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Nutrition for Endurance Athletes

Endurance performance isn't just about training volume—it's about fueling smart. Whether you're running marathons, cycling centuries, or competing in triathlons, your nutrition strategy can make or break your race day. This guide covers everything from daily training nutrition to race-day fueling protocols.

## 📖 The Story

Sarah: The Marathon Bonker​

Sarah had been training for her first marathon for six months. Her long runs were getting stronger, her pace was improving, and she felt confident. But during her 20-mile training runs, something kept happening around mile 18-20: her legs would turn to concrete, her pace would plummet, and she'd struggle to finish.

"I thought I just needed to train harder," Sarah recalls. "I didn't realize I was literally running out of fuel." She was training fasted in the mornings, eating a light breakfast, and only consuming water during her long runs. Her glycogen stores were depleting completely, causing her to "bonk."

After working with a sports dietitian, Sarah learned about carbohydrate periodization and race-day fueling. She started consuming 60g of carbs per hour during long runs, practiced with different fuel sources, and increased her overall carbohydrate intake on training days. Her next 20-miler? She negative split the second half.

Tom: The GI Disaster Triathlete​

Tom was a strong swimmer and cyclist, but his races were plagued by stomach issues. During his first half-Ironman, he had to make three bathroom stops on the run. "I was following all the nutrition advice I read online," he said. "Carb loading, energy gels every 30 minutes, sports drinks. But my stomach couldn't handle it."

Tom's mistake was trying protocols he'd never practiced in training. He was consuming unfamiliar products, taking in too much concentrated carbohydrate, and not accounting for his individual GI tolerance. The race-day stress amplified everything.

He spent six months training his gut—gradually increasing carbohydrate intake during training, testing different products, and learning which ratios of glucose to fructose worked for him. He discovered that real food (dates, rice cakes) worked better than gels for the bike, and that diluted sports drinks prevented the osmotic overload that caused his distress.

At his next half-Ironman, Tom had zero GI issues and finished 45 minutes faster.

Ana: The Ultra-Running Master​

Ana didn't start as a nutrition expert—she learned through hundreds of miles of trial and error. As an ultramarathoner running 50-100 mile races, she knew that nutrition wasn't just important, it was survival.

"In ultras, the saying is 'it's not a running race, it's an eating race,'" Ana explains. She learned to fuel early and often, consuming 200-300 calories per hour from diverse sources: salty potatoes, PB&J squares, broth, gels, and cola. She practiced in training, eating while running until it became automatic.

But Ana's real breakthrough came when she understood periodization. She didn't fuel the same way every day. Easy runs were sometimes fasted or low-carb, teaching her body to burn fat efficiently. Hard workouts and long runs were carb-fueled, training her gut to process food on the move. This metabolic flexibility made her resilient during races when fueling plans inevitably went sideways.

Now Ana coaches other ultra-runners, and her first lesson is always: "Your gut needs training just like your legs do."

🚶 Journey​

The Endurance Athlete's Nutrition Timeline

Your fueling strategy should evolve throughout your training cycle. Here's how nutrition periodizes across a typical season:

Focus: Build aerobic capacity and metabolic flexibility

Nutrition Approach:

  • Moderate overall carbohydrate intake (4-6g/kg body weight)
  • Occasional fasted easy runs (30-60 minutes) to enhance fat oxidation
  • Quality protein at each meal (1.4-1.6g/kg/day)
  • Emphasize nutrient density and anti-inflammatory foods
  • Practice race nutrition during one long run per week

Training Fueling:

  • Easy runs <90 minutes: water only or minimal carbs
  • Hard workouts: 30-60g carbs/hour
  • Long runs: practice race-day protocols (60-90g carbs/hour)

Why This Matters: Base phase is perfect for building metabolic flexibility—your ability to efficiently use both fat and carbohydrate for fuel. This makes you more resilient on race day.

## 🧠 The Science

Understanding the science behind endurance nutrition helps you make smarter fueling decisions. Here are the key physiological principles:

Energy Systems in Endurance Exercise​

Your body uses three primary fuel sources during endurance activity:

  1. Carbohydrate (Glycogen/Glucose): High-energy, rapidly available, limited storage (~2000 kcal)
  2. Fat (Fatty Acids): Lower intensity fuel, virtually unlimited storage, slower oxidation
  3. Protein: Minimal contributor (<5%), increases when carbs are depleted

The Critical Insight: You can store enough fat to run multiple marathons, but only enough glycogen for about 90-120 minutes of moderate-to-high intensity exercise. This is why carbohydrate fueling is paramount for endurance performance.

Glycogen Storage and Depletion​

Storage Capacity:

  • Muscle glycogen: ~400-600g (1600-2400 kcal)
  • Liver glycogen: ~80-100g (320-400 kcal)
  • Blood glucose: ~20g (80 kcal)
  • Total: ~2000-3000 kcal of stored carbohydrate

Depletion Rates:

  • Easy pace (60-70% VO2max): 1-2g/minute
  • Marathon pace (75-85% VO2max): 2-3g/minute
  • Threshold pace (85-95% VO2max): 3-4g/minute

At marathon pace, you'll deplete glycogen in 90-120 minutes without supplemental carbs. This is "the wall" or "bonking."

