness parameters in 153 women. Subjects were classified as premenopausal (n = 42; 40.8 +/- 5.7 yr) if they had regular menstrual periods, early postmenopausal (n = 49; 56.7 +/- 3.6 yr) if they had been postmenopausal for more than >1 yr but <7 yr (5.5 +/- 1.3 yr), and postmenopausal (n = 62; 72.2 +/- 4.5 yr) if they had been postmenopausal for >7 yr. All women studied had a body mass index (BMI) <30 kg/m(2). Adiponectin values were higher (P < 0.05) in middle-aged (12.0 +/- 5.1 microg/ml) and older (15.3 +/- 7.3 microg/ml) postmenopausal women compared with middle-aged premenopausal women (8.4 +/- 3.2 microg/ml). Mean plasma adiponectin concentration in the total group of women (n = 153) was 12.2 +/- 6.3 microg/ml and was positively related (P < 0.05) to age, indexes of overall obesity (BMI, body fat mass), and cardiorespiratory fitness (PWC) values. In addition, a negative association (P < 0.05) between adiponectin with central obesity (waist-to-hip and waist-to-thigh ratio), fat-free mass, bone mineral (bone mineral content, total and lumbar spine bone mineral density), and leptin and insulin resistance (insulin, fasting insulin resistance index) values was observed. However, multivariate regression analysis revealed that only age, fasting insulin resistance index, and leptin were independent predictors of adiponectin concentration. In conclusion, circulating adiponectin concentrations increase with age in normal-weight middle-aged and older women. It appears that adiponectin is independently related to age, leptin, and insulin resistance values in women across the age span and menstrual status.     

Reliability and validity of body composition measures in female athletes.

The purpose of this investigation was to determine the reliability and validity of bioelectrical impedance (BIA) and near-infrared interactance (NIR) for estimating body composition in female athletes. Dual-energy X-ray absorptiometry was used as the criterion measure for fat-free mass (FFM). Studies were performed in 132 athletes [age = 20.4 +/- 1.5 (SD) yr]. Intraclass reliabilities (repeat and single trial) were 0.987-0.997 for BIA (resistance and reactance) and 0.957-0.980 for NIR (optical densities). Validity of BIA and NIR was assessed by double cross-validation. Because correlations were high (r = 0.969-0.983) and prediction errors low, a single equation was developed by using all 132 subjects for both BIA and NIR. Also, an equation was developed for all subjects by using height and weight only. Results from dual-energy X-ray absorptiometry analysis showed FFM = 49.5 +/- 6.0 kg, which corresponded to %body fat (%BF) of 20.4 +/- 3.1%. BIA predicted FFM at 49.4 +/- 5.9 kg (r = 0.981, SEE = 1.1), and NIR prediction was 49. 5 +/- 5.8 kg (r = 0.975, SEE = 1.2). Height and weight alone predicted FFM at 49.4 +/- 5.7 kg (r = 0.961, SEE = 1.6). When converted to %BF, prediction errors were approximately 1.8% for BIA and NIR and 2.9% for height and weight. Results showed BIA and NIR to be extremely reliable and valid techniques for estimating body composition in college-age female athletes.     

Estimation of skeletal muscle mass by bioelectrical impedance analysis.

The purpose of this study was to develop and cross-validate predictive equations for estimating skeletal muscle (SM) mass using bioelectrical impedance analysis (BIA). Whole body SM mass, determined by magnetic resonance imaging, was compared with BIA measurements in a multiethnic sample of 388 men and women, aged 18-86 yr, at two different laboratories. Within each laboratory, equations for predicting SM mass from BIA measurements were derived using the data of the Caucasian subjects. These equations were then applied to the Caucasian subjects from the other laboratory to cross-validate the BIA method. Because the equations cross-validated (i.e., were not different), the data from both laboratories were pooled to generate the final regression equation SM mass (kg) = [(Ht²/ R x 0.401) + (gender x 3.825) + (age x -0. 071)] + 5.102 where Ht is height in centimeters; R is BIA resistance in ohms; for gender, men = 1 and women = 0; and age is in years. The r(2) and SE of estimate of the regression equation were 0.86 and 2.7 kg (9%), respectively. The Caucasian-derived equation was applicable to Hispanics and African-Americans, but it underestimated SM mass in Asians. These results suggest that the BIA equation provides valid estimates of SM mass in healthy adults varying in age and adiposity.     

