Nutrition is a cornerstone of marathon training. Proper fueling supports training adaptations, speeds recovery, maintains immune function, and powers performance on race day. Understanding macronutrients, hydration, electrolyte balance, and fueling strategies allows runners to optimize energy availability and maximize training benefits.
This article covers the fundamental principles of endurance nutrition: carbohydrates, fats, protein, hydration, electrolytes, and practical fueling strategies throughout training cycles.
Why nutrition matters for marathon training
Supports training adaptations
Role:
- Provides raw materials for muscle repair and growth
- Fuels energy systems during workouts
- Supports mitochondrial biogenesis and aerobic adaptations
Consequence of poor nutrition:
- Impaired recovery
- Reduced training capacity
- Increased injury and illness risk
Powers workouts and recovery
Role:
- Adequate glycogen stores enable quality training sessions
- Post-workout nutrition accelerates muscle repair
- Hydration and electrolytes maintain performance
Consequence of poor nutrition:
- Early fatigue during runs
- Prolonged soreness
- Incomplete recovery between sessions
Optimizes race-day performance
Role:
- Proper fueling strategy delays glycogen depletion
- Hydration and electrolyte balance prevent cramping and bonking
Consequence of poor nutrition:
- Hitting the wall
- Gastrointestinal distress
- Premature fatigue
Carbohydrates: The primary fuel
Why carbohydrates matter
Primary energy source:
- Carbohydrates are stored as glycogen in muscles and liver
- Glycogen is the preferred fuel for moderate to high-intensity running
- Limited storage (~1,800-2,000 calories worth) makes availability critical
Impact on performance:
- Adequate glycogen supports sustained efforts
- Depletion leads to "hitting the wall" and severe fatigue
How much carbohydrate do runners need?
General guidelines (grams per kg body weight per day):
Low training volume (<1 hour/day):
- 3-5 g/kg
Moderate training volume (1-2 hours/day):
- 5-7 g/kg
High training volume (2-3 hours/day):
- 7-10 g/kg
Very high training volume (>3 hours/day):
- 10-12 g/kg
Example:
- 70 kg (154 lb) runner training 1.5 hours/day
- Target: 5-7 g/kg = 350-490 g carbs/day
Timing carbohydrate intake
Before training:
- Eat a carb-rich meal 2-4 hours before running
- Goal: Top off glycogen stores without GI distress
During training (runs >90 minutes):
- Consume 30-60 g carbs/hour to delay depletion
- Use gels, chews, sports drinks, or real food
After training:
- Consume carbs within 30-60 minutes post-run
- Goal: Replenish glycogen quickly for next session
- Target: 1-1.2 g/kg body weight
Types of carbohydrates
Simple carbohydrates (quick energy):
- Sugars, honey, sports drinks, gels
- Rapidly absorbed
- Ideal during and immediately after runs
Complex carbohydrates (sustained energy):
- Whole grains, oats, rice, pasta, potatoes, fruits
- Slower digestion, sustained release
- Ideal for daily meals and pre-run fueling
Fiber:
- Important for overall health
- Limit high-fiber foods immediately before runs to avoid GI issues
Fats: Sustained energy and health
Why fats matter
Energy source:
- Virtually unlimited fat stores provide energy for easy-paced running
- Training enhances fat oxidation, sparing glycogen
Essential functions:
- Hormone production
- Cell membrane structure
- Vitamin absorption (A, D, E, K)
How much fat do runners need?
General guideline:
- 20-35% of total daily calories
- Approximately 0.8-1.5 g/kg body weight
Example:
- 70 kg runner consuming 2,500 calories/day
- 20-35% from fat = 500-875 calories = 56-97 g fat/day
Types of fats
Unsaturated fats (prioritize these):
- Monounsaturated: Olive oil, avocados, nuts
- Polyunsaturated (including omega-3s): Fatty fish, flaxseeds, walnuts
Saturated fats (moderate intake):
- Found in meat, dairy, coconut oil
- Not inherently harmful in moderation
Trans fats (avoid):
- Processed and fried foods
- Increase inflammation and health risks
Fat adaptation and endurance
Concept:
- Training the body to rely more on fat oxidation at a given pace
- Spares limited glycogen stores
Training approach:
- Consistent easy aerobic running enhances fat oxidation
- Some runners experiment with low-carb availability on select easy runs
- Not necessary for most runners; adequate carb intake remains essential
Protein: Recovery and repair
Why protein matters
Muscle repair:
- Training breaks down muscle tissue; protein provides amino acids for repair
- Supports adaptation and growth
Immune function:
- Protein supports immune system, critical during heavy training
Satiety:
- Helps maintain healthy body composition
How much protein do runners need?
