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Respective oxidation of 13C-labeled lactate and glucose ingested simultaneously during exercise
F Péronnet1, Y Burelle, D Massicotte
1Département d'Education Physique, Université de Montréal, Province of Quebec, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1997
Summary
During prolonged exercise, the body oxidizes similar percentages of ingested glucose and lactate. However, less lactate is oxidized due to tolerance limits, contributing less to energy yield than glucose.
Area of Science:
- Exercise Physiology
- Nutritional Biochemistry
- Metabolic Studies
Background:
- Understanding fuel utilization during endurance exercise is crucial for optimizing athletic performance and recovery.
- Exogenous carbohydrates, like glucose and lactate, are potential energy sources during prolonged physical activity.
- Individual substrate oxidation rates and contributions to energy expenditure require precise measurement.
Purpose of the Study:
- To quantify and compare the oxidation rates of simultaneously ingested exogenous glucose and lactate during prolonged exercise.
- To determine the contribution of exogenous glucose and lactate to overall energy production.
- To investigate the metabolic fate of ingested lactate, specifically its potential conversion to glucose.
Main Methods:
- Utilizing stable isotope (13C) labeling to trace the oxidation of ingested substrates.
- Administering controlled doses of exogenous glucose (75g) and lactate (25g) in water during a 120-minute exercise bout.
- Measuring substrate oxidation rates and plasma glucose isotopic enrichment in physically active male subjects.
- Analyzing the 13C/12C ratio in plasma glucose to assess substrate conversion.
Main Results:
- The percentage of oxidized exogenous glucose (48%) and lactate (45%) was comparable.
- Significantly less exogenous lactate (11.1g) was oxidized compared to glucose (36.3g) due to gastrointestinal discomfort.
- Exogenous lactate contributed minimally (2.6%) to energy yield, versus 8.4% for exogenous glucose.
- Ingested lactate did not appear to be converted to glucose prior to oxidation, as indicated by unchanged plasma glucose 13C/12C ratios.
Conclusions:
- While similar proportions of ingested glucose and lactate are oxidized, the practical amount oxidized is limited by lactate's palatability and tolerance.
- Exogenous glucose serves as a more significant energy contributor than exogenous lactate during prolonged exercise under these conditions.
- Lactate ingested during exercise is primarily oxidized directly and not converted into glucose for energy utilization.