Improved insulin action following short-term exercise training: role of energy and carbohydrate balance

Extracellular Vesicles in Metabolic and Vascular Insulin Resistance

BACKGROUND

Insulin resistance is a major etiological factor in obesity, type 2 diabetes, and cardiovascular disease (CVD). Endothelial dysfunction may precede impairments in insulin-stimulated glucose uptake, thereby making it a key feature in development of CVD. However, the mechanism by which vascular tissue becomes dysfunctional is not clear.

SUMMARY

Extracellular vesicles (EVs) have emerged as potential mediators of insulin resistance and vascular dysfunction. EVs are membrane-bound particles released by tissues following cellular stress or activation. They carry "cargo" (e.g., insulin signaling proteins, eNOS-nitric oxide, and miRNA) that are believed to promote inter-cellular and interorgan communications. Herein, we review the underlying physiology of EVs in relation to type 2 diabetes and CVD risk. Specifically, we discuss how EVs may modulate metabolic (e.g., skeletal muscle, liver, and adipose) insulin sensitivity, and propose that EVs may modulate vascular insulin action to influence both endothelial function and arterial stiffness. We lastly identify how EVs may play a unique role following exercise to promote metabolic and vascular insulin sensitivity changes.

KEY MESSAGE

Gaining insight toward insulin-mediated EV mechanism has potential to identify novel pathways regulating cardiometabolic health and provide foundation for examining EVs as unique biomarkers and targets to prevent and/or treat chronic diseases.

Acute exercise decreases insulin-stimulated extracellular vesicles in conjunction with augmentation index in adults with obesity

Extracellular vesicles (EVs) are often elevated in obesity and may modulate disease risk. Although acute exercise reduces fasting EVs in adults with obesity, no data exist on insulin-mediated EV responses. This study evaluated the effects of exercise on EV responses to insulin in relation to vascular function. Ten (5M/5F) sedentary adults with obesity (34.3 ± 3.7 kg/m2 ) completed an evening control and acute exercise condition (70%V ̇ O 2 max ${\dot{V}_{{{\rm{O}}_{\rm{2}}}{\rm{max}}}}$ to expend 400 kcal). Following an overnight fast, participants underwent a 2 h euglycaemic-hyperinsulinaemic clamp (90 mg/dl; 40 mU/m2 /min) to determine metabolic insulin sensitivity (M-value), phenotypes of medium- to large-sized EVs, and aortic waveform measures. Endothelial (CD105+ , CD41- /CD31+ )-, leukocyte (CD45+ )-, platelet (CD41+ , CD41+ /31+ )- and tetraspanin (TX+ )-derived EVs, as well as platelet endothelial cell adhesion molecule (CD31+ ), were determined before and after the clamp using high resolution spectral flow cytometry. Although exercise did not alter fasting haemodynamics, it lowered the augmentation index (AIx75, P = 0.024) and increased the M-value (P = 0.042). Further, exercise decreased all fasting EVs (P < 0.01) and decreased insulin-stimulated TX+ (P = 0.060), CD31+ (P = 0.060) and CD41- /31+ (P = 0.045) compared to rest. Interestingly, greater insulin-stimulated decreases in CD41- /31+ were associated with reduced AIx75 during the clamp (r = 0.62, P = 0.059), while insulin-stimulated decreases in CD41+ (r = -0.68, P = 0.031), CD41+ /31+ (r = -0.69, P = 0.262), TX+ (r = -0.66, P = 0.037) and CD31+ (r = -0.69, P = 0.028) correlated with M-value following exercise. Thus, acute exercise may decrease fasting and insulin-stimulated medium- to large-size EVs in conjunction with improved M-value and AIx75. More research is needed to understand effects of exercise on EVs in the regulation of glucose homeostasis and vascular function. KEY POINTS: Extracellular vesicles (EVs) are increased in states of obesity and may play a role in altered insulin sensitivity and blood pressure; aerobic exercise decreases fasting EV concentrations the following day in adults with obesity. This study directly tested the effects of insulin on EVs and how a single bout of exercise impacts these responses. Together, these data highlight the positive effects of a single bout of exercise on fasting and insulin-stimulated EVs, with the latter relating to increased insulin sensitivity and decreased augmentation index. These results support future research identifying EVs as mechanistic factors in glucose regulation and vascular function as well as clinical use of exercise to reduce cardiovascular disease risk.

Impact of Physical Exercise on Platelets: Focus on Its Effects in Metabolic Chronic Diseases

Chronic disorders are strongly linked to cardiovascular (CV) diseases, and it is unanimously accepted that regular exercise training is a key tool to improving CV risk factors, including diabetes, dyslipidemia, and obesity. Increased oxidative stress due to an imbalance between reactive oxygen species production and their scavenging by endogenous antioxidant capacity is the common ground among these metabolic disorders, and each of them affects platelet function. However, the correction of hyperglycemia in diabetes and lipid profile in dyslipidemia as well as the lowering of body weight in obesity all correlate with amelioration of platelet function. Habitual physical exercise triggers important mechanisms related to the exercise benefits for health improvement and protects against CV events. Platelets play an important role in many physiological and pathophysiological processes, including the development of arterial thrombosis, and physical (in)activity has been shown to interfere with platelet function. Although data reported by studies carried out on this topic show discrepancies, the current knowledge on platelet function affected by exercise mainly depends on the type of applied exercise intensity and whether acute or habitual, strenuous or moderate, thus suggesting that physical activity and exercise intensity may interfere with platelet function differently. Thus, this review is designed to cover the aspects of the relationship between physical exercise and vascular benefits, with an emphasis on the modulation of platelet function, especially in some metabolic diseases.

A single bout of exercise improves vascular insulin sensitivity in adults with obesity

OBJECTIVE

This crossover study explored the impact of a single bout of exercise on insulin-stimulated responses in conduit arteries and capillaries.

METHODS

Twelve sedentary adults (49.5 [7.8] years; maximal oxygen consumption [VO₂ max]: 23.7 [5.4] mL/kg/min) with obesity (BMI 34.5 [4.3] kg/m² ) completed a control and exercise bout (70% VO₂ max to expend 400 kcal). Sixteen hours later, participants underwent a 2-hour euglycemic-hyperinsulinemic clamp (90 mg/dL; 40 mU/m² /min) to determine vascular and metabolic insulin sensitivity. Endothelial and capillary functions were assessed by brachial artery flow-mediated dilation and contrast-enhanced ultrasound, respectively. Metabolized glucose infusion rate, substrate oxidation (indirect calorimetry), nonoxidative glucose disposal (NOGD), and inflammation were also determined.

RESULTS

Exercise increased insulin-stimulated preocclusion diameter (p = 0.01) and microvascular blood flow (condition effect: p = 0.04) compared with control. Furthermore, exercise improved metabolic insulin sensitivity by 21%, which paralleled rises in NOGD (p = 0.05) and decreases in soluble receptors for advanced glycation end products (condition effect: p = 0.01). Interestingly, changes in NOGD were related to increased insulin-stimulated microvascular blood flow (r = 0.57, p = 0.05).

CONCLUSIONS

A single bout of exercise increases vascular insulin sensitivity in adults with obesity. Additional work is needed to determine vascular responses following different doses of exercise in order to design lifestyle prescriptions for reducing chronic disease risk.

