CHO Oxidation Rates Research Articles

Effects of Multiple Carbohydrates and Protein on Time Trial Performance in Trained Cyclists

Ingestion of multiple carbohydrate (CHO) types (e.g., dextrose+fructose) during exercise can increase CHO oxidation rates compared to ingesting a single CHO (e.g., dextrose), and may improve endurance performance. It has been reported that adding protein to a multiple-CHO beverage increased cycling time to exhaustion compared to a single CHO beverage alone. However, it is unclear whether the improved performance was due to the multiple CHOs or the addition of protein. PURPOSE: This study aimed to determine whether the addition of 1.2% protein to a 3% multiple-CHO beverage improved performance and muscle strength recovery in 2 same-day time trials compared to an isocaloric multiple CHO-only beverage. METHODS: 11 cyclists (39.9±11.8 y; VO2max 53.7±6.9 ml/kg/min) performed 3 trials, a familiarization trial and 2 randomly ordered, double-blinded experimental trials. Each trial consisted of a pre-trial leg strength measurement, 40km time trial (TT), 30 min recovery, 10km TT, and post-trial leg strength testing. Subjects ingested 275 mL of a multiple-CHO (MCO) or multiple-CHO+protein (MCP) beverage at 7 time points during the protocol. Blood glucose, lactate, heart rate (HR) and rating of perceived exertion (RPE) were measured. Leg strength was assessed using a custom Isometric Leg Strength System. Continuous variables were analyzed with paired t-tests. Repeated measures were analyzed with repeated measures ANOVA. RESULTS: No significant differences were found between MCO and MCP in 40km TT time (82.3±2.6 vs 82.8±2.8 min, respectively, p=0.32) and power output (233.3±16.0 vs 231.6±16.7 W, p=0.55) nor in 10km time (24.4±0.9 vs 24.5±1.1 min, p=0.61) or power output (238.2±16.7 vs 237.3±17.7 W, p=.83). No differences were found in leg strength recovery (pre-post trial) as well (p=0.22). Blood glucose, lactate, HR, and RPE were also not different between treatments. CONCLUSION: While addition of protein to CHO has been shown to improve TTE, it may not be beneficial in shorter race events. We speculate that in this study, exercise time and intensity were not great enough to deplete glycogen stores or cause muscle damage. Differences in experimental design likely explain the conflicting findings among studies.

High-intensity, but not moderate-intensity, exercise increases post-exercise rate of fat oxidation in type 2 diabetics

Aerobic exercise is recommended for glycemic and weight control in type 2 diabetes (T2D), but exercise intensity that increase post-exercise fat oxidation has not been established yet. It is expected that high-intensity exercise induce higher absolute oxidations and rates of oxidation of CHO (during) and fat (after) in normoglycemic, but in hyperglycemic it is unclear. To compare the effects of exercise intensity on CHO and fat oxidation during and after exercise in individuals with T2D. Eleven persons with T2D, randomly underwent three experimental sessions 72 hours apart: 1) 20 minute of high-intensity exercise (120% of lactate threshold (LT) - 120%LT), 2) 20 minute of moderate-intensity exercise (80% of LT - 80%LT), and 3) 20 minute of control session (CON) - no exercise was performed and the individuals remained seated during the whole time. Percentages of CHO and fat contribution and CHO and fat oxidation rate (mg/min) were analyzed during and after sessions. The rate of CHO oxidation during exercise was significantly higher during 120%LT in relation to 80%LT and CON (18.2 ± 5.6 vs. 9.5 ± 2.7 vs. 1.1 ± 0.4 mg∙min-1), the absolute rate of fat oxidation was significantly higher in 120%LT compared to 80%LT and CON during exercise (13.5 ± 3.3, 9.5 ± 2.2, and 0.7 ± 0.2 mg∙min-1, respectively, p < 0.05). During the post-exercise oxygen consumption recovery period, only the 120%LT had higher fat oxidation (94.5% vs. 68.1%, p < 0.05), when compared to CON. Both exercise sessions equally elicited a lowered glycaemia during the post-exercise period, but CHO oxidation was lower after 120%LT than CON (0.1 ± 0.2 vs. 0.9 ± 0.5 mg∙min-1, p < 0.05). Higher intensity elicited an elevated CHO oxidation rate during exercise and a higher percentage of fat utilization during the post-exercise recovery period compared to moderate-intensity exercise and control sessions. High-intensity aerobic exercise, even of short duration, may benefit individuals with T2D on the substrate oxidation related to the body fat. Exercise can be an important tool for the prevention and management of T2D due to its effects on carbohydrate and fat metabolism, reduction of body fat, and control of blood glucose.

