Impact of prolonged overfeeding on skeletal muscle mitochondria in healthy individuals.

AIMS/HYPOTHESES: Reduced mitochondrial capacity in skeletal muscle has been observed in obesity and type 2 diabetes. In humans, the aetiology of this abnormality is not well understood but the possibility that it is secondary to the stress of nutrient overload has been suggested. To test this hypothesis, we examined whether sustained overfeeding decreases skeletal muscle mitochondrial content or impairs function. METHODS: Twenty-six healthy volunteers (21 men, 5 women, age 25.3 ± 4.5 years, BMI 25.5 ± 2.4 kg/m2) underwent a supervised protocol consisting of 8 weeks of high-fat overfeeding (40% over baseline energy requirements). Before and after overfeeding, we measured systemic fuel oxidation by indirect calorimetry and performed skeletal muscle biopsies to measure mitochondrial gene expression, content and function in vitro. Mitochondrial function in vivo was measured by 31P NMR spectroscopy. RESULTS: With overfeeding, volunteers gained 7.7 ± 1.8 kg (% change 9.8 ± 2.3). Overfeeding increased fasting NEFA, LDL-cholesterol and insulin concentrations. Indirect calorimetry showed a shift towards greater reliance on lipid oxidation. In skeletal muscle tissue, overfeeding increased ceramide content, lipid droplet content and perilipin-2 mRNA expression. Phosphorylation of AMP-activated protein kinase was decreased. Overfeeding increased mRNA expression of certain genes coding for mitochondrial proteins (CS, OGDH, CPT1B, UCP3, ANT1). Despite the stress of nutrient overload, mitochondrial content and mitochondrial respiration in muscle did not change after overfeeding. Similarly, overfeeding had no effect on either the emission of reactive oxygen species or on mitochondrial function in vivo. CONCLUSIONS/INTERPRETATION: Skeletal muscle mitochondria are significantly resilient to nutrient overload. The lower skeletal muscle mitochondrial oxidative capacity in human obesity is likely to be caused by reasons other than nutrient overload per se. TRIAL REGISTRATION: ClinicalTrials.gov NCT01672632.

Cardiovascular risk escalation with caloric excess: a prospective demonstration of the mechanics in healthy adults.

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].

Year-long changes in protein metabolism in elderly men and women supplemented with a nutrition cocktail of beta-hydroxy-beta-methylbutyrate (HMB), L-arginine, and L-lysine.

BACKGROUND: A major contributing factor to the loss of mobility in elderly people is the gradual and continuous loss of lean body mass. OBJECTIVES: To determine whether supplementation of an amino acid cocktail daily for 1 year could improve the age-associated changes in protein turnover and lean body mass in elderly people. DESIGN: Elderly (76+/-1.6 years) women (n=39) and men (n=38) were recruited for a double-blinded controlled study. Study participants were randomly assigned to either an isonitrogenous control-supplement (n=37) or a treatment-supplement (HMB/Arg/Lys) consisting of beta-hydroxy-beta-methylbutyrate, L-arginine, and L-lysine (n=40) for the 1-year study. Lean tissue mass was measured using both bioelectrical-impedance analysis (BIA) and dual energy x-ray absorptiometry (DXA). Rates of whole-body protein turnover were estimated using primed/intermittent oral doses of 15N-glycine. RESULTS: In subjects taking the HMB/Arg/Lys supplement, lean tissue increased over the year of study while in the control group, lean tissue did not change. Compared with control, HMB/Arg/Lys increased body cell mass (BIA) by 1.6% (P=.002) and lean mass (DXA) by 1.2% (P=.05). The rates of protein turnover were significantly increased 8% and 12% in the HMB/Arg/Lys-supplemented group while rates of protein turnover decreased 11% and 9% in the control-supplemented subjects (P<.01), at 3 and 12 months, respectively. CONCLUSIONS: Consumption of a simple amino acid-related cocktail increased protein turnover and lean tissue in elderly individuals in a year-long study.

Metabolic adaptation is not observed after 8 weeks of overfeeding but energy expenditure variability is associated with weight recovery.