Carbohydrate Restriction with or without Exercise Training Improves Blood Pressure and Insulin Sensitivity in Overweight Women

Objective: The purpose of this study was to evaluate the effects of a 4-week low-carbohydrate diet (LC) with or without exercise training on cardiometabolic health-related profiles in overweight/obese women. Methods: Fifty overweight/obese Chinese women (age: 22.2 ± 3.3 years, body mass index (BMI): 25.1 ± 3.1 kg·m⁻²) were randomized to either a LC control group (LC-CON, n = 16), a LC and high-intensity interval training group (LC-HIIT, n = 17), or a LC and moderate-intensity continuous training group (LC-MICT, n = 17). All groups consumed LC for 4 weeks, while the LC-HIIT and LC-MICT groups followed an additional five sessions of HIIT (10 × 6 s cycling sprints and 9 s rest intervals, 2.5 min in total) or MICT (cycling continuously at 50–60% of peak oxygen uptake (VO_2peak) for 30 min) weekly. Blood pressure, fasting glucose, insulin sensitivity, and several metabolic or appetite regulating hormones were measured before and after intervention. Results: Significant reductions in body weight (− ~2.5 kg, p < 0.001, η² = 0.772) and BMI (− ~1 unit, p < 0.001, η² = 0.782) were found in all groups. Systolic blood pressure was reduced by 5–6 mmHg (p < 0.001, η² = 0.370); fasting insulin, leptin, and ghrelin levels were also significantly decreased (p < 0.05), while insulin sensitivity was improved. However, there were no significant changes in fasting glucose, glucagon, and gastric inhibitory peptide levels. Furthermore, no group differences were found among the three groups, suggesting that extra training (i.e., LC-HIIT and LC-MICT) failed to trigger additional effects on these cardiometabolic profiles. Conclusions: The short-term carbohydrate restriction diet caused significant weight loss and improved blood pressure and insulin sensitivity in the overweight/obese women, although the combination with exercise training had no additional benefits on the examined cardiometabolic profiles. Moreover, the long-term safety and effectiveness of LC needs further study.

Interactive effects of acute exercise and carbohydrate-energy replacement on insulin sensitivity in healthy adults

This study investigated whether carbohydrate-energy replacement immediately after prolonged endurance exercise attenuates insulin sensitivity the following morning, and whether exercise improves insulin sensitivity the following morning independent of an exercise-induced carbohydrate deficit. Oral glucose tolerance and whole-body insulin sensitivity were compared the morning after 3 evening conditions, involving (1) treadmill exercise followed by a carbohydrate replacement drink (200 or 150 g maltodextrin for males and females, respectively; CHO-replace); (2) treadmill exercise followed by a non-caloric, taste-matched placebo (CHO-deficit); or (3) seated rest with no drink provided (Rest). Treadmill exercise involved 90 minutes at ∼80% age-predicted maximum heart rate. Seven males and 2 females (aged 23 ± 1 years; body mass index 24.0 ± 2.7 kg·m^-2) completed all conditions in a randomised order. Matsuda index improved by 22% (2.2 [0.3, 4.0] au, p = 0.03) and HOMA2-IR improved by 10% (-0.04 [-0.08, 0.00] au, p = 0.04) in CHO-deficit versus CHO-replace, without corresponding changes in postprandial glycaemia. Outcomes were similar between Rest and other conditions. These data suggest that improvements to insulin sensitivity in healthy populations following acute moderate/vigorous intensity endurance exercise may be dependent on the presence of a carbohydrate-energy deficit. Novelty: Restoration of carbohydrate balance following acute endurance exercise attenuated whole-body insulin sensitivity. Exercise per se failed to enhance whole-body insulin sensitivity. Maximising or prolonging the post-exercise carbohydrate deficit may enhance acute benefits to insulin sensitivity.

Energy Deficit Required for Exercise-induced Improvements in Glycemia the Next Day

PURPOSE

This study determined the impact of an exercise-induced energy deficit on postprandial and 24 h glycemic control the day after a session of exercise.

METHODS

Fifteen healthy participants (m/f = 5/10, 27 ± 6 yr, body mass index = 24 ± 3 kg·m, peak oxygen consumption [V˙O2peak] = 36 ± 9 mL·kg·min) completed two separate 5-d experimental trials performed under "free-living" conditions. On day 1 of each trial, participants were fitted with a continuous glucose monitor and abstained from exercise. Day 2 served as a nonexercise control (NoEx). On day 3, participants exercised at 3:00 PM (65% V˙O2peak) until they expended 350 kcals (~45 min). The diet during both experimental trials was identical with the exception of meals after this exercise session. During one trial, the dinner after exercise did not replenish the 350 kcal expended during exercise, thereby establishing an exercise energy deficit (ExDEF). During the other experimental trial, the dinner after exercise contained an additional 350 kcal to compensate for the energy expended during exercise, and thereby maintained energy balance after exercise (ExBAL). Free-living glycemia was measured the day before exercise (NoEx) and the day after exercise under ExDEF and ExBAL conditions.

RESULTS

The day after exercise, 3 h postprandial area under the curve was lower after breakfast in ExDEF compared with ExBAL (16.0 ± 1.8 vs 17.0 ± 1.6 mmol·L·h per 3 h, P = 0.01), but did not differ between groups after lunch (P = 0.24), dinner (P = 0.39), or evening snack (P = 0.45). Despite differences in the glycemic response to breakfast, 24 h glycemia did not differ between ExDEF and ExBAL (area under the curve = 128 ± 10 vs 131 ± 10 mmol·L·h per 24 h, respectively; P = 0.54).

CONCLUSIONS

An exercise-induced energy deficit lowered the glycemic response to breakfast the next day-but this energy deficit did not impact total 24 h glycemia, the day after exercise in metabolically healthy adults.

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.

Exercise-Induced Improvements to Whole Body Glucose Metabolism in Type 2 Diabetes: The Essential Role of the Liver

Type 2 diabetes (T2D) is a metabolic disease characterized by obesity, insulin resistance, and the dysfunction of several key glucoregulatory organs. Among these organs, impaired liver function is recognized as one of the earliest contributors to impaired whole-body glucose homeostasis, with well-characterized hepatic insulin resistance resulting in elevated rates of hepatic glucose production (HGP) and fasting hyperglycemia. One portion of this review will provide an overview of how HGP is regulated during the fasted state in healthy humans and how this process becomes dysregulated in patients with T2D. Less well-appreciated is the liver's role in post-prandial glucose metabolism, where it takes up and metabolizes one-third of orally ingested glucose. An abundance of literature has shown that the process of hepatic glucose uptake is impaired in patients with T2D, thereby contributing to glucose intolerance. A second portion of this review will outline how hepatic glucose uptake is regulated during the post-prandial state, and how it becomes dysfunctional in patients with T2D. Finally, it is well-known that exercise training has an insulin-sensitizing effect on the liver, which contributes to improved whole-body glucose metabolism in patients with T2D, thereby making it a cornerstone in the management of the disease. To this end, the impact of exercise on hepatic glucose metabolism will be thoroughly discussed, referencing key findings in the literature. At the same time, sources of heterogeneity that contribute to inconsistent findings in the field will be pointed out, as will important topics for future investigation.

Accounting for the Nutritional Context to Correctly Interpret Results from Studies of Exercise and Sedentary Behavior

There is a wealth of research lauding the benefits of exercise to oppose cardiometabolic disease such as diabetes, CVD and hypertension. However, in the great majority of these studies, the nutritional context (energy balance, deficit, or surplus) has been ignored, despite its profound effect on responses to both exercise and inactivity. Even a minor energy deficit or surplus can strongly modulate the magnitude and duration of the metabolic responses to an intervention; therefore, failure to account for this important confounding variable obscures clear interpretation of the results from studies of exercise or inactivity. The aim of this review is to highlight key lessons from studies examining the interaction between exercise and sedentary behavior, energy status, and glucose and insulin regulation. In addition to identifying notable problems, we suggest a few potential solutions.

The Effect of Consuming a Liquid Diet vs a Solid Diet 24-hr Preexperimental Trials on Adherence in Athletes

Discrepancies in energy and macronutrient intakes between tests are apparent even when a solid prepackaged diet (Sdiet) is used to standardize dietary intake for preexperimental trials. It is unknown whether a liquid prepackaged diet (Ldiet) leads to improved adherence, resulting in lower variability in energy and macronutrient intakes. This study assesses the ability of athletes to replicate a diet when an Ldiet or Sdiet was used as a dietary standardization technique. In a cross-over design, 30 athletes were randomly assigned to either Sdiet or Ldiet. Each diet was consumed for two nonconsecutive days. Participants were instructed to consume all the meals provided and to return any leftovers. The coefficient of variation (CV) was calculated for each nutrient for the two methods and reported as the average CV. The Bland-Altman plots show that differences between Days 1 and 2 in energy and macronutrient intakes for both diets were close to zero, with the exception of some outliers. The %CV for Sdiet was higher than Ldiet (5% and 3% for energy, 5% and 3% for carbohydrate, 5% and 2% for protein, and 5% and 3% for fat, respectively). There was a strong positive correlation for energy and all macronutrients between Days 1 and 2 for both methods (r > .80; p < .05). Ldiet is an effective technique to standardize diet preexperimental trials and could be used as an alternative to Sdiet. Furthermore, Ldiet may lead to additional improvements in the compliance of participants to the diet and also decrease the cost and time of preparation.