Carbohydrate Periodization: Train Low, Compete High​

Research shows that strategic training with low carbohydrate availability can enhance fat oxidation and metabolic flexibility, while competing with high carbohydrate availability optimizes performance.

"Train Low" Strategies:

  • Fasted easy runs (30-90 minutes)
  • Twice-daily training (second session in depleted state)
  • Sleep-low protocol (train hard in evening, restrict carbs before bed, train easy fasted next morning)

Benefits:

  • Increased mitochondrial density
  • Enhanced fat oxidation enzymes
  • Greater metabolic flexibility
  • Improved exercise efficiency

"Compete High" Approach:

  • Carb loading before races (8-12g/kg for 24-48 hours)
  • High carb intake during competition (60-90g/hour)
  • Maximized glycogen stores + exogenous carbs = sustained performance

Critical Caveat: Always fuel high-intensity workouts and long runs properly. "Train low" applies only to easy aerobic sessions.

Gut Training and Carbohydrate Absorption​

Your gut is trainable. Athletes who regularly consume carbohydrates during exercise develop:

  • Increased glucose transporter expression (SGLT1)
  • Faster gastric emptying
  • Reduced GI distress
  • Higher maximal carbohydrate absorption rates

Carbohydrate Transport Systems:

Key Insight: Using multiple types of carbohydrate (glucose + fructose in 2:1 ratio) can increase absorption from 60g/hour to 90g/hour or more, because they use different transporters.

GI Distress: Causes and Prevention​

Gastrointestinal problems affect 30-50% of endurance athletes. Understanding the causes helps prevent them:

Mechanical Factors:

  • Jostling of internal organs (especially running)
  • Reduced blood flow to gut (diverted to muscles)
  • Dehydration (reduces gastric emptying)

Osmotic Overload:

  • Too concentrated carbohydrate solutions draw water into gut
  • Causes cramping, bloating, diarrhea
  • Solution: dilute drinks, use isotonic formulas

FODMAP Sensitivity:

  • Fructose (when consumed alone or in excess)
  • Sugar alcohols (sorbitol, mannitol in some gels)
  • Certain fibers
  • Solution: choose glucose-based or glucose-fructose products

Prevention Strategies:

  1. Train your gut progressively
  2. Use 2:1 glucose-to-fructose ratios
  3. Practice with race-day products
  4. Avoid high-fiber, high-fat foods before events
  5. Stay adequately hydrated
  6. Consider low-FODMAP diet before important races

Hydration and Electrolyte Balance​

Fluid Needs:

  • Highly individual (sweat rate varies 0.5-2.5 L/hour)
  • Goal: limit body weight loss to <2-3%
  • Overhydration (hyponatremia) is dangerous—drink to thirst

Sweat Testing:

  • Weigh before and after 1-hour run in race conditions
  • Weight loss (kg) = sweat loss (L)
  • Account for any fluid consumed
  • This gives your hourly sweat rate

Sodium Needs:

  • Average sweat sodium concentration: 500-1000mg/L
  • Heavy/salty sweaters may lose >1500mg/L
  • Target: 500-700mg sodium/hour for most athletes
  • Signs of sodium depletion: cramping, bloating, nausea

Electrolyte Strategy:

  • Use sports drinks with sodium (not just water)
  • Consider salt tablets for events >2 hours or heavy sweaters
  • Practice electrolyte intake in training
  • Don't rely on gels alone—they're high carb, low sodium

Fat Adaptation vs. Carbohydrate Dependence​

Fat Adaptation Philosophy:

  • Train with low carb intake to maximize fat oxidation
  • Theoretically spares glycogen during races
  • Popular in ultra-endurance communities

The Evidence:

  • Fat-adapted athletes DO oxidize more fat at given intensities
  • BUT: high-intensity performance (race pace) suffers
  • Carbohydrate oxidation rates decrease (metabolic inflexibility)
  • No performance advantage over periodized carb approach

The Winning Strategy:

  • Metabolic flexibility: ability to use both fat AND carbs efficiently
  • Train easy runs with some low-carb availability
  • Fuel all high-intensity work and races with ample carbs
  • This gives you the best of both worlds

👀 Signs & Signals​

Well-Fueled vs. Underfueled Athlete

Signs of Proper Fueling​

In Training:

  • ✅ Sustained energy throughout workouts
  • ✅ Ability to complete prescribed intensities
  • ✅ Good recovery between sessions (not dragging)
  • ✅ Stable mood and motivation
  • ✅ Minimal GI issues during training
  • ✅ Regular menstrual cycles (for females)
  • ✅ Healthy immune function (not getting sick frequently)
  • ✅ Adequate sleep quality
  • ✅ Body composition supports performance
  • ✅ Strong finishes to long runs/rides

On Race Day:

  • ✅ Even pacing throughout event
  • ✅ Ability to push in final third
  • ✅ Mental clarity and focus
  • ✅ No sudden energy crashes
  • ✅ Minimal cramping
  • ✅ GI system tolerating fuel well
  • ✅ Meeting time goals

Warning Signs of Underfueling or Overtraining​

Energy and Performance:

  • ⚠️ Bonking or hitting the wall regularly
  • ⚠️ Progressive decline in workout quality
  • ⚠️ Inability to complete prescribed intensities
  • ⚠️ Heavy legs that don't respond to taper
  • ⚠️ Declining race performances despite training
  • ⚠️ Excessive fatigue throughout the day

