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New findings What is the central question of this study? Obesity is associated with complex perturbations to iron homeostasis: is plasma ferritin concentration (a biomarker of whole-body iron stores) related to the abundance of ferritin (the key tissue iron storage protein) in skeletal muscle in adults with obesity? What is the main finding and its importance? Plasma ferritin concentration was tightly correlated with the abundance of ferritin in skeletal muscle, and this relationship persisted when accounting for sex, age, body mass index and plasma C-reactive protein concentration. Our findings suggest that skeletal muscle may be an important iron store. Abstract Obesity is associated with complex perturbations to whole-body and tissue iron homeostasis. Recent evidence suggests a potentially important influence of iron storage in skeletal muscle on whole-body iron homeostasis, but this association is not clearly resolved. The primary aim of this study was to assess the relationship between whole-body and skeletal muscle iron stores by measuring the abundance of the key iron storage (ferritin) and import (transferrin receptor) proteins in skeletal muscle, as well as markers of whole-body iron homeostasis in men (n = 19) and women (n = 43) with obesity. Plasma ferritin concentration (a marker of whole-body iron stores) was highly correlated with muscle ferritin abundance (r = 0.77, P = 2 × 10-13 ) and negatively associated with muscle transferrin receptor abundance (r = -0.76, P = 1 × 10-12 ). These relationships persisted when accounting for sex, age, BMI and plasma C-reactive protein concentration. In parallel with higher whole-body iron stores in our male versus female participants, men had 2.2-fold higher muscle ferritin abundance (P = 1 × 10-4 ) compared with women. In accordance with lower muscle iron storage, women had 2.7-fold higher transferrin receptor abundance (P = 7 × 10-10 ) compared with men. We conclude that muscle iron storage and import proteins are tightly and independently related to plasma ferritin concentration in adults with obesity, suggesting that skeletal muscle may be an underappreciated iron store.

Background In people with obesity, β-cell function may adapt to insulin resistance. We describe β-cell function in people with severe obesity and normal fasting glucose (NFG), impaired fasting glucose (IFG), and type 2 diabetes (T2DM), as assessed before, 3 to 6 months after, and 2 years after medical weight loss to describe its effects on insulin sensitivity, insulin secretion, and β-cell function. Methods Fifty-eight participants with body mass index (BMI) ≥ 35 kg/m2 (14 with NFG, 24 with IFG, and 20 with T2DM) and 13 normal weight participants with NFG underwent mixed meal tolerance tests to estimate insulin sensitivity (S[I]), insulin secretion (Φ), and β-cell function assessed as model-based Φ adjusted for S(I). All 58 obese participants were restudied at 3 to 6 months and 27 were restudied at 2 years. Results At 3 to 6 months, after a 20-kg weight loss and a decrease in BMI of 6 kg/m2, S(I) improved in all obese participants, Φ decreased in obese participants with NFG and IFG and tended to decrease in obese participants with T2DM, and β-cell function improved in obese participants with NFG and tended to improve in obese participants with IFG. At 2 years, β-cell function deteriorated in participants with NFG and T2DM but remained significantly better in participants with IFG compared to baseline. Conclusions Short-term weight loss improves β-cell function in participants with NFG and IFG, but β-cell function tends to deteriorate over 2 years. In participants with IFG, weight loss improves longer-term β-cell function relative to baseline and likely relative to no intervention, suggesting that obese people with IFG are a subpopulation whose β-cell function is most likely to benefit from weight loss.

Although the health benefits of exercise in adults with obesity are well described, the direct effects of exercise on adipose tissue that may lead to improved metabolic health are poorly understood. The primary aims of this study were to perform an unbiased analysis of the subcutaneous abdominal adipose tissue transcriptomic response to acute exercise in adults with obesity, and to compare the effects of moderate-intensity continuous exercise versus high-intensity interval exercise on this response. Twenty-nine adults with obesity performed a session of either high-intensity interval exercise (HI; 10 × 1 min at 90%HRpeak, 1 min recovery between intervals; n = 14) or moderate-intensity continuous exercise (MI; 45 min at 70%HRpeak; n = 15). Groups were well matched for BMI (HI 33 ± 3 vs. MI 33 ± 4 kg/m(2)), sex (HI: 9 women vs. MI: 10 women), and age (HI: 32 ± 6 vs. MI: 29 ± 5). Subcutaneous adipose tissue was collected before and 1 h after the session of HI or MI, and samples were processed for RNA sequencing. Gene set enrichment analysis revealed 7 of 21 gene sets enriched postexercise overlapped between HI and MI. Interestingly, both HI and MI upregulated gene sets involved in inflammation (IL6-JAK-STAT3 signaling, allograft rejection, TNFα signaling via NFκB, and inflammatory response; FDR q value < 0.25). Exercise also downregulated adipogenic and oxidative metabolism gene sets in both groups. Overall, these data suggest genes involved in subcutaneous adipose tissue metabolism and inflammation may be an important part of the initial response after a session of exercise. NEW & NOTEWORTHY This study compared the effects of a single session of high-intensity interval exercise versus moderate-intensity continuous exercise on transcriptional changes in subcutaneous abdominal adipose tissue collected from adults with obesity. Our novel findings indicate exercise upregulated inflammation-related gene sets, while it downregulated metabolism-related gene sets – after both high-intensity and moderate-intensity exercise. These data suggest exercise can alter the adipose tissue transcriptome 1 h after exercise in ways that may impact inflammation and metabolism.

Calorie restriction (CR) and the resultant weight-loss are known to improve metabolic health, but the effects of CR on factors regulating white adipose tissue (WAT) metabolic function and remodeling remain unclear. The purpose of this study was to examine the effects of 8 weeks of CR on markers of lipid storage/release, endoplasmic reticulum (ER) stress, and apoptosis in inguinal and epididymal WAT collected from aged rats. We harvested inguinal and epididymal adipose tissue from 24-month-old male Fischer-344 x Brown Norway rats that were either fed an ad libitum chow diet (AL, n=6) or subjected to CR (consuming 35% below AL intake) of the same diet (n=6) for 8 weeks. Using standard immunoblotting methods, inguinal WAT from CR had a greater abundance of phosphorylated hormone sensitive lipase (pHSL) than AL (11.1±6.6 vs. 4.5±3.3 arbitrary units (AU); P=0.05) indicative of elevated lipase activity in CR, and a lower protein abundance of the esterification marker, diacylglycerol acyltransferase (DGAT; 1.0±0.2 vs. 2.4±0.6 AU; P In summary, CR-mediated responses in WAT of aged rats appeared to be depot-specific and CR may contribute to important metabolic modifications and may impact cellular remodeling of inguinal adipose tissue. Disclosure P. Varshney: None. M. W. Schleh: None. C. Ahn: None. A. Zheng: None. E. B. Arias: None. G. D. Cartee: None. J. F. Horowitz: None. Funding National Institutes of Health (R01DK077966, P30DK089503, R01AG010026)

Low sensitivity to the antilipolytic effects of insulin in adipose tissue has been linked with impaired insulin-mediated glucose uptake in skeletal muscle. The aims of this study were: 1) to compare adipose tissue morphology in obese adults with high- (HIGH) vs. low-sensitivity (LOW) to the antilipolytic effects of insulin, and 2) compare the effects of exercise training on adipose tissue from HIGH vs. LOW subjects. Using isotopic dilution methods before and during a hyperinsulinemic-euglycemic clamp, we measured the antilipolytic response to insulin in a total of 36 obese adults - and we identified sub-cohorts of 13 LOW (64±7% lipolytic suppression by insulin; BMI: 34±4kg/m2) and 13 HIGH (82±3% lipolytic suppression by insulin; BMI:33±3kg/m2). Abdominal subcutaneous adipose tissue (aSAT) samples were collected before the clamp (non-insulin stimulated). Measurements were made before and after a 12-week endurance exercise training program (4 days/week). Before training, capillary density (# of capillaries/mm2) in aSAT samples for LOW was significantly lower than HIGH (p=0.004). Collagen abundance in aSAT extracellular matrix (ECM) was lower in LOW (p=0.013). In response to training, the antilipolytic response to insulin was significantly improved in LOW (72±5% lipolytic suppression by insulin; p In summary, aSAT from obese adults with low antilipolytic sensitivity to insulin displayed lower capillarization and ECM collagen abundance compared with obese adults with high sensitivity to the antilipolytic effects of insulin. Importantly, morphological adaptations to exercise training accompanied an increased antilipolytic sensitivity to insulin in subjects with low antilipolytic sensitivity before training. Disclosure C. Ahn: None. M. W. Schleh: None. B. J. Ryan: None. A. Ludzki: None. P. Varshney: None. J. B. Gillen: None. S. Chen: None. J. F. Horowitz: None. Funding National Institutes of Health (R01DK077966, P30DK089503, T32DK007245, F32DK117522); Canadian Institutes of Health Research (DFS146190, 338735)

Provocative rodent studies taken together with cross-sectional human epidemiological data have shown that there may be a cross-talk between circulating leptin levels and whole-body iron metabolism.1 2 In this study, we aim to discover the effects of recombinant leptin administration on iron parameters in patients with partial lipodystrophy. We studied serum samples from 19 patients with partial lipodystrophy (median age: 42 years, IQR: 34–57, male/female: 3/16) gathered from an open-label study previously performed at the University of Michigan (ClinicalTrials.gov identifier: NCT01679197; article in press). All patients included in this analysis had familial partial lipodystrophy. We measured iron (assay range: 5–1000 µg/dL), soluble transferrin receptor (sTfR; assay range: 3.0–80.0 nmol/L), hepcidin (assay range: 2.5–1000 ng/mL), and high-sensitive C reactive protein (hs-CRP; assay range 0.1–80 mg/L) levels using commercially available assays. We integrated the results into an existing database of metabolic parameters. Repeated-measures analysis of variance was used to compare multiple time points. Paired t-test was used to compare month 6 values to baseline (a prespecified endpoint). Otherwise, multiplicity correction was performed. Normality was assessed by the Kolmogorov-Smirnov test and the Shapiro-Wilk’s W test and also by plotting a histogram of the variable of interest. Log transformation was used for skewed data. Data are presented as median, IQR. At baseline, ferritin levels were positively correlated with fasting glucose (r=0.533; p=0.023; figure 1A) and HbA1c (r=0.510; p=0.031; figure 1B). We …