Validity and reliability of dual-energy X-ray absorptiometry for the assessment of abdominal adiposity.

A number of methods exist for the estimation of abdominal obesity, ranging from waist-to-hip ratio to computed tomography (CT). Although dual-energy X-ray absorptiometry (DXA) was originally used to measure bone density and total body composition, recent improvements in software allow it to determine abdominal fat mass. Sixty-five men and women aged 18-72 yr participated in a series of studies to examine the validity and reliability of the DXA to accurately measure abdominal fat. Total body fat and abdominal regional fat were measured by DXA using a Lunar DPX-IQ. Multislice CT scans were performed between L1 and L4 vertebral bodies (region of interest) using a Picker PQ5000 CT scanner, and volumetric analyses were carried out on a Voxel Q workstation. Both abdominal total tissue mass (P = 0.02) and abdominal fat mass (P < 0.0001) in the L1-L4 region of interest were significantly lower as measured by DXA compared with multislice CT. However, Bland-Altman analysis demonstrated good concordance between DXA and CT for abdominal total tissue mass (i.e., limits of agreement = -1.56-2.54 kg) and fat mass (i.e., limits of agreement = -0.40-1.94 kg). DXA also showed excellent reliability among three different operators to determine total, fat, and lean body mass in the L1-L4 region of interest (intraclass correlations, R = 0.94, 0.97, and 0.89, respectively). In conclusion, the DXA L1-L4 region of interest compared with CT proved to be both reliable and accurate method to determine abdominal obesity.     

Single Slice vs. Volumetric MR Assessment of Visceral Adipose Tissue: Reliability and Validity Among the Overweight and Obese

Visceral adipose tissue (VAT) is associated with abnormal cardiovascular and metabolic profiles. Total VAT volume of the abdominal compartment by magnetic resonance imaging (MRI) is the gold-standard measurement for VAT but is costly and time consuming. Prior studies suggest VAT area on a single slice MR image may serve as a surrogate for total VAT volume but it is unknown if this relationship is maintained in overweight and obese men and women. Untreated sleep apnea subjects enrolled into the Icelandic Sleep Apnea Cohort (ISAC) underwent abdominal MRI. VAT area and subcutaneous adipose tissue (SAT) area at the L2-L3 and L4-L5 interspaces and total VAT and SAT volumes were determined by manual examination using image analysis software; 539 men and 129 women with mean ages of 54.1 and 58.8 years and mean BMI of 32.2 kg/m(2) and 33.7 kg/m(2), respectively, were studied. Mean total VAT volume was 40% smaller and mean total SAT was 25% larger among females compared with males. The correlation with VAT volume was significantly larger for L2-L3 VAT area (r = 0.96) compared to L4-L5 VAT area (r = 0.83). The difference in correlation coefficients was statistically significant (nonparametric bootstrap P < 0.001 with 95% confidence interval (CI) for the difference from 0.11 to 0.15. VAT area at L2-L3 was also significantly better correlated with VAT volume than traditional anthropometric variables. Linear regression analyses demonstrated that L2-L3 area alone was sufficient for predicting total VAT volume and that the nature of the linear association was maintained across all levels of obesity and in both genders.     

Adipose tissue volume measured by magnetic resonance imaging and computerized tomography in rats

The primary purpose of this study was to investigate the viability of magnetic resonance imaging (MRI) as a means of measuring the body composition of rodents. To do so we compared adipose tissue (AT) volumes measured by MRI with those obtained by X-ray computerized tomography (CT) in a group of rats (n = 17) varying in weight (465-815 g) and percent body fat (5.4-31.1%), with the latter determined by chemical analysis. For both MRI and CT, AT volumes (cm3) per transverse slice (3-mm thickness, 21-mm centers) were determined using a computer-based image analysis system that permitted detailed comparisons of both visceral and subcutaneous AT depots. Total AT volumes were calculated using a linear interpolation of AT areas obtained on consecutive slices. Correlation coefficients between MRI and CT for visceral [r = 0.98, standard error of estimate (SEE) = 6.8 cm3], subcutaneous (r = 0.98, SEE = 6.5 cm3), and total AT volumes (r = 0.99, SEE = 9.0 cm3) were highly significant (P less than 0.001). Both MRI- and CT-predicted AT mass (assuming fat density = 0.90 g/ml) correlated strongly with chemically extracted lipid (grams) values (r = 0.98, SEE 9.6 g and r = 0.99, SEE = 6.9 g, respectively). Post hoc Scheffé contrasts demonstrated that the mean AT and lipid mass values derived by the three methods were not significantly different (P = 0.01). No systematic differences were observed because the regression lines derived for either MRI or CT vs. chemical analysis were not significantly different from the identity line.(ABSTRACT TRUNCATED AT 250 WORDS)     

