Impact of exercise-nutritional state interactions in patients with type 2 diabetes

Introduction This study examines the role of nutritional status during exercise training in patients with type 2 diabetes mellitus by investigating the effect of endurance-type exercise training in the fasted versus the fed state on clinical outcome measures, glycemic control, and skeletal muscle characteristics in male type 2 diabetes patients. Methods Twenty-five male patients (glycated hemoglobin (HbA1c), 57 ± 3 mmol·mol−1 (7.4% ± 0.3%)) participated in a randomized 12-wk supervised endurance-type exercise intervention, with exercise being performed in an overnight-fasted state (n = 13) or after consuming breakfast (n = 12). Patients were evaluated for glycemic control, blood lipid profiles, body composition and physical fitness, and skeletal muscle gene expression. Results Exercise training was well tolerated without any incident of hypoglycemia. Exercise training significantly decreased whole-body fat mass (−1.6 kg) and increased high-density lipoprotein concentrations (+2 mg·dL−1), physical fitness (+1.7 mL·min−1·kg−1), and fat oxidation during exercise in both groups (PTIME 0.05). HbA1c concentrations significantly decreased after exercise training (PTIME < 0.001), with a significant greater reduction after consuming breakfast (−0.30% ± 0.06%) compared with fasted state (−0.08% ± 0.06%; mean difference, 0.21%; PTIME × GROUP = 0.016). No interaction effects were observed for skeletal muscle genes related to lipid metabolism or oxidative capacity. Conclusions Endurance-type exercise training in the fasted or fed state do not differ in their efficacy to reduce fat mass, increase fat oxidation capacity, and increase cardiorespiratory fitness and high-density lipoprotein concentrations or their risk of hypoglycemia in male patients with type 2 diabetes. HbA1c seems to be improved more with exercise performed in the postprandial compared with the postabsorptive state

Effect of manipulations in exercise and breakfast on metabolism in overweight and non-overweight children and adolescents

Obesity and insulin resistance are serious health concerns in children and adolescents (young people). Interventions to increase the potential for fat oxidation and improve insulin sensitivity could have widespread clinical relevance. Although exercise is often advocated for health, the factors implicated in the relationship between exercise, fat oxidation and insulin resistance are not well understood in young people. This thesis has investigated the effect of manipulations in exercise and breakfast on metabolism in young people, focusing on fat oxidation and postprandial blood glucose control. The first experimental study, Chapter 4, compared two different exercise protocols for estimating the intensity corresponding to maximal fat oxidation (Fatmax) in non-overweight prepubertal children. A 3 min incremental protocol was recommended to provide an estimation of Fatmax using a wide range of intensities in this population. Using this protocol, Chapter 5 demonstrated that Fatmax was higher for treadmill compared with cycling exercise in pre- to early pubertal children. Furthermore, treadmill exercise resulted in higher rates of fat oxidation over a range of absolute and relative intensities and fat oxidation remained high over a wider range of intensities. Therefore, treadmill exercise (walking or slow running) is clearly preferential for promoting fat oxidation in this population. Subsequently, Chapter 6 examined the effect of mixed breakfast meals containing high (HGI) and low (LGI) glycaemic index carbohydrates on blood glucose, plasma insulin and fat oxidation in overweight and non-overweight girls. Breakfast GI did not affect fat oxidation during the postprandial rest period or subsequent exercise. However, the main finding of this study related to blood glucose; the higher blood glucose response following the HGI compared with LGI breakfast was more pronounced in the overweight girls. This suggested a reduced ability to cope with the metabolic demands of HGI breakfast consumption in overweight girls and highlighted that strategies to reduce insulin resistance in this population are required. Consequently, Chapter 7 investigated the effect of treadmill exercise at Fatmax performed 16 h prior to HGI breakfast consumption on blood glucose, plasma insulin and fat oxidation in overweight and non-overweight girls. Fatmax exercise reduced the postprandial insulin response in the non-overweight, but not the overweight, girls while blood glucose was unchanged in both groups. More encouragingly, fat oxidation was increased after exercise in both the overweight and non-overweight girls. Collectively, the four experimental studies within this thesis have demonstrated that treadmill exercise at Fatmax is an effective means of elevating fat oxidation both during and up to 16 h after exercise. When considering postprandial glucose and insulin responses to HGI breakfast consumption, LGI breakfasts should be recommended for overweight girls, whilst acute treadmill exercise at Fatmax can reduce postprandial insulin concentrations in non-overweight girls. Walking or slow running (Fatmax treadmill exercise) and LGI breakfast consumption may be best advocated in combination for promoting fat oxidation and improving postprandial blood glucose control in young people. These two simple lifestyle-related strategies may provide an effective, safe and attractive means for preventing and treating obesity, insulin resistance and related disorders. Key words: exercise, metabolism, substrate oxidation, fat oxidation, glucose, insulin, glycaemic index, overweight, children, adolescents

Update on the effects of physical activity on insulin sensitivity in humans.

