Endothelial function after high-sugar-food ingestion improves with endurance exercise performed on the previous day

No acute hyperglycemia induced impairment in brachial artery flow-mediated dilation before or after aerobic exercise training in young recreationally active males

There is some evidence that transient endothelial dysfunction induced by acute hyperglycemia may be attenuated by a single bout of aerobic exercise. However, the impact of aerobic exercise training on acute hyperglycemia-induced endothelial dysfunction has not been explored. The purpose of this study was to determine the impact of aerobic exercise training on the endothelial function response to acute hyperglycemia. Brachial artery flow-mediated dilation (FMD) was assessed in 24 healthy males (21 ± 1 years) pre-, 60 and 90 min post ingestion of 75 g of glucose. Participants completed a four-week control (CON; n = 13) or exercise training (EX; n = 11) intervention. The EX group completed four weeks of cycling exercise (30 min, 4×/week at 65% work rate peak). Cardiorespiratory fitness ([Formula: see text]O2peak) increased and resting HR decreased in EX, but not CON post-intervention (p < 0.001). Glucose and insulin increased (p < 0.001) following glucose ingestion, with no significant difference pre- and post-intervention. In contrast to previous research, FMD was unaffected by glucose-ingestion, pre- and post-intervention in both groups. In conclusion, acute hyperglycemia did not impair endothelial function, before or after exercise training. Relatively high baseline fitness ([Formula: see text]O2peak ~ 46 mL/kg/min) and young age may have contributed to the lack of impairment observed. Further research is needed to examine the impact of exercise training on hyperglycemia-induced impairments in endothelial function in sedentary males and females.

The impact of preconditioning exercise on the vascular response to an oral glucose challenge

Exercise elicits direct benefits to insulin sensitivity but may also indirectly improve glucose uptake by hemodynamic conditioning of the vasculature. The purpose of this study was to examine the modifying effect of 3 different types of exercise on the vascular response to an oral glucose challenge. Twenty healthy adults (9 women, 11 men; aged 23 ± 3 years) completed a standard oral glucose tolerance test (OGTT) at rest, as well as 1.5 hours after moderate continuous cycling exercise (30 min; 65% peak oxygen consumption), high-intensity interval cycling exercise (10 × 1 min at 90% peak heart rate), and lower-load higher-repetition resistance exercise (25-35 repetitions/set, 3 sets). Brachial and superficial femoral artery blood flow, conductance, and oscillatory shear index were measured throughout the OGTT. Regardless of rested state or exercise preconditioning, the OGTT induced reductions in brachial artery blood flow and conductance (p < 0.001), and transient increases in brachial and superficial femoral artery oscillatory shear index and retrograde blood flow (p < 0.01). Continuous cycling and resistance exercise were followed with a small degree of protection against prolonged periods of oscillatory flow. Our findings imply transient peripheral vasoconstriction and decreased limb blood flow during a standard OGTT, for which prior exercise was unable to prevent in healthy adults. Novelty: We investigated the impact of continuous, interval, and resistance exercise on the hemodynamic response to an OGTT. Our findings suggest decreased upper-limb blood flow during an OGTT is not prevented by prior exercise in healthy adults.

Impact of Lifestyles (Diet and Exercise) on Vascular Health: Oxidative Stress and Endothelial Function

Healthy lifestyle and diet are associated with significant reduction in risk of obesity, type 2 diabetes, and cardiovascular diseases. Oxidative stress and the imbalance between prooxidants and antioxidants are linked to cardiovascular and metabolic diseases. Changes in antioxidant capacity of the body may lead to oxidative stress and vascular dysfunction. Diet is an important source of antioxidants, while exercise offers many health benefits as well. Recent findings have evidenced that diet and physical factors are correlated to oxidative stress. Diet and physical factors have debatable roles in modulating oxidative stress and effects on the endothelium. Since endothelium and oxidative stress play critical roles in cardiovascular and metabolic diseases, dietary and physical factors could have significant implications on prevention of the diseases. This review is aimed at summarizing the current knowledge on the impact of diet manipulation and physical factors on endothelium and oxidative stress, focusing on cardiovascular and metabolic diseases. We discuss the friend-and-foe role of dietary modification (including different diet styles, calorie restriction, and nutrient supplementation) on endothelium and oxidative stress, as well as the potential benefits and concerns of physical activity and exercise on endothelium and oxidative stress. A fine balance between oxidative stress and antioxidants is important for normal functions in the cells and interfering with this balance may lead to unfavorable effects. Further studies are needed to identify the best diet composition and exercise intensity.

Metformin May Contribute to Inter-individual Variability for Glycemic Responses to Exercise

Metformin and exercise independently improve glycemic control. Metformin traditionally is considered to reduce hepatic glucose production, while exercise training is thought to stimulate skeletal muscle glucose disposal. Collectively, combining treatments would lead to the anticipation for additive glucose regulatory effects. Herein, we discuss recent literature suggesting that metformin may inhibit, enhance or have no effect on exercise mediated benefits toward glucose regulation, with particular emphasis on insulin sensitivity. Importantly, we address issues surrounding the impact of metformin on exercise induced glycemic benefit across multiple insulin sensitive tissues (e.g., skeletal muscle, liver, adipose, vasculature, and the brain) in effort to illuminate potential sources of inter-individual glycemic variation. Therefore, the review identifies gaps in knowledge that require attention in order to optimize medical approaches that improve care of people with elevated blood glucose levels and are at risk of cardiovascular disease.