Acute Effects of Exercise Intensity on Insulin Sensitivity under Energy Balance

Exercise is known to improve insulin sensitivity (SI); however, studies to date have been confounded by negative energy deficits after exercise.

PURPOSE

The primary objective of this study was to assess the effect of 8 to 16 wk of aerobic exercise training on the SI of untrained women under rigorously controlled energy-balanced conditions. The secondary objective was to determine if one acute bout of moderate-intensity continuous (MIC) or high-intensity interval (HII) exercise further affected SI.

METHODS

Insulin sensitivity was assessed in 28 untrained women at baseline, after 8 to 16 wk of training with no-exercise (NE) before assessment, 22 h after MIC (50% V˙O2peak), and 22 h after HII (84% V˙O2peak) using a hyperinsulinemic-euglycemic clamp. Participants were in a whole-room indirect calorimeter during each condition, and food intake was adjusted to ensure energy balance across 23 h before each clamp.

RESULTS

There were no significant differences in acute energy balance between each condition. Results indicated a significant main effect of time, such that SI was higher during the HII condition compared with both baseline and NE (P < 0.05). No significant differences in SI were observed after NE or MIC.

CONCLUSIONS

Widely reported improvements in SI in response to chronic exercise training may be mediated in part by shifts in energy balance. However, an acute bout of HII exercise may increase SI even in the context of energy balance.

Carbohydrate Loading Followed by High Carbohydrate Intake During Prolonged Physical Exercise and Its Impact on Glucose Control in Individuals With Diabetes Type 1-An Exploratory Study

Background: Prolonged physical exercise (PE) is a challenge in type 1 diabetes with an increased incidence of both hypoglycemia and hyperglycemia. Purpose: To evaluate the impact of two consecutive days of carbohydrate (CHO) loading, followed by high intermittent CHO-intake during prolonged PE, facilitated by a proactive use of Real-Time Continuous Glucose Monitoring (rtCGM), on glucose control in individuals with type 1 diabetes. Methods: Ten physically active individuals with type 1 diabetes were invited to participate in a 3-day long sports camp with the objective to evaluate CHO-loading and high intermittent CHO-intake during prolonged PE. 1.5 months later the same procedure was evaluated in relation to a 90 km cross-country skiing race (Vasaloppet). Participants were instructed to act proactively using rtCGM with predictive alerts to maintain sensor glucose values within target range, defined as 72-180 mg/dl (4-10 mmol/l). Results: Mean glucose values during CHO-loading were: day 1; 140.4 ± 45.0 mg/dl (7.8 ± 2.5 mmol/l) and day 2; 120.6 ± 41.4 mg/dl (6.7 ± 2.3 mmol/l). Mean sensor glucose at start of PE was 126.0 ± 25.2 mg/dl (7.0 ± 1.4 mmol/l) and throughout PE 127.8 ± 25.2 mg/dl (7.1 ± 1.4 mmol/l). Percentage of time spent in range (TIR) respective time spent in hypoglycemia was: CHO-loading 74.7/10.4% and during PE 94.3/0.6%. Conclusions: High intermittent CHO-intake during prolonged PE combined with proactive use of rtCGM is associated with good glycemic control during prolonged exercise in individuals with diabetes type 1. However, the time spent in hypoglycemia during the 2-days of CHO-loading was 10.4% and therefore a lower insulin dose might be suggested to reduce the time spent in hypoglycemia. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT03722225.

Post-Exercise Carbohydrate-Energy Replacement Attenuates Insulin Sensitivity and Glucose Tolerance the Following Morning in Healthy Adults

The carbohydrate deficit induced by exercise is thought to play a key role in increased post-exercise insulin action. However, the effects of replacing carbohydrate utilized during exercise on postprandial glycaemia and insulin sensitivity are yet to be determined. This study therefore isolated the extent to which the insulin-sensitizing effects of exercise are dependent on the carbohydrate deficit induced by exercise, relative to other exercise-mediated mechanisms. Fourteen healthy adults performed a 90-min run at 70% V˙O2max starting at 1600–1700 h before ingesting either a non-caloric artificially-sweetened placebo solution (CHO-DEFICIT) or a 15% carbohydrate solution (CHO-REPLACE; 221.4 ± 59.3 g maltodextrin) to precisely replace the measured quantity of carbohydrate oxidized during exercise. The alternate treatment was then applied one week later in a randomized, placebo-controlled, and double-blinded crossover design. A standardized low-carbohydrate evening meal was consumed in both trials before overnight recovery ahead of a two-hour oral glucose tolerance test (OGTT) the following morning to assess glycemic and insulinemic responses to feeding. Compared to the CHO-DEFICIT condition, CHO-REPLACE increased the incremental area under the plasma glucose curve by a mean difference of 68 mmol·L⁻¹ (95% CI: 4 to 132 mmol·L⁻¹; p = 0.040) and decreased the Matsuda insulin sensitivity index by a mean difference of −2 au (95% CI: −1 to −3 au; p = 0.001). This is the first study to demonstrate that post-exercise feeding to replaceme the carbohydrate expended during exercise can attenuate glucose tolerance and insulin sensitivity the following morning. The mechanism through which exercise improves insulin sensitivity is therefore (at least in part) dependent on carbohydrate availability and so the day-to-day metabolic health benefits of exercise might be best attained by maintaining a carbohydrate deficit overnight.

Serum metabolomic response to exercise training in spontaneously hypertensive rats

Chronic aerobic exercise training exhibits blood pressure protective effects, but the mechanism in metabolic level remains largely unclear. This study aims to investigate the effect of exercise training from serum metabolic profiles on the development of hypertension in spontaneously hypertensive rats (SHRs). Exercise training was performed, and the serum metabolites were measured by integrating gas chromatography-mass spectrometer and correlation-based network analysis. After a period of 6 weeks of chronic aerobic exercise training, systolic blood pressure was significant lower in the exercise training group (SHR + EX) rats than the control group (SHR). Principal component analysis indicated a clearly separation of metabolomic profiles between SHR + EX and SHR. Nineteen of 63 metabolites in serum were identified (P < .05, variable importance in projections > 1, false discovery rate < 0.1), including fatty acids, amino acids, and others. Lower levels of six fatty acids were observed in SHR + EX. Besides, pathway analysis indicated a significant alteration of fatty acid metabolism. The correlation-based (Pearson correlation coefficient > 0.83) network of serum metabolites revealed a decreased correlation linkage of SHR + EX than SHR rats. Higher activities of hexokinase, citrate synthase, aspartate aminotransferase, and alanine aminotransferase were detected in liver, left ventricle, and skeletal muscle of SHR + EX groups. In summary, these findings provided essential biochemistry information about the metabolic alteration to exercise training in SHR, which may in part explain the protective effect of exercise in hypertensive individuals.

One bout of exercise alters free-living postprandial glycemia in type 2 diabetes

PURPOSE

Elevated postprandial glycemic (PPG) excursions are significant risk factors for cardiovascular disease in type 2 diabetes patients. In this study, we tested if and for how many meals a single bout of exercise would reduce PPG responses to subsequent meals in type 2 diabetes (T2D) patients using a continuous glucose monitor system (CGMS).

METHODS

We recruited nine sedentary (<30 min·wk(-1) of exercise) individuals with T2D (mean ± SD; body mass index = 36.0 ± 1.1 kg·m(-2), age = 60.3 ± 1.0 yr, HbA1c = 6.3% ± 0.2%). The subjects consumed a eucaloric diet (51% carbohydrate, 31% fat, and 18% protein) consisting of three meals, identical in composition, for a 2-d period while wearing a continuous glucose monitor system in two different conditions (exercise [EX], one 60-min bout at 60%-75% of heart rate reserve performed before breakfast), vs a sedentary [SED] condition). We quantified 24-h average glucose, PPG area under the curve (AUC; 4-h glucose AUC after meals), and PPG-2 h (2 h postprandial glucose).