PURPOSE AND METHODS: This review presents established knowledge on the effects of physical activity (PA) on whole-body insulin sensitivity (SI) and summarises the findings of recent (2013-2016) studies. DISCUSSION AND CONCLUSIONS: Recent studies provide further evidence to support the notion that regular PA reduces the risk of insulin resistance, metabolic syndrome and type 2 diabetes, and SI improves when individuals comply with exercise and/or PA guidelines. Many studies indicate a dose response, with higher energy expenditures and higher exercise intensities, including high intensity interval training (HIIT), producing greater benefits on whole-body SI, although these findings are not unanimous. Aerobic exercise interventions can improve SI without an associated increase in cardiorespiratory fitness as measured by maximal or peak oxygen consumption. Both aerobic and resistance exercise can induce improvements in glycaemic regulation, with some suggestions that exercise regimens including both may be more efficacious than either exercise mode alone. Some studies report exercise-induced benefits to SI that are independent of habitual diet and weight loss, while others indicate an association with fat reduction, hence the debate over the relative importance of PA and weight loss continues. During exercise, muscle contraction stimulated improvements in SI are associated with increases in AMPK activity, which deactivates TCB1D1, promoting GLUT4 translocation to the cell membrane and thereby increasing glucose uptake. Postexercise, increases in Akt deactivate TCB1D4 and thereby increase GLUT4 translocation to the cell membrane. The reduction in intramuscular saturated fatty acids and concomitant reductions in ceramides, but not diacylglycerols, provide a potential link between intramuscular lipid content and SI. Increased skeletal muscle capillarisation provides another independent adaptation through which SI is improved, as does enhanced β cell activity. Recent studies are combining exercise interventions with dietary and feeding manipulations to investigate the potential for augmenting the exercise-induced improvements in SI and glycaemic control

The effect of run sprint interval training on diabetic metabolic markers in prediabetic adults

Abstract Purpose: The primary purpose of this study was to compare the effects of an 8-week run-sprint interval training (R-SIT) and continuous moderate-intensity training (MIT) on fasting blood glucose, HbA1c, insulin sensitivity, and β-cell function in sedentary, prediabetic adults. Secondary outcomes of the study included anthropometric, body composition variables, and aerobic capacity. Methods: Sedentary, physician diagnosed prediabetic individuals were randomized into R-SIT (n=7, BMI 36.76 ± 9.79) or MIT (n=8, BMI 40.59 ± 12.49) interventions. Subjects participated in supervised exercise three times a week and attended a Diabetes Prevention Program course, once weekly. R-SIT participants performed 4-6 x 30-second “all-out” treadmill sprints, interspersed with a 4-minute active recovery at 2-2.5 mph. MIT participants performed 30-40 minutes of continuous moderate-intensity exercise at 45-55% HRR. Analysis of fasting blood glucose, HbA1c, and fasting insulin were obtained at baseline and 8-weeks. Insulin sensitivity (%) and β-cell function (%) were assessed via HOMA2-IR. Body composition, assessed via dual x-ray absorptiometry, and aerobic capacity assessed during a treadmill ramp protocol, were also obtained before and after 8-weeks of training. Results: Across groups, HbA1c improved across time (p = 0. 042). There were no significant changes in fasting blood glucose, insulin sensitivity, or β-cell function in either group. Relative VO2max significantly improved in the R-SIT participants (+1.63 ± 1.75mL*kg-1*min-1), whereas no change in relative VO2max occurred in the MIT participants. Significant differences in body composition following 8-weeks of exercise occurred only in the MIT group, as measured by body weight (-9.35 ± 6.21 lb.), BMI (-1.21 ± 1.07 kg/m2), BF% (-2.02 ± 1.88%), and LM% (+2.05 ± 1.84%). Conclusion: Eight weeks of exercise improved HbA1c in prediabetic participants. Although no other improvements in glycemic control were demonstrated in either group, R-SIT participants demonstrated improvements in aerobic capacity, despite exercising at maximal intensities for only two to three minutes per session. In contrast, body composition significantly improved in the MIT group only. These findings suggest that 8-weeks of R-SIT training may be an effective strategy for improving cardiorespiratory fitness levels in overweight and obese prediabetic individuals, but is not effective in improving body composition

