We investigated the hormonal and metabolic response to a 100-g sucrose load given 15 min after adaptation to moderate-intensity (50% Vmaxo2) long-duration (4-h) exercise in healthy volunteers. The effect of a 100-mg dose of the α-glucosidase inhibitor Acarbose ingested with the sucrose load was also investigated. “Naturally labeled [13C] sucrose” was used to follow the conversion to expired-air CO2 of the sugar ingested by isotope-ratio mass spectrometry. Circulating hormone and metabolite data were obtained in nine subjects, and indirect calorimetry and stable isotope methodology were applied to six of them. Under placebo, 93 ± 4 g sucrose were entirely oxidized during the 4 h of exercise, total carbohydrate utilization was 235 ± 14 g, endogenous carbohydrate utilization was 142 ± 13 g, and total lipid oxidation was 121 ± 7 g. A single oral dose of 100 mg Acarbose ingested with the sucrose load did not significantly modify total carbohydrate (239 ± 2 g/4 h) or lipid (122 ± 6 g/4 h) oxidation. In contrast, sucrose oxidation was reduced to 53 ± 6 g/4 h and endogenous carbohydrate utilization increased to 186 ± 7 g/4 h. Reduction of the rises in blood glucose and fructose and of the increases in plasma insulin and C peptide under Acarbose confirmed these effects, whereas lower circulating levels of alanine suggested a higher rate of gluconeogenesis.
These data show that a 100-g glucose load ingested soon after initiation of exercise is a perfect available metabolic substrate. Furthermore, the simultaneous ingestion of 100 mg Acarbose significantly reduces the availability of sucrose during exercise, a finding that has to be considered if this or other compounds with similar properties are envisaged for the treatment of diabetic patients.