New findings What is the central question of this study? Does exercise training modify tissue iron storage in adults with obesity? What is the main finding and its importance? Twelve weeks of moderate-intensity exercise or high-intensity interval training lowered whole-body iron stores, decreased the abundance of the key iron storage protein in skeletal muscle (ferritin) and tended to lower hepatic iron content. These findings show that exercise training can reduce tissue iron storage in adults with obesity and might have important implications for obese individuals with dysregulated iron homeostasis. Abstract The regulation of iron storage is crucial to human health, because both excess and deficient iron storage have adverse consequences. Recent studies suggest altered iron storage in adults with obesity, with increased iron accumulation in their liver and skeletal muscle. Exercise training increases iron use for processes such as red blood cell production and can lower whole-body iron stores in humans. However, the effects of exercise training on liver and muscle iron stores in adults with obesity have not been assessed. The aim of this study was to determine the effects of 12 weeks of exercise training on whole-body iron stores, liver iron content and the abundance of ferritin (the key iron storage protein) in skeletal muscle in adults with obesity. Twenty-two inactive adults (11 women and 11 men; age, 31 ± 6 years; body mass index, 33 ± 3 kg/m2 ) completed 12 weeks (four sessions/week) of either moderate-intensity continuous training (MICT; 45 min at 70% of maximal heart rate; n = 11) or high-intensity interval training (HIIT; 10 × 1 min at 90% of maximal heart rate, interspersed with 1 min active recovery; n = 11). Whole-body iron stores were lower after training, as indicated by decreased plasma concentrations of ferritin (P = 3 × 10-5 ) and hepcidin (P = 0.02), without any change in C-reactive protein. Hepatic R2*, an index of liver iron content, was 6% lower after training (P = 0.06). Training reduced the skeletal muscle abundance of ferritin by 10% (P = 0.03), suggesting lower muscle iron storage. Interestingly, these adaptations were similar in MICT and HIIT groups. Our findings indicate that exercise training decreased iron storage in adults with obesity, which might have important implications for obese individuals with dysregulated iron homeostasis.

Adipose tissue pathology in obese patients often features impaired adipogenesis, angiogenesis, and chronic low-grade inflammation, all of which are regulated in large part by adipose tissue stromal vascular cells [SVC; i.e., non-adipocyte cells within adipose tissue including preadipocytes, endothelial cells (ECs), and immune cells]. Exercise is known to increase subcutaneous adipose tissue lipolysis, but the impact of exercise on SVCs in adipose tissue has not been explored. The purpose of this study was to assess the effects of a session of exercise on preadipocyte, EC, macrophage, and T cell content in human subcutaneous adipose tissue. We collected abdominal subcutaneous adipose tissue samples from 10 obese adults (BMI 33 ± 3 kg/m2, body fat 41 ± 7%) 12 h after a 60 min acute session of endurance exercise (80 ± 3%HRpeak) vs. no acute exercise session. SVCs were isolated by collagenase digestion and stained for flow cytometry. We found that acute exercise reduced preadipocyte content (38 ± 7 vs. 30 ± 13%SVC; p = 0.04). The reduction was driven by a decrease in CD34hi preadipocytes (18 ± 5 vs. 13 ± 6%SVC; p = 0.002), a subset of preadipocytes that generates high lipolytic rate adipocytes ex vivo. Acute exercise did not alter EC content. Acute exercise also did not change total immune cell, macrophage, or T cell content, and future work should assess the effects of exercise on subpopulations of these cells. We conclude that exercise may rapidly regulate the subcutaneous adipose tissue preadipocyte pool in ways that may help attenuate the high lipolytic rates that are commonly found in obesity.

The primary aim of this study was to determine the impact of high-intensity interval training [HIIT] and moderate-intensity continuous training [MICT] on skeletal muscle lipidomic profile in obese adults. 17 obese adults (BMI = 34±3 kg·m-2; age = 31±6 years) completed 12 weeks of either HIIT (10 x 1 min @ 90%HRmax + 1 min recovery between intervals; n=8) or MICT (45 min steady-state exercise at 70% HRmax; n=9). Subjects exercised 4d/week and body weight was strictly maintained to assess the direct effects of exercise, independent of changes in body weight or fat mass. Skeletal muscle samples were collected from the vastus lateralis after an overnight fast both before training and 4 days after the last exercise session (to wash out the acute effects of exercise). Using shotgun lipidomics (LC MS/MS) we detected 734 lipid species from 26 different classes. Neither MICT nor HIIT significantly altered abundance of the primary muscle acylglycerides (tri- and di-acylglyceride) or ceramide abundance. Muscle acylcarnitine abundance increased after both MICT and HIIT (main effect, P = 0.04), specifically polyunsaturated acylcarnitines (P = 0.03). We also found phosphatidylcholine (PC) increased after training in both groups (main effect, P = 0.03), while the increase in phosphatidylethanolamine (PE) was greater after HIIT compared with MICT (P = 0.01). When normalized to cardiolipin (which is found almost exclusively in the inner mitochondrial membrane), the increased abundances of PC and PE were no longer apparent. Therefore, the training-induced increase in these phospholipids may largely reflect increased mitochondrial biosynthesis with training. In contrast, the observed increase in polyunsaturated acylcarnitines may represent an important adaptive response in the coordination of fatty acid metabolism in skeletal muscle after training. Overall, changes in muscle lipid profile were surprisingly similar in HIIT and MICT. Disclosure M.W. Schleh: None. B.J. Ryan: None. A. Ludzki: None. J.B. Gillen: None. J.F. Horowitz: None. Funding National Institutes of Health (R01DK077966, P30DK089503, F32DK117522, U24DK097153, UL1TR002240); Canadian Institutes of Health Research (DFS146190)

Mechanisms underlying the direct effects of exercise on metabolic health (independently of weight loss) are poorly understood, and very little is known about the effects of exercise on adipose tissue. The purpose of this study was to examine the effects of exercise training on the key extracellular matrix (ECM) modifiers, matrix metalloproteinase 2 (MMP2) and MMP9, in abdominal subcutaneous adipose tissue (aSAT) of obese adults. Seven obese adults (BMI=33±4 kg/m2; age=32±6) completed 12 weeks of exercise training (either 45min of steady-state exercise at 70% HRmax or 10x1min intervals at 90% HRmax with 1min recovery between intervals), and they were required to maintain body weight throughout. aSAT biopsies were collected before training (Pre) and twice after training - 1 day post exercise (1d PEX) and again 4 days post exercise (4d PEX; to wash out the acute effects of exercise). Using standard immunoblotting methods, we found no evidence for effects of training on either MMP2 or MMP9. However, using gelatin zymography (a technique with more than 100-fold higher sensitivity than immunoblotting) we found a strong trend for an increased MMP9 abundance 1d PEX (3.7±1.0 vs. 3.0±1.4 arbitrary units (AU), for 1d PEX vs. Pre; P=0.08). Interestingly, however, MMP9 returned to Pre training levels by 4d PEX (1.9±1.3 AU; P In summary, because increased abundance and activity of MMPs may alter the fibrotic content and composition of the ECM, exercise-induced increases in MMP2 and MMP9 within aSAT may contribute to favorable modifications within adipose tissue ECM of obese adults. Disclosure P. Varshney: None. B.J. Ryan: None. C. Ahn: None. M.W. Schleh: None. J.F. Horowitz: None. Funding National Institutes of Health (R01DK077966, P30DK089503, F32DK117522, UL1TR002240)

Objective We compared the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on insulin sensitivity and other important metabolic adaptations in adults with obesity. Methods Thirty-one inactive adults with obesity (age: 31 ± 6 years; body mass index: 33 ± 3 kg/m2) completed 12 weeks (4 sessions/week) of either HIIT (10 × 1-minute at 90%HRmax, 1-minute active recovery; n = 16) or MICT (45 minutes at 70%HRmax; n = 15). To assess the direct effects of exercise independent of weight/fat loss, participants were required to maintain body mass. Results Training increased peak oxygen uptake by ~10% in both HIIT and MICT (P Conclusion Despite large differences in training intensity and exercise time, 12 weeks of HIIT and MICT induce similar acute improvements in peripheral insulin sensitivity the day after exercise, and similar longer term metabolic adaptations in skeletal muscle in adults with obesity. These findings support the notion that the insulin-sensitizing effects of both HIIT and MICT are mediated by factors stemming from the most recent exercise session(s) rather than adaptations that accrue with training.

OBJECTIVE Lipodystrophy syndromes are a heterogeneous group of disorders associated with selective absence of fat. Currently, the diagnosis is established only clinically. RESEARCH DESIGN AND METHODS We developed a new method from DXA scans called a “fat shadow,” which is a color-coded representation highlighting only the fat tissue. We conducted a blinded retrospective validation study to assess its usefulness for the diagnosis of lipodystrophy syndromes. RESULTS We evaluated the fat shadows from 16 patients (11 female and 5 male) with generalized lipodystrophy (GL), 57 (50 female and 7 male) with familial partial lipodystrophy (FPLD), 2 (1 female and 1 male) with acquired partial lipodystrophy, and 126 (90 female and 36 male) control subjects. FPLD was differentiated from control subjects with 85% sensitivity and 96% specificity (95% CIs 72–93 and 91–99, respectively). GL was differentiated from nonobese control subjects with 100% sensitivity and specificity (95% CIs 79–100 and 92–100, respectively). CONCLUSIONS Fat shadows provided sufficient qualitative information to infer clinical phenotype and differentiate these patients from appropriate control subjects. We propose that this method could be used to support the diagnosis.