Aerobic exercise offsets endothelial dysfunction induced by repetitive consumption of sugar-sweetened beverages in young healthy men

Consumption of a single, sugar-sweetened beverage (SSB) impairs vascular endothelial function. Regular aerobic exercise improves endothelium-dependent vasodilation; however, it is unknown whether these beneficial effects persist with frequent SSB consumption. Therefore, the purpose of this study was twofold; we studied the effects of repetitive SSB consumption (75 g d-glucose, 3 times/day) for 1 wk (Glu, n = 13, 23 ± 4 yr, 23.5 ± 3.4 kg/m²) on endothelium-dependent vasodilation (FMD). Then, in a separate cohort, we investigated whether 45 min of moderate-intensity aerobic exercise on five separate days offset the hypothesized decrease in FMD during the Glu protocol (Glu+Ex, n = 11, 21 ± 3 yr, 23.8 ± 2.4 kg/m²). Baseline, fasting [glucose] (P = 0.15), [insulin] (P = 0.25), %FMD (P = 0.48), absolute FMD (P = 0.66), and shear rate area under the curve (SR_AUC; P = 0.82) were similar between groups. Following the interventions, fasting [glucose] (Glu: 94 ± 6 to 92 ± 6 mg/dL, Glu+Ex: 89 ± 8 to 87 ± 6 mg/dL, P = 0.74) and [insulin] (Glu: 11.3 ± 6.2 to 11.8 ± 8.9 μU/mL, Glu+Ex: 8.7 ± 2.9 to 9.4 ± 3.2 μU/mL, P = 0.89) were unchanged. %FMD was reduced in Glu (6.1 ± 2.2 to 5.1 ± 1.3%) and increased in Glu+Ex (6.6 ± 2.2 to 7.8 ± 2.4%, P < 0.05 for both). SR_AUC increased similarly in both Glu [17,715 ± 8,275 to 22,922 ± 4,808 arbitrary units (A.U.)] and Glu+Ex (18,216 ± 4,516 to 21,666 ± 5,392 A.U., main effect of time P < 0.05). When %FMD was adjusted for SR_AUC, attenuation was observed in Glu (0.41 ± 0.18 to 0.23 ± 0.08%/s × 103, P < 0.05) but not Glu+Ex (0.38 ± 0.14 to 0.38 ± 0.13%/s × 103, P = 0.88). Despite unchanged fasting [glucose] and [insulin], repeated consumption of SSBs impaired conduit artery vascular endothelial function. Additionally, subjects who engaged in regular moderate-intensity aerobic exercise did not demonstrate the same SSB-induced endothelial dysfunction. Collectively, these data suggest aerobic exercise may offset the deleterious effects of repetitive SSB consumption.

Impact of Short-Term Continuous and Interval Exercise Training on Endothelial Function and Glucose Metabolism in Prediabetes

INTRODUCTION

The impact of interval (INT) vs. continuous (CONT) exercise training on endothelial function in relation to glucose metabolism prior to clinically meaningful weight loss is unknown in adults with prediabetes.

METHODS

Twenty-six subjects with prediabetes (60 ± 1 y; 33 ± 1 kg/m2; 2-hr-PG OGTT: 145 ± 7 mg/dl) were randomized to 60 min of CONT (n = 12; 70% of HRpeak) or work-matched INT exercise training (n = 14; alternating 3 min at 90 and 50% HRpeak) for 2 weeks. Aerobic fitness (VO2peak) and body composition (bioelectrical impedance) were assessed before and after training. Flow-mediated dilation (FMD) was measured during a 2 h 75 g OGTT (0, 60, and 120 min) to assess endothelial function. Postprandial FMD was calculated as incremental area under the curve (iAUC). Glucose tolerance and insulin were also calculated by iAUC. Fasting plasma VCAM, ICAM, and hs-CRP were also assessed as indicators of vascular/systemic inflammation.

RESULTS

Both interventions increased VO2peak (P = 0.002) but had no effect on body fat (P = 0.20). Although both treatments improved glucose tolerance (P = 0.06) and insulin iAUC (P = 0.02), VCAM increased (P = 0.01). There was no effect of either treatment on ICAM, hs-CRP, or fasting as well as postprandial FMD. However, 57% of people improved fasting and iAUC FMD following CONT compared with only 42% after INT exercise (each: P = 0.04). Elevated VCAM was linked to blunted fasting FMD after training (r = -0.38, P = 0.05). But, there was no correlation between fasting FMD or postprandial FMD with glucose tolerance (r = 0.17, P = 0.39 and r = 0.02, P = 0.90, respectively) or insulin iAUC following training (r = 0.34, P = 0.08 and r = 0.04, P = 0.83, respectively).

CONCLUSION

Endothelial function is not improved consistently after short-term training, despite improvements in glucose and insulin responses to the OGTT in obese adults with prediabetes.

