Macros for Endurance Athletes: Nutrition for Triathlons, Marathons, and Cycling

Endurance sports push the limits of human physiology. Whether you’re training for an Ironman, chasing a Boston Qualifier, or conquering centuries on the bike, your nutrition determines whether you thrive or barely survive.

The demands are extreme. A marathon burns 2,500-3,500 calories. An Ironman triathlon can deplete 8,000-10,000 calories. A century ride torches 4,000-6,000 calories. Your body’s fuel stores can’t keep up—you have to master the art of strategic fueling.

This guide covers everything you need to know about macros for endurance athletes, from daily nutrition to race-day protocols that can make or break your performance.

Ready to calculate your baseline? Start with our macro calculator for personalized targets.

The Unique Demands of Endurance Sports

Endurance athletes face nutritional challenges that set them apart from every other sport.

The Energy Equation

Hours of training: While a powerlifter might train 4-6 hours per week, endurance athletes often log 10-25+ hours. More hours = more fuel needed.

Calorie burn: A 150-lb runner burns approximately 100 calories per mile. That’s 2,600 calories for a marathon—on top of normal daily energy needs.

Glycogen limitation: Your body stores roughly 1,500-2,000 calories of carbohydrate (glycogen) in muscles and liver. After 90-120 minutes of sustained effort, those stores run low. Without strategic fueling, you “bonk” or “hit the wall.”

The Three Energy Systems

Your body uses different fuel systems depending on intensity and duration:

System	Duration	Primary Fuel	Intensity
ATP-CP	0-10 seconds	Stored ATP/creatine	Maximum sprint
Glycolytic	10 sec - 2 min	Glycogen	High intensity
Oxidative	2+ minutes	Glycogen + fat	Endurance pace

For endurance athletes: The oxidative system dominates. At lower intensities, fat provides more fuel. As intensity increases, carbohydrate (glycogen) becomes the primary source. You can burn fat all day at an easy pace, but the moment you pick up the pace, you need glycogen.

The Endurance Athlete’s Dilemma

Here’s the challenge: you need to:

1. Consume enough total calories to fuel training
2. Maintain adequate glycogen for performance
3. Time nutrition around long sessions
4. Fuel during extended efforts
5. Recover sufficiently between sessions

Most recreational athletes undereat, undertrain their gut, and wonder why they feel terrible in races.

Learn the fundamentals in our guide to what macronutrients are.

The Optimal Macro Ratio for Endurance Athletes

Endurance athletes need more carbohydrates than almost any other athlete. Here’s the evidence-based framework.

The Research-Backed Targets

Macronutrient	Target Range	Notes
Carbohydrates	5-12g per kg body weight	Scales with training volume
Protein	1.2-1.7g per kg body weight	Higher for heavy training
Fat	20-35% of total calories	Don’t go below 20%

For a 150-pound (68kg) endurance athlete training 12+ hours weekly:

• Carbs: 340-680g per day (1,360-2,720 calories)
• Protein: 82-116g per day (328-464 calories)
• Fat: 60-100g per day (540-900 calories)
• Total: 2,800-4,000+ calories

How Training Volume Affects Your Macros

Weekly Training Hours	Carb Target	Total Calorie Range
5-8 hours	5-6g/kg	2,200-2,800
8-12 hours	6-8g/kg	2,800-3,500
12-15 hours	8-10g/kg	3,500-4,500
15-20+ hours	10-12g/kg	4,500-6,000+

Key insight: An Ironman athlete in peak training might need 4,000-5,000+ calories daily. Underfueling is the most common mistake—and the most devastating for performance.