Alterations in the inflammatory state, metabolic function, and structure of subcutaneous adipose tissue (SAT) can impact the development of insulin resistance in obesity. Exercise can improve metabolic health in obesity, but the effects of exercise on SAT are not well known. The purpose of this study was to examine the effects of acute exercise and habitual exercise training on mRNA expression of markers of lipid metabolism, inflammation, fibrosis, and hypoxia/angiogenesis in SAT, as well as adipocyte cell size. We recruited overweight-to-obese adults who exercised regularly (ACTIVE: n = 8) or were sedentary (SED: n = 12). The groups were well matched for age (27 ± 1 vs. 24 ± 2 yr), body mass index (29 ± 1 vs. 27 ± 1 kg/m2), and body composition (30 ± 1 vs. 29 ± 1% body fat), but as expected, cardiorespiratory fitness was greater in ACTIVE vs. SED (V̇o2peak: 51 ± 3 vs. 42 ± 1 ml·kg fat-free mass−1·min−1; P = 0.01). Abdominal SAT biopsy samples were obtained before and 1 h after a single session of aerobic exercise (60 min at ~65% V̇o2peak). The exercise session increased SAT mRNA expression of VEGFA, an important regulator of angiogenic processes, in both groups. In addition, SAT from ACTIVE subjects had greater mRNA expression of the endothelial cell marker CD31 compared with SED, which may be a cumulative effect of the transient increases in VEGFA with regular exercise. We also magnetically sorted CD14+ immune cells from SAT samples and found that IL-6 expression was elevated in ACTIVE compared with SED. In conclusion, exercise initiates increases in factors related to angiogenic processes and may promote alterations in macrophage inflammation in SAT. NEW & NOTEWORTHY Acute exercise in overweight/obese adults increased subcutaneous adipose tissue (SAT) mRNA expression of VEGFA, an important regulator of angiogenesis and capillary growth. In addition, subjects that regularly exercise had elevated SAT CD31 mRNA expression and elevated IL-6 mRNA in adipose tissue macrophages compared with nonexercisers. This study demonstrates that aerobic exercise may alter processes related to whole body metabolic outcomes in obesity, such as angiogenesis and immune response, in the SAT of overweight/obese adults.

Infiltration of pro-inflammatory adipose tissue macrophages (ATMs) is implicated in systemic low-grade inflammation that underlies metabolic health complications in obesity. Exercise training has been linked to reduced adipose tissue and systemic inflammation, but these observations are often confounded by concomitant weight loss. Many metabolic benefits of exercise are a cumulative effect of each bout of exercise, thus the aim of this study was to determine changes in ATMs (using flow cytometry) in response to a single exercise session. We collected subcutaneous abdominal adipose tissue samples from 10 obese (BMI: 33±3kg/m2; fat mass: 41±20kg) and 14 lean (BMI: 23±13kg/m2; fat mass: 16±5kg) adults, 12 hours after exercising for 60 minutes at 70% VO2max (EX); and again 3 days after their most recent exercise session (No-EX). To characterize the cellular response to exercise without the confounding influence of exercise novelty, all subjects were habitual exercisers. The exercise session did not alter total immune cell number (OBESE: 30±7 vs. 31±7; LEAN: 27±9 vs. 28±8% live cells) or total ATM number (OBESE: 3.9±1.7 vs. 4.0±1.6; LEAN: 3.5±1.5 vs. 4.3±1.9% live cells; for No-EX and EX, respectively). However, there was a main effect for exercise to increase the number of CD11c- ATMs (OBESE: 1.3±1.4 vs. 1.5±1.5; LEAN: 1.0±0.6 vs. 2.0±1.6% live cells; P=0.03), indicating the abundance of resident ATMs increased after exercise. Surprisingly, the response to exercise was not different in lean vs. obese subjects. Although the change in resident ATM content after exercise was rather subtle in this cohort of healthy regular exercisers, these are the first single cell data to suggest each session of exercise may induce a phenotypic shift in subcutaneous ATMs. This could be a mechanism contributing to the anti-inflammatory health benefits of exercise. Disclosure A. Ludzki: None. E.M. Krueger: None. T.C. Baldwin: None. N.M. Taylor: None. L.A. Muir: None. C. Lumeng: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966) Canadian Institutes of Health Research (DFS146190)

Abnormalities in muscle lipid metabolism in obesity have been linked to insulin resistance. Exercise training alters skeletal muscle lipid abundance and localization, but the direct effects of exercise training (independent of weight loss) on skeletal muscle lipolytic proteins are not clearly understood, and data are lacking regarding influence of training intensity on factors regulating muscle lipid metabolism in obesity. Our aim was to examine the effects of high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MICT) on skeletal muscle lipolytic proteins in obese humans. Eighteen sedentary, obese adults completed 12 weeks (4 sessions weekly) of either HIIT (10 x 1 min at 90% HRmax, 1 min recovery; n=8) or MICT (45 min at 70% HRmax; n=10). Muscle biopsies (vastus lateralis) were collected before and after training. Subjects maintained body weight and fat mass and the post-training biopsy occurred 3 days after the final exercise session. Both exercise training programs increased aerobic capacity (VO2max) by ~10% (p=0.003), with no significant difference between HIIT and MICT. In muscle samples, hormone-sensitive lipase (HSL) protein abundance increased ~2-fold after training in HIIT (P In summary, HIIT and MICT result in similar modifications to lipolytic proteins in skeletal muscle, although our findings suggest that HIIT may be a more potent stimulus for increasing HSL abundance. Future work is needed to determine if the concomitant increases in protein abundance of CGI-58 and G0S2 with training may improve lipid handling in obesity. Disclosure B.J. Ryan: None. M.W. Schleh: None. P. Varshney: None. A. Ludzki: None. J.B. Gillen: None. K. Foug: None. B.D. Carr: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966, P30DK089503, T32DK007245); Canadian Institutes of Health Research (DFS146190)

Excessive fatty acid (FA) mobilization from subcutaneous adipose tissue into systemic circulation underlies many metabolic health complications associated with obesity, such as insulin resistance. Exercise is often used to help treat and/or prevent insulin resistance, but the direct effects of exercise training (without weight loss) on systemic FA mobilization are unclear. The aim of this study was to determine the effect of both high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on FA rate of appearance (FA Ra) into systemic circulation and factors regulating FA mobilization from subcutaneous adipose tissue. 18 obese adults (33±3 kg•m-2) were randomized to 12 weeks (4 d/week) of either HIIT (10 x 1 min at 90% HRmax with 1 min recovery; n=8) or MICT (45 min at 70% HRmax; n=10), and were required to maintain bodyweight throughout. Resting FA Ra (13C palmitate dilution) and abdominal subcutaneous adipose tissue samples were collected in the overnight fasted state before and after training (72h following their final exercise session). The abundance of key lipolytic and lipid storage proteins in adipose tissue were measured via immunoblot. Aerobic fitness (VO2peak) increased ∼10% after training (P = 0.002), with no difference between HIIT and MICT. Body weight remained unchanged after training (HIIT: 98±12 vs. 98±13 kg, MICT: 101±12 vs. 100±13), as did fat mass (HIIT: 40±5 vs. 39±5 kg, MICT: 42±8 vs. 41±9). Training did not affect resting FA Ra in either HIIT (16.5±3.2 vs. 15.3±1.8 μmol•kg FM-1•min-1) or MICT (16.5±2.6 vs. 15.8±1.4 μmol•kg FM-1•min-1). In line with this finding, neither HIIT nor MICT altered adipose tissue abundance or phosphorylation-state of the lipolytic enzymes ATGL and HSL, or other factors involved in FA mobilization and storage in adipose tissue (e.g., GPAT, DGAT, CGI-58, G0S2, CD36). In summary, in the absence of weight loss, 12 weeks HIIT or MICT did not alter the regulation of resting FA mobilization from subcutaneous adipose tissue. Disclosure M.W. Schleh: None. B.J. Ryan: None. J.B. Gillen: None. P. Varshney: None. K. Foug: None. A. Ludzki: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966, P30DK089503, T32DK007245); Canadian Institutes of Health Research (DFS146190)

Many metabolic health complications in obese adults are linked to abnormalities within their enlarged adipose tissue mass, which include hypertrophic adipocytes, a fibrotic extracellular matrix (ECM), and suppressed capillary density. Exercise training is a first-line treatment for obesity-related diseases, but the direct effects of exercise on adipose tissue structure and metabolic function remain unclear. The purpose of this study was to determine the effects of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on subcutaneous adipose tissue morphology. 17 obese adults were randomly assigned to 12 weeks (4 days/week) of MICT (45 minutes at 70% HRmax, n=9) or HIIT (10 X 1 minutes at 90% HRmax, 1 minute recovery, n=8) and were required to maintain their body weight throughout. Abdominal subcutaneous adipose tissue biopsy samples were collected before and after training for histological and immunoblot measures to assess adipocyte cell size, markers of ECM remodeling and capillarization. Aerobic fitness (VO2peak) improved ∼10% in both MICT and HIIT (P In summary, exercise training, perhaps especially HIIT, may increase adipogenic and angiogenic capacity in adipose tissue, as well as trigger adipose ECM remodeling. Disclosure C. Ahn: None. B.J. Ryan: None. J.B. Gillen: None. A. Ludzki: None. M.W. Schleh: None. B.A. Reinheimer: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966, P30DK089503, T32DK007245); Canadian Institutes of Health Research (DFS146190)