RESULTS

EX significantly reduced average [glucose] during the first 24-h period (P = 0.03). EX caused a reduction in PPG-AUC (P = 0.02) for all of the meals during the 2 d (main effect between conditions). A comparison between the EX and the SED conditions at each meal revealed that EX reduced PPG-AUC after the second meal of day 1 (lunch) (P = 0.04). PPG-2 h was not significantly different between EX and SED.

CONCLUSIONS

Although a single EX bout does lower 24-h average [glucose], it only significantly lowered PPG-AUC at the second meal after the bout, suggesting that daily exercise may be needed to most effectively improve PPG at the advent of exercise training in T2D patients.

Enhancing Exercise Responsiveness across Prediabetes Phenotypes by Targeting Insulin Sensitivity with Nutrition

Exercise is a cornerstone therapy for chronic diseases related to multiorgan insulin resistance. However, not all individuals show the anticipated improvement in insulin sensitivity following exercise and these individuals are considered exercise resistant. Caloric restriction is an approach to enhance the effect of exercise on increasing peripheral and hepatic insulin sensitivity, as replenishing expended calories blunts these benefits. Alternatively, restricting carbohydrate intake, independent of energy balance, following exercise provides an additive effect on peripheral insulin sensitivity when compared to refeeding carbohydrate. Although carbohydrate composition modulates insulin sensitivity, few have studied effects of low glycemic index or whole-grain diets following exercise across prediabetes phenotypes on insulin sensitivity. Herein, we propose the novel hypothesis that the combination of individualized nutrition therapy and exercise should be based on the clinical pathology of prediabetes to overcome exercise resistance and improve responsiveness in people at risk for type 2 diabetes and cardiovascular disease.

Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) comprises a disease spectrum ranging from benign hepatic steatosis to non-alcoholic steatohepatitis with inflammation (NASH) and liver cirrhosis. NAFLD is now recognised as the hepatic manifestation of the metabolic syndrome. Simple steatosis is benign, whereas NASH can progress to cirrhosis with its resultant complications. Liver biopsy remains the gold standard in the diagnosis of NAFLD/NASH. Lifestyle and dietary modifications to achieve sustained weight loss is the cornerstone of NAFLD/NASH treatment.

Frequent interruptions of sedentary time modulates contraction- and insulin-stimulated glucose uptake pathways in muscle: Ancillary analysis from randomized clinical trials

Epidemiological studies have observed associations between frequent interruptions of sitting time with physical activity bouts and beneficial metabolic outcomes, even in individuals who regularly exercise. Frequent interruptions to prolonged sitting reduce postprandial plasma glucose. Here we studied potential skeletal muscle mechanisms accounting for this improved control of glycemia in overweight adults under conditions of one day uninterrupted sitting and sitting interrupted with light-intensity or moderate-intensity walking every 20-min (n = 8); and, after three days of either uninterrupted sitting or light-intensity walking interruptions (n = 5). Contraction- and insulin-mediated glucose uptake signaling pathways as well as changes in oxidative phosphorylation proteins were examined. We showed that 1) both interventions reduce postprandial glucose concentration, 2) acute interruptions to sitting over one day stimulate the contraction-mediated glucose uptake pathway, 3) both acute interruptions to sitting with moderate-intensity activity over one day and light-intensity activity over three days induce a transition to modulation of the insulin-signaling pathway, in association with increased capacity for glucose transport. Only the moderate-intensity interruptions resulted in greater capacity for glycogen synthesis and likely for ATP production. These observations contribute to a mechanistic explanation of improved postprandial glucose metabolism with regular interruptions to sitting time, a promising preventive strategy for metabolic diseases.

Evaluation of glucose control when a new strategy of increased carbohydrate supply is implemented during prolonged physical exercise in type 1 diabetes

PURPOSE

In healthy individuals, high carbohydrate intake is recommended during prolonged exercise for maximum performance. In type 1 diabetes (T1D), this would alter the insulin requirements. The aim of the study was to evaluate the safety of high glucose supplementation during prolonged exercise and the glucose control when a novel strategy of increased carbohydrate supply was implemented during prolonged exercise in T1D.

METHODS

Eight subjects with T1D participated in a sports camp including sessions of prolonged exercise and individualized feedback during three consecutive days. This was later followed by a 90 km cross-country skiing race. Large amounts of carbohydrates, 75 g/h, were supplied during exercise and the insulin requirements were registered. Glucose was measured before, during and after exercise aiming at euglycaemia, 4-8 mmol/L (72-144 mg/dL). During the race, continuous glucose monitoring (CGM) was used as an aspect of safety and to allow direct and individual adjustments.

RESULTS

Compared to ordinary carbohydrate supply during exercise, the high carbohydrate supplementation resulted in significantly increased insulin doses to maintain euglycaemia. During the cross-country skiing race, the participants succeeded to reach mean target glucose levels; 6.5 ± 1.9 mmol/L (117 ± 34 mg/dL) and 5.7 ± 1.5 mmol/L (103 ± 27 mg/dL) at the start and finish of the race, respectively. Episodes of documented hypoglycemia (<4 mmol/L/72 mg/dL) were rare. CGM was used for adjustments.

CONCLUSION

In this study, large carbohydrate supplementation in T1D individuals during prolonged aerobic exercise is safe and allows the subjects to maintain glycaemic control and indicates the feasibility of CGM under these conditions.

Effect of adiposity on insulin action after acute and chronic resistance exercise in non-diabetic women

PURPOSE

Obesity may attenuate metabolic health improvements following lifestyle interventions. However, the effect of adiposity on insulin action following resistance exercise in young non-diabetic women is unknown. The purpose of this study was to test the hypothesis that adiposity attenuates improvements in insulin sensitivity and glucose-stimulated insulin secretion (INS0-60/GLC0-60) after both acute resistance exercise (ARE) and progressive training (PRT).

METHODS

Twenty-six young non-diabetic women (21.2 ± 0.7 years) were randomly assigned to control (C; n = 7; BF 40.1 ± 2.1 %) or exercise groups: normal body fat (NBF; n = 8; BF 29.9 ± 2.3 %) and high body fat (HBF; n = 12; BF 48.2 ± 1.4 %). Acute whole-body exercises were performed at 60 % of 1-RM for three sets of 8-12 repetitions, and PRT was performed 3 days/week for 7 weeks. A 75 g OGTT was conducted before and after ARE and PRT to estimate insulin sensitivity (Matsuda index) and INS0-60/GLC0-60. Insulin area under the curve (AUC) was calculated using the trapezoidal model.

RESULTS

ARE had no statistical effect on insulin action across groups. Strength and fat-free mass (via DXA) increased after PRT in both NBF and HBF (p < 0.05), but only HBF women decreased BF (p < 0.01). HBF women were less insulin sensitive at baseline compared to NBF women (p < 0.05). Insulin sensitivity increased 95 % and INS0-60/GLC0-60 decreased 32 % following PRT in NBF, but not HBF or C (p < 0.05). After training, enhanced insulin sensitivity was inversely related to decreased INS0-60/GLC0-60 (r = -0.71, p < 0.001), fasting insulin (r = -0.71, p < 0.001), and insulin AUC (r = -0.85, p < 0.001).

CONCLUSION

Seven weeks of PRT increases insulin sensitivity and reduces glucose-stimulated insulin secretion in NBF, but not HBF women. Obesity attenuates exercise-induced improvements in glucose regulation in young non-diabetic women.

Short-term aerobic exercise training increases postprandial pancreatic polypeptide but not peptide YY concentrations in obese individuals

Objective

Short-term exercise training improves glycemic control, but the effect of short-term training on postprandial satiety peptide responses or perceived satiety remains unknown. We tested the hypothesis that short-term aerobic exercise training (15 days) would alter postprandial pancreatic and gut peptide [pancreatic polypeptide (PP) and peptide YY (PYY)] responses and perceived appetite and satiety in obese individuals.