Endothelial function following interval exercise plus low-calorie diet treatment in obese females

We determined if interval exercise plus a low-calorie diet (LCD + INT) increases endothelial function more than an energy-matched LCD. Obese women (47.2 ± 2.6y, 37.5 ± 1.3kg/m2 ) were randomized to 13 days of a LCD (n = 12; mixed meals of ~ 1200kcal/d) or LCD + INT (n = 13; 12 supervised 60-min INT bouts of 3 min at 90% and 50% HRpeak ). LCD + INT subjects received 350kcal postexercise to equate energy availability with LCD. Fitness (VO2 peak) and body composition (BodPod) were determined and a 120 min, 75 g oral glucose tolerance test was performed to examine fasting and postprandial flow-mediated dilation (FMD, endothelial function), respiratory exchange ratio (RER) via indirect calorimetry as well as glucose and insulin incremental area under the curve (iAUC120min ). LCD + INT increased VO2 peak (P = 0.02) compared with LCD, and both treatments decreased fat mass (P < 0.001) and insulin iAUC120min (P = 0.03). There was no overall treatment effect on fasting or iAUC120min FMD. However, in participants who increased fasting endothelial function after each treatment (Δ > 50%; LCD n = 5, LCD + INT n = 7), LCD + INT increased fasted (P = 0.005) and decreased iAUC120min (P = 0.003) FMD compared with LCD. Enhanced fitness correlated with increased fasting FMD (r = 0.43, P = 0.03) and diminished FMD iAUC120min (r = -0.44, P = 0.03). Decreased FMD iAUC120min correlated with reduced glucose iAUC120min (r = 0.64, P = 0.001) as well as increased 60-min RER (r = -0.42, P = 0.04). Low baseline fasting and iAUC120min FMD was also linked to enhanced fasting and iAUC120min FMD post-treatment (r = -0.71, P < 0.001; r = -0.89, P < 0.001, respectively). In conclusion, increasing fitness via INT may increase the effect of LCD on lowering cardiovascular disease risk in obese women.

Consecutive days of exercise decrease insulin response more than a single exercise session in healthy, inactive men

PURPOSE

It is reported that a single bout of exercise can lower insulin responses 12-24 h post-exercise; however, the insulin responses to alternate or consecutive bouts of exercise is unknown. Thus, the purpose of this study was to examine the effect of exercise pattern on post-exercise insulin and glucose responses following a glucose challenge.

METHODS

Ten male participants (n = 10, mean ± SD, Age 29.5 ± 7.7 years; BMI 25.7 ± 3.0 kg/m²) completed three exercise trials of walking for 60 min at ~ 70% of VO_2max. The trials consisted of: three consecutive exercise days (3CON), three alternate exercise days (3ALT), a single bout of exercise (SB), and a no exercise control (R). Twelve to fourteen hours after the last bout of exercise or R, participants completed a 75 g oral glucose tolerance test (OGTT) and blood was collected at 30 min intervals for the measurement of glucose, insulin, and C-peptide.

RESULT

Calculated incremental area under the curve (_iAUC) for glucose and C-peptide was not different between the four trials. Insulin _iAUC decreased 34.9% for 3CON compared to R (p < 0.01).

CONCLUSION

Three consecutive days of walking at ~ 70% VO_2max improved insulin response following an OGTT compared to no exercise. It is possible, that for healthy males, the effect of a single bout of exercise or exercise bouts separated by more than 24 h may not be enough stimulus to lower insulin responses to a glucose challenge.

Effect of acute exercise on postprandial endothelial function in postmenopausal women: a randomized cross-over study

High-sugar intake may cause endothelial dysfunction. It is unknown if a bout of aerobic exercise improves endothelial dysfunction caused by a high-sugar meal in postmenopausal women. This study evaluated if prior aerobic exercise attenuates postprandial endothelial dysfunction in postmenopausal women. Twenty-two postmenopausal women (age [mean±SD]: 60.4±6.5 years; % body fat: 40.3%±7.5%) underwent an exercise (EX) or no exercise (NE) condition, in a random order, 13-16 hours prior to the high-sugar meal consumption. The EX condition included a 60 min bout of supervised aerobic exercise at 75% of age-predicted maximum heart rate. The high-sugar meal, consumed after a 12-hour fast, contained 33% of the subjects' daily energy needs, and 75.6% energy from carbohydrates. Flow-mediated dilation (FMD) and blood concentrations of glucose, insulin, endothelin-1 (ET-1), and nitric oxide (NO) were assessed at baseline and 60 min, 120 min, and 180 min postprandially. Repeated measures analysis test showed that there were no condition by time interaction or condition effects for FMD, glucose, insulin, or NO. There was a significant condition by time interaction but no condition effect for ET-1. Area under the curve was also not different by condition for insulin sensitivity or the above variables. In conclusion, prior aerobic exercise compared with NE did not affect FMD, blood glucose, insulin, ET-1 or NO concentrations, or insulin sensitivity following a high-sugar meal in postmenopausal women. Future studies should look at the effect of different EX intensities on meal-induced endothelial dysfunction in this population. Trial Registration: ClinicalTrials.gov Identifier: NCT02919488.