The direct effects of exercise on white adipose tissue morphology and metabolic function remain unclear, due in large part to confounding effects of the reduction in fat mass that often accompanies exercise training. The purpose of this study was to determine if a session of endurance exercise could impact the rate of adipogenesis. Eight lean, healthy human subjects performed a single session of exercise (1 hour of endurance exercise at 65% of their maximal aerobic capacity; VO2max). Blood samples were collected without prior exercise (No-EX) and immediately after exercise (EX). Serum was extracted, and human adipocyte precursor cells were incubated for 72 hours in vitro in either the No-EX or EX serum. This serum preincubation was immediately followed by a standard 14-day differentiation protocol. On both days 3 and 9 of differentiation, mRNA expression levels of differentiation markers, PPARG and FABP4, were significantly greater (P In summary, factors released into the circulation during and/or immediately after a session of endurance exercise can accelerate the rate of differentiation in human adipocyte precursor cells. Enhanced adipogenic signaling in response to exercise may have metabolic health benefits by priming adipose tissue for a more effective energy storage during periods of weight gain. Disclosure P. Varshney: None. L.M. Guth: None. C.M. Anderson: None. A. Raajendiran: None. M.J. Watt: None. J.F. Horowitz: Research Support; Self; American Diabetes Association. Funding National Institutes of Health (R01DK077966, T32DK101357)

Objective We studied the effects of exercise training alone or combined with dietary supplementation of omega-3 polyunsaturated fatty acids (Ω-3PUFA) and oleate on metabolic syndrome (MSyn) components and other markers of cardiometabolic health. Methods Thirty-six patients with MSyn underwent 24 weeks of high-intensity interval training. In a double-blind randomized design, half of the group ingested 500 mL/day of semi-skim milk (8 g of fat; placebo milk) whereas the other half ingested 500 mL/day of skim milk enriched with 275 mg of Ω-3PUFA and 7.5 g of oleate (Ω-3 + OLE). Results Ω-3 + OLE treatment elevated 30% plasma Ω-3PUFA but not significantly (P = 0.286). Improvements in VO2peak (12.8%), mean blood pressure (−7.1%), waist circumference (−1.8%), body fat mass (−2.9%), and trunk fat mass (−3.3%) were similar between groups. However, insulin sensitivity (measured by intravenous glucose tolerance test), serum concentration of C-reactive protein, and high-density lipoprotein improved only in the Ω-3 + OLE group by 31.5%, 32.1%, and 10.3%, respectively (all P < 0.05). Fasting serum triacylglycerol, glucose, and plasma fibrinogen concentrations did not improve in either group after 24 weeks of intervention. Conclusions Diet supplementation with Ω-3PUFA and oleate enhanced cardiometabolic benefits of intense aerobic exercise training in patients with MSyn.

NEW FINDINGS What is the central question of this study? Do obese women with relatively high whole-body iron stores exhibit elevated in vivo rates of fatty acid (FA) release from adipose tissue compared with a well-matched cohort of obese women with relatively low iron stores? What is the main finding and its importance? Obese women with high plasma [ferritin] (a marker of whole-body iron stores) had greater FA mobilization, lipolytic activation in adipose tissue and insulin resistance (IR) compared with obese women with lower plasma [ferritin]. Given that elevated FA mobilization is intimately linked with the development of IR, these findings suggest that elevated iron stores might contribute to IR in obesity by increasing systemic FA availability. ABSTRACT High rates of fatty acid (FA) mobilization from adipose tissue are associated with insulin resistance (IR) in obesity. In vitro evidence suggests that iron stimulates lipolysis in adipocytes, but whether iron is related to in vivo FA mobilization is unknown. We hypothesized that plasma ferritin concentration ([ferritin]), a marker of body iron stores, would be positively associated with FA mobilization. We measured [ferritin], the rate of appearance of FA in the systemic circulation (FA Ra; stable isotope dilution), key adipose tissue lipolytic proteins and IR (hyperinsulinaemic-euglycaemic clamp) in 20 obese, premenopausal women. [Ferritin] was correlated with FA Ra (r = 0.65; P = 0.002) and IR (r = 0.57; P = 0.008); these relationships remained significant after controlling for body mass index and plasma [C-reactive protein] (a marker of systemic inflammation) in multiple regression analyses. We then stratified subjects into tertiles based on [ferritin] to compare subjects with 'High-ferritin' versus 'Low-ferritin'. Plasma [hepcidin] was more than fivefold greater (P

Accumulating evidence suggests obese women maintain higher insulin sensitivity than obese men, but factors underlying this sex difference in insulin resistance remain unclear. We recently developed a semi-automated method for quantifying visceral and hepatic fat using advanced chemical shift-encoded magnetic resonance imaging (MRI). Using this method, we explored whether sex differences in ectopic fat accumulation may contribute to differences in insulin resistance. Twenty-one obese women (32 ± 6 year, 34.5 ± 3.1 kg/m2, 43.1 ± 5.5 kg fat mass (FM)) and a well-matched cohort of fifteen obese men (29 ± 6 year, 34.5 ± 3.3 kg/m2, 42.0 ± 7.8 kg FM) underwent an MRI scan during which 5mm axial slices were acquired from the abdominal region. Using 3D Slicer software, visceral fat area was quantified on three axial slices from the L2-L3 vertebrae region and averaged. Hepatic fat was quantified as the average percentage fat from three axial slices of the liver. On a separate day, subjects underwent a hyperinsulinemic-euglycemic clamp to quantify insulin sensitivity. Compared with men, women had lower hepatic (4.2 ± 5.5 vs. 13.1 ± 9.7%, p Disclosure J.B. Gillen: None. B.J. Ryan: None. R.A. Gioscia-Ryan: None. A. Ludzki: None. T.L. Chenevert: None. J.F. Horowitz: None.

Lipodystrophy (LD) syndromes are a heterogeneous group of disorders causing atypical diabetes, associated with selective absence of fat with diagnosis mostly depending on the clinical acumen of the physician. With niche therapies either approved or under investigation, development of objective diagnostic tools for these syndromes are urgently needed. Here we describe a new method using the built-in features of the enCore software v14.10 to render out non-fat tissues from Dual Energy X-ray Absorptiometry (DEXA) scans to derive a “fat-shadow” (Figure). We evaluated fat-shadows from 58 LD (50F:8M) patients and 91 non-LD patients (51F:40M). Among the LD, 3 had Generalized LD, 2 had Acquired Partial LD, and 53 had Familial Partial LD. Controls consisted of a mixed population of lean (12F:14M) or obese patients (39F:26M) with or without metabolic disease. There was substantial overlap in % body fat between the LD and non-LD groups (interquartile range: total, 22.2-39.8% vs. 33.6-45.9%; trunk, 27.0-46.8% vs. 39.1-50.2%; legs, 16.6-30.6% vs. 27.7-42.6%). However, fat-shadows obtained from patients with LD stood out due to the paucity of fat signal either in a generalized or regional manner compared to controls. Overall, fat-shadows provided sufficient qualitative information to infer clinical phenotype. We propose that these fat-shadows could be used for accurate documentation of fat distribution in LD. Disclosure R. Meral: None. B.J. Ryan: None. J.F. Horowitz: None. E.A. Oral: Advisory Panel; Self; Aegerion Pharmaceuticals. Research Support; Self; Aegerion Pharmaceuticals, Akcea Therapeutics. Advisory Panel; Self; Akcea Therapeutics. Research Support; Self; Ionis Pharmaceuticals, Inc., AstraZeneca. Other Relationship; Self; Aegerion Pharmaceuticals.

High body iron stores are positively related to insulin resistance in humans, but the underlying mechanisms remain unresolved. Iron stimulates lipolysis in murine adipocytes in vitro, but the influence of iron stores on lipolytic rate in vivo is unknown. Our aim was to determine if body iron stores are associated with lipolytic rate and whole-body insulin sensitivity in obese, pre-menopausal women. We studied 20 subjects with clinically-normal (20-200 ng/mL) plasma [ferritin], an index of body iron stores. Fatty acid rate of appearance into systemic circulation (FA Ra) was assessed by 13C-palmitate isotope dilution, insulin resistance was assessed by hyperinsulinemic-euglycemic clamp, and abdominal subcutaneous adipose tissue protein expression was assessed via immunoblot. [Ferritin] was significantly (p < 0.01), positively correlated with FA Ra (r2 = 0.42), adipose hormone sensitive lipaseser660 phosphorylation (p-HSLser660, a marker of lipolytic activation in adipose tissue; r2 = 0.41), and whole-body insulin resistance (r2 = 0.33). Importantly, [ferritin] remained a significant, independent predictor for these parameters in multiple regression models including body mass index, plasma [adiponectin], and plasma [CRP] as covariates. We stratified subjects into tertiles based on [ferritin] to compare high-normal and low-normal [ferritin] groups (138 ± 30 vs. 40 ± 15 ng/mL). Compared with the low-normal [ferritin] group, the high-normal [ferritin] group had significantly (p < 0.02) higher FA Ra (15.6 ± 5.5 vs. 8.8 ± 2.4 µmol/kg fat mass/min), adipose p-HSLser660 (1.3 ± 0.4 vs. 0.6 ± 0.2 AU) and whole-body insulin resistance (glucose infusion rate 9.2 ± 2.3 vs. 14.3 ± 3.5 mg/kg fat free mass/min). There were no between-group differences in anthropometric characteristics, plasma [adiponectin], or plasma [CRP]. Our findings suggest that iron-mediated activation of adipose lipolysis may be a mechanism linking body iron stores and insulin resistance in obese humans. Disclosure B.J. Ryan: None. D.W. Van Pelt: None. L.M. Guth: None. A. Ludzki: None. R.A. Gioscia-Ryan: None. C. Ahn: None. J.F. Horowitz: None.