BACKGROUND: A metabolic adaptation, defined as an increase in energy expenditure (EE) beyond what is expected with weight gain during overfeeding (OF), has been reported but also refuted. Much of the inconsistency stems from the difficulty in conducting large, well-controlled OF studies in humans. OBJECTIVES: The primary aim of this study was to determine whether a metabolic adaptation to OF exists and if so, attenuates weight gain. METHODS: Thirty-five young adults consumed 40% above their baseline energy requirements for 8 wk, and sleeping metabolic rate (SMR) and 24-h sedentary energy expenditure (24h-EE) were measured before and after OF. Subjects were asked to return for a 6-mo post-OF follow-up visit to measure body weight, body composition, and physical activity. RESULTS: After adjusting for gains in fat-free mass and fat mass, SMR increased by 43 ± 123 kcal/d more than expected (P = 0.05) and 24h-EE by 23 ± 139 kcal/d (P = 0.34), indicating an overall lack of metabolic adaptation during OF despite a wide variability in the response. Among the 30 subjects who returned for the 6-mo follow-up visit, those who had a lower-than-predicted SMR (basal EE) retained more of the fat gained during OF. Likewise, subjects displaying a higher-than-predicted sedentary 24h-EE lost significantly more fat during the 6-mo follow-up. CONCLUSIONS: Metabolic adaptation to OF was on average very small but variable between subjects, revealing "thrifty" or "spendthrift" metabolic phenotypes related to body weight loss 6 mo later. This trial was registered at clinicaltrials.gov as NCT01672632.

Physical activity in aging: comparison among young, aged, and nonagenarian individuals.

Physical activity (PA) is known to decline with age; however, there is a paucity of data on activity in persons who are in their nineties and beyond. We used objective and reliable methods to measure PA in nonagenarians (>or=90 yr; n=98) and hypothesized that activity would be similar to that of aged (60-74 yr; n=58) subjects but less than in young (20-34 yr; n=53) volunteers. Total energy expenditure (TEE) was measured by doubly labeled water over 14 days and resting metabolic rate (RMR) by indirect calorimetry. Measures of PA included activity energy expenditure adjusted for body composition, TEE adjusted for RMR, physical activity level (PAL), and activity over 14 days by accelerometry expressed as average daily durations of light and moderate activity. RMR and TEE were lower with increasing age group (P<0.01); however, RMR was not different between aged and nonagenarian subjects after adjusting for fat-free mass, fat mass, and sex. Nonagenarians had a lower PAL and were more sedentary than the aged and young groups (P<0.01); however, the nonagenarians who were more active on a daily basis walked further during a timed test, indicating higher physical functionality. For all measures of activity, no differences were found between young and aged volunteers. PA was markedly lower in nonagenarians compared with young and aged adults. Interestingly, PA was similar between young volunteers and those who were in their 60s and 70s, likely due to the sedentary nature of our society, particularly in young adults.

The role of physical activity in maintaining a reduced weight.

Current physical activity recommendations call for 30 minutes of moderate-intensity activity on most days of the week, or the equivalent of expending approximately 1000 kcal in activity per week. These recommendations were formulated based on reducing the risk for chronic disease, but they do not appear adequate for weight loss and maintenance. Data from epidemiologic studies and randomized trials indicate that closer to 60 to 90 minutes of moderate-intensity activity every day is required for maintaining a reduced body weight, equivalent to expending 2500 to 2800 kcal in activity per week. Relevant studies leading to this conclusion are reviewed in this manuscript. However, to make a dent in the prevalence of obesity by targeting physical activity and food intake, it is imperative to address the current "built" environment, which is conducive to a sedentary lifestyle and overconsumption of energy. Only then will rigorous activity recommendations be easier to implement.

Intramyocellular Lipid Droplet Size Rather Than Total Lipid Content is Related to Insulin Sensitivity After 8 Weeks of Overfeeding.

OBJECTIVE: Intramyocellular lipid (IMCL) is inversely related to insulin sensitivity in sedentary populations, yet no prospective studies in humans have examined IMCL accumulation with overfeeding. METHODS: Twenty-nine males were overfed a high-fat diet (140% caloric intake, 44% from fat) for 8 weeks. Measures of IMCL, whole-body fat oxidation from a 24-hour metabolic chamber, muscle protein extracts, and muscle ceramide measures were obtained before and after the intervention. RESULTS: Eight weeks of overfeeding did not increase overall IMCL. The content of smaller lipid droplets peripherally located in the myofiber decreased, while increases in larger droplets correlated inversely with glucose disposal rate. Overfeeding resulted in inhibition of Akt activity, which correlated with the reductions in smaller, peripherally located lipid droplets and drastic increases in ceramide content. Additionally, peripherally located lipid droplets were associated with more efficient lipid oxidation. Finally, participants who maintained a greater number of smaller, peripherally located lipid droplets displayed a better resistance to weight gain with overfeeding. CONCLUSIONS: These results show that lipid droplet size and location rather than mere IMCL content are important to understanding insulin sensitivity.

The use of a handheld calorimetry unit to estimate energy expenditure during different physiological conditions.