Physiological Red Flags:

  • ⚠️ Irregular or absent menstrual periods (amenorrhea)
  • ⚠️ Frequent injuries (stress fractures, tendonitis)
  • ⚠️ Recurring illnesses or infections
  • ⚠️ Persistent muscle soreness
  • ⚠️ Elevated resting heart rate
  • ⚠️ Poor sleep quality or insomnia
  • ⚠️ Constant hunger or loss of appetite

Psychological Indicators:

  • ⚠️ Persistent low mood or irritability
  • ⚠️ Loss of training motivation
  • ⚠️ Anxiety about eating or weight
  • ⚠️ Obsessive thoughts about food or training
  • ⚠️ Social withdrawal

RED-S Warning (Relative Energy Deficiency in Sport):

If you experience three or more of these symptoms, you may have RED-S, a serious condition where energy intake doesn't match energy expenditure:

  • Irregular or absent periods
  • Low bone density or stress fractures
  • Suppressed immune function
  • Cardiovascular issues (low heart rate, orthostatic intolerance)
  • GI dysfunction
  • Impaired training response

Action Required: Consult a sports medicine physician and sports dietitian immediately. RED-S can have serious long-term health consequences.

GI-Specific Signals​

Well-Trained Gut:

  • Can consume 60-90g carbs/hour without distress
  • Tolerates variety of fuel sources
  • Hunger cues during long efforts
  • Normal bowel movements

Gut Issues:

  • Nausea during or after fueling
  • Cramping, bloating, or side stitches
  • Diarrhea during or immediately after exercise
  • Unable to tolerate any solid food
  • Complete loss of appetite

If GI issues persist: Consider low-FODMAP trial, slower gut training progression, different carb sources, or consultation with gastroenterologist.

🎯 Practical Application​

Daily and Race Nutrition Protocols

Daily Fueling for Endurance Training​

Your daily nutrition should support your training load and goals. Here's how to structure it:

Carbohydrate Periodization by Training Day:

Training TypeCarbs (g/kg)Example (70kg athlete)
Rest/Easy day3-5 g/kg210-350g
Moderate training5-7 g/kg350-490g
Hard workout day6-8 g/kg420-560g
Long run day7-10 g/kg490-700g
Race day8-12 g/kg560-840g

Protein Needs:

  • Daily target: 1.4-1.8 g/kg body weight
  • Distribute across meals: 25-40g per meal, 4-5 times daily
  • Post-workout: 20-30g within 60 minutes of training
  • Before bed: 20-40g casein or whole food protein (supports overnight recovery)

Fat Intake:

  • Target: 20-30% of total calories
  • Focus on quality: omega-3s (fatty fish, walnuts, flax), olive oil, nuts, avocados
  • Timing: Keep lower around intense workouts (slows digestion)

Sample High-Carb Training Day (70kg runner, long run day):

Breakfast (2 hours pre-run):

  • 2 cups cooked oatmeal with banana, honey, handful of berries
  • 2 eggs
  • Coffee
  • ~100g carbs, 25g protein

During Long Run (90-120 minutes):

  • 60-90g carbs/hour: sports drink, gels, chews
  • 400-600ml fluid/hour
  • ~90-135g carbs

Post-Run (within 30-60 min):

  • Chocolate milk or recovery shake
  • Bagel with peanut butter
  • ~80g carbs, 30g protein

Lunch:

  • Large burrito bowl: rice, beans, chicken, veggies, avocado
  • Fruit
  • ~110g carbs, 40g protein

Afternoon Snack:

  • Greek yogurt with granola and honey
  • ~60g carbs, 20g protein

Dinner:

  • Pasta with turkey meatballs and marinara
  • Side salad with olive oil dressing
  • Garlic bread
  • ~130g carbs, 45g protein

Evening Snack:

  • Cottage cheese with berries
  • ~25g carbs, 20g protein

Daily Total: ~595-630g carbs (8.5-9 g/kg), ~180g protein (2.6 g/kg), adequate fats

Workout-Specific Fueling:

Easy Runs (<60 minutes, conversational pace):

  • Pre: optional light snack if hungry
  • During: water only
  • Post: regular meal within 1-2 hours

Threshold Workouts (intervals, tempo runs):

  • Pre (1-2 hours before): 1-2g/kg easily digestible carbs
  • During: 30-60g carbs/hour if >60 minutes
  • Post: 3:1 or 4:1 carb-to-protein ratio within 60 minutes

Long Runs/Rides (2+ hours):

  • Pre (2-3 hours before): substantial carb-rich meal
  • During: 60-90g carbs/hour from practiced sources
  • Electrolytes: 500-700mg sodium/hour
  • Post: aggressive refueling, high carbs + protein

📸 What It Looks Like​

Example Nutrition Days and Timelines

High-Carb Long Run Day​

Athlete: 65kg female marathon runner Training: 20-mile long run (3 hours) Target: ~550g carbs, ~120g protein

5:30 AM - Wake Up

  • Glass of water

6:00 AM - Pre-Run Breakfast

  • 1.5 cups oatmeal with 1 tbsp honey
  • 1 banana
  • 2 eggs scrambled
  • Coffee with splash of milk
  • Water
  • Totals: ~95g carbs, 20g protein

7:30 AM - Start Run

  • Well-hydrated, fueled, ready

During Run (7:30-10:30 AM):

