Abstract

The purpose of this study was to compare the oxidation of 13C-labeled glucose, fructose, and glucose polymer ingested (1.33 g/kg in 19 ml/kg water) during cycle exercise (120 min, 53 +/- 2 maximal O2 uptake) in six healthy male subjects. Oxidation of exogenous glucose and glucose polymer (72 +/- 15 and 65 +/- 18, respectively, of the 98.9 +/- 4.7 g ingested) was similar and significantly greater than exogenous fructose oxidation (54 +/- 13). A transient rise in plasma glucose concentration was observed with glucose ingestion only. However, plasma insulin levels were similar with glucose polymer ingestions and significantly higher than with water or fructose ingestion. Plasma free fatty acid and glycerol responses to exercise were blunted with carbohydrate ingestion. However, fat utilization was not significantly different with water (82 +/- 14 g), glucose (60 +/- 3 g), fructose (59 +/- 11 g), or glucose polymer ingestion (60 +/- 8g). Endogenous carbohydrate utilization was significantly lower with glucose (184 +/- 22g), glucose polymer (187 +/- 31 g), and fructose (211 +/- 18 g) than with water (239 +/- 30 g) ingestion. Plasma volume slightly increased with water ingestion (7.4 +/- 4.5), but the decrease was similar with glucose (-7.6 +/- 5.1) and glucose polymer (-8.2 +/- 4.6), suggesting that the rate of water delivery to plasma was similar with the two carbohydrates. These results 1) indicate that fructose ingested during prolonged exercise is less readily available for oxidation than ingested glucose and results in a lower endogenous carbohydrate sparing over a 2-h period of exercise and 2) suggest that the ingestion of a glucose polymer solution does not offer any advantage over ingestion of a free glucose solution in terms of metabolic or water balance. Verf.-Referat