Feeding Tolerance, Glucose Availability, and Whole-Body Total Carbohydrate and Fat Oxidation in Male Endurance and Ultra-Endurance Runners in Response to Prolonged Exercise, Consuming a Habitual Mixed Macronutrient Diet and Carbohydrate Feeding During Exercise

Using metadata from previously published research, this investigation sought to explore: (1) whole-body total carbohydrate and fat oxidation rates of endurance (e.g., half and full marathon) and ultra-endurance runners during an incremental exercise test to volitional exhaustion and steady-state exercise while consuming a mixed macronutrient diet and consuming carbohydrate during steady-state running and (2) feeding tolerance and glucose availability while consuming different carbohydrate regimes during steady-state running. Competitively trained male endurance and ultra-endurance runners (n = 28) consuming a balanced macronutrient diet (57 ± 6% carbohydrate, 21 ± 16% protein, and 22 ± 9% fat) performed an incremental exercise test to exhaustion and one of three 3 h steady-state running protocols involving a carbohydrate feeding regime (76–90 g/h). Indirect calorimetry was used to determine maximum fat oxidation (MFO) in the incremental exercise and carbohydrate and fat oxidation rates during steady-state running. Gastrointestinal symptoms (GIS), breath hydrogen (H2), and blood glucose responses were measured throughout the steady-state running protocols. Despite high variability between participants, high rates of MFO [mean (range): 0.66 (0.22–1.89) g/min], Fatmax [63 (40–94) % V̇O2max], and Fatmin [94 (77–100) % V̇O2max] were observed in the majority of participants in response to the incremental exercise test to volitional exhaustion. Whole-body total fat oxidation rate was 0.8 ± 0.3 g/min at the end of steady-state exercise, with 43% of participants presenting rates of ≥1.0 g/min, despite the state of hyperglycemia above resting homeostatic range [mean (95%CI): 6.9 (6.7–7.2) mmol/L]. In response to the carbohydrate feeding interventions of 90 g/h 2:1 glucose–fructose formulation, 38% of participants showed breath H2 responses indicative of carbohydrate malabsorption. Greater gastrointestinal symptom severity and feeding intolerance was observed with higher carbohydrate intakes (90 vs. 76 g/h) during steady-state exercise and was greatest when high exercise intensity was performed (i.e., performance test). Endurance and ultra-endurance runners can attain relatively high rates of whole-body fat oxidation during exercise in a post-prandial state and with carbohydrate provisions during exercise, despite consuming a mixed macronutrient diet. Higher carbohydrate intake during exercise may lead to greater gastrointestinal symptom severity and feeding intolerance.

Does isolated and combined acute supplementation of caffeine and carbohydrate feeding strategies modify 10-km running performance and pacing strategy? A randomized, crossover, double-blind, and placebo-controlled study

Background: Long distance practice running are growing and nutritional ergogenic are commonly used as a potential aid in final training and competition performance. Caffeine (CAF) and carbohydrates (CHO) are among the most commonly used supplements due to their expected ergogenic properties that can optimize energetic systems. The objective of this study was to examine potential changes in 10-km running performance with acute isolated and combined CAF and CHO supplementation. Material and method: Fifteen recreational endurance-trained runners performed four 10-km running performance on an official athletic track (400 m) under four supplementation conditions: placebo and placebo (PLA+PLA), placebo and caffeine (PLA+CAF), placebo and carbohydrates (PLA+CHO), caffeine and carbohydrates (CAF+CHO). CAF and CHO supplementation consisted of capsules of 6 mg·kg-1 and 8% CHO solution (1 g·kg-1) respectively, ingested 60 and 30 minutes before the performance tests. Placebo was obtained through empty capsules for CAF and juice for CHO without sugar (Clight®). During each trial running speed to calculate 10-km mean velocity (MV) and maximum heart rate (HRmax) were analyzed. Results: There was a difference in the pacing strategy adopted by the runners with higher MV during the initial phase for PLA+CAF and CAF+CHO groups and in the final phase for PLA+ CHO. However, there was no statistically significant difference in 10-km running performance between the conditions, as well as for HRmax. Conclusions: The use of acute, isolated and combined CAF+CHO supplementation had influence in the pacing strategy, but no in 10- km final performance, of recreational runners.

