Is a drink with electrolytes or carbohydrates more beneficial during a marathon?

Optimal Hydration During a Marathon: Electrolytes vs. Carbohydrates

During a marathon, a drink containing both electrolytes and carbohydrates is superior to either component alone, as this combination optimizes hydration, maintains performance, and reduces health risks.

Understanding Marathon Hydration Needs

Marathon running creates significant physiological demands that require proper fluid and nutrient replacement:

Electrolyte Requirements

• Prolonged exercise causes electrolyte loss through sweat, particularly sodium
• Sodium replacement is crucial for:
  • Maintaining plasma volume
  • Preventing hyponatremia (especially in races >4 hours)
  • Enhancing fluid retention
  • Stimulating thirst 1

Carbohydrate Requirements

• Marathons deplete glycogen stores, requiring carbohydrate supplementation
• Carbohydrate intake during exercise:
  • Maintains blood glucose levels
  • Delays fatigue
  • Enhances performance in events >60 minutes 2, 3

Evidence-Based Recommendations

For Marathon Performance and Safety

• For events lasting >1 hour (like marathons), consume beverages containing both carbohydrates (30-60g/hour) and electrolytes (0.5-0.7g sodium/L) 3, 4
• Optimal fluid should contain:
  • 4-8% carbohydrate concentration
  • 450-700mg sodium per liter 4
• Consumption rate: 600-1200ml/hour depending on individual sweat rate and environmental conditions 5

Physiological Rationale

• Carbohydrates and sodium work synergistically:
  • Glucose enhances intestinal sodium absorption
  • Sodium promotes water retention
  • Together they maintain plasma volume better than either alone 6
• Research shows that combined solutions empty from the stomach at rates similar to water when consumed regularly during prolonged exercise 6

Special Considerations

Avoiding Hyponatremia

• Risk factors include:
  • Race duration >4 hours
  • Female sex
  • Low body mass index
  • Excessive fluid intake 1
• Electrolyte-containing drinks reduce this risk compared to plain water 1

Avoiding Dehydration

• Dehydration exceeding 2% of body mass impairs performance 1
• "Drinking to thirst" may be insufficient during marathons, as thirst often underestimates fluid needs 1

Common Pitfalls to Avoid

1. Overhydration: Consuming excessive water without electrolytes increases hyponatremia risk 1
2. Underhydration: Relying solely on thirst can lead to >2% dehydration and performance decline 1
3. Improper concentration: Beverages with >8% carbohydrate concentration may delay gastric emptying 3
4. Ignoring individual factors: Sweat rates vary dramatically (1.0-2.5 L/hour) based on metabolic rate, environmental conditions, and acclimatization 1

Practical Application

For optimal marathon performance:

• Begin properly hydrated (6ml/kg body weight every 2-3 hours before event) 2
• Consume 500ml of fluid 1-2 hours before the race 3
• During the marathon, drink 600-1200ml/hour of a solution containing:
  • 4-8% carbohydrates (30-60g/hour)
  • 0.5-0.7g sodium/L 3, 4
• Adjust intake based on individual sweat rate, with higher volumes needed in hot conditions 4

By following these guidelines, marathon runners can maintain hydration status, electrolyte balance, and carbohydrate availability, ultimately supporting optimal performance and reducing health risks.