Do carbohydrates before running improve performance?

Carbohydrates Before Running: Performance Enhancement

Yes, consuming carbohydrates before running improves performance, particularly for runs lasting longer than 90 minutes, with optimal timing being 3-4 hours pre-exercise at a dose of 1-3 g/kg body weight. 1

Timing and Dosing Strategy

For Runs >90 Minutes (Endurance Events)

The most effective pre-run carbohydrate strategy involves consuming 1-3 g/kg body weight 3-4 hours before exercise. 1 This timing allows for:

• Restoration of liver glycogen stores, which can be depleted by approximately 50% after an overnight fast 1
• Adequate digestion time to minimize gastrointestinal discomfort during the run 1
• Optimal muscle glycogen availability when exercise begins 1

For events exceeding 90 minutes, a dedicated 36-48 hour carbohydrate loading period at 10-12 g/kg/day can further improve performance compared to no structured plan 1

For Runs <90 Minutes

Habitual carbohydrate intake of 7-10 g/kg/day is sufficient to maintain fully repleted glycogen stores, which maximizes performance for shorter duration exercise 1

Performance Benefits

The evidence demonstrates multiple performance improvements with pre-exercise carbohydrate intake:

• Delayed fatigue and enhanced capacity for high-intensity intermittent exercise 1
• Improved technical performance, including increased dribbling speed in athletes who consumed larger carbohydrate-rich breakfasts (500 vs 250 kcal with 60% carbohydrate) 135 minutes before exercise 1
• Extended endurance capacity: one study showed 108.8 minutes vs 101.4 minutes run time to exhaustion when comparing low vs high glycemic index meals 2

Critical Timing Caveat

Avoid consuming large amounts of carbohydrates in the 60 minutes immediately before exercise. 1 While this concern has been somewhat overstated in older literature, consuming elevated carbohydrate meals less than 60 minutes pre-exercise can cause:

• Reactive hypoglycemia in some individuals due to insulin surge 1
• Potential performance impairment from the metabolic disruption 1

However, recent evidence suggests this risk is minimal for most athletes, and the advice to completely avoid carbohydrates in the hour before exercise is largely unfounded 3

Practical Implementation

Choose easily digestible carbohydrate sources to reduce gastrointestinal problems such as reflux and discomfort 1

Consider individual comfort and rituals rather than rigid adherence to guidelines alone, as psychological readiness matters 1

Practice your pre-run fueling strategy during training sessions or lower-priority events before implementing it for important competitions 1

During-Run Carbohydrate Supplementation

For runs exceeding 1 hour, consume 30-60 g of carbohydrates per hour during exercise to maintain performance 1, 4. This can be achieved through:

• Sports drinks containing glucose/sucrose/maltodextrins 1
• Carbohydrate gels 1
• Even carbohydrate mouth rinsing can provide central nervous system benefits that reduce perceived effort 1

Substrate Utilization Considerations

Low glycemic index carbohydrate meals may shift substrate utilization toward greater fat oxidation during exercise compared to high glycemic index meals 2, 5, though performance outcomes appear similar between the two approaches 5. Women oxidize proportionally more fat and less carbohydrate than men at equivalent exercise intensities, which may influence individual carbohydrate requirements 1