BACKGROUND: Accurately determining rates of energy expenditure (EE) under free-living conditions is important in understanding the mechanisms involved in the development and prevention of obesity. Metabolic carts are not portable enough for most free-living situations. The purpose of this study was to compare a portable, handheld indirect calorimetry device (HealtheTech Incorporated, Golden, CO) to a metabolic cart (Physio-Dyne Instrument Corporation, Quogue, NY) during 3 different physiologic states. METHODS: EE was measured by both the handheld calorimeter (5-10 minutes) and the metabolic cart (15-20 minutes) in 20 healthy subjects (18-35 years of age). Measurements were made during 3 physiologic states: (1) postabsorptive rest (REE), (2) postprandial rest (fed energy expenditure, FEE), and (3) while walking in place (activity energy expenditure, AEE). RESULTS: There were no significant differences between the means of the cart vs the hand-held device for REE (mean +/- SE; kcal/d; 1552 +/- 64 vs 1551 +/- 63), FEE (1875 +/- 99 vs 1825 +/- 86), and AEE (3333 +/- 218 vs 3489 +/- 152). The range over which the techniques were tested was 1300-5000 kcal/d. The agreement between the 2 methods was excellent for REE (0.80, p < .0001), FEE (0.89, p < .0001), and AEE (0.75, p < .0002). CONCLUSIONS: Compared with the metabolic cart, the handheld device provided similar estimates of energy expenditure during resting, postprandial, and physically active states. This suggests that portable indirect calorimetry devices can provide reliable and valuable information in free-living research situations for which maximal energy expenditure is <5000 kcal/d.

Determinants of sedentary 24-h energy expenditure: equations for energy prescription and adjustment in a respiratory chamber.

BACKGROUND: Achieving energy balance is critical for the interpretation of results obtained in respiratory chambers. However, 24-h energy expenditure (24EE) predictions based on estimated resting metabolic rate and physical activity level are often inaccurate and imprecise. OBJECTIVE: We aimed to develop and validate equations to better achieve energy balance in a respiratory chamber by adding or subtracting food items. DESIGN: By using a randomized data set with measures of 24EE (n = 241) performed at the Pennington Biomedical Research Center, we developed equations to predict 24EE from anthropometric, demographic, and body composition variables before and at 3 and 7 h into the chamber measurement. The equations were tested on an independent data set (n = 240) and compared with published predictive equations. RESULTS: By using anthropometric and demographic variables, the equation was as follows: 24EE (kcal/d) = 11.6 [weight (kg)] + 8.03 [height (cm)] - 3.45 [age (y)] + 217 (male) - 52 (African American) - 235. The mean prediction error was -9 ± 155 kcal/d (2046 ± 305 compared with 2055 ± 343 kcal/d for measured 24EE; P = 0.36). The prediction achieved a precision of ±10% of measured 24EE in 83% of the participants. Energy prescription was then refined by equations with the use of energy expenditure values after 3 h, 7 h, or both into the chamber study. These later equations improved the precision (±10% of measured 24EE) to 92% (P = 0.003) and 96% (P < 0.0001) of the participants at 3 and 7 h, respectively. Body composition did not improve 24EE predictions. CONCLUSIONS: We showed the use of a set of equations to prescribe and adjust energy intake to achieve energy balance in respiratory chambers over 24 h. These equations may be used in most respiratory chambers and modified to accommodate exercise or specific feeding protocols.

Weight gain reveals dramatic increases in skeletal muscle extracellular matrix remodeling.

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.

Meta-analysis of global metabolomic data identifies metabolites associated with life-span extension.

The manipulation of distinct signaling pathways and transcription factors has been shown to influence life span in a cell-non-autonomous manner in multicellular model organisms such as Caenorhabditis elegans. These data suggest that coordination of whole-organism aging involves endocrine signaling, however, the molecular identities of such signals have not yet been determined and their potential relevance in humans is unknown. Here we describe a novel metabolomic approach to identify molecules directly associated with extended life span in C. elegans that represent candidate compounds for age-related endocrine signals. To identify metabolic perturbations directly linked to longevity, we developed metabolomic software for meta-analysis that enabled intelligent comparisons of multiple different mutants. Simple pairwise comparisons of long-lived glp-1, daf-2, and isp-1 mutants to their respective controls resulted in more than 11,000 dysregulated metabolite features of statistical significance. By using meta-analysis, we were able to reduce this number to six compounds most likely to be associated with life-span extension. Mass spectrometry-based imaging studies suggested that these metabolites might be localized to C. elegans muscle. We extended the metabolomic analysis to humans by comparing quadricep muscle tissue from young and old individuals and found that two of the same compounds associated with longevity in worms were also altered in human muscle with age. These findings provide candidate compounds that may serve as age-related endocrine signals and implicate muscle as a potential tissue regulating their levels in humans.