  • Miles 0-5: 20oz sports drink
  • Mile 6: Energy gel #1
  • Miles 7-10: 20oz sports drink
  • Mile 11: Energy gel #2
  • Miles 12-15: 20oz sports drink + 2 salt tabs
  • Mile 16: Energy gel #3
  • Miles 17-20: 16oz sports drink
  • Totals: ~270g carbs, sodium ~2100mg

10:45 AM - Immediate Post-Run

  • 16oz chocolate milk
  • Banana
  • Pretzels
  • Totals: ~85g carbs, 18g protein

12:00 PM - Lunch

  • Large chicken burrito bowl: rice, beans, chicken, veggies, cheese, salsa
  • Tortilla chips
  • Fruit cup
  • Totals: ~125g carbs, 45g protein

3:00 PM - Afternoon Snack

  • Greek yogurt (plain)
  • 1/2 cup granola
  • Berries
  • Drizzle of honey
  • Totals: ~65g carbs, 22g protein

6:30 PM - Dinner

  • Salmon (6oz)
  • Large sweet potato with butter
  • Quinoa (1 cup cooked)
  • Roasted vegetables
  • Side salad with olive oil
  • Dinner roll
  • Totals: ~95g carbs, 48g protein

9:00 PM - Evening Snack

  • Cottage cheese (1 cup)
  • Sliced peaches
  • Totals: ~25g carbs, 28g protein

Daily Total: ~560g carbs (8.6g/kg), ~181g protein (2.8g/kg)

Moderate Training Day​

Athlete: 75kg male triathlete Training: Easy 45-min run (morning) + 60-min moderate bike (evening) Target: ~400g carbs, ~135g protein

6:30 AM - Pre-Run

  • Banana
  • Water
  • Totals: ~25g carbs

7:00-7:45 AM - Easy Run

  • Water only

8:00 AM - Breakfast

  • 3 scrambled eggs
  • 2 slices whole grain toast with avocado
  • Mixed berries
  • Orange juice
  • Totals: ~70g carbs, 28g protein

11:00 AM - Mid-Morning Snack

  • Protein smoothie: protein powder, banana, milk, peanut butter, oats
  • Totals: ~55g carbs, 35g protein

1:30 PM - Lunch

  • Turkey sandwich on whole grain: turkey, cheese, veggies
  • Apple
  • Handful of almonds
  • Totals: ~60g carbs, 38g protein

4:00 PM - Pre-Bike Snack

  • Energy bar
  • Totals: ~35g carbs, 10g protein

5:00-6:00 PM - Moderate Bike

  • During: 20oz sports drink
  • Totals: ~35g carbs

6:30 PM - Dinner

  • Grilled chicken breast
  • Brown rice (1.5 cups cooked)
  • Stir-fried vegetables
  • Side salad
  • Totals: ~85g carbs, 50g protein

8:30 PM - Evening Snack

  • Greek yogurt
  • Granola
  • Totals: ~35g carbs, 20g protein

Daily Total: ~400g carbs (5.3g/kg), ~181g protein (2.4g/kg)

Race Morning Timeline​

Event: Marathon, 7:00 AM start Athlete: 70kg runner

3:30 AM - Wake Up

  • Set alarm, bathroom
  • Check weather for clothing decisions

3:45 AM - Pre-Race Meal

  • 1 bagel with 2 tbsp peanut butter
  • 1 banana
  • 16oz Gatorade
  • Totals: ~100g carbs
  • Goal: 90-140g carbs (1.3-2g/kg)

4:15-6:15 AM

  • Sip water gradually (8-12oz total)
  • Bathroom trips
  • Lay out race gear
  • Get dressed
  • Apply anti-chafe, sunscreen

6:00 AM - Pre-Race Caffeine

  • 16oz coffee or 2 caffeine gels
  • ~200mg caffeine (3mg/kg)

6:15 AM - Arrive at Race

  • Check gear, use bathroom (again)
  • Warm up jog (10 minutes easy)

6:45 AM - Final Prep

  • Last bathroom trip
  • Remove warm-up clothes
  • Pin on bib
  • Get to corral

6:55 AM - 5 Minutes to Start

  • Small sip of water
  • Mental prep, controlled breathing

7:00 AM - RACE START

  • First fuel scheduled: Mile 3 (20 minutes in)

During-Race Fueling Schedule​

Marathon Fueling Plan:

70kg runner, 3:30 marathon goal (8:00 min/mile pace) Strategy: 60g carbs/hour, 600mg sodium/hour

Pre-Race: 100g carbs, 200mg caffeine

TimeMileFuelCarbsSodiumNotes
:203Gel #125g100mgEarly fueling
:405Sports drink (8oz)14g110mgAid station
1:007Gel #225g100mgOn schedule
1:209Sports drink (8oz)14g110mgAid station
1:4011Gel #3 + water25g100mgHalfway
2:0013Sports drink (8oz)14g110mgAid station
2:2015Gel #425g100mgGetting tired
2:4017Sports drink (8oz)14g110mgAid station
3:0020Gel #5 (caffeinated)25g100mgFinal push
3:2023Sports drink (8oz)14g110mgNearly there
3:3026.2Finish!--Celebrate!

