13C-glucose-fructose labelling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew or co-ingestion

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Abstract

We examined the effects of carbohydrate (CHO) delivery form on exogenous CHO oxidation, gastrointestinal discomfort, and exercise capacity. In a randomised repeated measures design (after 24 h of high CHO intake (8 g·kg ^-1) and pre-exercise meal (2 g·kg ^-1)), nine trained males ingested 120 g CHO·h ^-1 from fluid (DRINK), semi-solid gel (GEL), solid jelly chew (CHEW), or a co-ingestion approach (MIX). Participants cycled for 180 min at 95% lactate threshold followed by an exercise capacity test (150% lactate threshold). Peak rates of exogenous CHO oxidation (DRINK, 1.56 ± 0.16; GEL, 1.58 ± 0.13; CHEW, 1.59 ± 0.08; MIX, 1.66 ± 0.02 g·min ^-1) and oxidation efficiency (DRINK, 72 ± 8; GEL, 72 ± 5; CHEW, 75 ± 5; MIX, 75 ± 6%) were not different between trials (all P > 0.05). Despite ingesting 120 g·h ^-1, participants reported minimal symptoms of gastrointestinal distress across all trials. Exercise capacity was also not significantly different (all P < 0.05) between conditions (DRINK, 446 ± 350; GEL, 529 ± 396; CHEW, 596 ± 416; MIX, 469 ± 395 sec). Data represent the first time that rates of exogenous CHO oxidation (via stable isotope methodology) have been simultaneously assessed using feeding strategies (i.e., pre-exercise CHO feeding and the different forms and combinations of CHO during exercise) commonly adopted by elite endurance athletes. We conclude 120 g·h ^-1 CHO (in a 1:0.8 ratio of maltodextrin or glucose:fructose) is a practically tolerable strategy to promote high CHO availability and oxidation during exercise.

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E Chambers, M Bridge, D A Jones (2009)

Exercise studies have suggested that the presence of carbohydrate in the human mouth activates regions of the brain that can enhance exercise performance but direct evidence of such a mechanism is limited. The first aim of the present study was to observe how rinsing the mouth with solutions containing glucose and maltodextrin, disguised with artificial sweetener, would affect exercise performance. The second aim was to use functional magnetic resonance imaging (fMRI) to identify the brain regions activated by these substances. In Study 1A, eight endurance-trained cyclists (VO2max 60.8 +/- 4.1 ml kg(-1) min(-1)) completed a cycle time trial (total work = 914 +/- 29 kJ) significantly faster when rinsing their mouths with a 6.4% glucose solution compared with a placebo containing saccharin (60.4 +/- 3.7 and 61.6 +/- 3.8 min, respectively, P = 0.007). The corresponding fMRI study (Study 1B) revealed that oral exposure to glucose activated reward-related brain regions, including the anterior cingulate cortex and striatum, which were unresponsive to saccharin. In Study 2A, eight endurance-trained cyclists (VO2max 57.8 +/- 3.2 ml kg(-1) min(-1)) tested the effect of rinsing with a 6.4% maltodextrin solution on exercise performance, showing it to significantly reduce the time to complete the cycle time trial (total work = 837 +/- 68 kJ) compared to an artificially sweetened placebo (62.6 +/- 4.7 and 64.6 +/- 4.9 min, respectively, P = 0.012). The second neuroimaging study (Study 2B) compared the cortical response to oral maltodextrin and glucose, revealing a similar pattern of brain activation in response to the two carbohydrate solutions, including areas of the insula/frontal operculum, orbitofrontal cortex and striatum. The results suggest that the improvement in exercise performance that is observed when carbohydrate is present in the mouth may be due to the activation of brain regions believed to be involved in reward and motor control. The findings also suggest that there may be a class of so far unidentified oral receptors that respond to carbohydrate independently of those for sweetness.

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Measures of substrate oxidation have traditionally been calculated from indirect calorimetry measurements using stoichiometric equations. Although this has proven to be a solid technique and it has become one of the standard techniques to measure whole body substrate metabolism, there are also several limitations that have to be considered. When indirect calorimetry is used during exercise most of the assumptions on which the method is based hold true although changes in the size of the bicarbonate pool at higher exercise intensities may invalidate the calculations of carbohydrate and fat oxidation. Most of the existing equations are based on stoichiometric equations of glucose oxidation and the oxidation of a triacylglycerol that is representative of human adipose tissue. However, in many exercise conditions, glycogen and not glucose is the predominant carbohydrate substrate. Therefore we propose slightly modified equations for the calculation of carbohydrate and fat oxidation for use during low to high intensity exercise. Studies that investigated fat oxidation over a wide range of intensities and that determined the exercise intensity at which fat oxidation is maximal have provided useful insights in the variation in fat oxidation between individuals and in the factors that affect fat oxidation. Fat oxidation during exercise can be influenced by exercise intensity and duration, diet, exercise training, exercise mode and gender. Although a number of important factors regulating fat oxidation have been identified, it is apparent that a considerable degree of inter-subject variability in substrate utilization persists and cannot be explained by the aforementioned factors. Future research should investigate the causes of the large inter-individual differences in fat metabolism between individuals and their links with various disease states.

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Diet, muscle glycogen and physical performance.

J. Bergström, Christian L Hermansen, E Hultman … (2015)

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Author and article information

Journal

Title: Journal of Applied Physiology

Abbreviated Title: Journal of Applied Physiology

Publisher: American Physiological Society

ISSN (Print): 8750-7587

ISSN (Electronic): 1522-1601

Publication date (Electronic): April 21 2022

Affiliations

[1 ]Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom

[2 ]Science in Sport PLC, London, United Kingdom

[3 ]Exercise and Nutrition Research Program, Mary MacKillop Institute for Health Research, Australian Catholic University, Melbourne, Australia

[4 ]Exercise Science, Physical and Health Education, University of Victoria, Victoria, Canada

[5 ]Pacific Institute for Sport Excellence, Canadian Sport Institute-Pacific, Victoria, Canada

[6 ]Centre for Nutrition, Exercise and Metabolism, University of Bath, Bath, United Kingdom

[7 ]Department for Health, University of Bath, Bath, United Kingdom

Article

DOI: 10.1152/japplphysiol.00091.2022

PubMed ID: 35446596

SO-VID: b8653301-8b5d-40c8-ac84-8a534972f4f7

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