Effects of running sprint interval training versus traditional endurance exercise on metabolic indices in sedentary, overweight and obese women

Evidence suggests that sprint interval training (SIT) is a time efficient alternative for improving aerobic fitness or insulin sensitivity due to its reduced training volume and is of increasing interest since most sedentary individuals indicate lack of time as their number one barrier to being physically active. However, most SIT research uses cycling exercise performed with healthy active males, and limited research examines its effects on women or individuals at higher risk for inactivity related diseases, as well as different modes of exercise. PURPOSE: To evaluate the effects of running SIT (R-SIT) versus moderate intensity endurance training (MIET) on aerobic capacity, resting HR, BP, body composition, blood lipids, and glucose in sedentary, overweight/obese women. METHODS: Twelve sedentary, overweight/obese women (30.7±7.4kg/m2, 33.6±5.8y, 27.9±6.5ml/kg/min) were randomly divided into two 12-week training protocols, each for 3 days per week. The R-SIT group (n=5) completed 4-10 bouts of 30s “all out” sprints on a motorized treadmill at a 3-5% incline with 4 min active recovery. The MIET group (n=7) completed 30-60 min of moderate intensity (45-55% HRR) walking on a treadmill at a 3-5% incline. RESULTS: VO2max significantly improved 19.7% with R-SIT (mean ± SD; 29.59±7.3 to 35.57±10.4 ml/kg/min) and 38.6% with MIET (26.74±35.29±6.6 ml/kg/min) pre to post (p0.05). CONCLUSION: Despite the reduced time commitment, R-SIT elicits similar improvements in aerobic fitness and was more effective at improving body composition than MIET in sedentary, overweight/obese women. Additionally, there is suggestive evidence that R-SIT may induce greater improvements in fat mass, triglycerides, and HbA1c measures. This study provides practical application for the implementation of R-SIT to reduce risk factors associated with cardiovascular disease in sedentary, overweight/obese population. More research is necessary to determine the extent of these reductions. x

An Examination of Light Intensity Physical Activity and Health in Older Adults

Research has begun to quickly emerge on the potential benefit of light intensity physical activity (LPA) to the health of adults. Little is known about LPA, and much of the current LPA research stems from sedentary behavior research. The purpose of this dissertation was to more fully understand, describe, and characterize potential health benefits of LPA by determining the prevalence, patterns, and health benefits of light intensity physical activity in older adults. Three individual studies were completed to address each portion of this purpose. Study 1: Light Intensity Physical Activity and Health in Adults: A Systematic Review. The purpose of this study was to critically examine the current literature pertaining to LPA and whether research supported a benefit or lack of benefit to adults. Upon search, five health categories emerged and were examined: 1) all cause mortality, 2) metabolic health, 3) cardiovascular health, 4) cancer risk, and 5) functional health. Overall findings suggested there may be benefit to incorporating LPA within the day in order to decrease risk of all-cause mortality, decrease insulin resistance, c-reactive protein, glucose, insulin, metabolic syndrome, physical function, and increase cognition. The results from this review suggested adults who were inactive, had been diagnosed with a chronic disease, or those who were older, showed a greater benefit to engaging in LPA than those who were healthy and physically active. Study 2: Contextual Analysis of Physical Activity. The second study was an observational study to describe the patterns and context of LPA in older adults by measuring their physical activity over seven days and the context of their LPA was recorded on one day for a simultaneous measurement. Our results suggested older adults engaged in over 250 min per day of LPA, in mostly short, frequent bouts (~2.5 min each bout). LPA was performed for a consistent 15-25 min each hour from 7am until 7pm. When activity domain was examined, over half of the activity occurred during participants’ leisure time. Popular specific activities included leisure-time activities such as multi-tasking while watching television or on the computer, shopping, and household activities such as cooking and cleaning. Contextual measurement revealed the LPA was more commonly performed inside when the participant was by themselves, as opposed to with a group. Understanding what LPA activities are already prevalent and specific to older adults, the social support necessary to elicit the behavior, and the location these activities most commonly occur to help identify potential barriers to the activity prescription (weather, transportation, resources, etc.). Study 3: Dose response to LPA and glucose dynamics in older adults. The purpose of this study was to determine whether there was a dose-response relationship between the total amount of time spent in LPA and post-prandial glucose response in older adults. Results from these trials showed there was a significant decrease in glucose area under the curve 3-hours post-meal when 40% of the measured time was spent in LPA. This effect was further compounded when time spent in LPA was increased to 60% of the measurement period. This study was one of the first with an explicit focus on LPA and provides evidence there is a metabolic health benefit to engaging in LPA, that can further increase in benefit with increasing time spent in lower intensity activities. Overall Conclusion. Together these studies provide evidence that LPA may be a feasible physical activity selection for older adults and these active behaviors, even at low intensities, may be health enhancing. Study 1 provides a solid foundation to understand what we already know by what has been published in the literature, Study 3 answered the question of whether or not LPA would provide a sufficient stimulus to alter glucose uptake and further still whether that response would be dose-dependent, and Study 2 results will assist health and fitness professionals and researchers in designing and developing appropriate LPA prescriptions. As our results directed, activity data from objectively measured LPA showed LPA activities, therefore prescription development, are not synonymous with moderate and vigorous activities and therefore should be considered individually. These outcomes provide an important, positive impact on population health by providing evidence for older adults to be physically active through a potentially more attainable approach in order to gain health benefits