The independent effects of exercise training (without weight loss) on glycemic control are controversial, and the influence of exercise intensity is not well understood. The aim of this study was to determine the effect of 12 weeks (4 sessions/week) of high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT) without weight loss, on “free-living” 24h glycemic control using continuous glucose monitoring (CGM). Eighteen obese adults (33±3 kg·m-2) performed HIIT, involving 10 x 1 min intervals at ∼90% HRmax interspersed with 1 min recovery (n=8), or MICT, involving 45 min at ∼70% HRmax (n=10). CGM was performed under standardized dietary control for 48h before and after training. After training, subjects exercised the day before, but not on Day 1 of CGM measurement. On Day 2 of post-training CGM data collection, participants performed their regular exercise session (HIIT or MICT) before breakfast. This approach allowed us to assess the effects of exercise training on glycemic control on a day with and without exercise. On Day 1 post-training, 24h glucose area under the curve (AUC) was modestly lower than pre-training in both groups (HIIT: 130±11 vs. 126±7 mM·h-1 · 24h; MICT: 138±7 vs. 133±7 mM·h-1 · 24h, p=0.02). There were no differences between HIIT and MICT (p=0.22). The improved 24h glycemic control after training was primarily due to modestly lower postprandial responses to breakfast (p=0.03) and dinner (p=0.002), with no differences between HIIT and MICT. On Day 2 post-training, which included a session of exercise, glycemic control remained better than pre-training in both groups (p=0.006), but interestingly was not improved further by the acute exercise session (p=0.82 for Day 1 vs. Day 2 post-training). In conclusion, exercise training improved 24h “free-living” glycemic responses in the absence of weight loss, and in general, the intensity of exercise training did not impact this improvement in glycemic control. Disclosure M.W. Schleh: None. B.J. Ryan: None. J.B. Gillen: None. A. Ludzki: None. J.F. Horowitz: None.

The aim of this study was to determine the effects of acute exercise on key factors regulating angiogenesis in adipose tissue. Adipose tissue Vegf-a messenger RNA expression was upregulated immediately after acute exercise (p < 0.05) in rats consuming a high-fat diet, but was lower after exercise (p < 0.05) in rats consuming a low-fat diet. Our working hypothesis is that acute exercise augments angiogenic signaling under conditions when adipose tissue is expanding, and with repeated exercise sessions these signals can accrue to enhance vascularization.

Local inflammation in obese adipose tissue has been shown to contribute to insulin resistance; however, the role of macrophage infiltration within skeletal muscle is still debatable. This study aimed to evaluate the association of skeletal muscle macrophage gene expression with adiposity levels and insulin sensitivity in obese patients. Twenty-two nondiabetic obese patients and 23 healthy lean controls were included. Obese patients underwent a 3-month weight loss intervention. Macrophage gene expression in skeletal muscle (quantitative real-time polymerase chain reaction), body composition (dual-energy X-ray absorptiometry), and insulin sensitivity (homeostatic model assessment (HOMA) and oral glucose tolerance test) were compared between groups and their associations were analyzed. To validate skeletal muscle findings, we repeated the analyses with macrophage gene expression in adipose tissue. Expression levels of macrophage genes (CD68, CD11b, CD206, CD16, CD40, and CD163) were lower in skeletal muscle tissue of obese versus lean participants. Macrophage gene expression was also found to be inversely associated with adiposity, fasting insulin, and HOMA (r = −0.4 ∼ −0.6, p < 0.05), as well as positively associated with insulin sensitivity (r = 0.4 ∼ 0.8, p < 0.05). On the other hand, adipose tissue macrophage gene expression showed higher levels in obese versus lean participants, presenting a positive association with adiposity levels. Macrophage gene expression, in both skeletal and adipose tissue samples, was only minimally affected by the weight loss intervention. In contrast with the established positive relationship between adiposity and macrophage gene expression, an unexpected inverse correlation between these 2 variables was observed in skeletal muscle tissue. Additionally, muscle macrophage gene expression was inversely correlated with insulin resistance.

Although the rate of fatty acid release from adipose tissue into the systemic circulation is very high in most obese adults, some obese adults maintain relatively low rates of fatty acid release, which helps protect them against the development of systemic insulin resistance. The primary aim of this study was to identify factors in adipose tissue that may underlie low vs. high rates of fatty acid mobilization in a relatively homogeneous cohort of obese adults. We measured systemic fatty acid rate of appearance (FA Ra) via 13C-palmitate isotope dilution, and we obtained subcutaneous abdominal adipose tissue samples from 30 obese adults (BMI: 38 ± 1 kg/m2, age: 30 ± 2 yr) after an overnight fast. We then measured insulin sensitivity using a hyperinsulinemic-euglycemic clamp. Confirming our previous work, insulin sensitivity was inversely proportional to FA Ra ( R2 = 0.50; P < 0.001). Immunoblot analysis of subcutaneous adipose tissue samples revealed that, compared with obese adults with high FA Ra, those with low FA Ra had lower markers of lipase activation and higher abundance of glycerol-3-phosphate acyltransferase, which is a primary enzyme for fatty acid esterification. Microarray and pathway analysis provided evidence of lower fibrosis and lower SAPK/JNK pathway activation in obese adults with low FA Ra compared with those with high FA Ra. Our findings suggest that alterations in factors regulating triglyceride storage in adipose tissue, along with lower fibrosis and inflammatory pathway activation, may underlie maintenance of a relatively low FA Ra in obesity, which may help protect against the development of insulin resistance.

Although regular exercise is associated with reduced cardiometabolic disease risk among overweight adults, it remains unclear whether much of the health benefits of exercise are derived from the most recent session(s) of exercise or if they are the result of adaptations stemming from weeks, months, or even years of training. The purpose of this study was to compare the effects of habitual and acute exercise on key markers of cardiometabolic disease risk in overweight adults. We compared insulin sensitivity index (ISI) using an oral glucose tolerance test, blood pressure (BP), blood lipids, and systemic inflammatory cytokines in 12 overweight to mildly obese adults (BMI: 27–34 kg/m2) who exercise regularly (EX; >2.5 h exercise per week) with a well-matched cohort of 12 nonexercisers (Non-EX). Baseline measurements in EX were performed exactly 3 days after exercise, whereas Non-EX remained sedentary. We repeated these measurements the day after a session of exercise in both groups. At baseline, ISI was significantly greater in EX versus Non-EX (3.1 ± 0.2 vs. 2.3 ± 0.2; p = 0.02), but BP, blood lipids, and plasma concentration of the systemic inflammatory cytokines we measured were not different between groups. Acute exercise increased ISI the next morning in Non-EX (2.3 ± 0.2 vs. 2.8 ± 0.3; p = 0.03) but not EX. As a result, ISI was similar between groups the morning after exercise. In summary, exercising regularly was accompanied by a persistent improvement in insulin sensitivity that lasted at least 3 days after exercise in overweight adults, but just one session of exercise increased insulin sensitivity among sedentary overweight adults to levels equivalent to the regular exercisers.

SummaryContext Partial lipodystrophy (PL) is associated with metabolic co-morbidities but may go undiagnosed as the disease spectrum is not fully described. Objective The objective of the study was to define disease spectrum in PL using genetic, clinical (historical, morphometric) and laboratory characteristics. Design Cross-sectional evaluation. Participants Twenty-three patients (22 with familial, one acquired, 78·3% female, aged 12–64 years) with PL and non-alcoholic fatty liver disease (NAFLD). Measurements Genetic, clinical and laboratory characteristics, body composition indices, liver fat content by magnetic resonance imaging (MRI), histopathological and immunofluorescence examinations of liver biopsies. Results Seven patients displayed heterozygous pathogenic variants in LMNA. Two related patients had a heterozygous, likely pathogenic novel variant of POLD1 (NM002691·3: c.3199 G>A; p.E1067K). Most patients had high ratios (>1·5) of percentage fat trunk to percentage fat legs (FMR) when compared to reference normals. Liver fat quantified using MR Dixon method was high (11·3 ± 6·3%) and correlated positively with haemoglobin A1c and triglycerides while leg fat by dual-energy X-ray absorptiometry (DEXA) correlated negatively with triglycerides. In addition to known metabolic comorbidities; chronic pain (78·3%), hypertension (56·5%) and mood disorders (52·2%) were highly prevalent. Mean NAFLD Activity Score (NAS) was 5 ± 1 and 78·3% had fibrosis. LMNA-immunofluorescence staining from select patients (including one with the novel POLD1 variant) showed a high degree of nuclear atypia and disorganization. Conclusions Partial lipodystrophy is a complex multi-system disorder. Metabolic parameters correlate negatively with extremity fat and positively with liver fat. DEXA-based FMR may prove useful as a diagnostic tool. Nuclear disorganization and atypia may be a common biomarker even in the absence of pathogenic variants in LMNA.

OBJECTIVE The purpose of this study was to determine the effect of a relatively modest session of exercise on insulin sensitivity and fatty acid uptake the next day in obese adults. RESEARCH DESIGN AND METHODS Eleven sedentary obese adults (male/female: 3/8; BMI 37 ± 1 kg/m2; peak oxygen uptake [VO2peak] 20 ± 1 mL/kg/min) completed three experimental trials. On two of these occasions, subjects exercised to expend 350 kcal in the afternoon. These two exercise trials were identical except for the exercise intensity (50% VO2peak [EX50] and 65% VO2peak [EX65]) and the duration of exercise necessary to expend 350 kcal (EX50 = ∼70 min; EX65 = ∼55 min). Subjects also completed a control trial (CON), without exercise. The next morning, we measured insulin sensitivity (hyperinsulinemic-euglycemic clamp) and whole-body fatty acid uptake (palmitate rate of disappearance from plasma [Rd]). RESULTS Exercise increased insulin sensitivity the next day, but whereas the 35% improvement after EX50 compared with CON was statistically significant (P = 0.01), the 20% improvement after EX65 was not (P = 0.17). Despite nearly identical values between CON and EX65 (P = 0.88), systemic fatty acid uptake was lower after EX50 compared with EX65 (P = 0.02), but not quite significant compared with CON (P = 0.07). Importantly, the change in fatty acid uptake after exercise compared with CON was negatively correlated with the change in insulin sensitivity for all trials (r = −0.60, P = 0.003). CONCLUSIONS A relatively modest single session of exercise in obese adults improved insulin sensitivity the next day, and a reduction in systemic fatty acid uptake in the several hours after exercise may be important for this effect.

