High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise

A recent study from our laboratory has shown that a mixture of glucose and fructose ingested at a rate of 1(.)8 g/min leads to peak oxidation rates of approximately 1(.)3 g/min and results in approximately 55% higher exogenous carbohydrate (CHO) oxidation rates compared with the ingestion of an isocaloric amount of glucose. The aim of the present study was to investigate whether a mixture of glucose and fructose when ingested at a high rate (2(.)4 g/min) would lead to even higher exogenous CHO oxidation rates (> 1(.)3 g/min). Eight trained male cyclists (VO2max: 68 +/- 1 ml/kg per min) cycled on three different occasions for 150 min at 50% of maximal power output (60 +/- 1% VO2max) and consumed either water (WAT) or a CHO solution providing 1(.)2 g/min glucose (GLU) or 1(.)2 g/min glucose + 1(.)2 g/min fructose (GLU+FRUC). Peak exogenous CHO oxidation rates were higher (P < 0(.)01) in the GLU+FRUC trial compared with the GLU trial (1(.)75 (SE 0(.)11) and 1(.)06 (SE 0(.)05) g/min, respectively). Furthermore, exogenous CHO oxidation rates during the last 90 min of exercise were approximately 50% higher (P < 0(.)05) in GLU+FRUC compared with GLU (1(.)49 ( SE 0(.)08) and 0(.)99(SE 0(.)06) g/min, respectively). The results demonstrate that when a mixture of glucose and fructose is ingested at high rates (2(.)4 g/ min) during 150 min of cycling exercise, exogenous CHO oxidation rates reach peak values of approximately 1(.)75 g/ min.