Regular Aerobic, Resistance, and Cross-Training Exercise Prevents Reduced Vascular Function Following a High Sugar or High Fat Mixed Meal in Young Healthy Adults

The postprandial state can negatively influence flow mediated dilation (FMD), a predictor of atherosclerosis and cardiovascular disease. This investigation was designed to determine the effect of regular aerobic and/or resistance exercise on postprandial FMD after a high sugar or high fat mixed meal. Forty-five healthy participants were recruited from one of four groups: lean sedentary (SED), runners, weight lifters, and cross-trainers. Participants were randomly crossed over to a high sugar meal (HSM) and a high fat mixed meal (HFMM; both fat and carbohydrate). Pre-and postprandial endothelial function was assessed for both meals using brachial artery FMD. Plasma lipids, insulin, glucose, hs-CRP, and SOD were also measured with both meals. Endothelium-independent dilation was determined via sublingual nitroglycerin. Brachial artery FMD was reduced in SED following the HSM (9.9 ± 0.9% at baseline, peak reduction at 60 min 6.5 ± 1.0%) and the HFMM (9.4 ± 0.9% at baseline, peak reduction at 120 min 5.9 ± 1.2%; P < 0.05 for both, Mean ± SEM). There was no change in FMD after either HSM or HFMM in runners, weight lifters, and cross-trainers. Post-prandial increases in blood glucose, insulin and triglycerides were less pronounced in the exercisers compared to SED. In addition, exercisers presented lower baseline plasma hs-CRP and higher SOD activity. Nitroglycerin responses were similar among groups. These results suggest that endothelial function is reduced in sedentary adults after a HSM or HFMM, but not in regular aerobic or resistance exercisers. This response may be due to favorable postprandial metabolic responses or lower postprandial levels of inflammation and oxidative stress. These findings may help to explain the cardioprotective effect of exercise.

High-intensity interval exercise attenuates but does not eliminate endothelial dysfunction after a fast food meal

We investigated whether two different bouts of high-intensity interval exercise (HIIE) could attenuate postprandial endothelial dysfunction. Thirteen young (27 ± 1 yr), nonexercise-trained men underwent three randomized conditions: 1) four 4-min intervals at 85-95% of maximum heart rate separated by 3 min of active recovery (HIIE 4 × 4), 2) 16 1-min intervals at 85-95% of maximum heart rate separated by 1 min of active recovery (HIIE 16 × 1), and 3) sedentary control. HIIE was performed in the afternoon, ~18 h before the morning fast food meal (1,250 kcal, 63g of fat). Brachial artery flow-mediated dilation (FMD) was performed before HIIE ( baseline 1), during fasting before meal ingestion ( baseline 2), and 30 min, 2 h, and 4 h postprandial. Capillary glucose and triglycerides were assessed at fasting, 30 min, 1 h, 2 h, and 4 h (triglycerides only). Both HIIE protocols increased fasting FMD compared with control (HIIE 4 × 4: 6.1 ± 0.4%, HIIE 16 × 1: 6.3 ± 0.5%, and control: 5.1 ± 0.4%, P < 0.001). For both HIIE protocols, FMD was reduced only at 30 min postprandial but never fell below baseline 1 or FMD during control at any time point. In contrast, control FMD decreased at 2 h (3.8 ± 0.4%, P < 0.001) and remained significantly lower than HIIE 4 × 4 and 16 × 1 at 2 and 4 h. Postprandial glucose and triglycerides were unaffected by HIIE. In conclusion, HIIE performed ~18 h before a high-energy fast food meal can attenuate but not entirely eliminate postprandial decreases in FMD. This effect is not dependent on reductions in postprandial lipemia or glycemia. NEW & NOTEWORTHY Two similar high-intensity interval exercise (HIIE) protocols performed ∼18 h before ingestion of a high-energy fast food meal attenuated but did not entirely eliminate postprandial endothelial dysfunction in young men largely by improving fasting endothelial function. Both HIIE protocols produced essentially identical results, suggesting high reproducibility of HIIE effects.

Improved arterial flow-mediated dilation after exertion involves hydrogen peroxide in overweight and obese adults following aerobic exercise training

OBJECTIVE

Acute strenuous physical exertion impairs arterial function in sedentary adults. We investigated the effects of 8 weeks of regular aerobic exercise training on acute physical exertion-induced arterial dysfunction in sedentary, overweight, and obese adults.

METHODS

Twenty-five overweight and obese adults (BMI 30.5 ± 7.2 years) were assigned to 8 weeks of aerobic training or to a control group. Brachial artery flow-mediated dilation (FMD) was assessed before and after acute leg press exercise at weeks 0 and 8. Gluteal adipose biopsies were performed at rest and post acute leg press to measure microvessel FMD with and without nitric oxide synthase inhibition via L-nitroarginine methyl ester or hydrogen peroxide (H2O2) scavenging with Catalase. Microvessel nitric oxide and H2O2 production were assessed via fluorescence microscopy.

RESULTS

Brachial artery dilation was reduced post acute leg press at week 0 in the aerobic exercise and control groups, but was preserved in the aerobic-exercise group post acute leg press at week 8 (P < 0.05). Post acute leg press microvessel FMD was preserved in the aerobic exercise group but impaired in the control group at week 8 (P < 0.05). Preserved dilation in the aerobic exercise group was more sensitive to H2O2 scavenging than inhibition of nitric oxide, and post acute leg press microvessel H2O2 production was increased compared with at rest (P < 0.05).

CONCLUSION

Aerobic exercise prevents acute exertion-induced arterial dysfunction in overweight and obese adults via a phenotypic switch from nitric oxide-mediated dilation at rest to a predominately H2O2-mediated dilation after acute physical exertion.

