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Carbohydrate Ingestion on Exercise Metabolism and Physical Performance
Timothy D Noakes1, Philip J Prins2, Alex Buga3
1Emeritus Faculty of Health Sciences, University of Cape Town, Cape Town 7700, South Africa.
Endocrine Reviews
|January 21, 2026
Summary
Carbohydrate ingestion during exercise prevents exercise-induced hypoglycemia (EIH), a key factor in fatigue. This strategy enhances athletic performance by maintaining blood glucose levels, not solely through glycogen replenishment.
Area of Science:
- Exercise Physiology
- Sports Nutrition
- Metabolic Regulation
Background:
- Historically, carbohydrate (CHO) intake during exercise was linked to performance improvements, primarily through preventing hypoglycemia and brain damage.
- Subsequent research focused on muscle glycogen depletion as the primary fatigue cause, often overlooking exercise-induced hypoglycemia (EIH).
- Emerging evidence suggests EIH plays a critical role in exercise fatigue, challenging the established paradigm.
Purpose of the Study:
- To comprehensively review over a century of research on carbohydrate ingestion, exercise metabolism, and athletic performance.
- To elucidate the primary mechanism by which carbohydrate ingestion enhances exercise performance.
- To re-evaluate the role of EIH and glycogenolysis in exercise termination and fatigue.
Main Methods:
- Systematic review and meta-analysis of over 160 studies spanning more than 100 years.
- Analysis of data on carbohydrate ingestion, exercise metabolism, and physical performance.
- Examination of neuroendocrine mechanisms and metabolic responses during exercise.
Main Results:
- Exercise-induced hypoglycemia (EIH) strongly correlates with exercise cessation, while muscle glycogen depletion alone does not cause fatigue.
- Carbohydrate ingestion preserves blood glucose by reducing liver glycogenolysis but can paradoxically increase muscle glycogen breakdown.
- High-fat-adapted athletes perform comparably with lower carbohydrate oxidation, indicating CHO is not always obligatory.
- Carbohydrate ingestion enhances performance, even in glycogen-depleted states, by preventing EIH.
Conclusions:
- The primary benefit of carbohydrate ingestion during prolonged exercise (>2-3 hours) is the prevention of EIH.
- This is particularly crucial for individuals with impaired hepatic gluconeogenesis.
- Findings necessitate revisions to sports nutrition guidelines regarding CHO intake timing and quantity for optimal athletic performance.
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