Altering fatty acid availability does not impair prolonged, continuous running to fatigue: evidence for carbohydrate dependence.

We determined the effect of suppressing lipolysis via administration of nicotinic acid (NA) on fuel substrate selection and half-marathon running capacity. In a single-blinded, Latin square design, 12 competitive runners completed four trials involving treadmill running until volitional fatigue at a pace based on 95% of personal best half-marathon time. Trials were completed in a fed or overnight fasted state: 1) carbohydrate (CHO) ingestion before (2 g CHO·kg(-1)·body mass(-1)) and during (44 g/h) [CFED]; 2) CFED plus NA ingestion [CFED-NA]; 3) fasted with placebo ingestion during [FAST]; and 4) FAST plus NA ingestion [FAST-NA]. There was no difference in running distance (CFED, 21.53 ± 1.07; CFED-NA, 21.29 ± 1.69; FAST, 20.60 ± 2.09; FAST-NA, 20.11 ± 1.71 km) or time to fatigue between the four trials. Concentrations of plasma free fatty acids (FFA) and glycerol were suppressed following NA ingestion irrespective of preexercise nutritional intake but were higher throughout exercise in FAST compared with all other trials (P < 0.05). Rates of whole-body CHO oxidation were unaffected by NA ingestion in the CFED and FAST trials, but were lower in the FAST trial compared with the CFED-NA trial (P < 0.05). CHO was the primary substrate for exercise in all conditions, contributing 83-91% to total energy expenditure with only a small contribution from fat-based fuels. Blunting the exercise-induced increase in FFA via NA ingestion did not impair intense running capacity lasting ∼85 min, nor did it alter patterns of substrate oxidation in competitive athletes. Although there was a small but obligatory use of fat-based fuels, the oxidation of CHO-based fuels predominates during half-marathon running.

High Carbohydrate Diet Induces Faster Final Sprint and Overall 10,000-m Times of Young Runners.

This study analyzed the pacing employed by young runners in 10,000 m time-trials under 3 dietary regimens of different carbohydrate (CHO) intakes. Nineteen boys (13-18 years) ate either their normal CHO diet (56% CHO), high (70% CHO), or low (25% CHO) CHO diets for 48 hr; the boys then performed a 10,000 m run (crossover design). The high CHO diet led to faster final sprint (14.4 ± 2.2 km·h⁻¹) and a better performance (50.0 ± 7.0 min) compared with the low CHO diet (13.3 ± 2.4 km·h⁻¹ and 51.9 ± 8.3 min, respectively, p < .05). However, the final sprint and performance time in the high CHO or low CHO diets were statistically not significantly different from the normal CHO diet (13.8 ± 2.2 km·h⁻¹ and 50.9 ± 7.4 min; p > .05). CHO oxidation rate during the constant load exercise at 65% of VO2max was elevated in high CHO diet (1.05 ± 0.38 g·min⁻¹) compared with low CHO diet (0.63 ± 0.36 g·min⁻¹). The rating of perceived exertion increased linearly throughout the trial, independently of the dietary regimen. In conclusion, the high CHO diet induced higher CHO oxidation rates, increased running speed in the final 400 m and enhanced overall running performance, compared with low CHO.

Self-selecting Fluid Intake while Maintaining High Carbohydrate Availability Does not Impair Half-marathon Performance

We aimed to test the hypothesis that self-selecting fluid intake but maintaining high exogenous CHO availability (60 g/h) does not compromise half-marathon performance. 15 participants completed 3 half-marathons while drinking a 6% CHO solution to guidelines (DRINK) or a non-caloric solution in self-selected volumes when consuming 3×glucose (20 g) gels (G-GEL) or glucose-fructose (13 g glucose+7 g fructose) gels (GF-GEL) per hour. Fluid intake (DRINK: 1 557±182, G-GEL: 473±234, GF-GEL: 404±144 ml) and percent body mass loss (DRINK: - 0.8±0.9, G-GEL: - 2.0±0.6, GF-GEL: -2.3±1.1) were different (P<0.05) between conditions, though race time did not differ (DRINK: 110.6±14.4, G-GEL: 110.3±14.6, GF-GEL: 113.7±12.8 min). In G-GEL, there was a positive correlation (P<0.05) between body mass loss and race time. Plasma glucose was lower (P<0.05) in GF-GEL compared with other conditions, and total CHO oxidation (DRINK: 3.2±0.5, G-GEL: 3.0±0.4, GF-GEL: 2.6±0.4 g/min) was lower (P=0.06) in this trial. Self-selecting fluid intake but maintaining high CHO availability does not impair half-marathon performance. Additionally, consuming glucose-fructose mixtures in sub-optimal amounts reduces plasma glucose and total rates of CHO oxidation.

Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations.

This systematic review examines the efficacy of carbohydrate (CHO) supplementation on exercise performance of varying durations. Included studies utilized an all-out or endurance-based exercise protocol (no team-based performance studies) and featured randomized interventions and placebo (water-only) trial for comparison against exclusively CHO trials (no other ingredients). Of the 61 included published performance studies (n = 679 subjects), 82% showed statistically significant performance benefits (n = 50 studies), with 18% showing no change compared with placebo. There was a significant (p = 0.0036) correlative relationship between increasing total exercise time and the subsequent percent increase in performance with CHO intake versus placebo. While not mutually exclusive, the primary mechanism(s) for performance enhancement likely differs depending on the duration of the exercise. In short duration exercise situations (∼1 h), oral receptor exposure to CHO, via either mouthwash or oral consumption (with enough oral contact time), which then stimulates the pleasure and reward centers of the brain, provide a central nervous system-based mechanism for enhanced performance. Thus, the type and (or) amount of CHO and its ability to be absorbed and oxidized appear completely irrelevant to enhancing performance in short duration exercise situations. For longer duration exercise (>2 h), where muscle glycogen stores are stressed, the primary mechanism by which carbohydrate supplementation enhances performance is via high rates of CHO delivery (>90 g/h), resulting in high rates of CHO oxidation. Use of multiple transportable carbohydrates (glucose:fructose) are beneficial in prolonged exercise, although individual recommendations for athletes should be tailored according to each athlete's individual tolerance.

Comparison of the Effects of Glucose and Fructose on Exercise Metabolism, Perceived Exertion, and Recovery in Untrained Females

This double-blinded, crossover randomized controlled trial study was designed to establish if combined ingestion of glucose and fructose (GLU + FRU) at the moderate rate 0.5 g·min−1 would result in higher rates of carbohydrate (CHO) oxidation compared with glucose (GLU) alone. Eight untrained females (VO2max: 25.8 ± 3.2 mL·kg−1·min−1) cycled on two different occasions for 60 min at 50% of maximal power output (60% ± 1 % VO2max) and consumed 12% CHO solution of either providing 0.33 g·min−1 glucose + 0.17 g·min−1 fructose (GLU + FRUC) or 0.5 g·min−1 of glucose (GLU) alone. Heart rate (HR) and rate of perceived exertion (RPE) were assessed during exercise and subjective exercise experience assessed two days after each trial. CHO oxidation was not significantly different (P&gt;0.05) between GLU + FRU and GLU (0.8 ± 0.06 g·min−1 and 0.78 ± 0.05 g·min−1, resp.). CHO oxidation rates during the final 30 min of the recovery period were not significantly different between GLU + FRU and GLU (0.17 ± 0.04 g·min−1 and 0.14 ± 0.05 g·min−1, resp.). Experience of distress was significantly higher (P&lt;0.05) for GLU compared to GLU + FRU. The results reveal that consuming modest amounts of glucose plus fructose does not boost CHO oxidation above that of glucose alone during submaximal exercise.

The ingestion of protein with a maltodextrin and fructose beverage on substrate utilisation and exercise performance