Prolonged overeating and the resultant weight gain are clearly linked with the development of insulin resistance and other cardiometabolic abnormalities, but adaptations that occur after relatively short periods of overeating are not completely understood. The purpose of this study was to characterize metabolic adaptations that may accompany the development of insulin resistance after 2 weeks of overeating. Healthy, nonobese subjects (n = 9) were admitted to the hospital for 2 weeks, during which time they ate ∼4000 kcals·day−1(70 kcal·kg−1fat free mass·day−1). Insulin sensitivity was estimated during a meal tolerance test, and a muscle biopsy was obtained to assess muscle lipid accumulation and protein markers associated with insulin resistance, inflammation, and the regulation of lipid metabolism. Whole-body insulin sensitivity declined markedly after 2 weeks of overeating (Matsuda composite index: 8.3 ± 1.3 vs. 4.6 ± 0.7, p < 0.05). However, muscle markers of insulin resistance and inflammation (i.e., phosphorylation of IRS-1-Ser312, Akt-Ser473, and c-Jun N-terminal kinase) were not altered by overeating. Intramyocellular lipids tended to increase after 2 weeks of overeating (triacylglyceride: 7.6 ± 1.6 vs. 10.0 ± 1.8 nmol·mg−1wet weight; diacylglyceride: 104 ± 10 vs. 142 ± 23 pmol·mg−1wet weight) but these changes did not reach statistical significance. Overeating induced a 2-fold increase in 24-h insulin response (area under the curve (AUC); p < 0.05), with a resultant ∼35% reduction in 24-h plasma fatty acid AUC (p < 0.05). This chronic reduction in circulating fatty acids may help explain the lack of a robust increase in muscle lipid accumulation. In summary, our findings suggest alterations in skeletal muscle metabolism may not contribute meaningfully to the marked whole-body insulin resistance observed after 2 weeks of overeating.

A two-arm, prospective, randomized, controlled trial study was conducted to investigate the effects of movement velocity during progressive resistance training (PRT) on the size and contractile properties of individual fibers from human vastus lateralis muscles. The effects of age and sex were examined by a design that included 63 subjects organized into four groups: young (20–30 yr) men and women, and older (65–80 yr) men and women. In each group, one-half of the subjects underwent a traditional PRT protocol that involved shortening contractions at low velocities against high loads, while the other half performed a modified PRT protocol that involved contractions at 3.5 times higher velocity against reduced loads. Muscles were sampled by needle biopsy before and after the 14-wk PRT program, and functional tests were performed on permeabilized individual fiber segments isolated from the biopsies. We tested the hypothesis that, compared with low-velocity PRT, high-velocity PRT results in a greater increase in the cross-sectional area, force, and power of type 2 fibers. Both types of PRT increased the cross-sectional area, force, and power of type 2 fibers by 8–12%, independent of the sex or age of the subject. Contrary to our hypothesis, the velocity at which the PRT was performed did not affect the fiber-level outcomes substantially. We conclude that, compared with low-velocity PRT, resistance training performed at velocities up to 3.5 times higher against reduced loads is equally effective for eliciting an adaptive response in type 2 fibers from human skeletal muscle.

OBJECTIVE Leptin therapy improves insulin sensitivity in people with leptin deficiency, but it is not known whether it improves insulin action in people who are not leptin deficient. The purpose of the current study was to determine whether leptin treatment has weight loss–independent effects on insulin action in obese subjects with type 2 diabetes. RESEARCH DESIGN AND METHODS We conducted a randomized, placebo-controlled trial in obese subjects (BMI: 35.4 ± 0.6 kg/m2; mean ± SE) with newly diagnosed type 2 diabetes. Subjects were randomized to treatment with placebo (saline), low-dose (30 mg/day), or high-dose (80 mg/day) recombinant methionyl human (r-Met hu) leptin for 14 days. Multiorgan insulin sensitivity before and after treatment was evaluated by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled tracer infusions to measure glucose, glycerol, and fatty acid kinetics. RESULTS Low-dose and high-dose leptin treatment resulted in a threefold (P < 0.01) and 150-fold (P < 0.001) increase in basal plasma leptin concentrations, respectively. However, neither low-dose nor high-dose therapy had an effect on insulin-mediated suppression of glucose, glycerol, or palmitate rates of appearance into plasma compared with placebo. In addition, leptin treatment did not increase insulin-mediated stimulation of glucose disposal compared with placebo (14.3 ± 3.1, 18.4 ± 3.6, 16.7 ± 2.4 vs. 17.5 ± 2.5, 20.7 ± 3.0, 19.1 ± 3.3 μmol/kg body wt/min before vs. after treatment in the placebo, low-dose, and high-dose leptin groups, respectively). CONCLUSIONS r-Met hu leptin does not have weight loss–independent, clinically important effects on insulin sensitivity in obese people with type 2 diabetes.

The very low GH concentration in obesity is commonly attributed to high body fat mass; however, the influence of overeating on GH secretion is not clear.The aim of the study was to examine the effects of 2 wk of overeating on changes in GH secretion.Subjects were admitted to the hospital and stayed within the Michigan Clinical Research Unit throughout the entire 2-wk overeating period.We studied seven healthy, nonobese men (body mass index, 24 ± 1 kg/m(2); age, 25 ± 1 yr).Subjects ate standardized meals containing 70 kcal/kg fat free mass/d (∼4000 kcal/d) for 2 wk.Twenty-four-hour plasma concentrations of GH (every 20 min) and insulin (every 2 h) were measured before overeating (baseline), on d 3, and after 2 wk of overeating.Compared with baseline, average 24-h plasma GH concentration declined nearly 80% by d 3 of overeating (1.30 ± 0.18 vs. 0.36 ± 0.09 ng/ml; P = 0.01). This marked suppression of GH secretion occurred in the absence of an increase in body weight (77.0 ± 2.2 vs. 76.4 ± 2.4 kg). At the same time, average 24-h insulin concentration doubled (16.6 ± 2.1 vs. 31.7 ± 5.8 μU/ml; P = 0.009). After 2 wk, body weight significantly increased (79.0 ± 2.1 kg; P0.001), and body fat increased by more than 10% (P = 0.002). However, this did not induce a further suppression in plasma GH concentration (0.33 ± 0.08 ng/ml).Only a few days of overeating markedly suppressed GH secretion before any measurable weight gain and was accompanied by chronic hyperinsulinemia. Increased body weight and body fat by 2 wk of overeating did not further suppress GH secretion.

Purpose Diets high in saturated fat acids (SFA) have been linked with cardio-metabolic disease risk. The purpose of this study was to determine whether only 1–2 weeks of a high SFA diet could impact disease risk factors in overweight adults who normally eat a relatively low proportion of SFA (i.e.

Obesity is characterized by excessive rates of plasma fatty acid mobilization and uptake, which play a key role in mediating insulin resistance. While weight loss via diet-only or a diet + exercise program clearly improves insulin sensitivity, the precise mechanisms modulating this improvement are not completely understood. The purpose of the present study was to determine the role of the reduced fatty acid mobilization and uptake after weight loss in obese women who were randomly assigned to lifestyle interventions of either weight loss without exercise (WL) (n= 7) or a weight loss + exercise program (WL + EX) (n= 10). Before and after losing 12% of their body weight, we measured insulin sensitivity (SI), systemic fatty acid rate of appearance (Ra) and disappearance (Rd), oxidative capacity, and markers for pro-inflammatory pathways in skeletal muscle. Fatty acid Ra and Rd were reduced by ∼30% after both interventions (P < 0.05). While oxidative capacity increased 25% in WL + EX (compared with no increase after WL), the improvement in SI was identical in both groups (∼60%; P < 0.05), and skeletal muscle pro-inflammatory pathways were reduced (P < 0.05) similarly in both groups. When we artificially increased fatty acid mobilization after weight loss to pre-weight-loss levels via an overnight lipid infusion, the improvement in SI was almost completely reversed. Importantly, WL + EX did not protect against this lipid-induced reversal in SI despite a significant increase in resting whole-body fat oxidation and a marked increase in skeletal muscle oxidative capacity. In conclusion, reduced fatty acid mobilization and uptake appears to be a primary mediator of improved insulin sensitivity after weight loss. Moreover, enhancing fatty acid oxidative capacity via exercise training is not sufficient to prevent the insulin resistance caused by high fatty acid mobilization, such as that found in obesity.

