EXOGENOUS CARBOHYDRATE OXIDATION FROM DIFFERENT CARBOHYDRATE SOURCES DURING EXERCISE

The exogenous carbohydrate (CHO) oxidation of naturally enriched [C-13]CHO sources with different solubilities was studied during cycling exercise (150 min, 60% maximum work output). Moreover, the effect of adding a C-13 tracer with different physical properties than the tracee on exogenous CHO oxidation was investigated. Test solutions (28.5 ml/kg body wt) were water for control of C-13 background, 15% soluble partially hydrolyzed corn starch (SOL), 15% insoluble corn starch (InSOL), and 15% InSOL with [C-13(6)]glucose as tracer. Both the mean and peak exogenous oxidation rates were significantly greater (P < 0.05) in the SOL trial than in the InSOL trial (mean oxidation rate, 0.84 +/- 0.21 and 0.50 +/- 0.15 g/min, respectively; peak oxidation rate, 1.10 +/- 0.18 and 0.81 +/- 0.25 g/min, respectively). The amount of the ingested CHO that was oxidized was significantly higher (P < 0.05) in the SOL trial (126 +/-31 g) than in the InSOL trial (75 +/- 25 g). When we added an extrinsic tracer ([C-13]glucose), the apparent mean and peak oxidation rates of the trial with InSOL and [C-13(6)]glucose were significantly (P < 0.05) higher (0.91 +/- 0.30 and 1.23 +/- 0.41, respectively) than the InSOL values. These results 1) indicate that the addition of the soluble [C-13]glucose tracer to an insoluble starch tracee leads to overestimation of the exogenous CHO oxidation rates and 2) suggest that soluble CHO is oxidized at a higher rate during exercise than isocaloric insoluble CHO.