Effect of 8 weeks of overfeeding on ectopic fat deposition and insulin sensitivity: testing the "adipose tissue expandability" hypothesis.

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.

Metabolic adaptation following massive weight loss is related to the degree of energy imbalance and changes in circulating leptin.

OBJECTIVE: To measure changes in resting metabolic rate (RMR) and body composition in obese subjects following massive weight loss achieved via bariatric surgery or calorie restriction plus vigorous exercise. METHODS: Body composition and RMR were measured in 13 pairs of obese subjects retrospectively matched for sex, body mass index, weight, and age who underwent either Roux-en-Y gastric bypass surgery (RYGB) or participated in "The Biggest Loser" weight loss competition (BLC). RESULTS: Both groups had similar final weight loss (RYGB: 40.2 ± 12.7 kg, BLC: 48.8 ± 14.9 kg; P = 0.14); however, RYGB lost a larger proportion of their weight as fat-free mass (FFM) (RYGB: 30 ± 12%, BLC: 16 ± 8% [P < 0.01]). In both groups, RMR decreased significantly more than expected based on measured body composition changes. The magnitude of this metabolic adaptation was correlated with the degree of energy imbalance (r = 0.55, P = 0.004) and the decrease in circulating leptin (r = 0.47, P = 0.02). CONCLUSIONS: Calorie restriction along with vigorous exercise in BLC participants resulted in preservation of FFM and greater metabolic adaption compared to RYGB subjects despite comparable weight loss. Metabolic adaptation was related to the degree of energy imbalance and the changes in circulating leptin.

Skeletal muscle mitochondria and aging: a review.

Aging is characterized by a progressive loss of muscle mass and muscle strength. Declines in skeletal muscle mitochondria are thought to play a primary role in this process. Mitochondria are the major producers of reactive oxygen species, which damage DNA, proteins, and lipids if not rapidly quenched. Animal and human studies typically show that skeletal muscle mitochondria are altered with aging, including increased mutations in mitochondrial DNA, decreased activity of some mitochondrial enzymes, altered respiration with reduced maximal capacity at least in sedentary individuals, and reduced total mitochondrial content with increased morphological changes. However, there has been much controversy over measurements of mitochondrial energy production, which may largely be explained by differences in approach and by whether physical activity is controlled for. These changes may in turn alter mitochondrial dynamics, such as fusion and fission rates, and mitochondrially induced apoptosis, which may also lead to net muscle fiber loss and age-related sarcopenia. Fortunately, strategies such as exercise and caloric restriction that reduce oxidative damage also improve mitochondrial function. While these strategies may not completely prevent the primary effects of aging, they may help to attenuate the rate of decline.

Effect of short-term thyroxine administration on energy metabolism and mitochondrial efficiency in humans.

The physiologic effects of triiodothyronine (T3) on metabolic rate are well-documented; however, the effects of thyroxine (T4) are less clear despite its wide-spread use to treat thyroid-related disorders and other non-thyroidal conditions. Here, we investigated the effects of acute (3-day) T4 supplementation on energy expenditure at rest and during incremental exercise. Furthermore, we used a combination of in situ and in vitro approaches to measure skeletal muscle metabolism before and after T4 treatment. Ten healthy, euthyroid males were given 200 µg T4 (levothyroxine) per day for 3 days. Energy expenditure was measured at rest and during exercise by indirect calorimetry, and skeletal muscle mitochondrial function was assessed by in situ ATP flux ((31)P MRS) and in vitro respiratory control ratio (RCR, state 3/state 4 rate of oxygen uptake using a Clark-type electrode) before and after acute T4 treatment. Thyroxine had a subtle effect on resting metabolic rate, increasing it by 4% (p = 0.059) without a change in resting ATP demand (i.e., ATP flux) of the vastus lateralis. Exercise efficiency did not change with T4 treatment. The maximal capacity to produce ATP (state 3 respiration) and the coupled state of the mitochondria (RCR) were reduced by approximately 30% with T4 (p = 0.057 and p = 0.04, respectively). Together, the results suggest that T4, although less metabolically active than T3, reduces skeletal muscle efficiency and modestly increases resting metabolism even after short-term supplementation. Our findings may be clinically relevant given the expanding application of T4 to treat non-thyroidal conditions such as obesity and weight loss.