Total during race: ~195g carbs, ~940mg sodium, ~1L fluid

Post-Race (immediately):

  • Grab provided snacks: banana, bagel, chocolate milk
  • Water
  • Find family/friends
  • Within 30 min: ~60g carbs, 20g protein

Ultra-Endurance Example​

Event: 50-mile trail ultra (10 hours) Strategy: Mix of real food and sports nutrition

Hourly Fueling Pattern:

Hour 1-2 (Miles 0-10):

  • Energy chews + sports drink
  • ~60g carbs/hour

Hour 3-4 (Miles 10-20):

  • Aid station: boiled potatoes with salt, cola
  • Between stations: gels, water
  • ~70g carbs/hour

Hour 5-6 (Miles 20-30):

  • Aid station: PB&J quarters, pretzels, broth
  • Between: sports drink
  • ~80g carbs/hour
  • Starting to include savory/real food

Hour 7-8 (Miles 30-40):

  • Aid station: quesadilla pieces, watermelon, pickle juice
  • Between: alternating gels and chews
  • ~70g carbs/hour
  • Flavor variety crucial now

Hour 9-10 (Miles 40-50):

  • Aid station: soup, crackers, candy
  • Between: caffeinated gels, cola
  • ~60g carbs/hour
  • Whatever stays down

Average: ~70g carbs/hour, mix of 50% sports products, 50% real food

🚀 Getting Started​

8-Week Endurance Nutrition Build Plan

This progressive plan helps you develop optimal fueling habits and gut tolerance over 8 weeks. Start this alongside your training plan.

Weeks 1-2: Baseline and Assessment​

Goals:

  • Establish current baseline
  • Begin daily carb periodization
  • Start easy gut training

Daily Nutrition:

  • Calculate your needs: track food for 3 days to see current intake
  • Match carbs to training: 5-7g/kg on hard/long days, 3-5g/kg easy days
  • Hit protein target: 1.4-1.6g/kg daily

Workout Fueling:

  • Easy runs: water only
  • Hard/long workouts: begin with 30g carbs/hour
  • Test ONE sports drink brand
  • Practice post-workout nutrition within 60 minutes

Week 1 Focus: Awareness and tracking Week 2 Focus: Consistent fueling around key workouts

Weeks 3-4: Increase Carb Tolerance​

Goals:

  • Increase during-exercise carb intake
  • Test multiple fuel sources
  • Build fueling habits

Daily Nutrition:

  • Continue carb periodization
  • Add pre-workout snacks (1-2 hours before hard sessions)
  • Emphasize carbs around key workouts (before + after)

Workout Fueling:

  • Easy runs: still water only
  • Hard workouts: 30-45g carbs/hour
  • Long runs: 45-60g carbs/hour
  • Test at least 3 different products: gels, chews, drinks
  • Practice drinking while running

Week 3 Focus: Tolerating 45g/hour on long run Week 4 Focus: Testing different fuel products

Weeks 5-6: Optimize Fueling Strategy​

Goals:

  • Reach 60g+ carbs/hour tolerance
  • Dial in personal preferences
  • Practice race-simulation fueling

Daily Nutrition:

  • Fine-tune carb periodization based on energy and recovery
  • Ensure adequate protein distribution across day
  • Consider strategic fasted easy runs (optional, 30-45 min)

Workout Fueling:

  • Long runs: 60-75g carbs/hour
  • Practice early fueling (start within 15 minutes)
  • Test 2:1 glucose-fructose products if tolerating 60g/hour
  • Simulate race-day fuel schedule on one long run

Week 5 Focus: Consuming 60g/hour comfortably Week 6 Focus: Race-simulation long run with full fueling plan

Weeks 7-8: Race Preparation and Fine-Tuning​

Goals:

  • Finalize race-day plan
  • Practice pre-race meal
  • Test carb-loading strategy
  • Perfect electrolyte protocol

Daily Nutrition:

  • Continue periodized approach
  • Test pre-race breakfast timing and composition
  • Practice carb-loading for 2 days (8-10g/kg)
  • Monitor how you feel with higher carb intake

Workout Fueling:

  • Execute planned race-day fueling on final long run(s)
  • Dial in fluid and electrolyte needs (sweat test)
  • Practice carrying/accessing fuel in race conditions
  • Test caffeinated gels if planning to use

Week 7 Focus: Full race-day simulation (meal, fueling, timing) Week 8 Focus: Confidence and minor tweaks only

Your Race Week Checklist​

7 Days Before:

  • All race nutrition purchased and ready
  • Nothing new—only tested products
  • Review fueling schedule and carry plan
  • Check race day weather forecast

3 Days Before:

  • Begin gradual carb increase
  • Reduce fiber and high-fat foods
  • Stay well-hydrated (not excessive)
  • Get adequate sleep

2 Days Before:

  • Carb loading: 8-10g/kg
  • Easily digestible carbs (white rice, pasta, bread)
  • Avoid GI-irritating foods
  • Organize race gear and fuel

1 Day Before:

  • Continue carb loading
  • Early, familiar dinner
  • Lay out all race morning items
  • Set multiple alarms
  • Hydrate normally, not excessively

Race Morning:

  • Wake 3-4 hours before start
  • Consume practiced pre-race meal (1-4g/kg carbs)
  • Coffee/caffeine if practiced
  • Sip fluids, don't chug
  • Bathroom visits
  • Arrive with time to spare
  • Warm up appropriately

