HIGH OXIDATION RATES OF MULTIPLE TRANSPORTABLE CARBOHYDRATES DURING PROLONGED CYCLING EXERCISE

Abstract

Studies that have investigated exogenous carbohydrate (CHO) oxidation during cycling exercise have reported peak oxidation rates of approximately 1 g/min. Suggestions have been made that intestinal CHO absorption is a limiting factor for exogenous CHO oxidation. Different CHOs use different intestinal transporters and hence ingestion of multiple transportable CHOs might increase the availability of CHO in the blood stream for oxidation. PURPOSE The purpose of the present study was to investigate whether combined ingestion of two CHOs that are absorbed by different intestinal transport mechanisms would lead to exogenous CHO oxidation rates higher than 1.0 g/min. METHODS Nine trained male cyclists (VO2max: 64±2 ml/kg/min) performed 4 exercise trials in random order and separated by at least one week. Each trial consisted of 150-min of cycling at 50% of maximal power output (60±1% VO2max) while subject received a solution providing either 1.8 g/min of glucose (GLU), 1.2 g/min of glucose + 0.6 g/min of sucrose (GLU+SUC), 1.2 g/min of glucose + 0.6 g/min of maltose (GLU+MAL) or water (WAT). RESULTS Peak exogenous CHO oxidation rates were significantly higher (P < 0.05) in the GLU+SUC trial (1.25±0.07 g/min) compared with the GLU and GLU+MAL trial (1.06±0.08 and 1.06±0.06 g/min, respectively). No difference was found in (peak) exogenous CHO oxidation rates between GLU and GLU+MAL. CONCLUSION When a mixture of glucose and sucrose is ingested at high rates (1.8 g/min) during cycling exercise, exogenous CHO oxidation rates reach peak values of ∼1.25 g/min. Furthermore, exogenous CHO oxidation rates are similar when a mixture of glucose and maltose is ingested compared with the ingestion of an isoenergetic amount of glucose. These findings support the hypothesis that exogenous CHO oxidation may be limited by the rate of intestinal CHO absorption. Supported by a grant of GlaxoSmithKline, Consumer Healthcare (UK)