Transient endothelial dysfunction induced by sugar-sweetened beverage consumption may be attenuated by a single bout of aerobic exercise

BACKGROUND

This study assessed whether aerobic exercise would attenuate microvascular endothelial dysfunction induced by commercial sugar-sweetened beverage (SSB) consumption.

METHODS

Eleven healthy males participated in this randomized, single-blind crossover study. Cutaneous microvascular endothelial function was assessed using laser speckle contrast imaging coupled with post-occlusive reactive hyperemia before and after a) consumption of water; b) consumption of a commercial SSB; c) 30min of aerobic exercise followed by water consumption; and d) 30 minutes of aerobic exercise followed by SSB consumption. Blood glucose and arterial pressure responses were also monitored. Volumes of water and SSB consumed (637.39±29.15 mL) were individualized for each participant, ensuring SSB consumption delivered 1 g of sucrose per kg of body weight. Exercise was performed at 75% of the maximal oxygen uptake heart rate.

RESULTS

Compared to water consumption, the commercial SSB elevated blood glucose concentrations in both sedentary (4.69±0.11 vs. 7.47±0.28 mmol/L, P<0.05) and exercised states (4.95±0.13 vs. 7.93±0.15 mmol/L, P<0.05). However, the decrease in microvascular endothelial function observed following sedentary SSB consumption, expressed as the percentage increase from baseline (208.60±22.40 vs. 179.83±15.80%, P=0.01) and the change in peak hyperemic blood flux from basal to post-intervention assessments (-0.04±0.03 vs. -0.12±0.02 ΔCVC, P=0.01), was attenuated following 30min of aerobic exercise.

CONCLUSIONS

To our knowledge, this is the first study to provide evidence that a single bout of aerobic exercise may prevent transient SSB-mediated microvascular endothelial dysfunction.

Postprandial Effects of Breakfast Glycemic Index on Vascular Function among Young Healthy Adults: A Crossover Clinical Trial

This study aimed to evaluate the postprandial effects of high and low glycemic index (GI) breakfasts on vascular function. It was a crossover trial that included 40 young healthy adults (50% women), aged 20-40 years, who were recruited at primary care settings. They consumed three experimental breakfasts in randomized order, each one separated by a 1-week washout period: (1) control conditions (only water); (2) low GI (LGI) breakfast (29.4 GI and 1489 KJ energy); and (3) high GI (HGI) breakfast (64.0 GI and 1318 KJ energy). Blood samples were collected at 60 and 120 min after each breakfast to determine glucose and insulin levels. Vascular parameters were measured at 15 min intervals. Augmentation index (AIx) was studied as a primary outcome. Secondary outcomes comprised glucose, insulin, heart rate (HR) and pulse pressures (PPs). We found a trend toward increased AIx, HR and PPs for the HGI versus the LGI breakfast. A significant interaction between the type of breakfast consumed and all measured parameters was identified (p < 0.05) except for central PP. Stratifying data by sex, this interaction remained significant for AIx and augmentation pressure only in males (p < 0.05). In conclusion, breakfast GI could affect postprandial vascular responses in young healthy adults.

Effects of Sugar-Sweetened Beverage Consumption on Microvascular and Macrovascular Function in a Healthy Population

Objective—

To assess vascular function during acute hyperglycemia induced by commercial sugar-sweetened beverage (SSB) consumption and its effect on underlying mechanisms of the nitric oxide pathway.

Approach and Results—

In a randomized, single-blind, crossover trial, 12 healthy male participants consumed 600 mL (20 oz.) of water or a commercial SSB across 2 visits. Endothelial and vascular smooth muscle functions were assessed in the microcirculation using laser speckle contrast imaging coupled with iontophoresis and in the macrocirculation using brachial artery ultrasound with flow- and nitrate-mediated dilation. Compared with water, SSB consumption impaired microvascular and macrovascular endothelial function as indicated by a decrease in the vascular response to acetylcholine iontophoresis (208.3±24.3 versus 144.2±15.7%, P <0.01) and reduced flow-mediated dilation (0.019±0.002 versus 0.014±0.002%/s, P <0.01), respectively. Systemic vascular smooth muscle remained preserved. Similar decreases in endothelial function were observed during acute hyperglycemia in an in vivo rat model. However, function was fully restored by treatment with the antioxidants, N -acetylcysteine and apocynin. In addition, ex vivo experiments revealed that although the production of reactive oxygen species was increased during acute hyperglycemia, the bioavailability of nitric oxide in the endothelium was decreased, despite no change in the activation state of endothelial nitric oxide synthase.

Conclusions—

To our knowledge, this is the first study to assess the vascular effects of acute hyperglycemia induced by commercial SSB consumption alone. These findings suggest that SSB-mediated endothelial dysfunction is partly due to increased oxidative stress that decreases nitric oxide bioavailability.

Clinical Trial Registration—

URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=366442&isReview=true . Australian New Zealand Clinical Trials Registry Number: ACTRN12614000614695.

Endothelial function following glucose ingestion in adults with prediabetes: Role of exercise intensity

OBJECTIVE

To determine whether high intensity exercise (HIE) would improve endothelial function more than an isocaloric bout of moderate intensity exercise (MIE) following glucose ingestion in adults with prediabetes.