Sport-Specific Considerations

Runners:

• High glycogen demands, especially for speed work
• Lower total calorie burn than cycling (no coasting)
• More GI sensitivity due to impact
• Carbs: 6-10g/kg

Cyclists:

• Can consume more food during activity (less GI stress)
• Very high calorie demands for long rides
• Can train the gut more easily
• Carbs: 6-12g/kg

Triathletes:

• Highest overall demands (three disciplines)
• Must fuel across different activities
• Complex race-day nutrition
• Carbs: 7-12g/kg

Ultrarunners:

• Extended duration requires fat adaptation + carbs
• GI tolerance is critical
• Lower intensity allows more fat burning
• Carbs: 5-8g/kg (varies by strategy)

Read our complete guide to carbohydrates for more on how carbs fuel performance.

Glycogen Management: Your Performance Currency

Glycogen—stored carbohydrate in your muscles and liver—is the limiting factor in endurance performance. Managing glycogen is the central skill of endurance nutrition.

Understanding Glycogen

Total storage capacity: ~400-600g (1,600-2,400 calories)

• Muscle glycogen: 300-400g
• Liver glycogen: 80-120g

Depletion rate:

• Easy pace: ~30-60g per hour
• Moderate pace: ~60-90g per hour
• Hard effort: ~90-120g per hour

The math problem: You store 2,000 calories of glycogen. A marathon at moderate pace depletes 150-180g of glycogen per hour. For a 4-hour marathon, that’s 600-700g of glycogen—far more than you store.

The solution: You must consume carbohydrates during extended efforts, and you must start with full glycogen stores.

Daily Glycogen Management

Post-training: Your muscles are primed to absorb glucose for 30-60 minutes after exercise. This is the optimal time to replenish glycogen.

Target: 1-1.2g carbs per kg body weight immediately post-workout

Between sessions: Adequate carb intake throughout the day keeps glycogen stores topped up. For athletes training twice daily, this is critical.

When Glycogen Becomes Critical

• Long sessions (90+ minutes): Glycogen depletion becomes a factor
• High-intensity intervals: Burns glycogen rapidly
• Back-to-back training days: Incomplete recovery = depleted stores
• Race week: Maximum stores are essential

Use our TDEE calculator to establish your baseline energy needs.

Race-Day Nutrition: Fueling for Peak Performance

Race day is where all your nutritional planning pays off—or falls apart. Here’s how to fuel for different endurance events.

The Carb-Loading Protocol

Carb loading increases glycogen stores by 25-40%, directly improving endurance performance for events over 90 minutes.

3-Day Loading Protocol (modern approach):

Day	Carbs	Activity
3 days before	10-12g/kg	Light training or rest
2 days before	10-12g/kg	Rest or very light activity
1 day before	10g/kg	Rest
Race morning	2-3g/kg	3-4 hours before start

For a 150-lb athlete, 10g/kg = ~680g of carbs per day.

That’s a LOT of carbs. Sample high-carb day:

• Breakfast: Large bowl oatmeal, banana, juice, toast = 150g
• Snack: Bagel with jam = 70g
• Lunch: Large pasta, bread, fruit = 160g
• Snack: Pretzels, sports drink = 80g
• Dinner: Rice, lean protein, bread = 140g
• Evening: More carbs as needed = 80g
• Total: ~680g

Carb loading tips:

• Reduce fiber (avoid GI issues)
• Reduce fat (leaves room for carbs)
• Stick to familiar foods
• You may gain 2-4 lbs (water stored with glycogen)—this is good!

Pre-Race Meal

Timing: 3-4 hours before start Target: 2-3g carbs per kg (150-200g for most athletes)

Ideal characteristics:

• High carbohydrate
• Moderate protein
• Low fat
• Low fiber
• FAMILIAR (nothing new on race day)

Example pre-race meals:

• White rice with small portion chicken, banana
• Bagel with jam, sports drink
• Oatmeal with honey, banana, toast
• Pancakes with syrup (light portion)

During-Race Fueling by Event

Half Marathon (1:30-2:30):

• Start fueling at 30-45 minutes
• Target: 30-60g carbs per hour
• 1-2 gels or equivalent

Marathon (3:00-5:00+):

• Start fueling at 30-45 minutes
• Target: 60-90g carbs per hour for trained gut
• 2-3 gels per hour, or equivalent in drink/chews