Subjects

Thirteen healthy obese men and women (age: 42±2 y; BMI: 30-45 kg/m²)

Measurements

Subjects were studied before and after 15 days of training (walking 1 h at 70-75% VO_2peak). On the study day, subjects consumed 1500 kcal as 6 meals (250 kcal: 9 g protein, 40 g CHO, 6 g fat) while blood samples and satiety measurements were taken at baseline and every 20 min for 12 h. Blood was analyzed for pancreatic polypeptide (PP), peptide YY (PYY), glucose, and insulin levels. Appetite and satiety was assessed with a visual analog scale throughout the day.

Results

Incremental area under the curve (iAUC) for PP increased significantly with training (pre 2788±753; post 3845±830 pg/ml·min for 12-h, p<0.001), but there was no difference in the PP response to each meal. The initial PP response to the first meal increased (ΔPP_{min 20-0}: pre 86±25; post 140±36 pg/ml, p<0.05) with training. PYY iAUC showed no significant changes with training but showed a significant main effect of time across meals, with the largest response being to the first meal (P<0.005). There were no changes in satiety, glucose, or insulin levels with training.

Conclusion

Short-term exercise training increases postprandial PP concentrations in obese individuals; however, PYY levels and glycemic control remain unaffected. Both PP and PYY show meal-induced increases at all meals but PYY has a greater response at the first meal with reduced responses at subsequent meals.

Effect of short-term reduced physical activity on cardiovascular risk factors in active lean and overweight middle-aged men

OBJECTIVES

An experimental reduction in physical activity is a useful tool for exploring the health benefits of physical activity. This study investigated whether similarly-active overweight men show a more pronounced response to reduced physical activity than their lean counterparts because of their atherogenic phenotype (i.e., greater abdominal adiposity).

METHODS

From 115 active men aged 45-64years, we recruited nine active lean (waist circumference <84cm) and nine active central overweight men (waist circumference >94cm). Fasting blood samples and responses to an oral glucose tolerance test (OGTT) were measured at baseline and following one week of reduced physical activity to simulate sedentary levels (removal of structured exercise and reduced habitual physical activity).

RESULTS

Glucose and insulin areas under the curve (AUC), CRP, ALT, TAG were all higher in the overweight group and remained so throughout (P<0.05). Insulin and glucose AUC responses to an OGTT, as well as fasting triglyceride (TAG) concentrations, increased in both groups as a result of the intervention (P<0.05). There was no change in interleukin-6, C-reactive protein (CRP), Tumour Necrosis Factor-α, soluble intracellular adhesion molecule 1, or alanine transaminase (ALT).

CONCLUSION

One-week of reduced activity similarly-impaired glucose control and increased fasting TAG in both lean and overweight men. Importantly, in spite of very similar (high) levels of habitual physical activity, central overweight men displayed a poorer profile for various inflammatory and metabolic outcomes (CRP, ALT, TAG, glucose AUC and insulin AUC).

Adaptive metabolic response to 4 weeks of sugar-sweetened beverage consumption in healthy, lightly active individuals and chronic high glucose availability in primary human myotubes

PURPOSE

Chronic sugar-sweetened beverage (SSB) consumption is associated with obesity and type 2 diabetes mellitus (T2DM). Hyperglycaemia contributes to metabolic alterations observed in T2DM, such as reduced oxidative capacity and elevated glycolytic and lipogenic enzyme expressions in skeletal muscle tissue. We aimed to investigate the metabolic alterations induced by SSB supplementation in healthy individuals and to compare these with the effects of chronic hyperglycaemia on primary muscle cell cultures.

METHODS

Lightly active, healthy, lean subjects (n = 11) with sporadic soft drink consumption underwent a 4-week SSB supplementation (140 ± 15 g/day, ~2 g glucose/kg body weight/day, glucose syrup). Before and after the intervention, body composition, respiratory exchange ratio (RER), insulin sensitivity, muscle metabolic gene and protein expression were assessed. Adaptive responses to hyperglycaemia (7 days, 15 mM) were tested in primary human myotubes.

RESULTS

SSB supplementation increased fat mass (+1.0 kg, P < 0.05), fasting RER (+0.12, P < 0.05), fasting glucose (+0.3 mmol/L, P < 0.05) and muscle GAPDH mRNA expressions (+0.94 AU, P < 0.05). PGC1α mRNA was reduced (-0.20 AU, P < 0.05). Trends were found for insulin resistance (+0.16 mU/L, P = 0.09), and MondoA protein levels (+1.58 AU, P = 0.08). Primary myotubes showed elevations in GAPDH, ACC, MondoA and TXNIP protein expressions (P < 0.05).

CONCLUSION

Four weeks of SSB supplementation in healthy individuals shifted substrate metabolism towards carbohydrates, increasing glycolytic and lipogenic gene expression and reducing mitochondrial markers. Glucose-sensing protein MondoA might contribute to this shift, although further in vivo evidence is needed to corroborate this.

The 24-h energy intake of obese adolescents is spontaneously reduced after intensive exercise: a randomized controlled trial in calorimetric chambers

Background

Physical exercise can modify subsequent energy intake and appetite and may thus be of particular interest in terms of obesity treatment. However, it is still unclear whether an intensive bout of exercise can affect the energy consumption of obese children and adolescents.

Objective

To compare the impact of high vs. moderate intensity exercises on subsequent 24-h energy intake, macronutrient preferences, appetite sensations, energy expenditure and balance in obese adolescent.

Design

This randomized cross-over trial involves 15 obese adolescent boys who were asked to randomly complete three 24-h sessions in a metabolic chamber, each separated by at least 7 days: (1) sedentary (SED); (2) Low-Intensity Exercise (LIE) (40% maximal oxygen uptake, VO₂max); (3) High-Intensity Exercise (HIE) (75%VO₂max).

Results

Despite unchanged appetite sensations, 24-h total energy intake following HIE was 6–11% lower compared to LIE and SED (p<0.05), whereas no differences appeared between SED and LIE. Energy intake at lunch was 9.4% and 8.4% lower after HIE compared to SED and LIE, respectively (p<0.05). At dinner time, it was 20.5% and 19.7% lower after HIE compared to SED and LIE, respectively (p<0.01). 24-h energy expenditure was not significantly altered. Thus, the 24-h energy balance was significantly reduced during HIE compared to SED and LIE (p<0.01), whereas those of SED and LIE did not differ.

Conclusions

In obese adolescent boys, HIE has a beneficial impact on 24-h energy balance, mainly due to the spontaneous decrease in energy intake during lunch and dinner following the exercise bout. Prescribing high-intensity exercises to promote weight loss may therefore provide effective results without affecting appetite sensations and, as a result, food frustrations.

Trial Registration

ClinicalTrial.gov NCT01036360

Effects of 1 day of inactivity on insulin action in healthy men and women: interaction with energy intake

Prolonged periods of limited muscle activity can reduce insulin action. Acute changes in low muscle activity (ie, sitting) have not been assessed. In addition, unless energy intake is reduced during sitting to match low expenditure, the concurrent energy surplus may explain lower insulin action. The objective of the study was to evaluate the acute effect of sitting, with and without energy surplus, on insulin action. Fourteen young (26.1 ± 4.5 years, mean ± SD), nonobese (23.7% ± 7.1% fat), fit (peak oxygen consumption = 49.1 ± 3.3 mL·kg(-1)·min(-1)) men (n = 7) and women (n = 7) completed three 24-hour conditions: (1) an active, no-sitting condition (high energy expenditure of 2944 ± 124 kcal with energy intake matched to expenditure) = NO-SIT; (2) low energy expenditure (sitting) of 2195 ± 121 kcal with no reduction in energy intake (energy surplus) = SIT; and (3) sitting with energy intake reduced to 2139 ± 118 kcal to match low expenditure (energy balance) = SIT-BAL. Insulin action was measured the following morning during a continuous infusion of [6,6-(2)H]-glucose. Data were analyzed using linear mixed-effects models with planned contrasts. Compared with NO-SIT, insulin action, defined as whole-body rate of glucose disappearance normalized to mean plasma insulin, was reduced by 39% in SIT (P < .001) and by 18% in SIT-BAL (P = .07). Insulin action was higher in SIT-BAL compared with SIT (P = .04). One day of sitting considerably reduced insulin action; this effect was minimized, but not prevented, when energy intake was reduced to match expenditure. Strategies to limit daily sitting may reduce metabolic disease risk.