General guideline:
- 1.2-1.7 g/kg body weight per day
- Higher end for heavy training or calorie deficit
Example:
- 70 kg runner: 84-119 g protein/day
Distribution:
- Spread intake across meals (20-30 g per meal)
- Supports sustained muscle protein synthesis
Timing protein intake
Post-workout:
- Consume protein within 1-2 hours after running
- Combine with carbohydrates for optimal recovery
- Target: 20-30 g protein
Throughout the day:
- Include protein at each meal
- Supports ongoing recovery
Protein sources
Complete proteins (contain all essential amino acids):
- Meat, poultry, fish
- Eggs, dairy (milk, yogurt, cheese)
- Soy, quinoa
Incomplete proteins (combine for complete profile):
- Beans, lentils, legumes
- Nuts, seeds
- Whole grains
Hydration: The foundation of performance
Why hydration matters
Performance impact:
- Even 2% dehydration (loss of 2% body weight) impairs performance
- Reduces blood volume, increases heart rate, elevates perceived effort
Thermoregulation:
- Sweat cools the body; inadequate hydration impairs cooling
- Greater risk of heat illness when dehydrated
Recovery:
- Hydration supports nutrient delivery and waste removal
How much should runners drink?
Daily baseline:
- General guideline: Half your body weight (lbs) in ounces of water
- Example: 150 lb runner = 75 oz (~2.2 liters) per day
Before running:
- 16-20 oz water 2-3 hours before
- 8-10 oz 10-20 minutes before
During running:
- Runs <60 minutes: Usually no hydration needed
- Runs 60-90 minutes: 4-8 oz every 15-20 minutes as needed
- Runs >90 minutes: 4-8 oz every 15-20 minutes, include electrolytes
After running:
- Replace 150% of fluid lost
- Weigh before and after to estimate loss
- Example: Lost 2 lbs → drink 48 oz (3 lbs of fluid)
Signs of dehydration
Mild dehydration:
- Thirst
- Dry mouth
- Dark yellow urine
Moderate to severe dehydration:
- Dizziness
- Rapid heart rate
- Confusion
- Cessation of sweating (危险)
Overhydration (hyponatremia)
What it is:
- Excessive water intake dilutes blood sodium levels
- Can be life-threatening
Risk factors:
- Drinking too much water without electrolytes
- Long races (4+ hours) with excessive plain water intake
Prevention:
- Drink to thirst, not on a rigid schedule
- Use electrolyte drinks during long runs and races
- Avoid drinking excessively beyond what thirst dictates
Electrolytes: Balance and function
Key electrolytes for runners
Sodium:
- Most important electrolyte lost in sweat
- Maintains fluid balance and nerve function
Potassium:
- Supports muscle contractions and heart function
Magnesium:
- Involved in energy production and muscle relaxation
Calcium:
- Bone health and muscle contraction
Sodium and endurance running
Why sodium matters:
- Lost in significant amounts through sweat (500-1,000+ mg/hour)
- Critical for fluid absorption and muscle function
Symptoms of sodium depletion:
- Muscle cramps
- Nausea
- Confusion
- Hyponatremia (low blood sodium)
Sodium replacement:
- Sports drinks: 100-200 mg per 8 oz
- Salt tabs: 100-200 mg per tab
- Salty snacks: Pretzels, crackers
- Add salt to meals during heavy training
Guidelines for long runs (>90 minutes):
- Aim for 300-600 mg sodium per hour
- Adjust based on sweat rate and conditions
Fueling strategies throughout training cycles
Base building phase
Nutritional focus:
- Adequate carbohydrates to support mileage
- Consistent protein for recovery
- Establish daily hydration habits
Fueling during runs:
- Most runs are <90 minutes; fueling not necessary
- Hydrate as needed
Build and peak phases
Nutritional focus:
- Increased carbohydrate intake to match training intensity
- Protein remains consistent
- Practice race-day fueling during long runs
Fueling during long runs:
- Begin fueling at 60-75 minutes
- 30-60 g carbs/hour
- Practice with gels, chews, or real food to identify preferences
Recovery nutrition:
- Post-long run: Carbs + protein within 30-60 minutes
- Example: Smoothie with banana, protein powder, oats
Taper phase
Nutritional focus:
- Maintain carbohydrate intake despite reduced mileage (carb-loading)