Olympic Triathlon (2:00-3:00):

• Primary fueling on bike
• Target: 60g carbs per hour on bike
• Minimal fueling needed on run

Half Ironman (4:30-7:00):

• Consistent fueling throughout
• Target: 60-90g carbs per hour
• Mix of liquid and solid nutrition

Full Ironman (8:00-17:00):

• Extensive fueling strategy required
• Target: 60-90g carbs per hour
• Must include real food, not just gels
• Train your gut extensively before race day

Century Ride (5:00-8:00):

• Less GI stress than running
• Target: 60-90g carbs per hour
• Can consume solid foods more easily
• Use aid stations and carry nutrition

Training Your Gut

Your gut is trainable. Athletes who practice race-day fueling during training can absorb more carbohydrate and experience fewer GI issues.

How to train your gut:

1. Start consuming carbs during long training sessions
2. Begin with 30g/hour and gradually increase
3. Practice with race-day products
4. Increase to 60g/hour, then 90g/hour if tolerated
5. Note which products work (and which don’t)

Timeline: Allow 8-12 weeks to fully adapt your gut for race-day fueling.

Meal Planning for Endurance Athletes

Daily nutrition builds the foundation for race-day performance. Here’s how to structure your eating.

Sample Day: High-Volume Training (15+ hours/week)

Target: 3,800 calories | 550g carbs | 130g protein | 90g fat

6:00 AM - Pre-Training (before 2-hour ride)

• 2 slices toast with jam
• Banana
• Small glass juice
• Macros: 80g carbs, 6g protein, 2g fat

8:30 AM - Post-Training Breakfast

• Large bowl oatmeal with milk
• 2 eggs
• 2 slices toast with peanut butter
• Orange juice
• Greek yogurt
• Macros: 120g carbs, 40g protein, 25g fat

12:00 PM - Lunch

• Large sandwich (turkey, cheese, vegetables)
• Pretzels
• Apple
• Sports drink
• Macros: 100g carbs, 35g protein, 15g fat

3:00 PM - Afternoon Snack

• Energy bar
• Banana
• Handful trail mix
• Macros: 70g carbs, 12g protein, 15g fat

6:00 PM - Dinner

• 6 oz salmon
• 2 cups pasta with marinara
• Side salad with olive oil
• Bread
• Macros: 100g carbs, 50g protein, 25g fat

9:00 PM - Evening Snack

• Cereal with milk
• Fruit
• Macros: 60g carbs, 15g protein, 5g fat

Daily Totals: ~530g carbs, 158g protein, 87g fat (~3,550 calories)

Sample Day: Recovery / Easy Day

Target: 2,600 calories | 350g carbs | 120g protein | 75g fat

7:00 AM - Breakfast

• 2 eggs
• 2 slices toast with butter
• Fruit
• Coffee with milk
• Macros: 40g carbs, 18g protein, 18g fat

10:00 AM - Snack

• Greek yogurt with granola
• Macros: 35g carbs, 18g protein, 8g fat

12:30 PM - Lunch

• Grilled chicken salad (large)
• Quinoa
• Bread
• Macros: 50g carbs, 45g protein, 15g fat

3:30 PM - Snack

• Apple with almond butter
• Macros: 35g carbs, 4g protein, 12g fat

6:30 PM - Dinner

• 5 oz steak
• Baked potato
• Vegetables
• Side salad
• Macros: 55g carbs, 40g protein, 20g fat

9:00 PM - Snack

• Casein shake with berries
• Macros: 20g carbs, 25g protein, 2g fat

Daily Totals: ~235g carbs, 150g protein, 75g fat (~2,200 calories)

Periodized Nutrition: Matching Food to Training

Smart endurance athletes adjust nutrition based on training phase.