Effects of a single exercise bout on insulin sensitivity in black and white individuals

BACKGROUND

Previous research suggests non-Hispanic blacks (blacks) are more insulin resistant than non-Hispanic whites (whites). Physical activity can play an important role in reducing insulin resistance. However, it is unknown whether racial differences exist in response to exercise. Therefore, the purpose of this study was to compare metabolic responses to a single bout of exercise in blacks and age-, sex-, and body mass index-matched whites.

METHODS

Whole-body insulin sensitivity, glucose storage, glucose oxidation, and respiratory exchange ratio (RER) were assessed during a hyperinsulinemic-euglycemic clamp in normoglycemic blacks (n = 11) and whites (n = 10). Outcome measures were evaluated in a sedentary control condition and 12 h after treadmill walking at 75% of maximal heart rate for 75 min.

RESULTS

In the control condition, there were no differences in insulin sensitivity between blacks and whites (P = 0.54). During the clamp, glucose oxidation and insulin-stimulated RER values were significantly higher in blacks compared with whites (P = 0.04 and P < 0.01, respectively). Despite similar RER values during exercise, RER values at 60, 90, and 120 min after exercise in blacks were also significantly higher compared with whites (P < 0.05). After exercise, there were no significant improvements in insulin sensitivity (P = 0.57) or glucose storage (P = 0.42) in blacks or whites; however, glucose oxidation was significantly lower in both racial groups (P < 0.05).

CONCLUSIONS

These data suggest that insulin sensitivity is similar in blacks and age-, sex-, and body mass index-matched whites, but the glucose disposal pathways (storage vs. oxidation) are somewhat different. Compared with whites, blacks appear to have a greater capacity to increase glucose oxidation immediately after exercise and during insulin stimulation.

High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals

Continuous high glycemic load and inactivity challenge glucose homeostasis and fat oxidation. Hyperglycemia and high intramuscular glucose levels mediate insulin resistance, a precursor state of type 2 diabetes. The aim was to investigate whether a carbohydrate (CHO)-reduced diet combined with high-intensity interval training (HIIT) enhances the beneficial effects of the diet alone on insulin sensitivity and fat oxidation in obese individuals. Nineteen obese subjects underwent 14 days of CHO-reduced and energy-restricted diet. Ten of them combined the diet with HIIT (4 min bouts at 90% VO(2peak) up to 10 times, 3 times a week). Oral glucose insulin sensitivity (OGIS) increased significantly in both groups; [diet-exercise (DE) group: pre 377 ± 70, post 396 ± 68 mL min(-1) m(-2); diet (D) group: pre 365 ± 91, post 404 ± 87 mL min(-1) m(-2); P < 0.001]. Fasting respiratory exchange ratio (RER) decreased significantly in both groups (DE group: pre 0.91 ± 0.06, post 0.88 ± 0.06; D group: pre 0.92 ± 0.07, post 0.86 ± 0.07; P = 0.002). VO(2peak) increased significantly in the DE group (pre 27 ± 5, post 32 ± 6 mL kg(-1) min(-1); P < 0.001), but not in the D group (pre 26 ± 9, post 26 ± 8 mL kg(-1) min(-1)). Lean mass and resistin were preserved only in the DE group (P < 0.05). Fourteen days of CHO-reduced diet improved OGIS and fat oxidation (RER) in obese subjects. The energy-balanced HIIT did not further enhance these parameters, but increased aerobic capacity (VO(2peak)) and preserved lean mass and resistin.

A 2-wk reduction of ambulatory activity attenuates peripheral insulin sensitivity

US adults take between approximately 2,000 and approximately 12,000 steps per day, a wide range of ambulatory activity that at the low range could increase risk for developing chronic metabolic diseases. Dramatic reductions in physical activity induce insulin resistance; however, it is uncertain if and how low ambulatory activity would influence peripheral insulin sensitivity. We aimed to explore if healthy, nonexercising subjects who went from a normal to a low level of ambulatory activity for 2 wk would display metabolic alterations including reduced peripheral insulin sensitivity. To do this, ten healthy young men decreased their daily activity level from a mean of 10,501+/-808 to 1,344+/-33 steps/day for 2 wk. Hyperinsulinemic-euglycemic clamps with stable isotopes and muscle biopsies, maximal oxygen consumption (VO2 max) tests, and blood samples were performed pre- and postintervention. A reduced number of daily steps induced a significant reduction of 17% in the glucose infusion rate (GIR) during the clamp. This reduction was due to a decline in peripheral insulin sensitivity with no effect on hepatic endogenous glucose production. The insulin-stimulated ratio of pAktthr308/total Akt decreased after step reduction, with a post hoc analysis revealing the most pronounced effect after 4 h of insulin infusion. In addition, the 2-wk period induced a 7% decline in VO2 max (ml/min; cardiovascular fitness). Lean mass of legs, but not arms and trunk, decreased concurrently. Taken together, one possible biological cause for the public health problem of Type 2 diabetes has been identified. Reduced ambulatory activity for 2 wk in healthy, nonexercising young men significantly reduced peripheral insulin sensitivity, cardiovascular fitness, and lean leg mass.

Randomized trial on the effects of a 7-d low-glycemic diet and exercise intervention on insulin resistance in older obese humans

BACKGROUND

The optimal combination of diet and exercise that produces the greatest reversal of obesity-related insulin resistance is unknown.

OBJECTIVES

We examined the effects of a combined 7-d low-glycemic index (low-GI) diet and exercise training intervention on insulin sensitivity in older obese humans.

DESIGN

Participants [n = 32; mean (+/-SEM) age: 66 +/- 1 y; body mass index (in kg/m(2)): 33.8 +/- 0.7] were randomly assigned to a parallel, double-blind, controlled-feeding trial and underwent supervised aerobic exercise (EX; 60 min/d at 80-85% maximum heart rate) in combination with either a low-GI (LoGI + EX: 41.1 +/- 0.4) or a high-GI (HiGI + EX: 80.9 +/- 0.6) diet. All meals were provided and were isocaloric to individual energy requirements. Insulin sensitivity and hepatic glucose production were assessed with a 40-mU x m(-2) x min(-1) hyperinsulinemic euglycemic clamp combined with a [6,6-(2)H(2)]-glucose infusion.

RESULTS

After the intervention, small decreases were observed in body weight (-1.6 +/- 0.2 kg; P < 0.0001) and fat mass (-1.7 +/- 0.9%; P = 0.004) in both groups. Maximal aerobic capacity ( O(2)max) also improved slightly (0.06 +/- 0.02 L/min; P = 0.004). Resting systolic blood pressure, fasting glucose, insulin, triglycerides, and cholesterol all decreased after the study (all P < 0.05). Larger changes in systolic blood pressure and O(2max) were seen in the LoGI + EX group. Insulin-stimulated glucose disposal (P < 0.001), insulin suppression of hepatic glucose production (P = 0.004), and postabsorptive fat oxidation (P = 0.03) improved equally in both groups after the intervention.

CONCLUSIONS

These findings suggest that the metabolic improvements after short-term exercise training in older obese individuals are dependent on increased physical activity and are not influenced by a low-GI diet. However, a low-GI diet has added benefit in alleviating hypertension, thus reducing the risk of diabetic and vascular complications.

Lifestyle modification as the primary treatment of NASH

This article reviews the rationale and data behind recommending lifestyle changes to prevent and reverse NASH, focusing specifically on changes that lead to increased physical activity in sedentary patients, changes in dietary habits, and decreased calorie consumption to achieve gradual and sustained weight loss in those who are overweight or obese. In a culture that values avoiding even minimal exertion these are not easy changes to make. Ultimately, the success of care providers in helping patients to recognize and overcome these barriers depends on a patient's motivation, but clinicians can be more persuasive and able to bolster this motivation when armed with a conviction based on data that establish this to be the best course of action for patients with NASH.