The study investigated the ingestion of maltodextrin, fructose, and protein on exogenous carbohydrate oxidation (CHOEXO) and exercise performance. Seven trained cyclists and (or) triathletes (maximal oxygen consumption, 59.20 ± 9.00 mL · kg(-1) · min(-1)) performed 3 exercise trials that consisted of 150 min of cycling at 50% maximal power output (160 ± 11 W), followed by a 60-km time trial. One of 3 beverages were randomly assigned during each trial and consumed at 15-min intervals: (i) 0.84 g · min(-1) maltodextrin + 0.52 g · min(-1) fructose + 0.34 g · min(-1) protein (MD+F+P); (ii) 1.10 g · min(-1) maltodextrin + 0.60 g · min(-1) fructose (MD+F); or (iii) 1.70 g · min(-1) maltodextrin (MD). CHO(EXO) and fuel utilisation were assessed via measurement of expired air (13)C content and indirect calorimetry, respectively. Mean total CHO oxidation (CHOTOT) rates were 2.35 ± 0.18, 2.76 ± 0.08, and 2.61 ± 0.17 g · min(-1) with MD, MD+F, and MD+F+P, respectively, although not significantly different. Peak CHO(EXO) rates with MD+F were significantly greater by 41.4% (p = 0.001) and 45.4% (p = 0.0001) compared with MD+F+P and MD, respectively (1.57 ± 0.22 g · min(-1), 1.11 ± 0.08 g · min(-1), and 1.08 ± 0.11 g · min(-1), respectively). Performance times were 2.2% and 5.0% faster with MD+F compared with MD+F+P and MD, respectively; however, they were not statistically significant. Ingestion of an MD-fructose-protein commercial sports beverage significantly reduced peak and mean CHO(EXO) rates compared with MD+F, but did not significantly influence CHOTOT. The addition of protein to an MD+F beverage did not enhance performance times.

Fructose–Maltodextrin Ratio Governs Exogenous and Other CHO Oxidation and Performance

Fructose coingested with glucose in carbohydrate (CHO) drinks increases exogenous-CHO oxidation, gut comfort, and physical performance. This study aimed to determine the effect of different fructose-maltodextrin-glucose ratios on CHO oxidation and fluid absorption while controlling for osmolality and caloricity. In a crossover design, 12 male cyclists rode 2 h at 57% peak power then performed 10 sprints while ingesting artificially sweetened water or three equiosmotic 11.25% CHO-salt drinks at 200 mL·15 min, comprising weighed fructose and maltodextrin-glucose in ratios of 0.5:1 (0.5 ratio), 0.8:1 (0.8 ratio), and 1.25:1 (1.25 ratio). Fluid absorption was traced with D2O, whereas C-fructose and C-maltodextrin-glucose permitted fructose and glucose oxidation rate evaluation. The mean exogenous-fructose and exogenous-glucose oxidation rates were 0.27, 0.39, and 0.46 g·min and 0.65, 0.71, and 0.58 g·min in 0.5, 0.8, and 1.25 ratio drinks, representing mean oxidation efficiencies of 54%, 59%, and 55% and 65%, 85%, and 86% for fructose and glucose, respectively. With the 0.8 ratio drink, total exogenous-CHO oxidation rate was 18% (90% confidence interval, ±5%) and 5.2% (±4.6%) higher relative to 0.5 and 1.25 ratios, respectively, whereas respective differences in total exogenous-CHO oxidation efficiency were 17% (±5%) and 5.3% (±4.8%), associated with 8.6% and 7.8% (±4.2%) higher fructose oxidation efficiency. The effects of CHO ratio on water absorption were inconclusive. Mean sprint power with the 0.8 ratio drink was moderately higher than that with the 0.5 ratio (2.9%; 99% confidence interval, ±2.8%) and 1.25 ratio (3.1%; ±2.7%) drinks, with total- and endogenous-CHO oxidation rate, abdominal cramps, and drink sweetness qualifying as explanatory mechanisms. Enhanced high-intensity endurance performance with a 0.8 ratio fructose-maltodextrin-glucose drink is characterized by higher exogenous-CHO oxidation efficiency and reduced endogenous-CHO oxidation. The gut-hepatic or other physiological site responsible requires further research.

Reduced fat oxidation rates during submaximal exercise in boys with cystic fibrosis