Base Building Phase

Training focus: Aerobic development, long slow distance

Nutrition approach:

• Moderate carbs (5-7g/kg)
• Build fat-burning capacity with some fasted training
• Focus on overall health and recovery
• Less concern about precise timing

Build Phase

Training focus: Increasing intensity, specific workouts

Nutrition approach:

• Increase carbs (7-9g/kg)
• Fuel all high-intensity sessions
• Practice race nutrition
• Prioritize recovery

Peak / Race Phase

Training focus: Sharpening, race preparation

Nutrition approach:

• Maximum carbs around key workouts (8-12g/kg)
• Carb loading protocols before races
• Minimize GI risk (reduce fiber, avoid new foods)
• Perfect race-day nutrition strategy

Recovery Phase

Training focus: Rest, easy activity, rebuilding

Nutrition approach:

• Moderate intake, reduce with reduced training
• Focus on nutrient-dense whole foods
• Address any deficiencies
• Mental break from strict tracking

Check out our guide on how to track your macros for monitoring your intake.

Common Mistakes Endurance Athletes Make

Mistake #1: Chronic Underfueling

The most devastating mistake. Signs include:

• Declining performance despite training
• Constant fatigue
• Frequent illness/injury
• Hormonal issues (missed periods, low testosterone)
• Mood changes, poor sleep
• Weight loss without trying

Fix: Calculate your actual needs. High-volume endurance training requires enormous fuel.

Mistake #2: Not Eating During Long Sessions

“I’ll just tough it out” leads to:

• Bonking/hitting the wall
• Impaired immune function
• Excessive muscle breakdown
• Compromised recovery

Fix: Fuel any session over 60-90 minutes. Start early, eat consistently.

Mistake #3: Trying New Foods on Race Day

Your GI system doesn’t like surprises, especially during racing. New foods = potential disaster.

Fix: Practice EVERYTHING in training. Race day is not for experiments.

Mistake #4: Neglecting Protein

Endurance athletes often over-focus on carbs and forget protein. This leads to:

• Muscle loss
• Poor recovery
• Increased injury risk
• Compromised immune function

Fix: Hit 1.2-1.7g/kg daily, even when carbs are the priority.

Mistake #5: Fearing Weight Gain

Some athletes restrict calories, thinking lighter = faster. But:

• Underfueling impairs performance more than extra weight
• You can’t train hard without adequate fuel
• Chronic restriction leads to injury and illness

Fix: Performance first. Fuel your training, then address body composition in the off-season if needed.

Mistake #6: Not Training the Gut

Your GI system must be trained to handle race-day fueling. Without practice:

• GI distress during races
• Inability to absorb sufficient carbs
• Bonking despite trying to fuel

Fix: Practice race nutrition during training. Start 8-12 weeks before key races.

See our guide on common macro tracking mistakes for more pitfalls to avoid.

Supplements for Endurance Athletes

Focus on food first. But some supplements have evidence for endurance performance.

Evidence-Based Supplements

Caffeine:

• Improves endurance performance by 2-4%
• Take 3-6mg/kg, 60 minutes before racing
• Test in training first

Carbohydrate supplements (gels, drinks, chews):

• Essential for fueling during long efforts
• Not a “supplement” per se—actual fuel
• Find what works for your gut

Sodium/electrolytes:

• Critical for long/hot events
• Replace losses from sweat
• 500-1000mg sodium per hour for heavy sweaters

Beta-alanine:

• May help buffer lactate
• 3-6g daily for 4+ weeks to see effect
• Causes harmless tingling sensation

Beetroot juice/nitrates:

• May improve efficiency by 1-3%
• 500mg nitrate, 2-3 hours before racing
• More effective for less-trained athletes

Supplements to Skip

• Most “fat burners” (ineffective or dangerous)
• BCAAs (just eat protein)
• Most “recovery” formulas (just eat real food)
• Expensive multi-ingredient blends (waste of money)

Frequently Asked Questions

How many carbs do endurance athletes need?

Endurance athletes need 5-12 grams of carbohydrates per kilogram of body weight daily, depending on training volume. A 150-lb athlete training 12+ hours weekly needs approximately 400-600g of carbs per day. Higher training volume requires higher carbohydrate intake.