[Physical activity in prevention and treatment of diabetes]

Effects and mechanisms of a single bout of physical load and of the regular exercise (training) on the carbohydrate and fat metabolism are reviewed. During exercise and in the following couple of hours sugar utilization improves, "activity functions like insulin". Proper exercise contributes to using up the fat reserves, and slimmer body, fat reduction can be maintained by the combination of exercise and diet-control. Instructions in "exercise for everybody" and particularly for both type diabetics are detailed. In prevention of cardio-metabolic pathologies the most important measure were avoiding the overweight state by rational alimentation and regular physical activity.

Influence of acute exercise with and without carbohydrate replacement on postprandial lipid metabolism

Acute exercise, undertaken on the day before an oral fat tolerance test (OFTT), typically reduces postprandial triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C). However, the benefits of acute exercise may be overstated when studies do not account for compensatory changes in dietary intake. The objective of this study was to determine the influence of acute exercise, with and without carbohydrate (CHO) replacement, on postprandial lipid metabolism. Eight recreationally active young men underwent an OFTT on the morning after three experimental conditions: no exercise [control (Con)], prolonged exercise without CHO replacement (Ex-Def) and prolonged exercise with CHO replacement to restore CHO and energy balance (Ex-Bal). The exercise session in Ex-Def and Ex-Bal consisted of 90 min cycle ergometry at 70% peak oxygen uptake (V̇o2peak) followed by 10 maximal 1-min sprints. CHO replacement was achieved using glucose solutions consumed at 0, 2, and 4 h postexercise. Muscle glycogen was 40 ± 4% ( P < 0.05) and 94 ± 3% ( P = 0.24) of Con values on the morning of the Ex-Def and Ex-Bal OFTT, respectively. Postprandial TG were 40 ± 14% lower and postprandial HDL-C, free fatty acids, and 3-hydroxybutyrate were higher in Ex-Def compared with Con ( P < 0.05). Most importantly, these exercise effects were not evident in Ex-Bal. Postprandial insulin and glucose and the homeostatic model assessment of insulin resistance (HOMAIR) were not significantly different across trials. There was no relation between the changes in postprandial TG and muscle glycogen across trials. In conclusion, the influence of acute exhaustive exercise on postprandial lipid metabolism is largely dependent on the associated CHO and energy deficit.

The effect of carbohydrate availability following exercise on whole-body insulin action

One bout of exercise enhances insulin-stimulated glucose uptake (insulin action), but the effect is blunted by consumption of carbohydrate-containing food after exercise. The independent roles of energy and carbohydrate in mediating post-exercise insulin action have not been systematically evaluated in humans. The purpose of this study was to determine if varying carbohydrate availability, with energy intake held constant, mediates post-exercise insulin action. Ten young (21 +/- 2 y, overweight (body fat 37% +/- 3%) men and women completed 3 conditions in random order: (i) no-exercise (BASE), (ii) exercise with energy balance but carbohydrate deficit (C-DEF), and (iii) exercise with energy and carbohydrate balance (C-BAL). In the exercise conditions, subjects expended 30% of total daily energy expenditure on a cycle ergometer at 70% VO2 peak. Following exercise, subjects consumed a meal that replaced expended energy (~3000 kJ) and was either balanced (intake = expenditure) or deficient (-100 g) in carbohydrate. Twelve hours later, insulin action was measured by continuous infusion of glucose with stable isotope tracer (CIG-SIT). Changes in insulin action were evaluated using a one-way ANOVA with repeated measures. During CIG-SIT, non-oxidative glucose disposal (i.e., glucose storage) was higher in C-DEF than in BASE (27.2 +/- 3.2 vs. 16.9 +/- 3.5 micromol.L-1.kg-1.min-1, p < 0.05). Conversely, glucose oxidation was lower in C-DEF (8.6 +/- 1.3 micromol.L-1.kg-1.min-1) compared with C-BAL (12.2 +/- 1.2 micromol.L-1.kg-1.min-1), and BASE (17.1 +/- 2.2 micromol.L-1.kg-1.min-1), p < 0.05). Fasting fat oxidation was higher in C-DEF than in BASE (109.8 +/- 10.5 vs. 80.7 +/- 9.6 mg.min-1, p < 0.05). In C-DEF, enhanced insulin action was correlated with the magnitude of the carbohydrate deficit (r = 0.82, p < 0.01). Following exercise, re-feeding expended energy, but not carbohydrate, increased fasting fat oxidation, and shifted insulin-mediated glucose disposal toward increased storage and away from oxidation.

Effects of exercise on energy-regulating hormones and appetite in men and women

When previously sedentary men and women follow exercise training programs with ad libitum feeding, men lose body fat, but women do not. The purpose of this study was to evaluate whether this observation could be related to sex differences in the way energy-regulating hormones and appetite perception respond to exercise. Eighteen (9 men, 9 women) overweight/obese individuals completed four bouts of exercise with energy added to the baseline diet to maintain energy balance (BAL), and four bouts without energy added to induce energy deficit (DEF). Concentrations of acylated ghrelin, insulin, and leptin, as well as appetite ratings were measured in response to a meal after a no-exercise baseline and both exercise conditions. In men, acylated ghrelin area under the curve (AUC) was not different between conditions. In women, acylated ghrelin AUC was higher after DEF (+32%) and BAL (+25%), and the change from baseline was higher than men (P < 0.05). In men, insulin AUC was reduced (-17%) after DEF (P < 0.05), but not BAL. In women, insulin AUC was lower (P < 0.05) after DEF (-28%) and BAL (-15%). Leptin concentrations were not different across conditions in either sex. In men, but not in women, appetite was inhibited after BAL relative to DEF. The results indicate that, in women, exercise altered energy-regulating hormones in a direction expected to stimulate energy intake, regardless of energy status. In men, the response to exercise was abolished when energy balance was maintained. The data are consistent with the paradigm that mechanisms to maintain body fat are more effective in women.

Effect of timing of energy and carbohydrate replacement on post-exercise insulin action

The nutritional environment surrounding an exercise bout modulates post-exercise insulin action. The purpose of this study was to determine how timing energy and carbohydrate replacement proximate to an exercise bout influences exercise-enhanced insulin action. To create an appropriate baseline, sensitivity to insulin was reduced in 9 healthy young men (n=6) and women (n=3) by 2 days of energy surplus and detraining. Then, insulin action (glucose uptake per unit plasma insulin) was assessed by stable isotope dilution during a continuous glucose infusion 12 h after a standardized meal under 4 conditions. In 3 conditions, the meal replaced the energy and carbohydrate expended during an exercise bout (62.9+/-2.8 min cycle ergometry at 65% VO2 peak followed by ten 30 s sprints). The meal was given before (Pre), immediately after (ImmPost), or 3 h after exercise (Delay). The 4th condition was a no-exercise control (Control). Data were analyzed using linear mixed-effects models with planned contrasts. Relative to Control, insulin action increased by 22% in Pre (p=0.05), 44% in ImmPost (p<0.01), and 19% in Delay (p=0.09). Non-oxidative disposal was higher, and oxidative disposal was lower in ImmPost relative to Control and Pre (p<0.05). Hepatic glucose production was suppressed by the infusion to a greater extent in Pre and Delay (76.9%+/-8.8% and 81.2%+/-4.7%) compared with ImmPost (64.7%+/-10.0%). A bout of exercise enhances insulin action even when expended energy and carbohydrate are replaced. Further, timing of energy and carbohydrate consumption subtly modulates the effectiveness of exercise to enhance insulin action.

