Exercise & Sports Performance

Carbohydrate Ingestion Eliminates Hypoglycemia & Improves Endurance Exercise Performance in Triathletes Adapted to Very Low & High Carbohydrate Isocaloric Diets

A randomized crossover trial explored how carbohydrate ingestion during exercise impacts performance and metabolic adaptations in triathletes following very-low-carbohydrate (LCHF) or high-carbohydrate (HCLF) isocaloric diets. The study spanned six weeks of dietary intervention, followed by time-to-exhaustion (TTE) endurance trials. Minimal carbohydrate supplementation at a rate of 10 grams per hour was tested for its effects on performance and metabolic markers.

Participants underwent stringent dietary and training controls, with the LCHF diet inducing nutritional ketosis. Performance, substrate oxidation, and blood glucose levels were closely monitored during TTE trials.

Key Results:

•  Performance:

→ TTE performance was equivalent between LCHF and HCLF diets.

→ Minimal carbohydrate supplementation eliminated exercise-induced hypoglycemia and enhanced TTE performance by 22% for both dietary groups.

• Substrate Oxidation:

→ LCHF diet increased fat oxidation, while HCLF emphasized carbohydrate oxidation.

→ Carbohydrate ingestion shifted substrate utilization, increasing glucose oxidation during exercise.

• Metabolic Adaptation:

→ Glycemic control improved with LCHF, with blood glucose normalizing after four weeks.

→ Blood ketones rose significantly during LCHF (mean blood ketone level: 0.5 mmol/L) and were sustained throughout exercise.

• Body Composition:

→ LCHF reduced body fat (16%) with no loss in lean mass, despite equivalent caloric intake between diets.

This study challenges the notion that high carbohydrate availability is essential for prolonged endurance performance. A four-week adaptation period to LCHF is necessary for metabolic normalization and sustained performance. These findings emphasize the role of metabolic flexibility and minimal carbohydrate intake in endurance sports.