HIGH CONCENTRATIONS OF CARBOHYDRATE INGESTED DURING EXERCISE SPARES ENDOGENOUS CHO
Jentjens, R. L., Achten, J., & Jeukendrup, A. E. (2004). High oxidation rates from a mixture of glucose, sucrose, and fructose during prolonged exercise. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 151.
"It has been demonstrated that oxidation of carbohydrate (CHO) ingested during cycling exercise does not exceed ~1 g/min. Suggestions have been made that intestinal CHO absorption could be a potential factor limiting the rate of exogenous CHO oxidation. Sucrose and fructose are absorbed by intestinal transport mechanisms that are, at least in part, different from intestinal glucose transport which may become saturated at an ingestion rate of 1.2 g/min. Recent studies from our laboratory have shown that a mixture of glucose and sucrose or glucose and fructose when ingested at a high rate (1.8 g/min) leads to peak oxidation rates of ~1.25 g/min and results in ~20 to 50% higher exogenous CHO oxidation rates compared with the ingestion of an isoenergetic amount of glucose. Combined ingestion of glucose, sucrose and fructose at high rates might provide CHO for these different transport mechanisms and this might further increase the rate of exogenous CHO oxidation" (p. S19).
Eight trained male cyclists cycled on three different occasions separated by at least one week in random order. Each trial consisted of 150-min of cycling at 50% of maximal power output while subjects received a solution providing either 2.4 g/min of glucose (GLU) or 1.2 g/min of glucose plus 0.6 g/min of fructose plus 0.6 g/min of sucrose (MIX) or plain water.
Peak exogenous CHO oxidation rates were ~44% higher in the MIX condition compared with the GLU trial. Endogenous CHO oxidation was lower in the MIX condition compared with the GLU condition.
Implication. When glucose, fructose, and sucrose are ingested simultaneously at high rates (2.4 g/min) during cycling exercise, exogenous CHO oxidation rates can reach peak values of ~1.7 g/min and endogenous CHO oxidation is reduced compared with the ingestion of an isoenergetic amount of glucose.
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