Should endurance athletes do low-carb or keto?

Low-carbohydrate diets impair high-intensity performance and are generally not recommended for serious endurance athletes. While fat adaptation has some role in ultra-endurance, any effort requiring sustained moderate-to-high intensity depends on carbohydrates. Most endurance athletes perform best with high carb intake.

How much should I eat during a marathon?

During a marathon, aim for 60-90 grams of carbohydrates per hour, starting at 30-45 minutes into the race. This typically means 2-3 gels per hour, or equivalent from sports drinks, chews, or other carb sources. Train your gut to handle this intake during long training runs.

What should I eat the night before a race?

The night before, eat a familiar meal that’s high in carbohydrates, moderate in protein, and low in fat and fiber. Examples include pasta with marinara sauce, rice with chicken, or a similar carb-focused meal. Avoid anything new, spicy, or high in fiber to minimize GI risk.

How do I avoid hitting the wall?

Prevent bonking by: (1) carb loading for 2-3 days before races over 90 minutes, (2) eating a proper pre-race meal 3-4 hours before start, (3) consuming 60-90g carbs per hour during the event, and (4) starting fueling early, not when you’re already depleted.

How much protein do endurance athletes need?

Endurance athletes need 1.2-1.7 grams of protein per kilogram of body weight daily. For a 150-lb athlete, that’s 82-116g of protein. This supports muscle repair, immune function, and recovery between training sessions.

What should I eat for recovery after a long workout?

Within 30-60 minutes after long training, consume 1-1.2g carbs per kg body weight plus 0.3-0.4g protein per kg. A 150-lb athlete should aim for 75-90g carbs and 20-30g protein. Chocolate milk, a smoothie with banana and protein, or a balanced meal all work well.

How do I fuel for an Ironman triathlon?

Ironman fueling requires extensive planning: carb load for 3 days before, eat a substantial pre-race meal (150-200g carbs), and consume 60-90g carbs per hour throughout the race (8-17 hours). Mix gels, sports drinks, and real food. Practice your exact fueling plan during training.

Is it bad to train fasted for endurance?

Occasional fasted easy training can enhance fat-burning capacity and is fine for sessions under 60-90 minutes. However, regularly training fasted, especially for hard or long sessions, impairs performance, accelerates muscle breakdown, and compromises training quality. Fuel your key sessions.

How do I know if I’m eating enough as an endurance athlete?

Signs of adequate fueling: consistent energy, good recovery between sessions, stable or improving performance, healthy immune function, normal hormonal markers, and stable mood. Signs of underfueling: constant fatigue, frequent illness/injury, declining performance, hormonal disruption, and mood changes.

Your Endurance Nutrition Action Plan

Step 1: Calculate your needs Use our macro calculator for baseline, then adjust for training volume:

• 5-8 hours/week: Maintenance + 200-400 calories
• 8-12 hours/week: Maintenance + 500-800 calories
• 12-20 hours/week: Maintenance + 800-1,500 calories

Step 2: Set your macros

• Carbs: 5-12g/kg based on training volume
• Protein: 1.2-1.7g/kg
• Fat: Remaining calories (minimum 20%)

Step 3: Master the timing

• Pre-training: Carb-focused meal 2-4 hours before
• During: 30-90g carbs/hour for sessions over 60-90 minutes
• Post-training: Carbs + protein within 60 minutes

Step 4: Train your gut Start practicing race nutrition 8-12 weeks out. Gradually increase carb intake during long sessions until you can handle race-day quantities.

Step 5: Perfect race-day protocol

• Carb load 2-3 days before
• Familiar pre-race meal 3-4 hours before
• Execute fueling strategy during race
• Nothing new—ever

Endurance sports demand more from your nutrition than almost any other athletic pursuit. Get it right, and you’ll train harder, race faster, and recover better.

Related guides: Macros for Runners | Carbohydrates Explained | How to Track Your Macros