During Race:

  • Start fueling within 15-20 minutes
  • Stick to your plan (written on hand/arm if needed)
  • Adjust only if GI issues arise
  • Trust your training

🔧 Troubleshooting​

Common Endurance Nutrition Problems and Solutions

Problem 1: Bonking / Hitting the Wall​

Symptoms:

  • Sudden, dramatic energy loss
  • Heavy legs, inability to maintain pace
  • Mental fog, difficulty concentrating
  • Usually occurs at predictable point (mile 18-20 in marathon)

Causes:

  • Inadequate carbohydrate intake before or during exercise
  • Depleted glycogen stores
  • Insufficient fueling for effort level and duration
  • Starting too fast (burns through glycogen faster)

Solutions:

Immediate (during event):

  • Consume quick carbs: gel, chews, cola, sports drink
  • Slow pace temporarily to let fuel absorb
  • Continue fueling more aggressively
  • Switch to lower intensity (more fat burning)

Prevention (for next time):

  • Increase during-exercise carbs: aim for 60-90g/hour for efforts >90 minutes
  • Start fueling earlier: within first 15-20 minutes
  • Proper carb loading: 8-12g/kg for 24-48 hours before race
  • Pre-race meal: 1-4g/kg carbs 3-4 hours before
  • Don't start race too fast (pace discipline preserves glycogen)
  • Train your gut to tolerate more carbs

Testing Your Fueling: Calculate what you're actually consuming:

  • 2 gels/hour (25g each) + 16oz sports drink (28g) = only 78g/hour
  • May need 3 gels/hour or more sports drink to hit 90g target

Problem 2: GI Distress During Racing​

Symptoms:

  • Nausea, cramping, bloating
  • Urgent need for bathroom
  • Inability to tolerate any fuel
  • Sometimes vomiting

Causes:

  • Too much concentrated carbohydrate (osmotic overload)
  • Dehydration (slows gastric emptying)
  • Untrained gut (never practiced at this intensity)
  • High-FODMAP or problematic fuel sources
  • Excessive jostling (especially running)
  • Anxiety and race-day stress

Solutions:

During event (damage control):

  • Slow down or walk briefly (increases gut blood flow)
  • Dilute sports drinks more
  • Switch to easily tolerated carbs: cola (flat), bananas, pretzels
  • Small, frequent sips rather than large amounts
  • If nauseous: try ginger chews, avoid more fuel until settled
  • Ice chips or cold water can help

Prevention:

  • Progressive gut training: gradually increase carb intake during training over 8-12 weeks
  • Practice with race-day products: never use new fuel on race day
  • Use 2:1 glucose-to-fructose ratio (better absorption, less GI upset)
  • Dilute drinks appropriately (isotonic solutions work best)
  • Avoid high-fiber, high-fat foods 24 hours before event
  • Consider low-FODMAP diet week before important races
  • Stay hydrated (but don't overdrink)
  • Experiment with solid vs. liquid vs. gel sources

Long-term strategy:

  • Test products in training, not races
  • Keep food log to identify trigger foods
  • Consider consultation with sports dietitian or gastroenterologist if persistent
  • Some athletes do better with real food (rice cakes, waffles) than gels

Problem 3: Cramping​

Symptoms:

  • Painful muscle spasms
  • Usually in calves, quads, or hamstrings
  • Often occurs in latter stages of event
  • Can be debilitating

Causes:

  • Muscle fatigue (primary cause)
  • Electrolyte imbalance (especially sodium)
  • Dehydration
  • Inadequate training for distance
  • Going out too fast

Solutions:

Immediate:

  • Stop and stretch affected muscle gently
  • Massage area
  • Consume sodium: salt packet, pickle juice, salt tablet, pretzels
  • Rehydrate with electrolyte beverage
  • Slow pace until cramp resolves

Prevention:

  • Adequate sodium intake: 500-700mg/hour minimum, more for heavy/salty sweaters
  • Know your sweat rate: weigh before/after training runs
  • Don't rely on gels alone for electrolytes (they're low in sodium)
  • Use sports drinks with sodium or take salt tablets
  • Proper pacing (cramping often results from going out too fast)
  • Adequate training (build mileage appropriately)
  • Consider magnesium supplementation if deficient

Assessment:

  • Do a sweat test: weigh naked before and after 1-hour run in race-like conditions
  • Check your current sodium intake: read labels, calculate per hour
  • Very salty sweater? (white residue on skin/clothes, stinging eyes) = need more sodium

Problem 4: Flavor Fatigue with Gels​

Symptoms:

  • Can't stand the thought of another sweet gel
  • Gagging on familiar flavors
  • Difficulty consuming planned nutrition
  • Mental resistance to fueling

Causes:

  • Monotony of sweet flavors over hours
  • Taste bud fatigue
  • Nausea amplifying aversion
  • Simply human nature during long events

Solutions:

Immediate:

  • Switch to savory options: pretzels, salted potatoes, broth, pickles
  • Try different texture: chews, waffles, real food vs. gels
  • Rinse mouth with water
  • Chase sweet with salty
  • Use unflavored/bland options: plain water, white bread, rice

Prevention:

  • Variety is key: bring multiple flavor profiles
  • Alternate sweet and savory
  • Mix textures: gels, chews, bars, real food
  • Include neutral options: bananas, rice cakes, plain potatoes
  • Caffeinated gels taste different—save for late race
  • Practice with variety in training

Product Alternatives:

  • Sweet: standard gels, chews, sports drink, candy
  • Savory: pretzels, salted nuts, rice cakes with nut butter
  • Neutral: bananas, white bread, boiled potatoes
  • Refreshing: watermelon, orange slices, cola
  • Soothing: broth, ginger chews

Problem 5: Weight Management for Endurance Performance​

The Challenge: Many endurance athletes struggle with the balance between fueling for performance and managing body composition. Underfueling hurts performance and health. Overfueling can lead to unwanted weight gain.