Effects of aging, phenotype and carbohydrate feeding on caloric efficiency and adiposity in the LA/Ntul//-cp (corpulent) rat

Obesity develops in the obese phenotype of the LA/Ntul//-cp (corpulent) specific pathogen-free rat strain by 5 to 6 weeks of age. Groups [n=12 -20 rats/phenotype] of female congenic lean and obese LA/Ntul//-cp (corpulent) rats were fed ad libitum standardized Purina diets for 4, 14, or 24 months or the same diet plus a 16% (w/v) sucrose solution supplement from 12 weeks of age, and measures of body weight, caloric intake, and caloric efficiency (CE) determined at each age group. Body weights of lean animals remained similar at all ages studied, while body weights of obese phenotype were significantly greater than their lean littermates at each age studied. The sucrose supplement was without significant effect on final body weights in the lean phenotypes at all ages studied (p=n.s.) but were associated with greater body weights at ages 4, 14 and 24 months of age in the obese phenotype (p=<0.05). CE was determined as the ratio of kcal/gram of body weight per day remained relatively constant in lean animals throughout the age range, but CE was more efficient in the obese phenotype at all ages studied and became progressively more efficient with the sucrose supplement feeding with increasing age. The results of this study indicate that CE is associated with the predisposition for the development of obesity in the obese phenotype of this strain and likely implicates multiple metabolic factors that contribute to a greater efficiency of energy utilization and or energy conservation in the obese than in the lean phenotype of this strain, and the metabolic impact of added sucrose was associated with an additive impact on the CE of weight gain and adiposity in the obese phenotype of this congenic rodent strain

Carbohydrate Requirements for Prolonged, Fasted Exercise with and without Basal Rate Reductions in Adults with Type 1 Diabetes on Continuous Subcutaneous Insulin Infusion (CSII)

<b>Objective:</b> Exercising while fasted in type 1 diabetes facilitates weight loss, however the best strategy to maintain glucose stability remains unclear. <p><b>Research Design and Methods:</b> Fifteen adults on CSII completed three sessions of fasted walking (120min at 45%VO_2peak) in a randomized crossover design: 50% basal rate reduction set 90min pre-exercise (-90_min50%_BRR); usual basal rate with carbohydrate intake (0.3g/kg/hr; CHO-only); and combined 50%basal rate reduction set at exercise onset with carbohydrate (0.3g/kg/hr; Combo). </p> <p><b>Results:</b> Combo had a smaller change in glucose (5±47mg/dL) vs CHO-only (-49±61mg/dL, <i>P</i>=0.03) or -90_min50%_BRR (-34±45mg/dL). -90_min50%_BRR produced higher b-hydroxybutyrate levels (0.4±0.3 vs 0.1±0.1mmol/L) and greater fat oxidation (0.51±0.2 vs 0.39±0.1g/min) than CHO-only (both <i>P</i><0.05).</p> <b>Conclusions:</b> All strategies examined produced stable glycemia for fasted exercise, but a 50%basal rate reduction set 90 min pre-exercise eliminates carbohydrate needs and enhances fat oxidation better than carbohydrate feeding with or without a basal rate reduction set at exercise onset.

Carbohydrate Requirements for Prolonged, Fasted Exercise with and without Basal Rate Reductions in Adults with Type 1 Diabetes on Continuous Subcutaneous Insulin Infusion (CSII)