- Reduce overall calories slightly to match lower expenditure
- Hydrate consistently
Carb-loading (final 2-3 days before race):
- Increase carbs to 8-10 g/kg body weight
- Reduce fat and fiber slightly to avoid GI issues
- Stay hydrated
Race-day fueling strategy
Pre-race meal (2-4 hours before)
Goals:
- Top off glycogen stores
- Avoid GI distress
Example meals:
- Oatmeal with banana and honey
- Toast with peanut butter and jam
- Bagel with a small amount of cream cheese
Guidelines:
- Familiar foods only (nothing new on race day)
- 200-400 calories, primarily carbs
- Low fiber, low fat
During the marathon
Carbohydrate intake:
- Begin fueling at 45-60 minutes
- Target: 30-60 g carbs/hour
- Options: Gels (20-25 g each), chews, sports drinks
Hydration:
- Drink 4-8 oz every 15-20 minutes
- Use sports drinks for combined carbs and electrolytes
- Avoid overdrinking
Electrolytes:
- Sodium: 300-600 mg/hour
- Use sports drinks or salt tabs
Post-race recovery
Immediate (within 30 minutes):
- Focus on rehydration first
- Light carbs and protein (smoothie, chocolate milk)
First meal (1-2 hours post-race):
- Balanced meal with carbs, protein, healthy fats
- Example: Rice bowl with chicken and vegetables
Common nutrition mistakes
Running on empty
Mistake: Skipping meals or inadequate carbs before key workouts Result: Poor performance, incomplete recovery
Solution: Plan carb-rich meals 2-4 hours before hard runs
Inadequate post-workout nutrition
Mistake: Delaying or skipping recovery nutrition Result: Prolonged soreness, slower adaptation
Solution: Eat carbs + protein within 30-60 minutes post-run
Trying new foods on race day
Mistake: Experimenting with unfamiliar gels, foods, or drinks during the race Result: GI distress, bonking
Solution: Practice fueling strategy during long training runs
Ignoring hydration
Mistake: Not drinking enough daily or during long runs Result: Dehydration, impaired performance, increased injury risk
Solution: Monitor urine color; drink consistently throughout the day
Over-restricting calories
Mistake: Severe calorie deficit while training hard Result: Poor recovery, loss of muscle mass, hormonal disruption, injury
Solution: Fuel adequately to support training; prioritize nutrient-dense foods
Practical nutrition checklist
Daily habits
- ✅ Eat balanced meals with carbs, protein, and healthy fats
- ✅ Hydrate consistently (urine pale yellow)
- ✅ Include fruits and vegetables for vitamins and minerals
- ✅ Prioritize whole foods over processed options
Pre-run
- ✅ Eat a carb-rich snack or meal 2-4 hours before
- ✅ Hydrate 16-20 oz water 2-3 hours before
During long runs (>90 minutes)
- ✅ Fuel with 30-60 g carbs/hour
- ✅ Hydrate 4-8 oz every 15-20 minutes
- ✅ Include electrolytes (sodium 300-600 mg/hour)
Post-run
- ✅ Consume carbs + protein within 30-60 minutes
- ✅ Rehydrate (150% of fluid lost)
Race week
- ✅ Carb-load 2-3 days before race
- ✅ Stay hydrated
- ✅ Avoid new foods
Summary
Nutrition is essential for marathon training success. Carbohydrates are the primary fuel source, with needs ranging from 3-12 g/kg body weight per day depending on training volume. Timing carbohydrate intake before, during, and after runs optimizes glycogen availability and recovery. Fats provide sustained energy and support essential physiological functions; 20-35% of daily calories should come from healthy fats. Protein supports muscle repair and adaptation; runners need 1.2-1.7 g/kg body weight per day, distributed across meals. Hydration is critical for performance and thermoregulation; runners should drink to thirst and replace 150% of fluid lost. Electrolytes, especially sodium, must be replaced during long efforts to prevent cramping and hyponatremia. Fueling strategies evolve throughout training phases, with particular attention to race-day nutrition including pre-race meals, in-race fueling (30-60 g carbs/hour), and post-race recovery. Avoiding common mistakes—running on empty, inadequate recovery nutrition, race-day experiments, dehydration, and over-restriction—supports consistent training and optimal performance.