Endothelial Dysfunction: An Early Cardiovascular Risk Marker in Asymptomatic Obese Individuals with Prediabetes.

AIMS: To elucidate if endothelial dysfunction is an early CV risk marker in obese men and women with prediabetes. STUDY DESIGN: Cross-sectional study. PLACE AND DURATION OF STUDY: Clinical Research Unit, Pennington Biomedical Research Center, Baton Rouge, LA. United States. METHODOLOGY: Overweight and obese status denotes an increasing adipose tissue burden which spills over into ectopic locations, including the visceral compartment, muscle and liver. Associated co-morbidities enhance cardiovascular (CV) risk. Endothelium which is the largest receptor-effector end-organ in our bodies, while responding to numerous physical and chemical stimuli maintains vascular homeostasis. Endothelial dysfunction (ED) is the initial perturbation, which precedes fatty streak known to initiate atherosclerosis: insidious process which often culminates as sudden catastrophic CV adverse event. Asymptomatic men and women; [n=42] coming in after an overnight fast had demographic, anthropometric, clinical chemistry and resting endothelial function [EF: increased test finger peripheral arterial tone (PAT) relative to control; expressed as relative hyperemia index (RHI)] assessments. RESULTS: Adults with desirable weight [n=12] and overweight [n=8] state, had normal fasting plasma glucose [Mean(SD)]: FPG [91.1(4.5), 94.8(5.8) mg/dL], insulin [INS, 2.3(4.4), 3.1(4.8) µU/ml], insulin sensitivity by homeostasis model assessment [HOMA-IR, 0.62(1.2), 0.80(1.2)] and desirable resting clinic blood pressure [SBP/DBP, 118(12)/74(5), 118(13)/76(8) mmHg]. Obese adults [n=22] had prediabetes [FPG, 106.5(3.5) mg/dL], hyperinsulinemia [INS 18.0(5.2) µU/ml], insulin resistance [HOMA-IR 4.59(2.3)], prehypertension [PreHTN; SBP/DBP 127(13)/81(7) mmHg] and endothelial dysfunction [ED; reduced RHI 1.7(0.3) vs. 2.4(0.3); all p<0.05]. Age-adjusted RHI correlated with BMI [r=-0.53; p<0.001]; however, BMI-adjusted RHI was not correlated with age [r=-0.01; p=0.89]. CONCLUSION: Endothelial dysfunction reflective of cardiometabolic changes in obese adults can be an early risk marker for catastrophic CV events.

Metabolic slowing with massive weight loss despite preservation of fat-free mass.

CONTEXT: An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate. OBJECTIVE: Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR). PARTICIPANTS AND INTERVENTION: We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16). RESULTS: At baseline, participants were severely obese (× ± SD; body mass index 49.4 ± 9.4 kg/m(2)) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (-38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (-244 ± 231 and -504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg.d at wk 6 and 6.0 ± 4.1 kcal/kg.d at wk 30 (P < 0.001 vs. zero). CONCLUSIONS: Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

Low macrophage accumulation in skeletal muscle of obese type 2 diabetics and elderly subjects.

In addition to adipose tissue, recent studies suggest that skeletal muscle may also be a source of low-grade inflammation, particularly in inactive and/or overweight individuals. The aim of this study was to examine the presence of macrophages in skeletal muscle from obese subjects with type 2 diabetes (T2D) before and after a 9-month exercise program (vs. a non-exercising control group) (Study 1) and in young vs. elderly subjects (Study 2). In both studies, CD68(+) macrophages in vastus lateralis biopsies were determined by immunohistochemistry and inflammation gene expression measured. Macrophage content (%) was calculated by the number of macrophages per 100 muscle fibers. In Study 1, we found relatively low numbers (2-3%) of CD68(+) macrophages in skeletal muscle in obese T2D subjects (BMI = 37.3 ± 5.2 kg/m(2)), which were unchanged after a 9-month exercise program (P = 0.42). Similarly, in Study 2 (BMI = 27.1 ± 2.5 kg/m(2)), CD68(+) macrophages were relatively low in muscle (4-5%) and were not different between young and elderly individuals (P = 0.42). However, elderly subjects had twofold higher CD68 and CD206 gene expression (both P < 0.002) than young participants. In both studies, CD68(+) muscle macrophages were not associated with BMI. In conclusion, we found little evidence of macrophage accumulation in skeletal muscle in obese T2D subjects or in elderly individuals. A 9-month exercise program was not associated with a decrease in macrophage content.

Ectopic lipid accumulation and reduced glucose tolerance in elderly adults are accompanied by altered skeletal muscle mitochondrial activity.

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.