High rates of exogenous carbohydrate oxidation from starch ingested during prolonged exercise

This study compared the gastric emptying and oxidation of two 15% carbohydrate (CHO) solutions: a 22-chain-length glucose polymer (GP) and soluble starch (SS). Six endurance-trained subjects ingested 1,200 ml of either GP or SS while cycling for 90 min at 70% of maximal oxygen consumption (VO2max). Whereas the calculated total CHO oxidation (GP 266.8 +/- 41.9 g; SS 263.6 +/- 28.9 g) and the volume emptied from the stomach (GP 813 +/- 130 ml; SS 919 +/- 116 ml) were similar, the appearance of the 14C label in plasma occurred more rapidly from ingested SS than from GP (P less than 0.001). This resulted in a significantly greater rate of SS oxidation than that from GP (SS 105.9 +/- 21.9 g, GP 49.6 +/- 10.2 g; P less than 0.001). Exogenous CHO oxidation from GP accounted for 19% of total CHO oxidation, whereas the corresponding value for SS was 40%. This study suggests that the oxidation of SS and GP solutions ingested during exercise at 70% VO2max is not limited by gastric emptying. Rather, it appears to be either the rate of digestion or absorption of these solutions that determines their utilization.