Exercise is a viable form of therapy for children with cystic fibrosis (CF). Understanding the energy sources used during exercise would aid CF patients in obtaining proper nutrition in order to sustain an active lifestyle. Six boys with CF (mean age ± SD: 14.8 ± 2.3 yrs, FEV1: 99 ± 18% predicted) and six matched controls (14.0 ± 2.2 yrs) completed a session of two 30 min bouts of cycling at an intensity set at 50% peak mechanical power. Rates of total fat and carbohydrate (CHO) oxidation were calculated from expired gases. Plasma insulin, glucose and free fatty acid (FFA) were determined before, during and at the end of the exercise. Rates of fat oxidation (expressed in mean mg × kg body weight(-1) × min(-1) ± SD) were significantly lower in children with CF (5.7 ± 1.6) compared to controls (8.6 ± 1.8, p < 0.05). Children with CF also had lower values than controls in amount of fat oxidized (CF: 17.3 ± 5.0 g, controls: 26.1 ± 5.9 g, p < 0.05) and percent of total energy expenditure from fat (CF: 32 ± 6%, controls: 43 ± 7%, p < .0.05), but a higher contribution from CHO (CF: 68 ± 6%, controls: 57 ± 7% p < .0.05). Plasma FFA was significantly lower in children with CF compared to controls during (CF: 252.5 ± 117.9 μM, controls: 602.2 ± 295.6) and at the end of exercise (CF: 430.9 ± 180.6, controls: 1147.5 ± 473.5). There were no differences in the rates of CHO oxidation, insulin or glucose between groups. Fat metabolism during exercise is impaired in boys with CF and may be attributed to an inability to mobilize FFA.

Indirect measures of substrate utilisation following exercise-induced muscle damage

This study investigated whether exercise-induced muscle damage (EIMD) resulted in changes to whole-body substrate utilisation during exercise performed during the subsequent 48 hours. Eight males (31±6 years) performed 30 minutes of bench-stepping exercise. One leg performed eccentric contractions (Ecc) by lowering the body whilst the control leg performed concentric contractions (Con) by raising the body. On the two days following bench-stepping exercise participants performed measures of muscle function on an isokinetic dynamometer and undertook a bout of one leg cycling exercise, at two differing workloads, with the first workload (WL1) at 1.5±0.25 W/kg and the second workload (WL2) at 1.8±0.25 W/kg with each leg. Expired respiratory gases were collected during cycling to estimate whole body substrate utilisation. There were significant decrements in measures of muscular performance (isometric force, concentric and eccentric torque) and increased perception of soreness in Ecc compared with Con (P < 0.05). The effect of the Ecc treatment on substrate utilisation during one-legged cycling revealed a significant trial×time interaction with higher rates of CHO oxidation in the Ecc condition compared with Con that were further increased 48 hours later (P = 0.02). A significant treatment×time×effort interaction (P < 0.01) indicated the effect of the treatment altered as workload increased with higher rates of CHO oxidation occurring in WL2. This is consistent with greater reliance upon muscle glycogen. Suggesting that in EIMD, reductions in strength and increased feelings of soreness can be associated with greater reliance upon intramuscular CHO oxidation, than lipid, during subsequent concentric work.

Cashew apple juice supplementation enhanced fat utilization during high-intensity exercise in trained and untrained men

BackgroundExercise training is known to increase fat utilization during exercise. Diets containing antioxidants and branch chain amino acids (BCAAs) are also reported to have potential effects on fat utilization. Cashew apple juice (CAJ) comprises many nutritional components including vitamin C and BCAAs. This study aimed to investigate the effect of CAJ supplementation on substrate utilization during high-intensity exercise in trained and untrained subjects.MethodsTen trained and ten untrained men were randomly supplemented with either placebo (PLA) or CAJ at 3.5 ml/kg body mass (BM) /day for 4 weeks with a 4-week washout between treatments in a randomized cross-over design. Before and after the 4-week supplementations all subjects performed cycling exercise at 85% of maximal oxygen consumption for 20 minutes. At rest, before, and immediately after the exercise, venous blood samples were taken to determine glucose, insulin and lipid concentrations. Expired air was collected during the 20 minutes of exercise to calculate substrate utilization.ResultsDuring the exercise in both trained and untrained groups, there were lower carbohydrate (CHO) and higher fat oxidation rates and contributions to total energy expenditure after the CAJ supplementation compared to the PLA supplementation (p<0.05). These values were greater in the trained group than the untrained group except CHO oxidation rates (p<0.05), which were not significantly different. Moreover, in both trained and untrained groups, resting plasma vitamin C concentrations were significantly higher after the CAJ supplementation compared to the PLA supplementation, without any change after the PLA supplementation. These values were greater in the trained group than the untrained group (p<0.05). There were no significant differences in glucose, insulin or lipid concentrations between the groups’ blood samples.ConclusionThe findings of this study suggest that CAJ supplementation enhanced fat oxidation during exercise may enhance endurance performance, but specific studies are needed to assess this possibility.

