Exogenous carbohydrate oxidation from maltose and glucose ingested during prolonged exercise

  • John A. Hawley
  • Steven C. Dennis
  • Andrea Nowitz
  • Fred Brouns
  • Timothy D. Noakes


Intestinal perfusion studies have shown that glucose absorption from maltose occurs faster than from isocaloric glucose. To determine whether ingested maltose might be a superior source of carbohydrate (CHO) for endurance athletes, we compared the rates of gastric emptying, absorption and oxidation of 15 g · 100 ml−1 solutions of maltose and glucose. Six endurance-trained cyclists drank 1200 ml of either U-14C maltose or U-14C glucose as a 400-ml loading bolus immediately before exercise, and as 8 × 100-ml drinks at 10-min intervals during a 90-min ride at 700% of maximal oxygen consumption. The rates of gastric emptying [maltose 690 (SD 119) ml · 90 min−1; glucose 655 (SD 93) ml · 90 min−1], the appearance of U-14C label in the plasma, and the peak rates of exogenous CHO oxidation [maltose 1.0 (SD 0.09) g · min−1; glucose 0.9 (SD 0.09) g · min−1] were not significantly different. Further, the 51 (SD 8) g of maltose and the 49 (SD 9) g of glucose oxidised during exercise were similar. Each accounted for approximately 2001o of the total CHO oxidised during the 90 min of exercise. Since only half of the CHO delivered to the intestine was oxidised in the 90-min ride (maltose 49%; glucose 50%), we conclude that neither the rate of gastric emptying, nor digestion limited the rate of ingested CHO utilisation during the early stages of exercise. Rather, we hypothesise that, initially, it could be the rate at which the CHO diffuses across the unstirred water layer of the brush-border of the intestinal villi that limits the utilisation of soluble CHO ingested during prolonged exercise.

Key words

Gastric emptying U-14C maltose Prolonged exercise 


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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • John A. Hawley
    • 1
  • Steven C. Dennis
    • 1
  • Andrea Nowitz
    • 1
  • Fred Brouns
    • 2
  • Timothy D. Noakes
    • 1
  1. 1.The Liberty Life Chair of Exercise and Sports Science and MRC/UCT Bioenergetics of Exercise Research Unit, Department of PhysiologyUniversity of Cape Town Medical SchoolSouth Africa
  2. 2.Wander Research LaboratoriesBernSwitzerland

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