Endurance Nutrition Guide: What to Eat During Long Workouts and Races

Fueling during endurance exercise (>90 minutes) is fundamentally about maintaining carbohydrate availability, fluid balance, and electrolyte homeostasis. Performance degradation (“bonking”) is primarily driven by glycogen depletion and dehydration, both of which are preventable with a deliberate nutrition strategy.

Modern endurance nutrition has evolved from conservative intake targets toward aggressive carbohydrate feeding strategies, especially among elite athletes. This article outlines normative ranges, individualized assessment, and emerging high-carb approaches.

1. Carbohydrate Intake During Exercise - Standard Recommendations (Normative Values)

Carbohydrate intake should scale with duration and intensity:
• 30 g/hour → low intensity / <2 hours
• 60 g/hour → moderate intensity / ~2–3 hours
• 60–90 g/hour → long-duration (>2.5–3 hours) events

These values align with traditional sports nutrition guidance aimed at preserving glycogen and maintaining blood glucose.

Physiological constraint
The intestine absorbs glucose via the SGLT1 transporter, which saturates at ~60 g/hour. Above this threshold, multiple transportable carbohydrates (glucose + fructose) are required.

Emerging Elite Practice: High-Carbohydrate Intake (90–120+ g/hour)
Elite athletes are increasingly targeting:
• 90 g/hour (now standard in elite marathons/triathlon)
• 100–120 g/hour (or higher) in cutting-edge protocols

Why higher works:
• Uses dual transporters (SGLT1 + GLUT5)
• Increases exogenous carbohydrate oxidation
• Spares muscle glycogen more effectively
• Supports higher sustained power outputs

Limiting factor: Gastrointestinal tolerance, not metabolism
This is why “gut training”—progressively increasing carbohydrate intake in training—is now considered essential.

1. Practical Carbohydrate Assessment

To individualize intake:

Step 1: Determine baseline tolerance
• Start at 40–60 g/hour
• Increase gradually (e.g., +10 g/hour per week)

Step 2: Monitor key markers
• GI distress (bloating, nausea)
• Energy stability vs. “bonk”
• Ability to maintain pace late in session

Step 3: Match intake to event demands
• Short races: lower end of range
• Long/hard races: push toward 90–120 g/hour

2. Sodium Requirements

Normative Sodium Intake

Typical ranges:
• 300–600 mg/hour (baseline)
• 400–700 mg/hour common recommendation
• Up to 1000 mg/hour for heavy/salty sweaters

Sodium helps:
• Maintain plasma volume
• Improve fluid absorption
• Reduce risk of hyponatremia

Variability in Sodium Needs

Sodium loss varies widely:
• Sweat sodium: ~300 mg/L → >1000 mg/L
• Sweat rate: 0.5 → >1.5 L/hour
This creates 10× differences between athletes.

Sodium Assessment Methods

1. Sweat Rate Testing
• Weigh before/after exercise
• 1 kg loss ≈ 1 L fluid loss

2. Qualitative indicators
• Salt stains on clothing
• Cramping history
• Burning eyes (salt in sweat)

3. Practical adjustment
• Start ~500 mg/hour
• Increase if:
o Cramping occurs
o Large sweat losses
o Hot conditions

3. Hydration Requirements - Normative Fluid Intake

Typical guidelines:
• 400–800 mL/hour (most athletes)
• Up to 1–1.2 L/hour in high heat or heavy sweating

Goal:
• Limit body mass loss to <2–3%

Hydration Physiology
• Dehydration → reduced plasma volume → increased cardiovascular strain
• Overhydration → dilution of sodium → hyponatremia risk
Thus, modern guidance emphasizes: Drink to thirst + informed by sweat rate

Hydration Assessment

1. Sweat Rate Calculation
• Pre/post weight difference
• Adjust for fluid consumed

2. Urine Color (baseline hydration)
• Pale yellow → adequate
• Dark → dehydrated

3. Performance indicators
• Rising heart rate at fixed pace
• Early fatigue
• Reduced sweat output (late-stage dehydration)

4. Integrating Carbs, Sodium, and Fluids
These variables are interdependent:
• Carbohydrates improve fluid absorption
• Sodium enhances fluid retention
• Adequate fluid enables carbohydrate delivery

A practical “system” per hour:
Component Typical Range
Carbohydrates 60–90 g (up to 120 g elite)
Fluids 400–800 mL
Sodium 300–700 mg

5. Personalization Framework

Step-by-Step Protocol

Step 1: Establish baseline
• 60 g carbs/hour
• 500 mL fluid/hour
• 400–600 mg sodium/hour

Step 2: Measure responses
• GI comfort
• Performance stability
• Body weight changes

Step 3: Adjust variables
• Increase carbs → performance limiter
• Increase fluids → dehydration signs
• Increase sodium → cramping/salt loss

6. Common Errors

Under fueling carbohydrates
• Most common limiter of endurance performance
• Leads to glycogen depletion and pace collapse

Overhydration without sodium
• Can cause hyponatremia

Not practicing race nutrition
• Gut tolerance must be trained

Static plans
• Needs change with:
o Temperature
o Intensity
o Duration

7. Key Takeaways

• Carbohydrates are the primary performance driver during endurance exercise
• Modern targets are shifting toward 90–120 g/hour in trained athletes
• Hydration and sodium must be individualized, not generalized
• The limiting factor is often gut tolerance, not physiology
• The optimal strategy is one that is tested repeatedly in training

To work with Coach Paul to help with your training follow this link: https://www.pxpendurance.com/coaching.php