METHODS

Twelve subjects with prediabetes completed all three conditions: time-course matched control and isocaloric exercise (∼200 kcal) at moderate (MIE; at lactate threshold) and high intensity (HIE; 75% of difference between lactate threshold and VO2 peak). Brachial artery flow-mediated dilation (FMD) was measured before exercise (baseline), within 30 min postexercise, and 1 and 2 hr following a 75 g oral glucose tolerance test (OGTT). Plasma F2-isoprostanes were also assessed during the protocol (i.e., baseline to 2 hr OGTT) as a biomarker of oxidative stress.

RESULTS

MIE reduced postexercise F2-isoprostanesAUC compared with time-course matched control and HIE. Although exercise had no statistical effect on FMD postexercise or during the OGTT, elevations in FMDAUC after MIE and HIE were associated with reduced postexercise F2-isoprostanesAUC .

CONCLUSIONS

Exercise at either intensity had no effect on FMD immediately postexercise following glucose administration. However, individuals with reduced oxidative stress responses to exercise had greater exercise-induced improvement in FMD. Further work is required to identify the mechanism by which exercise alters oxidative stress to enhance endothelial function.

Acute Hyperglycemia Impairs Vascular Function in Healthy and Cardiometabolic Diseased Subjects

Objectives—

Controversy exists over the effect of acute hyperglycemia on vascular function. In this systematic review, we compared the effect of acute hyperglycemia on endothelial and vascular smooth muscle functions across healthy and cardiometabolic diseased subjects.

Approach and Results—

A systematic search of MEDLINE, EMBASE, and Web of Science from inception until July 2014 identified articles evaluating endothelial or vascular smooth muscle function during acute hyperglycemia and normoglycemia. Meta-analyses compared the standardized mean difference (SMD) in endothelial and vascular smooth muscle functions between acute hyperglycemia and normoglycemia. Subgroup analyses and metaregression identified sources of heterogeneity. Thirty-nine articles (525 healthy and 540 cardiometabolic subjects) were analyzed. Endothelial function was decreased (39 studies; n=1065; SMD, −1.25; 95% confidence interval, −1.52 to −0.98; P <0.01), whereas vascular smooth muscle function was preserved (6 studies; n=144; SMD, −0.07; 95% confidence interval, −0.30 to 0.16; P =0.55) during acute hyperglycemia compared with normoglycemia. Significant heterogeneity was detected among endothelial function studies ( P <0.01). A subgroup analysis revealed that endothelial function was decreased in the macrocirculation (30 studies; n=884; SMD, −1.40; 95% confidence interval, −1.68 to −1.12; P <0.01) but not in the microcirculation (9 studies; n=181; SMD, −0.63; 95% confidence interval, −1.36 to 0.11; P =0.09). Similar results were observed according to health status. Macrovascular endothelial function was inversely associated with age, blood pressure, and low-density lipoprotein cholesterol and was positively associated with the postocclusion interval of vascular assessment.

Conclusions—

To our knowledge, this is the first systematic review and meta-analysis of its kind. In healthy and diseased subjects, we found evidence for macrovascular but not microvascular endothelial dysfunction during acute hyperglycemia.

Arterial stiffness after glucose ingestion in exercise-trained versus untrained men

Postprandial hyperglycemia increases arterial stiffness. Arterial stiffness and insulin resistance are lower in exercise-trained humans than in untrained humans. However, the effect of exercise on arterial stiffness after glucose ingestion in young adults remains unknown. The present study investigates the effect of regular aerobic exercise on arterial stiffness after glucose ingestion in young males. Ten exercise-trained males (age, 20.8 ± 0.2 years; ETR) and 9 healthy untrained males (age, 22.2 ± 0.7 years; UTR) participated in this study. Carotid-femoral (aortic) pulse wave velocity (PWV), femoral-ankle (leg) PWV, carotid augmentation index (AIx) (applanation tonometry), brachial and ankle blood pressure (BP), heart rate (oscillometric device and electrocardiography), and blood glucose (glucose oxidase method) were measured at 30 min before (baseline) and 30, 60, and 120 min after a 75-g oral glucose tolerance test. Leg PWV at 30 min after glucose ingestion was significantly higher (P < 0.01) in the UTR group than in the ETR group. Ankle systolic BP at 30 min after glucose ingestion was also significantly higher in the UTR group than in the ETR group (P < 0.05). Blood glucose increased from baseline at 30 min (P < 0.01) and 60 min (P < 0.05) after glucose ingestion in both groups. Aortic PWV, carotid AIx, and brachial systolic BP did not change from baseline after glucose ingestion in both groups. The present findings indicate that leg PWV and ankle systolic BP after glucose ingestion were significantly lower in the ETR group than in the UTR group.

Acute exercise increases resistance to oxidative stress in young but not older adults

A single bout of acute exercise increases oxidative stress and stimulates a transient increase in antioxidant enzymes. We asked whether this response would induce protection from a subsequent oxidative challenge, different from that of exercise, and whether the effects were affected by aging. We compared young (20 ± 1 years, n = 8) and older (58 ± 6 years, n = 9) healthy men and women. Resistance to oxidative stress was measured by the F2-isoprostane response to forearm ischemia/reperfusion (I/R) trial. Each participant underwent the I/R trial twice, in random order; once after performing 45 min of cycling on the preceding day (IRX) and a control trial without any physical activity (IRC). Baseline F2-isoprostane levels were significantly lower at IRX compared to IRC (P < 0.05) and not different between groups. F2-isoprostane response to IRX was significantly lower compared to IRC in young (P < 0.05) but not different in the older group. Superoxide dismutase activity in response to acute exercise was significantly higher in young compared to older adults (P < 0.05). These data suggest that signal transduction of acute exercise may be impaired with aging. Repeated bouts of transient reactive oxygen species production as seen with regular exercise may be needed to increase resistance to oxidative stress in older individuals.