Preexercise Galactose and Glucose Ingestion on Fuel Use during Exercise

This study determined the effect of ingesting galactose and glucose 30 min before exercise on exogenous and endogenous fuel use during exercise. Nine trained male cyclists completed three bouts of cycling at 60% W(max) for 120 min after an overnight fast. Thirty minutes before exercise, the cyclists ingested a fluid formulation containing placebo, 75 g of galactose (Gal), or 75 g of glucose (Glu) to which (13)C tracers had been added, in a double-blind randomized manner. Indirect calorimetry and isotope ratio mass spectrometry were used to calculate fat oxidation, total carbohydrate (CHO) oxidation, exogenous CHO oxidation, plasma glucose oxidation, and endogenous liver and muscle CHO oxidation rates. Peak exogenous CHO oxidation was significantly higher after Glu (0.68 ± 0.08 g.min(-1), P < 0.05) compared with Gal (0.44 ± 0.02 g.min(-1)); however, mean rates were not significantly different (0.40 ± 0.03 vs. 0.36 ± 0.02 g.min(-1), respectively). Glu produced significantly higher exogenous CHO oxidation rates during the initial hour of exercise (P < 0.01), whereas glucose rates derived from Gal were significantly higher during the last hour (P < 0.01). Plasma glucose and liver glucose oxidation at 60 min of exercise were significantly higher for Glu (1.07 ± 0.1 g.min(-1), P < 0.05, and 0.57 ± 0.08 g.min(-1), P < 0.01) compared with Gal (0.64 ± 0.05 and 0.29 ± 0.03 g.min(-1), respectively). There were no significant differences in total CHO, whole body endogenous CHO, muscle glycogen, or fat oxidation between conditions. The preexercise consumption of Glu provides a higher exogenous source of CHO during the initial stages of exercise, but Gal provides the predominant exogenous source of fuel during the latter stages of exercise and reduces the reliance on liver glucose.

Effect of Fat and CHO Meals on Intermittent Exercise in Soccer Players

Pre-exercise meals containing carbohydrates (CHO) are recommended to athletes, although there is evidence to suggest that a high fat meal prior to exercise increases utilisation of fats yet may not adversely affect performance. This study investigated the effect of a high fat and high CHO pre-exercise meal prior to high intensity intermittent exercise. Ten male recreational soccer players performed a soccer specific protocol followed by a 1 km time trial 3 ½ h after ingesting one of 2 test meals, high fat meal (HFM) or a high CHO meal (HCM). Blood glucose, fatty acids (FA), glycerol, β-hydroxybutyrate, lactate and insulin were assessed prior to the meal, pre-exercise, half-time, and post-exercise, whilst rates of CHO and fat oxidation were determined at 4 time points during the exercise as well as heart rate (HR) and rating of perceived exertion (RPE). Significant increases in FA, glycerol, β-hydroxybutyrate and fat oxidation after the HFM were observed, while CHO oxidation was significantly higher following the HCM (P<0.05). No performance effect was found for the 1 km time trial (HFM: 228.6+14.4 s; HCM: 229.4+26.5 s) (mean+SD). These findings suggest that the type of meal ingested prior to soccer simulated exercise has an impact on metabolism, but not on the subsequent performance as determined in the present study.

Coingesting Glucose and Fructose in the Cold Potentiates Exogenous CHO Oxidation

Current understanding of exogenous CHO metabolism during cold exposure is limited but suggests that exogenous glucose oxidation reaches a maximum of ~200 mg · min(-1) at a glucose ingestion rate of 400 mg · min(-1). The aim of the present study was to determine whether ingesting glucose in combination with fructose (GLU + FRU) after 60 min of cold exposure could increase the rate of exogenous CHO oxidation and reduce the reliance on endogenous CHO reserves compared with ingesting a glucose drink (GLU). Six healthy non-cold-acclimatized men were exposed to low-intensity shivering (~2.5 times resting metabolic rate) for a duration of 150 min on two occasions. Subjects consumed a (13)C-enriched CHO drink ((13)C-enriched glucose and fructose) providing 400 mg · min(-1) of glucose + 400 mg · min(-1) of fructose (GLU + FRU) or 800 mg · min(-1) of glucose alone (GLU) after 60 min of cold exposure. The peak exogenous CHO oxidation rate was 30% greater in GLU + FRU compared with GLU (209 ± 62 vs 159 ± 42 mg · min(-1), respectively, P < 0.05). This contributed to a 16% increase in total CHO oxidation (406 ± 100 vs 351 ± 80 mg · min(-1), respectively, P < 0.05). The utilization of endogenous CHO sources was the same between experimental conditions but was nearly 2.5 times lower than values previously reported by our laboratory when only water was ingested (192-197 vs 456 mg · min(-1), respectively). This study demonstrates that the greater exogenous and total CHO oxidation rate observed in the GLU + FRU condition was a result of increased systemic appearance of CHO from consuming multiple transportable CHO and/or the supplementary substrate provided from fructose conversion to glucose and lactate in the liver.