Healthy Approach:

Priorities (in order):

  1. Health: adequate energy availability, healthy hormones, bone health
  2. Performance: properly fueled training, good recovery
  3. Body composition: natural result of training and balanced nutrition

Strategies:

  • Carb periodization: higher carbs on hard/long days, moderate on easy days (natural calorie variation)
  • Nutrient timing: front-load carbs around training, lighter evenings on easy days
  • Protein emphasis: 1.6-2.0g/kg preserves muscle during any deficit
  • Quality over quantity: nutrient-dense whole foods, limit processed foods
  • Don't cut during peak training: maintain weight during high-volume blocks
  • Gradual changes: aim for 0.5-1% body weight change per week maximum
  • Track performance, not just weight: if training quality declines, eat more

Red Flags (seek professional help):

  • Menstrual irregularities or loss of period
  • Frequent injuries or illness
  • Declining performance despite training
  • Obsessive thoughts about food/weight
  • Restricting entire food groups
  • Training quality suffering

Remember: A properly fueled athlete who weighs slightly more will outperform an underfueled athlete who weighs less. Performance comes from being well-fueled, not from being light.

Problem 6: Low Energy Availability (RED-S)​

What is RED-S? Relative Energy Deficiency in Sport occurs when energy intake doesn't match energy expenditure, leading to low energy availability (EA). This impairs physiological functioning.

Energy Availability = Energy Intake - Exercise Energy Expenditure

Optimal EA: >45 kcal/kg fat-free mass/day Low EA: <30 kcal/kg fat-free mass/day

Warning Signs:

  • Irregular or absent menstrual periods (primary red flag for females)
  • Frequent injuries (stress fractures, tendonitis)
  • Recurrent illness
  • Decreased performance despite training
  • Poor recovery
  • Low bone density
  • Mood disturbances, depression
  • Constant fatigue

Health Consequences:

  • Bone health: osteoporosis, stress fractures
  • Reproductive health: infertility, pregnancy complications
  • Metabolic: hormonal disruption, low metabolism
  • Cardiovascular: low heart rate, orthostatic intolerance
  • Psychological: depression, anxiety, eating disorders

If You Suspect RED-S:

IMMEDIATE ACTIONS:

  1. Consult sports medicine physician
  2. See registered sports dietitian
  3. Consider mental health professional if needed
  4. Reduce training volume
  5. Increase energy intake

Recovery Process:

  • Prioritize health over performance
  • Increase calories gradually (don't fear weight gain—it's necessary)
  • Balanced nutrition: adequate carbs, protein, fats
  • May need 6-12+ months for full recovery
  • Regular monitoring: hormones, bone density, labs
  • Return to training only when cleared medically

Prevention:

  • Fuel adequately for training volume
  • Don't ignore menstrual irregularities
  • Monitor for warning signs
  • Avoid extreme restriction or "cutting" during heavy training
  • Value health and longevity over short-term performance

Resources:

For Mo​

For Mo: Assessing Endurance Nutrition Needs

When a user indicates they're training for endurance events (marathon, triathlon, cycling, etc.), gather this information:

Event-Specific:

  • What event(s) are you training for? (distance, terrain, expected duration)
  • When is your goal race?
  • What's your current training volume? (hours/week, long run distance)
  • What phase are you in? (base, build, peak, recovery)

Current Fueling Approach:

  • What does a typical training day look like food-wise?
  • How do you currently fuel during long runs/rides? (what products, how much, when)
  • Have you practiced race-day nutrition in training?
  • Do you periodize carbs based on training intensity/volume?

GI History:

  • Have you experienced GI issues during training or racing?
  • What have you tried that worked well? What didn't work?
  • Any known food sensitivities or intolerances?
  • Can you currently tolerate 60+ grams of carbs per hour during exercise?

Race Experience:

  • Have you raced this distance before?
  • Did you "bonk" or hit the wall in previous races?
  • How did previous race nutrition plans go?

Goals and Constraints:

  • What are your performance goals?
  • Any dietary restrictions (vegetarian, allergies, preferences)?
  • Do you have access to sports nutrition products or prefer real food?

Red Flag Screening:

  • For females: Are your menstrual periods regular?
  • Any history of stress fractures or frequent injuries?
  • How's your energy throughout the day and during training?
  • Any concerning weight changes or obsessive thoughts about food/weight?

Based on responses, provide:

  1. Specific daily carb/protein targets based on body weight and training phase
  2. Personalized during-exercise fueling plan (products, timing, amounts)
  3. Race-week and race-day protocols
  4. Gut training progression if needed
  5. Troubleshooting for specific issues mentioned
  6. Red flag warnings if any concerning patterns emerge (refer to professional)

Key Principle: Endurance nutrition is highly individual. What works for one athlete may not work for another. Encourage experimentation in training, never on race day.

