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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)

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 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.

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)

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.

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.

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.