Effects of GI Meals on Intermittent Exercise

Pre-exercise meals or single foods containing low glycaemic index (LGI) carbohydrates (CHO) have been shown to enhance performance prior to prolonged steady state exercise compared to high glycaemic index (HGI) CHO. This study investigated the impact of HGI and LGI pre-exercise meals on intermittent high intensity exercise. Nine male recreational football players performed a football specific protocol followed by a 1 km time trial 3.5 h after ingesting 1 of 2 isoenergetic test meals (HGI: 870.3 kcal, LGI: 889.5 kcal), which were either HGI (GI: 80) or LGI (GI: 44). Blood glucose, fatty acids (FA), glycerol, β-hydroxybutyrate, lactate and insulin were assessed before, during, and after the exercise bout, whilst rates of CHO and fat oxidation were determined at 4 time points during the protocol. No significant differences were found for the 1 km time trial (LGI: 210.2 ± 19.1 s: HGI: 215.8 ± 22.6 s) (mean ± SD), nor for any of the other variables measured (P>0.05) apart from a significant condition effect with FA and significant interaction effects observed for glucose, β-hydroxybutyrate and lactate (P<0.05). These findings suggest that the type of CHO ingested in a pre-match meal has no significant impact on performance or metabolic responses during 90 min of intermittent high intensity exercise.

Isomaltulose Improves Glycemia and Maintains Run Performance in Type 1 Diabetes

Individuals with type 1 diabetes mellitus (T1DM) are encouraged to reduce rapid-acting insulin and consume CHO to prevent hypoglycemia during or after exercise. However, research comparing the metabolic and performance effects of different CHO is limited. This study compared the alterations in metabolism and fuel oxidation in response to performance running after preexercise ingestion of isomaltulose or dextrose in T1DM. After preliminary testing, on two occasions, seven T1DM individuals consumed 0.6 g·kg⁻¹ body mass of either dextrose (DEX; glycemic index = 96) or isomaltulose (ISO; glycemic index = 32), 2 h before a discontinuous incremental run to 80% V˙O2peak on a motorized treadmill followed by a 10-min all-out performance test on a nonmotorized treadmill. Blood glucose (BG), acid-base, and cardiorespiratory parameters were measured 2 h before, during, and after both run tests. Data (mean ± SEM) were analyzed using repeated-measures ANOVA. Preexercise BG area under the curve was lower under ISO in comparison with DEX (ISO = +4.0 ± 0.3 mmol·L⁻¹·h⁻¹ vs DEX = +7.0 ± 0.6 mmol·L⁻¹·h⁻¹, P < 0.01). Resting blood lactate concentrations and rate of CHO oxidation under ISO were greater than those elicited under DEX (P < 0.05). There were no metabolic or cardiorespiratory differences between conditions in response to submaximal exercise despite lower BG concentrations under ISO (P < 0.05). T1DM individuals completed the same distance at the same speed during the 10-min run test under both conditions (not significant). Consumption of isomaltulose alongside rapid-acting insulin reduction improves BG responses to exercise and produces a similar high-intensity run performance compared with dextrose in T1DM individuals.