The endothelial cell: an "early responder" in the development of insulin resistance

Vascular endothelium is an important insulin target and plays a pivotal role in the development of metabolic insulin resistance provoked by the Western lifestyle. It acts as a "first-responder" to environmental stimuli such as nutrients, cytokines, chemokines and physical activity and regulates insulin delivery to muscle and adipose tissue and thereby affecting insulin-mediated glucose disposal by these tissues. In addition, it also regulates the delivery of insulin and other appetite regulating signals from peripheral tissues to the central nervous system thus influencing the activity of nuclei that regulate hepatic glucose production, adipose tissue lipolysis and lipogenesis, as well as food consumption. Resistance to insulin's vascular actions therefore broadly impacts tissue function and contribute to metabolic dysregulation. Moreover, vascular insulin resistance negatively impacts vascular health by affecting blood pressure regulation, vessel wall inflammation and atherogenesis thereby contributing to the burden of vascular disease seen with diabetes and metabolic syndrome. In the current review, we examined the evidence that supports the general concept of vascular endothelium as a target of insulin action and discussed the biochemical and physiological consequences of vascular insulin resistance.

Postprandial improvement in insulin sensitivity after a single exercise session in adolescents with low aerobic fitness and physical activity

The purpose of this study was to determine the acute and residual impact of a single exercise bout on meal glucose control in adolescents with habitually low physical activity. Twelve adolescents (seven females/five males, 14 ± 2 yr) completed three trials. One trial [No Exercise (No Ex)] was completed after refraining from vigorous activity for ≥ 3 d. On the other two trials, a 45-min aerobic exercise bout at 75% peak heart rate was performed either 17-h Prior Day Exercise (Prior Day Ex) trial or 1-h Same Day Exercise (Same Day Ex) trial before consuming the test meal (2803 kJ, 45/40/15% energy as carbohydrate/fat/protein, respectively). Compared to No Ex, insulin sensitivity (SI) (minimal model analysis) was increased by 45% (p < 0.03) and 78% (p < 0.01) on the Prior Day Ex and Same Day Ex trials, respectively. This improvement in glucose control was supported by corresponding reductions in the net area under the curve for glucose, insulin, and c-peptide, although there was no change in postprandial suppression of fatty acids. These results show that SI is improved with a single bout of moderate intensity exercise in adolescents with habitually low physical activity and that the residual beneficial effect of exercise lasts at least 17 h. This finding highlights the plasticity of exercise responses in youth and the importance of daily exercise for metabolic health.

International Society of Sports Nutrition position stand: energy drinks

Position Statement: The International Society of Sports Nutrition (ISSN) bases the following position stand on a critical analysis of the literature on the safety and efficacy of the use of energy drinks (ED) or energy shots (ES). The ISSN has concluded the following. 1. Although ED and ES contain a number of nutrients that are purported to affect mental and/or physical performance, the primary ergogenic nutrients in most ED and ES appear to be carbohydrate and/or caffeine. 2. The ergogenic value of caffeine on mental and physical performance has been well-established but the potential additive benefits of other nutrients contained in ED and ES remains to be determined. 3. Consuming ED 10-60 minutes before exercise can improve mental focus, alertness, anaerobic performance, and/or endurance performance. 4. Many ED and ES contain numerous ingredients; these products in particular merit further study to demonstrate their safety and potential effects on physical and mental performance. 5. There is some limited evidence that consumption of low-calorie ED during training and/or weight loss trials may provide ergogenic benefit and/or promote a small amount of additional fat loss. However, ingestion of higher calorie ED may promote weight gain if the energy intake from consumption of ED is not carefully considered as part of the total daily energy intake. 6. Athletes should consider the impact of ingesting high glycemic load carbohydrates on metabolic health, blood glucose and insulin levels, as well as the effects of caffeine and other stimulants on motor skill performance. 7. Children and adolescents should only consider use of ED or ES with parental approval after consideration of the amount of carbohydrate, caffeine, and other nutrients contained in the ED or ES and a thorough understanding of the potential side effects. 8. Indiscriminant use of ED or ES, especially if more than one serving per day is consumed, may lead to adverse events and harmful side effects. 9. Diabetics and individuals with pre-existing cardiovascular, metabolic, hepatorenal, and neurologic disease who are taking medications that may be affected by high glycemic load foods, caffeine, and/or other stimulants should avoid use of ED and/or ES unless approved by their physician.