Context: Fasting is associated with suppressed insulin and augmented GH secretion. The involvement of each mechanism in the regulation of fuel mobilization during fasting is unknown. Objective: To ascertain the role of GH in the regulation of the rates of lipolysis, proteolysis, and hepatic glucose production (HGP) during the physiological daily feed/fast cycle and after 2 d of complete fasting, we used a model of selective GH suppression by the administration of GHRH receptor antagonist (GHRH-A). Design and Setting: We conducted an open label in-patient study in the General Clinical Research Center at the University of Michigan. Participants: Six healthy, nonobese volunteers participated. Main Outcome Measures: We assessed 24-h plasma GH concentration and rates of lipolysis, proteolysis, and HGP using stable isotope techniques after an overnight fast and after 2 d of fasting. Results: GHRH-A suppressed plasma GH by about 65% during the fed state (P = 0.015) but did not alter the rates of lipolysis, proteolysis, or HGP. Fasting for 2 d suppressed plasma insulin concentration by about 80% and elevated plasma GH about 4-fold (both P < 0.01). This was accompanied by a doubling in the rate of lipolysis, an approximately 40% increase in proteolysis, and an approximately 30% decline in HGP (all P < 0.05). Preventing the fasting-induced increase in GH with GHRH-A largely abolished the increase in the rate of lipolysis. GHRH-A also augmented the fasting-induced reduction in HGP but did not alter proteolysis. Conclusions: Endogenous GH plays a very limited metabolic role during the daily feed/fast cycle but is essential for the increased lipolytic rate found with more prolonged fasting.

Fatty acid oversupply is a key mediator of skeletal muscle insulin resistance in obesity, primarily via accumulation of fatty acid metabolites and activation of proinflammatory pathways. Herein, we demonstrate that fatty acid-induced insulin resistance in humans is completely prevented the day after 1 session of endurance exercise. Because skeletal muscle is the primary site for systemic glucose disposal and is highly susceptible to impaired insulin action by elevated fatty acid availability, we obtained skeletal muscle samples to investigate possible mechanisms mediating this protective effect of exercise. Prevention of fatty acid-induced insulin resistance after exercise accompanied enhanced skeletal muscle protein expression of key lipogenic enzymes and an increase in muscle triglyceride synthesis. Partitioning more fatty acids toward triglyceride synthesis within muscle reduced the accumulation of fatty acid metabolites and suppressed the proinflammatory response in skeletal muscle, as evidenced by decreased phosphorylation and activation of JNK and increased abundance of inhibitor of NF-kappaB alpha (I kappa B-alpha) and I kappa B-beta. We believe this is the first study to demonstrate that 1 session of exercise completely reverses fatty acid-induced insulin resistance in humans. Reversal of insulin resistance accompanied enhanced lipogenic capacity within skeletal muscle, reduced accumulation of highly bioactive fatty acid metabolites, and suppressed activation of proinflammatory pathways known to impair insulin action.

Although the increase in fatty acid oxidation after endurance exercise training has been linked with improvements in insulin sensitivity and overall metabolic health, the mechanisms responsible for increasing fatty acid oxidation after exercise training are not completely understood. The primary aim of this study was to determine the effect of adding endurance exercise training to a weight loss program on fat oxidation and the colocalization of the fatty acid translocase FAT/CD36 with carnitine palmitoyltransferase I (CPT I) in human skeletal muscle. We measured postabsorptive fat oxidation and acquired a muscle sample from abdominally obese women before and after 12% body weight loss through either dietary intervention with endurance exercise training (EX + DIET) or dietary intervention without endurance exercise training (DIET). Immunoprecipitation techniques were used on these muscle samples to determine whether the association between FAT/CD36 and CPT I is altered after DIET and/or EX + DIET. FAT/CD36 was found to coimmunoprecipitate with CPT I, and the amount of FAT/CD36 that coimmunoprecipitated with CPT I increased by ∼25% after EX + DIET ( P < 0.005) but was unchanged after DIET. In addition, the increase in the amount of FAT/CD36 that coimmunoprecipitated with CPT I in EX + DIET was strongly correlated with the increase in whole body fat oxidation ( R2= 0.857, P < 0.003). In conclusion, the findings from this study indicate that exercise training alters the localization of FAT/CD36 and increases its association with CPT I, which may help augment fat oxidation.

The lipemic response to a high-fat meal is greater in men than in women. However, sex-related differences in the metabolic fate of ingested fat are not well understood. The purpose of this study was to measure the recovery of ingested fat in plasma fractions of chylomicrons (CHYLO), VLDL, and plasma fatty acids, as well as in expired breath (i.e., oxidation) in men and women. Nonobese subjects (n = 10; 5 men, 5 women) consumed 0.7 g fat/kg body weight containing 7 mg/kg of [1,1,1 - 13 C]-trioleate the morning after an overnight fast. Plasma total triglyceride (TG) concentration and 13 C recovery in the CHYLO, VLDL, and plasma fatty acid fractions, as well as expired breath samples, were measured over the 11 -h period after the meal. Plasma total TG excursion was greater (P < 0.05) in men than in women during the 11 -h period after the meal. Similarly, the recovery of the ingested tracer-labeled fat in the CHYLO fraction was greater in men than in women (main effect for sex; P < 0.05). Recovery of ingested tracer-labeled fat in VLDL, the plasma fatty acid fraction, and expired breath did not differ in men and women. Therefore, the elevated postprandial lipemia found in men compared with women was due to a prolonged availability of the lipid in chylomicrons, but was not related to differences in oxidation rates or incorporation of the ingested lipid into VLDL by the liver.

Alterations in dietary macronutrient intake can influence protein turnover.The purpose of this study was to assess the influence of a low-carbohydrate/high-protein diet (LC/HP) on skeletal muscle protein synthesis and whole-body proteolysis, without the confounding influence of a negative energy balance.Nine-day dietary intervention was applied.Subjects remained in the General Clinical Research Center throughout the 9-d study.Eight young, healthy volunteers participated.Subjects ate a typical Western diet (60% carbohydrate, 30% fat, 10% protein) for 2 d, followed immediately by 7 d of an isocaloric LC/HP (5% carbohydrate, 60% fat, 35% protein).Skeletal muscle fractional synthetic rate and whole-body proteolysis [leucine rate of appearance in plasma (Ra)] were measured after an overnight fast before and after 2 and 7 d of LC/HP. We also measured plasma concentrations of insulin, GH, and IGF-I.Leucine Ra was increased (P = 0.03) after 2 and 7 d of LC/HP, and muscle fractional synthetic rate was approximately 2-fold higher (P0.01) after 7 d of LC/HP. Fat free mass was not altered by LC/HP. Average 24-h plasma insulin concentration was 50% lower (P0.001) after 2 and 7 d of LC/HP, whereas GH secretion and total plasma IGF-I concentrations were unchanged with LC/HP. However, plasma free IGF-I decreased by approximately 30% after 7 d of LC/HP (P = 0.002), whereas muscle IGF-I mRNA increased about 2-fold (P = 0.05).Increasing dietary protein content during a 7-d carbohydrate restricted diet stimulated muscle protein synthesis and whole-body proteolysis without a measurable change in fat free mass.

Dietary carbohydrate restriction (CR) presents a challenge to glucose homeostasis. Despite the popularity of CR diets, little is known regarding the metabolic effects of CR. The purpose of this study was to examine changes in whole body carbohydrate oxidation, glucose availability, endogenous glucose production, and peripheral glucose uptake after dietary CR, without the confounding influence of a negative energy balance. Postabsorptive rates of glucose appearance in plasma (Ra; i.e., endogenous glucose production) and disappearance from plasma (Rd; i.e., glucose uptake) were measured using isotope dilution methods after a conventional diet [60% carbohydrate (CHO), 30% fat, and 10% protein; kcals = 1.3 × resting energy expenditure (REE)] and after 2 days and 7 days of CR (5% CHO, 60% fat, and 35% protein; kcals = 1.3 × REE) in eight subjects (means ± SE; 29 ± 4 yr; BMI 24 ± 1 kg/m2) during a 9-day hospital visit. Postabsorptive plasma glucose concentration was reduced ( P = 0.01) after 2 days but returned to prediet levels the next day and remained at euglycemic levels throughout the diet (5.1 ± 0.2, 4.3 ± 0.3, and 4.8 ± 0.4 mmol/l for prediet, 2 days and 7 days, respectively). Glucose Ra and glucose Rd were reduced to below prediet levels (9.8 ± 0.6 μmol·kg−1·min−1) after 2 days of CR (7.9 ± 0.3 μmol·kg−1·min−1) and remained suppressed after 7 days (8.3 ± 0.4 μmol·kg−1·min−1; both P < 0.001). A greater suppression in carbohydrate oxidation, compared with the reduction in glucose Rd, led to an increased (all P ≤ 0.05) rate of nonoxidative glucose disposal at 7 days (5.2 ± 0.5 μmol·kg−1·min−1), compared with 2 days (2.7 ± 0.5 μmol·kg−1·min−1) and prediet (1.6 ± 0.8 μmol·kg−1·min−1). In response to eucaloric CR, a marked increase in nonoxidative glucose disposal may help maintain systemic glucose availability.

High plasma fatty acid availability and a positive energy balance in sedentary individuals reduce insulin sensitivity. This study's purpose was to determine whether high plasma fatty acid availability and systemic caloric excess after exercise also impair insulin sensitivity. On two separate occasions, seven nonobese women performed 90 min of exercise at ∼65% peak oxygen uptake. In one trial, a lipid + heparin emulsion (Lipid) was infused overnight to increase plasma fatty acid availability. In the other trial, saline was infused as control. The next morning, a muscle biopsy was taken to measure muscle glycogen and intramuscular triglyceride (IMTG) concentrations. Three hours after the overnight infusion was stopped, insulin sensitivity was assessed with an intravenous glucose tolerance test, using minimal model analysis (Si). During the overnight infusions, plasma fatty acid concentration was approximately fourfold higher [means (SD): 0.84 (0.36) vs. 0.22 (0.09) mmol/l; P = 0.003], and the next morning IMTG concentration was ∼30% greater [49.2 (6.6) vs. 38.3 (7.7) mmol/kg dry wt; P = 0.036] in Lipid compared with saline. However, muscle glycogen concentration was not different between trials ( P = 0.82). Lipid caused a 24-h surplus of ∼1100 kcal above energy balance ( P = 0.00001), whereas energy balance was maintained in saline. Despite these differences in fatty acid and energy availability, Si the morning after exercise was not different between trials ( P = 0.72). Thus insulin sensitivity the morning after a single exercise session was not reduced despite overnight exposure to a fourfold increase in plasma fatty acid concentration, elevated IMTG concentration, and systemic delivery of ∼1,100-kcal excess.