Weight loss in postmenopausal obesity: no adverse alterations in body composition and protein metabolism

We sought to determine if decrements in the mass of fat-free body mass (FFM) and other lean tissue compartments, and related changes in protein metabolism, are appropriate for weight loss in obese older women. Subjects were 14 healthy weight-stable obese (BMI > or =30 kg/m(2)) postmenopausal women >55 yr who participated in a 16-wk, 1, 200 kcal/day nutritionally complete diet. Measures at baseline and 16 wk included FFM and appendicular lean soft tissue (LST) by dual-energy X-ray absorptiometry; body cell mass (BCM) by (40)K whole body counting; total body water (TBW) by tritium dilution; skeletal muscle (SM) by whole body MRI; and fasting whole body protein metabolism through L-[1-(13)C]leucine kinetics. Mean weight loss (+/-SD) was 9.6+/-3.0 kg (P<0.0001) or 10.7% of initial body weight. FFM decreased by 2.1+/-2.6 kg (P = 0.006), or 19.5% of weight loss, and did not differ from that reported (2.3+/-0.7 kg). Relative losses of SM, LST, TBW, and BCM were consistent with reductions in body weight and FFM. Changes in [(13)C]leucine flux, oxidation, and synthesis rates were not significant. Follow-up of 11 subjects at 23.7 +/-5.7 mo showed body weight and fat mass to be below baseline values; FFM was nonsignificantly reduced. Weight loss was accompanied by body composition and protein kinetic changes that appear appropriate for the magnitude of body mass change, thus failing to support the concern that diet-induced weight loss in obese postmenopausal women produces disproportionate LST losses.     

Weight stability masks sarcopenia in elderly men and women

Skeletal muscle loss or sarcopenia in aging has been suggested in cross-sectional studies but has not been shown in elderly subjects using appropriate measurement techniques combined with a longitudinal study design. Longitudinal skeletal muscle mass changes after age 60 yr were investigated in independently living, healthy men (n = 24) and women (n = 54; mean age 73 yr) with a mean +/- SD follow-up time of 4.7 +/- 2.3 yr. Measurements included regional skeletal muscle mass, four additional lean components (fat-free body mass, body cell mass, total body water, and bone mineral), and total body fat. Total appendicular skeletal muscle (TSM) mass decreased in men (-0.8 +/- 1.2 kg, P = 0.002), consisting of leg skeletal muscle (LSM) loss (-0.7 +/- 0.8 kg, P = 0.001) and a trend toward loss of arm skeletal muscle (ASM; -0.2 +/- 0.4 kg, P = 0.06). In women, TSM mass decreased (-0.4 +/- 1.2 kg, P = 0.006) and consisted of LSM loss (-0.3 +/- 0.8 kg, P = 0.005) and a tendency for a loss of ASM (-0.1 +/- 0.6 kg, P = 0.20). Multiple regression modeling indicates greater rates of LSM loss in men. Body weight in men at follow-up did not change significantly (-0.5 +/- 3.0 kg, P = 0.44) and fat mass increased (+1.2 +/- 2.4 kg, P = 0.03). Body weight and fat mass in women were nonsignificantly reduced (-0.8 +/- 3.9 kg, P = 0.15 and -0.8 +/- 3.5 kg, P = 0.12). These observations suggest that sarcopenia is a progressive process, particularly in elderly men, and occurs even in healthy independently living older adults who may not manifest weight loss.     

Unreliable use of standard muscle hydration value in obesity

Intramuscular water content is assumed to be constant in humans independent of their anthropometric characteristics. To verify whether this assumption is correct, intramuscular water, proteins, glycogen, and both total and intramyocytic triglycerides were measured in 51 samples of rectus abdominis muscle obtained from 16 lean and 35 overweight and obese subjects (body mass index cutoff 24.9 kg/m2). Data (referred to as wet tissue) were analyzed by means of a composition model at the cellular level of the skeletal muscle (SM). The average SM water content was 76.3 +/- 3.3% in normal-weight individuals and 65.7 +/- 5.8% in obese subjects (P < 0.0001). Total triglycerides were 5.5 +/- 2.3% in controls and 19.0 +/- 7.0% in obese subjects (P < 0.0001). The intramyocytic triglyceride fraction was also increased in obese subjects. The composition model provides an explanation for the negative correlation between total triglycerides and intramuscular water, and some of the model parameters were determined from the experimental data. In conclusion, although the hydration of fat-free SM mass may be unchanged in obese subjects, the hydration of in toto muscle mass decreases as its lipid content increases.     