<b>Objective:</b> Exercising while fasted in type 1 diabetes facilitates weight loss, however the best strategy to maintain glucose stability remains unclear. <p><b>Research Design and Methods:</b> Fifteen adults on CSII completed three sessions of fasted walking (120min at 45%VO_2peak) in a randomized crossover design: 50% basal rate reduction set 90min pre-exercise (-90_min50%_BRR); usual basal rate with carbohydrate intake (0.3g/kg/hr; CHO-only); and combined 50%basal rate reduction set at exercise onset with carbohydrate (0.3g/kg/hr; Combo). </p> <p><b>Results:</b> Combo had a smaller change in glucose (5±47mg/dL) vs CHO-only (-49±61mg/dL, <i>P</i>=0.03) or -90_min50%_BRR (-34±45mg/dL). -90_min50%_BRR produced higher b-hydroxybutyrate levels (0.4±0.3 vs 0.1±0.1mmol/L) and greater fat oxidation (0.51±0.2 vs 0.39±0.1g/min) than CHO-only (both <i>P</i><0.05).</p> <b>Conclusions:</b> All strategies examined produced stable glycemia for fasted exercise, but a 50%basal rate reduction set 90 min pre-exercise eliminates carbohydrate needs and enhances fat oxidation better than carbohydrate feeding with or without a basal rate reduction set at exercise onset.

The Development of an Exercise Advisor App for Type 1 Diabetes: Digitization Facilitates More Individualized Guidance

Maintaining blood glucose levels in the target range during exercise can be onerous for people with type 1 diabetes (T1D). Using evidence-based research and consensus guidelines, we developed an exercise advisor app to reduce some of the burden associated with diabetes management during exercise. The app will guide the user on carbohydrate feeding strategies and insulin management strategies before, during, and after exercise and provide targeted and individualized recommendations. As a basis for the recommendations, the decision trees for the app use various factors including the type of insulin regimen, time of activity, previous insulin boluses, and current glucose level. The app is designed to meet the various needs of people with T1D for different activities to promote safe exercise practices.

Islet Health, Hormone Secretion, and Insulin Responsivity with Low-Carbohydrate Feeding in Diabetes

Exploring new avenues to control daily fluctuations in glycemia has been a central theme for diabetes research since the Diabetes Control and Complications Trial (DCCT). Carbohydrate restriction has re-emerged as a means to control type 2 diabetes mellitus (T2DM), becoming increasingly popular and supported by national diabetes associations in Canada, Australia, the USA, and Europe. This approval comes from many positive outcomes on HbA1c in human studies; yet mechanisms underlying their success have not been fully elucidated. In this review, we discuss the preclinical and clinical studies investigating the role of carbohydrate restriction and physiological elevations in ketone bodies directly on pancreatic islet health, islet hormone secretion, and insulin sensitivity. Included studies have clearly outlined diet compositions, including a diet with 30% or less of calories from carbohydrates.

Dietary α-Linolenic Acid Counters Cardioprotective Dysfunction in Diabetic Mice: Unconventional PUFA Protection

Whether dietary omega-3 (n-3) polyunsaturated fatty acid (PUFA) confers cardiac benefit in cardiometabolic disorders is unclear. We test whether dietary α-linolenic acid (ALA) enhances myocardial resistance to ischemia-reperfusion (I-R) and responses to ischemic preconditioning (IPC) in type 2 diabetes (T2D); and involvement of conventional PUFA-dependent mechanisms (caveolins/cavins, kinase signaling, mitochondrial function, and inflammation). Eight-week male C57Bl/6 mice received streptozotocin (75 mg/kg) and 21 weeks high-fat/high-carbohydrate feeding. Half received ALA over six weeks. Responses to I-R/IPC were assessed in perfused hearts. Localization and expression of caveolins/cavins, protein kinase B (AKT), and glycogen synthase kinase-3β (GSK3β); mitochondrial function; and inflammatory mediators were assessed. ALA reduced circulating leptin, without affecting body weight, glycemic dysfunction, or cholesterol. While I-R tolerance was unaltered, paradoxical injury with IPC was reversed to cardioprotection with ALA. However, post-ischemic apoptosis (nucleosome content) appeared unchanged. Benefit was not associated with shifts in localization or expression of caveolins/cavins, p-AKT, p-GSK3β, or mitochondrial function. Despite mixed inflammatory mediator changes, tumor necrosis factor-a (TNF-a) was markedly reduced. Data collectively reveal a novel impact of ALA on cardioprotective dysfunction in T2D mice, unrelated to caveolins/cavins, mitochondrial, or stress kinase modulation. Although evidence suggests inflammatory involvement, the basis of this “un-conventional” protection remains to be identified.