Advancing the Use of Exercise Testing as a Tool to Assess Whole-Body Substrate Selectivity and Metabolic Function in Individuals at Risk for Developing Type 2 Diabetes

Type 2 diabetes is a metabolic disease marked by an abnormally high level of glucose (sugar) in the blood. Type 2 diabetes is now reaching an epidemic level with more than 30 million adults in the United States afflicted and 1.5 million new cases documented every year. Type 2 diabetes is linked with obesity, heart disease, hypertension, and liver disease, and individuals with type 2 diabetes are at an increased risk for heart failure, stroke, blindness, kidney failure, and amputation. According to the Centers for Disease Control and Prevention, more than $245 billion was spent in the United States in 2012 on medical expenses related to diabetes and despite that, nearly a quarter of a million Americans are losing their lives due to this disease each year. Indeed, type 2 diabetes is one of the leading causes of death in the United States and worldwide; its prevalence has almost doubled in the last 35 years, from 4.7% of the total population in 1980 to 8.5% in 2014. Consequently, more than 400 million people are at high risk for severe health problems and complications, poor quality of life, and early death. Research such as the Diabetes Prevention Program (DPP), the Finnish Diabetes Prevention Study (DPS), the Vesterbotten Intervention Program (VIP), and the Diabetes Prevention Program Outcome Study (DPPOS) suggests that type 2 diabetes can be delayed, and even prevented, with a lifestyle behavioral modification program that includes healthy eating and/or exercise. Therefore, focus has been shifted from management to prevention. An early manifestation of dysfunction in the progression of type 2 diabetes is insulin resistance, a metabolic impairment associated with obesity. Indeed, it is estimated that ~90% of people with type 2 diabetes also are obese. The link between insulin resistance and obesity is well-established; however, the mechanistic basis(es) underpinning this link is/are still debated with multiple candidate molecules, systems, and pathways potentially involved. One theory that has gained traction in recent years suggests that type 2 diabetes, and the insulin-resistant state that predates it, are rooted in dysfunctional lipid metabolism (i.e., a reduced capacity to use lipid for energy production in circumstances where lipid would be preferred, such as in the basal fasting condition, after a high-fat meal, and during light- and moderate-intensity exercise). However, there are conflicting findings regarding the degree to which the ability to oxidize lipid during these circumstances is compromised for individuals with the overweight/obesity that is associated with the disease progression. The reason(s) for this ambiguity is/are unclear but might have to do with a number of factors that were poorly controlled when substrate selectivity (i.e., lipid vs. carbohydrate oxidation rates) were compared between normal-weight individuals and those with the overweight/obese condition. These include: (a) acute energy balance and macronutrient composition of the diet; (b) the intensity and duration of the exercise bout; and (c) subject characteristics including the amount of muscle tissue they possess, their cardiorespiratory fitness level, and, perhaps most importantly, their insulin-sensitivity state. The purpose of this dissertational work is to: (a) help to resolve this ambiguity by identifying the degree to which conflicting results that have been reported might be explained by factors that were left unaccounted for and/or inadequately controlled in previous research; and (b) compare substrate selectivity in normal-weight individuals and those with the overweight/obesity condition during a physiologically-equivalent exercise challenge with the aforementioned factors rigidly controlled