The effect of calcium co-ingestion on exogenous glucose oxidation during endurance exercise in healthy men: A pilot study

Abstract

The benefits of high exogenous glucose availability for endurance exercise performance are well-established. Exogenous glucose oxidation rates are thought to be limited by intestinal glucose transport. Extracellular calcium in rodent intestine increases the translocation of the intestinal glucose transporter GLUT2 which, if translated to humans, could increase the capacity for exogenous glucose availability during exercise. Therefore, this pilot study aimed to explore the effect of calcium co-ingestion during endurance exercise on exogenous glucose oxidation in healthy men. Eight healthy men cycled for 2 h at 50% peak power output, ingesting either 1.2 g min⁻¹ dextrose alone (GLU) or with the addition of 2000 mg calcium (GLU + CAL), in a randomised crossover design. Expired breath samples were collected to determine whole-body and exogenous glucose oxidation. Peak exogenous glucose oxidation during GLU was 0.83 ± 0.15 g min⁻¹, and was not enhanced during GLU + CAL (0.88 ± 0.11 g min⁻¹, p = 0.541). The relative contributions of exogenous carbohydrate (19 ± 3% vs. 20 ± 2%, p = 0.434), endogenous carbohydrate (65 ± 3% vs. 65 ± 3%, p = 0.822) and fat (16 ± 3% vs. 15 ± 3%, p = 0.677) to total substrate utilisation did not differ between trials. These results suggest the addition of calcium to glucose ingestion, at saturating glucose ingestion rates, does not appear to alter exogenous glucose oxidation during endurance exercise in healthy men.

Keywords:

• Calcium
• carbohydrate
• sports nutrition
• endurance exercise
• metabolism
• intestinal absorption
• exogenous glucose oxidation

Acknowledgements

This work was supported by a Nutrition Society Summer Studentship award. J.T.G. has received research funding and/or has acted as a consultant for Arla Foods Ingredients, Lucozade Ribena Suntory, Kenniscentrum Suiker and Voeding, and PepsiCo. G.A.W has received research funding and/or has acted as a consultant for GlaxoSmithKline Ltd, Sugar Nutrition UK, Lucozade Ribena Suntory Ltd, Dairy Management Inc. and Volac International Ltd. Author Contributions: B.J.N., G. A. W. and J. T. G.: conception and design, data analysis and interpretation. B.J.N. and J.T.G.: manuscript writing. B.J.N.: data collection. All authors read and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by The Nutrition Society UK [grant number N/A].