Subcutaneous abdominal preadipocyte differentiation in vitro inversely correlates with central obesity

Expansion of adipose tissue mass results from increased number and size of adipocyte cells. We hypothesized that subcutaneous abdominal preadipocytes in obese individuals might have an intrinsically higher propensity to differentiate into adipocytes. Thus we investigated the relationship between obesity and the level of in vitro preadipocyte differentiation in Pima Indians. Subcutaneous abdominal stromal vascular fractions containing preadipocytes were cultured from 58 nondiabetic subjects [31 M/27 F, 30 +/- 6 yr, body fat 34 +/- 8% by dual-energy X-ray absorptiometry (means +/- SD)]. The average percentage of preadipocyte differentiation (PDIFF; cell count by microscopy) was 11 +/- 11% (range 0.2-51%). PDIFF correlated negatively with percent body fat (r = -0.35, P = 0.006) and waist circumference (r = -0.45, P = 0.0004). Multiple regression analysis indicated that waist circumference (P = 0.01), sex (P = 0.01), and percent body fat (P = 0.05) were significant determinants of PDIFF. Molecular characterization of predifferentiated cultured cells was performed by real-time PCR measurements of glucocorticoid receptor-alpha (GRalpha), insulin-like growth factor I receptor (IGF-IR), peroxisome proliferator-activated receptor-gamma (PPARgamma), enhancer-binding protein GATA-3, CCAAT/enhancer-binding protein-alpha undifferentiated protein (CUP/AP-2alpha), and endothelial cell-specific marker 2 (ECSM2). The mRNA concentrations of GRalpha correlated with PDIFF (r = 0.29, P = 0.03), but the others did not (IGF-IR, r = 0.003, P = 1.0; PPARgamma, r = -0.1, P = 0.5; GATA-3, r = 0.02, P = 0.9; CUP/AP-2alpha, r = -0.2, P = 0.1; ECSM2, r = 0.04, P = 0.7). Contrary to our hypothesis, the results may indicate a blunted in vitro differentiation potential of preadipocytes in centrally obese individuals. The lower differentiation potential of preadipocytes in the obese subjects might be due, at least partly, to decreased glucocorticoid receptor expression.     

Relation between trunk fat volume and reduction of total lung capacity in obese men

Reduction in total lung capacity (TLC) in obese men is associated with restricted expansion of the thoracic cavity at full inflation. We hypothesized that thoracic expansion was reduced by the load imposed by increased total trunk fat volume or its distribution. Using MRI, we measured internal and subcutaneous trunk fat and total abdominal and thoracic volumes at full inflation in 14 obese men [mean age: 52.4 yr, body mass index (BMI): 38.8 (range: 36-44) kg/m(2)] and 7 control men [mean age: 50.1 yr, BMI: 25.0 (range: 22-27.5) kg/m(2)]. TLC was measured by multibreath helium dilution and was restricted (<80% of the predicted value) in six obese men (the OR subgroup). All measurements were made with subjects in the supine position. Mean total trunk fat volume was 16.65 (range: 12.6-21.8) liters in obese men and 6.98 (range: 3.0-10.8) liters in control men. Anthropometry and mean total trunk fat volumes were similar in OR men and obese men without restriction (the ON subgroup). Mean total intraabdominal volume was 9.41 liters in OR men and 11.15 liters in ON men. In obese men, reduced thoracic expansion at full inflation and restriction of TLC were not inversely related to a large volume of 1) intra-abdominal or total abdominal fat, 2) subcutaneous fat volume around the thorax, or 3) total trunk fat volume. In addition, trunk fat volumes in obese men were not inversely related to gas volume or estimated intrathoracic volume at supine functional residual capacity. In conclusion, this study failed to support the hypotheses that restriction of TLC or impaired expansion of the thorax at full inflation in middle-aged obese men was simply a consequence of a large abdominal volume or total trunk fat volume or its distribution.