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

Energy surplus raises circulating concentrations of leptin and insulin while lowering plasma ghrelin. Exercise has the opposite effects. The purpose of this study was to determine whether exercise counters the hormonal effects of energy surplus independent of changes in energy balance. To do that, we assessed plasma concentrations of leptin, insulin, and ghrelin at baseline, after overfeeding, and after overfeeding plus exercise. Baseline (B) leptin and insulin concentrations and ghrelin area under the curve were measured during an oral glucose challenge in 9 healthy, active subjects (6 male, 3 female) after 2 days in energy balance without exercise. Measurements were repeated after subjects were overfed by +3213 +/- 849 kJ/d for 3 more sedentary days (OF). In the third condition, the same net energy surplus (+3125 +/- 933 kJ/d) was generated for 24 hours by doubling the overfeeding (+6284 +/- 1669 kJ/d) and countering it with a bout of exercise (expenditure = 3063 +/- 803 kJ); and measurements were made the next day (OF + EX). Compared with B, leptin went up (5.8 +/- 8.2 to 7.6 +/- 10.6 ng/mL) after OF, but was not significantly higher after OF + EX (7.1 +/- 10.2 ng/mL). Compared with B, insulin was +36% and +43% higher after OF and OF + EX, respectively. In contrast, ghrelin area under the curve did not change after OF but was significantly lower (-14%) than B or OF after OF + EX (indicating greater suppression). These data suggest that the effect of short-term exercise on fasting leptin and insulin depends on energy balance but the ghrelin response may be partially mediated by effects of exercise independent of energy balance.

Short-term aerobic exercise training in obese humans with type 2 diabetes mellitus improves whole-body insulin sensitivity through gains in peripheral, not hepatic insulin sensitivity

CONTEXT

Short-term aerobic exercise training can improve whole-body insulin sensitivity in humans with type 2 diabetes mellitus; however, the contributions of peripheral and hepatic tissues to these improvements are not known.

OBJECTIVE

Our objective was to determine the effect of 7-d aerobic exercise training on peripheral and hepatic insulin sensitivity during isoglycemic/hyperinsulinemic clamp conditions.

DESIGN

Subjects were randomly assigned to one of two groups. The energy balance group consumed an isocaloric diet consisting of 50% carbohydrate, 30% fat, and 20% protein for 15 d. The energy balance plus exercise group consumed a similar diet over the 15 d and performed 50-min of treadmill walking at 70% of maximum oxygen consumption maximum during the second 7 d of the 15-d study period. Each subject underwent an initial isoglycemic/hyperinsulinemic clamp after 1-wk dietary control and a second clamp after completing the study.

SETTING

The study was performed at Ohio State University's General Clinical Research Center.

PARTICIPANTS

There were 18 obese, mildly diabetic humans included in the study.

INTERVENTION

Aerobic exercise training was performed for 7 d.

MAIN OUTCOME MEASURES

Whole-body, peripheral, and hepatic insulin sensitivity were measured.

RESULTS

Exercise training did not have an impact on peripheral glucose uptake or endogenous glucose production during the basal state or low-dose insulin. Likewise, it did not alter endogenous glucose production during high-dose insulin. However, 1-wk of exercise training increased both whole-body (P<0.05) and peripheral insulin sensitivity (P<0.0001) during high-dose insulin.

CONCLUSION

Improvements to whole body insulin sensitivity after short-term aerobic exercise training are due to gains in peripheral, not heptic insulin sensitivity.

High and low BMI increase the risk of miscarriage after IVF/ICSI and FET

BACKGROUND

The extremes of BMI are associated with an increased risk of miscarriage both in spontaneously conceived pregnancies and after fertility treatment. The aim of the present study was to study the effect of BMI on miscarriage rate (MR) in fresh IVF/ICSI, and in spontaneous and hormonally substituted frozen-thawed embryo (FET) cycles.

METHODS

Analysis was carried out on 3330 first pregnancy cycles, performed during the years 1999-2004, of which 2198 were fresh, 666 were spontaneous and 466 were hormonally substituted FET cycles. A categorical, a linear and a quadratic models of the effect of BMI on miscarriage were studied by logistic regression. Factors related to patient characteristics, protocol and embryo parameters were also examined.

RESULTS

MR was higher in hormonally substituted FET (23.0%), compared with the fresh cycles (13.8%) and spontaneous FET (11.4%, P < 0.0001). Multivariate logistic regression revealed that the relationship between BMI and the risk of miscarriage is not linear but quadratic (U-shaped) (P = 0.01), indicating a higher risk of miscarriage in underweight and obese women. Hormonal substitution for FET was also associated with a 1.7-fold higher MR, compared with the fresh cycles (P = 0.002, 95% confidence interval 1.2-2.3).

CONCLUSIONS

Obese and underweight women have an increased risk of miscarriage, and hormonally substituted FET is associated with an even higher MR.

A single bout of brisk walking increases basal very low-density lipoprotein triacylglycerol clearance in young men

Very low-density lipoprotein triacylglycerol (VLDL-TG) turnover rate was evaluated in the morning, 12 hours after a single bout of brisk walking (90 minutes at approximately 60% of VO2max; EXE), compared to a resting control period (CON) in 10 recreationally active men. VLDL-TG fractional catabolic rate was calculated from the decay in isotopic enrichment after a bolus injection of [2H5]glycerol. Plasma VLDL-TG concentration was 24% lower in the morning after the EXE trial compared to control (0.47+/-0.04 and 0.36+/-0.04 mmol L(-1), for CON and EXE, respectively; P<.01). Serum insulin (7.4+/-0.7 and 5.6+/-0.4 mIU L(-1), CON and EXE, respectively; P<.05) and plasma glucose (5.6+/-0.1 and 5.4+/-0.1 mmol/L, CON and EXE, respectively; P<.05) concentrations were also significantly lower in the EXE trial. Insulin sensitivity (homeostasis model assessment [HOMA] index) was improved by 27% in EXE compared with the CON trial (P<.05).VLDL-apolipoprotein B-100 and plasma fatty acid concentrations were similar in the two trials. Hepatic VLDL-TG secretion rates were not significantly affected by exercise (13.1+/-1.2 and 13.2+/-1.6 micromol.min(-1) for the CON and EXE trials, respectively), whereas VLDL-TG clearance rate increased by 36% (28.1+/-1.3 and 38.1+/-3.5 mL.min(-1) for the CON and EXE trials, respectively; P<.05). It is concluded that the decrease in fasting plasma VLDL-TG concentration observed 12 hours after brisk walking is related mainly to increased VLDL-TG clearance from plasma.

Effects of acute exercise and training on insulin action and sensitivity: focus on molecular mechanisms in muscle

A single bout of exercise increases insulin sensitivity for several hours and the effect is mainly restricted to the muscles recruited during exercise. When exercise is repeated over time, adaptations to physical training occur that include more long-lasting increases in insulin sensitivity. The present review explores the molecular mechanisms involved in both the acute and chronic effects of exercise on insulin sensitivity in skeletal muscle.

Interactions between energy surplus and short-term exercise on glucose and insulin responses in healthy people with induced, mild insulin insensitivity

Short-term exercise can enhance insulin action, but the effect may be negated by the opposing action of energy surplus. The purpose of this investigation was to test the hypothesis that a single exercise bout would increase insulin action, even when opposed by a concurrent energy surplus. After 2 days in energy balance without exercise, baseline glucose and insulin areas under the curve and the insulin sensitivity index (C-ISI) were measured during an oral glucose tolerance test in 9 healthy, habitually active subjects (6 males, 3 females). A state of relative insulin insensitivity was then induced by systematic overfeeding (OF) to generate a daily energy surplus of 768 +/- 203 kcal/d for 3 days, and the oral glucose tolerance test was repeated. In the following 24 hours, the OF was increased approximately 2-fold (+6284 +/- 1669 kJ/d) and subjects performed a single bout of exercise (expenditure = 3063 +/- 803 kJ) to maintain the same energy surplus (+3125 +/- 933 kJ/d; OF and exercise) as OF. After OF, fasting insulin tended to be higher (+36%, P = .099), insulin AUC rose by 38% (P = .002), and C-ISI declined from 6.6 +/- 3.1 to 4.6 +/- 1.8 (P = .007) compared with baseline. After OF and exercise, fasting insulin remained elevated (+43% compared with baseline; P = .043) and C-ISI rose only slightly (4.6 +/- 1.8 to 5.2 +/- 2.3; P = .058), but insulin AUC declined by 20% (P = .048) compared with OF. A single exercise bout, opposed by a concurrent energy surplus, decreased the insulin response to a glucose challenge, but only partially restored the insulin AUC to baseline and had no impact on C-ISI or fasting insulin concentrations.