A single session of exercise increases insulin sensitivity for hours and even days, and dietary carbohydrate ingested after exercise alters the magnitude and duration of this effect. Although increasing systemic fatty acid availability is associated with insulin resistance, it is uncertain whether increasing dietary fat availability after exercise alters the exercise-induced increase in insulin sensitivity. The purpose of this study was to determine whether adding fat calories to meals after exercise alters glucose tolerance the next day. Seven healthy men cycled 90 min at 66 +/- 2% peak oxygen uptake followed by a maximum of five high-intensity intervals. During the hours after exercise, subjects ingested three meals containing either low-fat (5% energy from fat) or high-fat (45% energy from fat) foods (Low-Fat and High-Fat groups, respectively). Each diet contained the same amount of carbohydrate and protein. An oral glucose tolerance test was performed the next morning. Muscle glycogen and intramuscular triglyceride (IMTG) concentrations were measured in muscle biopsy samples obtained immediately before exercise and the next morning. The day after exercise, muscle glycogen concentration was identical in High-Fat and Low-Fat (393 +/- 70 and 379 +/- 38 mmol/kg dry wt). At the same time, IMTG concentration was approximately 20% greater during High-Fat compared with Low-Fat (42.5 +/- 3.4 and 36.3 +/- 3.3 mmol/kg dry wt; P0.05). Despite the addition of approximately 165 g of fat to meals after exercise ( approximately 1,500 kcal) and a resultant elevation in IMTG concentration, glucose tolerance was identical in High-Fat and Low-Fat (composite index: 8.7 +/- 1.0 and 8.4 +/- 1.0). In summary, as long as meals ingested in the hours after exercise contain the same carbohydrate content, the addition of approximately 1500 kcal from fat to these meals did not alter muscle glycogen resynthesis or glucose tolerance the next day.

Numerous studies indicate an inflammatory link between obesity and type 2 diabetes. The inflammatory kinases IKKɛ and TBK1 are elevated in obesity; their inhibition in obese mice reduces weight, insulin resistance, fatty liver and inflammation. Here we studied amlexanox, an inhibitor of IKKɛ and TBK1, in a proof-of-concept randomized, double-blind, placebo-controlled study of 42 obese patients with type 2 diabetes and nonalcoholic fatty liver disease. Treatment of patients with amlexanox produced a statistically significant reduction in Hemoglobin A1c and fructosamine. Interestingly, a subset of drug responders also exhibited improvements in insulin sensitivity and hepatic steatosis. This subgroup was characterized by a distinct inflammatory gene expression signature from biopsied subcutaneous fat at baseline. They also exhibited a unique pattern of gene expression changes in response to amlexanox, consistent with increased energy expenditure. Together, these data suggest that dual-specificity inhibitors of IKKɛ and TBK1 may be effective therapies for metabolic disease in an identifiable subset of patients.

Insulin receptor substrate 1 (IRS1) is a key mediator of insulin signal transduction. Perturbations involving IRS1 complexes may lead to the development of insulin resistance and type 2 diabetes (T2D). Surprisingly little is known about the proteins that interact with IRS1 in humans under health and disease conditions. We used a proteomic approach to assess IRS1 interaction partners in skeletal muscle from lean healthy control subjects (LCs), obese insulin-resistant nondiabetic control subjects (OCs), and participants with T2D before and after insulin infusion. We identified 113 novel endogenous IRS1 interaction partners, which represents the largest IRS1 interactome in humans and provides new targets for studies of IRS1 complexes in various diseases. Furthermore, we generated the first global picture of IRS1 interaction partners in LCs, and how they differ in OCs and T2D patients. Interestingly, dozens of proteins in OCs and/or T2D patients exhibited increased associations with IRS1 compared with LCs under the basal and/or insulin-stimulated conditions, revealing multiple new dysfunctional IRS1 pathways in OCs and T2D patients. This novel abnormality, increased interaction of multiple proteins with IRS1 in obesity and T2D in humans, provides new insights into the molecular mechanism of insulin resistance and identifies new targets for T2D drug development.

Data obtained from studies conducted in animal models and humans suggest that gender affects the metabolic response to fasting. However, differences in body composition between males and females confound the interpretation of these studies, because increased adiposity itself alters the metabolic response to short-term fasting. We evaluated whole body lipid and glucose kinetics during basal (14-h fast) and short-term fasting (22-h fast) conditions in six women and six men who were matched for adiposity (24 ± 2 and 23 ± 2% body wt as fat, respectively). Substrate kinetics were measured by infusing stable isotope labeled tracers of glucose ([2H2]glucose) and glycerol ([2H5]glycerol). Basal glycerol rate of appearance (Ra) in plasma, an indicator of whole body lipolytic rate, was greater in women than in men (2.1 ± 0.2 vs. 1.5 ± 0.1 μmol · kg body wt−1· min−1; P < 0.05). However, the relative increase in glycerol Rawith continued fasting was blunted in women compared with men (40 ± 7 vs. 80 ± 4% increase; P < 0.05), resulting in similar lipolytic rates in both genders at 22 h (2.8 ± 0.2 and 2.6 ± 0.1 μmol · kg body wt−1· min−1for women and men, respectively). In contrast, glucose Rawas similar in men and women at 14 h (11 ± 0.6 vs. 12 ± 0.7 μmol · kg body wt−1· min−1) and 22 h of fasting (9 ± 0.6 vs. 10 ± 0.6 μmol · kg body wt−1· min−1). These data demonstrate the presence of sexual dimorphism in lipid, but not glucose, metabolism during both basal and short-term fasting conditions.

Although obesity is commonly linked with metabolic disease risk, some obese adults do not develop metabolic abnormalities, such as insulin resistance.The primary aim of this study was to determine whether alterations in fatty acid mobilization and uptake underlie differences in insulin sensitivity (Si) among a seemingly homogeneous cohort of obese women.Insulin sensitivity (frequently sampled intravenous glucose tolerance test), basal fatty acid rate of disappearance from plasma (Rd), resting whole-body fat oxidation, intramyocellular triacylglycerol (IMTG) concentration and markers of skeletal muscle inflammation were measured in 21 obese women. Participants were divided into tertiles based on their S(i). The subset of participants with the lowest S(i) (LOW-S(i); S(i) ⩽ 2.1 (mU/l)(-1) min(-1); n = 7) was compared with the subset of participants with the highest S(i), who exhibited relatively normal insulin sensitivity (NORM-S(i); S(i) ⩾ 3.4 (mU/l)(-1) min(-1); n = 8).Despite nearly identical physical characteristics in LOW-S(i) vs NORM-S(i) (body mass index: 34 ± 2 vs 34 ± 1 kg m(-2); %body fat: 48 ± 1 vs 47 ± 1%; waist circumference: 104 ± 2 vs 104 ± 2 cm; VO2 max: 2.2 ± 0.2 vs 2.3 ± 0.1 l min(-1)), fatty acid Rd was nearly 30% lower in NORM (P=0.02). Importantly, the greater rate of fatty acid uptake in LOW-S(i) vs NORM-S(i) did not translate to higher rate of fat oxidation (3.5 ± 0.2 vs 3.7 ± 0.2 μmol kg(-1) min(-1)) or to a measureable difference in IMTG content (68.3 ± 12.7 vs 63.7 ± 6.7 μmol g(-1) dry weight). In conjunction with the lower fatty acid Rd in NORM-S(i) vs LOW-S(i), activation of inflammatory pathways known to impair insulin action in skeletal muscle was also lower (lower phosphorylated c-jun N-terminal kinase (JNK) and higher inhibitor of κB (IκB-α) abundance). In contrast, LOW-S(i) and NORM-S(i) exhibited no differences in plasma markers of inflammation (TNFα, IL-6 (interleukin-6), MCP-1).These findings suggest that obese women who maintain a relatively low rate of endogenous fatty acid uptake may be somewhat 'protected' against the development of insulin resistance potentially by less activation of inflammatory pathways within skeletal muscle.

We evaluated plasma fatty acid availability and plasma and whole body fatty acid oxidation during exercise in five lean and five abdominally obese women (body mass index = 21 ± 1 vs. 38 ± 1 kg/m2), who were matched on aerobic fitness, to test the hypothesis that obesity alters the relative contribution of plasma and nonplasma fatty acids to total energy production during exercise. Subjects exercised on a recumbent cycle ergometer for 90 min at 54% of their peak oxygen consumption. Stable isotope tracer methods ([13C]palmitate) were used to measure fatty acid rate of appearance in plasma and the rate of plasma fatty acid oxidation, and indirect calorimetry was used to measure whole body substrate oxidation. During exercise, palmitate rate of appearance increased progressively and was similar in obese and lean groups between 60 and 90 min of exercise [3.9 ± 0.4 vs. 4.0 ± 0.3 μmol · kg fat free mass (FFM)−1 · min−1]. The rate of plasma fatty acid oxidation was also similar in obese and lean subjects (12.8 ± 1.7 vs. 14.5 ± 1.8 μmol · kg FFM−1 · min−1; P = not significant). However, whole body fatty acid oxidation during exercise was 25% greater in obese than in lean subjects (21.9 ± 1.2 vs. 17.5 ± 1.6 μmol · kg FFM−1 · min−1; P < 0.05). These results demonstrate that, although plasma fatty acid availability and oxidation are similar during exercise in lean and obese women, women with abdominal obesity use more fat as a fuel by oxidizing more nonplasma fatty acids.