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; endurance exercise; exogenous glucose oxidation; intestinal absorption; metabolism; sports nutrition.