The acute and residual effect of a single exercise session on meal glucose tolerance in sedentary young adults

The study goals were to (1) establish the variability in postprandial glucose control in healthy young people consuming a mixed meal and, then (2) determine the acute and residual impact of a single exercise bout on postprandial glucose control. In study 1, 18 people completed two similar mixed meal trials and an intravenous glucose tolerance test (IVGTT). There were strong test-retest correlations for the post-meal area under the curve (AUC) for glucose, insulin, and Cpeptide (r = 0.73–0.83) and the Matsuda insulin sensitivity index (ISI, r = 0.76), and between meal and IVGTT-derived ISI (r = 0.83). In study 2, 11 untrained young adults completed 3 trials. One trial (No Ex) was completed after refraining from vigorous activity for ≥3 days. On the other 2 trials, a 45-min aerobic exercise bout was performed either 17-hours (Prior Day Ex) or 1-hour (Same Day Ex) before consuming the test meal. Compared to No Ex and Prior Day Ex, which did not differ from one another, there were lower AUCs on the Same Day Ex trial for glucose (6%), insulin (20%) and C-peptide (14%). Thus, a single moderate intensity exercise session can acutely improve glycemic control but the effect is modest and short-lived.

Is the beneficial effect of prior exercise on postprandial lipaemia partly due to redistribution of blood flow?

Preprandial aerobic exercise lowers postprandial lipaemia (a risk factor for coronary heart disease); however, the mechanisms responsible are still not clear. The present study investigated whether blood flow to skeletal muscle and/or the liver was increased in the postprandial period after exercise, relative to a control trial, and whether this resulted from increased cardiac output or redistribution of flow. Eight overweight inactive males, aged 49.4±10.5 years (mean±S.D.), acted as their own controls in a counterbalanced design, either walking briskly for 90 min at 60% V̇O2max (maximal oxygen uptake), or resting in the lab, on the evening of day 1. The following morning, a fasting blood sample was collected, participants consumed a high-fat breakfast, and further venous blood samples were drawn hourly for 6 h. Immediately after blood sampling, Doppler ultrasound was used to measure cardiac output and blood flow through both the femoral artery of one leg and the hepatic portal vein, with the ultrasonographer blinded to trial order. The total postprandial triacylglycerol response was 22% lower after exercise (P=0.001). Blood flow through the femoral artery and the hepatic portal vein was increased by 19% (P<0.001) and 16% (P=0.033), respectively, during the 6-h postprandial period following exercise; however, postprandial cardiac output did not differ between trials (P=0.065). Redistribution of blood flow, to both exercised skeletal muscle and the liver, may therefore play a role in reducing the plasma triacylglycerol response to a high-fat meal on the day after an exercise bout.

Comparison of mechanisms involved in impaired vascular reactivity between high sucrose and high fat diets in rats

BACKGROUND

To determine the effects of high sucrose diets on vascular reactivity. We hypothesized that similar to high fat diets (HFD), HSD feeding would lead to increased adiposity resulting in inflammation and oxidative stress-mediated impairment of vasodilation.

METHODS

Male Sprague-Dawley rats were fed control chow (Chow), HSD or HFD diets for 6 weeks. The role of inflammation and oxidative stress on impaired vasodilation were assessed in isolated mesenteric arterioles.

RESULTS

HSD and HFD induced increased adiposity, oxidative stress and inflammation. HFD rats developed fasting hyperglycemia. Both HSD and HFD rats developed impaired glucose tolerance and hyperleptinemia. Nitric oxide (NO)-mediated vasodilation was significantly attenuated in both HSD and HFD rats but was normalized by treatment with antioxidants or anti-inflammatory drugs. Endothelial NO synthase (eNOS) protein expression was not affected by diet. Sensitivity to NO was reduced since NOS inhibition attenuated vasodilation in Chow rats but did not further impair vasodilation in HSD or HFD rats. Likewise, responsiveness to a NO donor was attenuated in both experimental groups.

CONCLUSIONS

Oxidative stress diminishes vasodilatory responsiveness in HSD and HFD rats through ROS-mediated scavenging of NO and decreased smooth muscle sensitivity to NO. Inflammation also plays a significant role in the impaired vasodilation.

Assessing individual metabolic responsiveness to a lipid challenge using a targeted metabolomic approach

The development of assessment techniques with immediate clinical applicability is a priority for resolving the growing epidemic in metabolic disease. Many imbalances in diet-dependent metabolism are not detectable in the fasted state. Resolving the high inter-individual variability in response to diet requires the development of techniques that can detect metabolic dysfunction at the level of the individual. The intra- and inter-individual variation in lipid metabolism in response to a standardized test meal was determined. Following an overnight fast on three different days, three healthy subjects consumed a test meal containing 40% of their daily calories. Plasma samples were collected at fasting, and 1, 3, 6, and 8 h after the test meal. Plasma fatty acid (FA) concentrations within separated lipid classes and lipoprotein fractions were measured at each time point. The intra-individual variation within each subject across three days was lower than the inter-individual differences among the three subjects for over 50% of metabolites in the triacylglycerol (TG), FA, and phosphatidylcholine (PC) lipid classes at 6 h, and for 25-50% of metabolites across lipid classes at 0, 1, 3, and 8 h. The consistency of response within individuals was visualized by principal component analysis (PCA) and confirmed by ANOVA. Three representative metabolites that discriminated among the three individuals in the apolipoprotein B (ApoB) fraction, TG16:1n7, TG18:2n6, and PC18:3n3, are discussed in detail. The postprandial responses of individuals were unique within metabolites that were individual discriminators (ID) of metabolic phenotype. This study shows that the targeted metabolomic measurement of individual metabolic phenotype in response to a specially formulated lipid challenge is possible even without lead-in periods, dietary and lifestyle control, or intervention over a 3-month period in healthy free-living individuals.