Effects of Exercise Intensity and Altered Substrate Availability on Cardiovascular and Metabolic Responses to Exercise After Oral Carnitine Supplementation in Athletes

The effects of 15 d of supplementation with L-carnitine L-tartrate (LC) on metabolic responses to graded-intensity exercise under conditions of altered substrate availability were examined. Fifteen endurance-trained male athletes undertook exercise trials after a 2-d high-carbohydrate diet (60% CHO, 25% fat) at baseline (D0), on Day 14 (D14), and after a single day of high fat intake (15% CHO, 70% fat) on Day 15 (D15) in a double-blind, placebo-controlled, pair-matched design. Treatment consisted of 3 g LC (2 g L-carnitine/d; n = 8) or placebo (P, n = 7) for 15 d. Exercise trials consisted of 80 min of continuous cycling comprising 20-min periods at each of 20%, 40%, 60%, and 80% VO2peak. There was no significant difference between whole-body rates of CHO and fat oxidation at any workload between D0 and D14 trials for either the P or LC group. Both groups displayed increased fat and reduced carbohydrate oxidation between the D14 and D15 trials (p < .05). During the D15 trial, heart rate (p < .05 for 20%, 40%, and 60% workloads) and blood glucose concentration (p < .05 for 40% and 60% workloads) were lower during exercise in the LC group than in P. These responses suggest that LC may induce subtle changes in substrate handling in metabolically active tissues when fatty-acid availability is increased, but it does not affect whole-body substrate utilization during short-duration exercise at the intensities studied.

Carbohydrate intake reduces fat oxidation during exercise in obese boys

The recent surge in childhood obesity has renewed interest in studying exercise as a therapeutic means of metabolizing fat. However, carbohydrate (CHO) intake attenuates whole body fat oxidation during exercise in healthy children and may suppress fat metabolism in obese youth. To determine the impact of CHO intake on substrate utilization during submaximal exercise in obese boys, seven obese boys (mean age: 11.4 ± 1.0 year; % body fat: 35.8 ± 3.9%) performed 60 min of exercise at an intensity that approximated maximal fat oxidation. A CHO drink (CARB) or a placebo drink (CONT) was consumed in a double-blinded, counterbalanced manner. Rates of total fat, total CHO, and exogenous CHO (CHO(exo)) oxidation were calculated for the last 20 min of exercise. During CONT, fat oxidation rate was 3.9 ± 2.4 mg × kg fat-free mass (FFM)(-1 )× min(-1), representing 43.1 ± 22.9% of total energy expenditure (EE). During CARB, fat oxidation was lowered (p = 0.02) to 1.7 ± 0.6 mg × kg FFM(-1 )× min(-1), contributing to 19.8 ± 4.9% EE. Total CHO oxidation rate was 17.2 ± 3.1 mg × kg FFM(-1 )× min(-1) and 13.2 ± 6.1 mg × kg FFM(-1) × min(-1) during CARB and CONT, respectively (p = 0.06). In CARB, CHO(exo) oxidation contributed to 23.3 ± 4.2% of total EE. CHO intake markedly suppresses fat oxidation during exercise in obese boys.

Isomaltulose Improves Postexercise Glycemia by Reducing CHO Oxidation in T1DM

individuals with type 1 diabetes mellitus (T1DM) are encouraged to consume CHO to prevent hypoglycemia during or after exercise. However, the research comparing specific types of CHO is limited. This study compared the alterations in metabolism and fuel oxidation in response to running after preexercise ingestion of isomaltulose or dextrose in T1DM. after preliminary testing, on two occasions, eight T1DM individuals consumed 75 g of either dextrose (DEX; GI = 96) or isomaltulose (ISO; GI = 32), 2 h before performing 45 min of treadmill running at 80% ± 1% VO(2peak). Blood glucose (BG) was measured for 2 h before and 3 h after exercise. Cardiorespiratory parameters were collected at rest and during exercise. Data (mean ± SEM) were analyzed using repeated-measures ANOVA. there was a smaller increase in BG in the preexercise period under ISO with peak BG occurring at 120 min after ingestion compared with 90 min under DEX (Δ+4.5 ± 0.4 vs Δ+9.1 ± 0.6 mmol·L, P < 0.01). During the final 10 min of exercise, there were lower CHO (ISO 2.85 ± 0.07 vs DEX 3.18 ± 0.08 g·min, P < 0.05) and greater lipid oxidation rates (ISO 0.33 ± 0.03 vs DEX 0.20 ± 0.03 g·min, P < 0.05) under ISO. After exercise, ISO BG was lower than DEX for the entire 180-min period, with BG area under the curve and mean BG concentrations being 21% ± 3% and 3.0 ± 0.4 mmol·L lower, respectively (P < 0.05). consumption of ISO improves BG responses during and after exercise through reduced CHO and improved lipid oxidation during the later stages of exercise.