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Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise
N J Rehrer1, A J Wagenmakers, E J Beckers
1Department of Sports Medicine and Human Physiology, Free University of Brussels, Belgium.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1992
Summary
During exercise, lower carbohydrate concentrations (4.5% glucose) facilitated faster gastric emptying and water absorption compared to higher concentrations (17% glucose, 17% maltodextrin). Higher carbohydrate beverages did not increase total carbohydrate oxidation during exercise.
Area of Science:
- Exercise Physiology
- Gastrointestinal Physiology
- Sports Nutrition
Background:
- Optimal fueling during prolonged exercise is crucial for performance.
- Understanding the digestive and absorptive capacities for carbohydrates and water is essential for developing effective hydration and fueling strategies.
- Previous research suggests that high carbohydrate concentrations may slow gastric emptying and fluid absorption.
Purpose of the Study:
- To investigate how different orally ingested carbohydrate (CHO) concentrations affect gastric emptying, water absorption, and exogenous CHO oxidation during prolonged exercise.
- To determine the impact of 4.5% glucose, 17% glucose, and 17% maltodextrin beverages on digestive function compared to water.
- To assess the relationship between gastric emptying, water uptake, and CHO oxidation rates.
Main Methods:
- Eight male subjects completed a crossover study involving 80-minute cycling sessions at 70% maximal oxygen consumption.
- Four beverages were tested: water, 4.5% glucose (4.5G), 17% glucose (17G), and 17% maltodextrin (17MD), consumed at set intervals.
- Gastric emptying was measured by residual volume, water uptake by deuterium (2H2O) accumulation in blood, and exogenous CHO oxidation using 13C-enriched beverages.
- Jejunal perfusion tests were conducted at rest to assess net water absorption from each beverage.
Main Results:
- Gastric emptying was significantly faster with water and 4.5G compared to 17G and 17MD.
- Water absorption was more rapid with water and 4.5G; net absorption occurred with 4.5G and 17MD, while 17G resulted in net secretion.
- Total exogenous CHO oxidized was similar across all beverages, but the rate of oxidation increased over time more with 17G and 17MD than with 4.5G.
- 54% of ingested CHO was oxidized with 4.5G, versus 19% with 17G and 18% with 17MD.
Conclusions:
- Lower carbohydrate concentrations (4.5% glucose) enhance gastric emptying and water absorption during exercise compared to higher concentrations.
- While higher carbohydrate beverages do not increase total CHO oxidation, they may provide a substrate for oxidation later in exercise.
- These findings have implications for optimizing sports drink formulations to balance fluid delivery and energy provision during endurance activities.