❓ Common Questions​

Frequently Asked Questions

Q1: Is carb loading really necessary, or is it bro-science?​

Short answer: Carb loading is scientifically validated and beneficial for events lasting >90 minutes at race pace.

The science: Research shows that increasing carbohydrate intake to 8-12g/kg body weight for 24-48 hours before endurance events increases muscle glycogen stores by 20-40% above normal levels. This "glycogen super-compensation" translates to improved endurance performance.

When it helps:

  • Marathon and longer distances
  • Half-marathon for competitive runners
  • Cycling events >2 hours
  • Triathlons
  • Any sustained effort >90 minutes at moderate-high intensity

When it's less critical:

  • Events <60 minutes (glycogen rarely depleted)
  • Ultra-endurance at lower intensities (relying more on fat oxidation)
  • Recreational efforts where you'll fuel abundantly during

How to do it:

  • 48-72 hours before: 8-12g carbs/kg/day
  • Choose easily digestible carbs (white rice, pasta, bread, potatoes)
  • Reduce fiber and fat slightly
  • Don't overeat to discomfort—just emphasize carbs

Bottom line: For marathon or longer, carb loading provides a meaningful performance advantage. The research supports it.

Q2: Should I use gels or "real food" during races?​

Short answer: Either can work—choose based on personal tolerance, event type, and what you've practiced.

Advantages of Sports Gels/Chews:

  • Precise carbohydrate dosing
  • Convenient to carry and consume
  • Rapid absorption (engineered for it)
  • Less GI load (no fiber, fat, protein)
  • Work well for running (minimal chewing)
  • Wide availability at aid stations

Advantages of Real Food:

  • Better flavor variety, less monotony
  • More satisfying psychologically
  • Provides some sodium, minerals
  • Often cheaper
  • Can be easier on sensitive stomachs (for some)
  • Better for ultra-endurance (food sounds appealing, gels don't)

Best Approach:

  • Running/high intensity: Gels and sports drinks usually work best (running jostles stomach, making digestion harder)
  • Cycling/lower intensity: Real food often tolerated well (rice cakes, waffles, bananas, PB&J)
  • Ultra-endurance: Combination approach—gels early when you can tolerate them, real food later when you crave it
  • Personal tolerance: Some athletes do great with gels; others can't stomach them. Test in training.

Real Food Options:

  • Bananas (25g carbs)
  • Dates (18g carbs each)
  • Rice cakes with honey or jam
  • Mini PB&J sandwiches
  • Boiled potatoes with salt
  • Stroopwafels (wafer cookies)
  • Homemade energy bites

Recommendation: Use what you've practiced and what sits well. There's no "should"—there's only what works for you. Many athletes use gels/chews for precise fueling but bring real food for variety.

Q3: How much caffeine should I use, and when?​

Short answer: 3-6mg/kg body weight, consumed 30-60 minutes before or during endurance events, provides a performance benefit.

The science: Caffeine is one of the most evidence-based ergogenic aids. It works by:

  • Reducing perceived exertion (effort feels easier)
  • Enhancing fat oxidation (spares glycogen)
  • Improving alertness and focus
  • Delaying fatigue

Effective dose:

  • Low responders / caffeine-habituated: 5-6mg/kg
  • Moderate users: 3-4mg/kg
  • Caffeine-naive or sensitive: 1-3mg/kg

Example (70kg athlete):

  • Low: 200mg (2 cups coffee or 2 caffeinated gels)
  • Moderate: 280mg (3 cups coffee or 3 caffeinated gels)
  • High: 400mg (4 cups coffee)

Timing strategies:

Pre-race:

  • 30-60 minutes before start
  • Allows peak blood levels during race
  • Good for events <2 hours

During race:

  • Later in race (mile 18-20 in marathon)
  • Provides mental boost when fatigue sets in
  • Useful for longer events (marathon, ultra, Ironman)

Both:

  • Pre-race dose + additional during race
  • For events >3 hours

Practical tips:

  • Practice caffeine strategy in training (don't test on race day)
  • Consider personal tolerance (some get jittery or GI upset)
  • Habitual users may need higher doses for same effect
  • Don't megadose—more isn't better, and >9mg/kg increases side effects
  • Sources: coffee, caffeinated gels, energy chews, cola

Cautions:

  • Dehydrating effects are minimal during exercise
  • May increase heart rate and anxiety in sensitive individuals
  • Can worsen GI issues for some
  • Not recommended for those with heart conditions (consult doctor)

Q4: Should I try fat adaptation or low-carb training?​

Short answer: Strategic low-carb training has a place, but full fat-adaptation (chronic low-carb diet) impairs high-intensity performance. The best approach is metabolic flexibility, not metabolic rigidity.

What is fat adaptation? Following a chronic low-carbohydrate, high-fat diet to maximize the body's ability to burn fat for fuel. Popular in ultra-endurance circles.

The theory:

  • Humans store ~2000 kcal of glycogen but 50,000+ kcal of fat
  • If you train your body to burn fat efficiently, you won't bonk
  • Reduced reliance on external carbohydrate during events

What the research shows:

Confirmed benefits:

  • Increased fat oxidation rates at submaximal intensities
  • Reduced carbohydrate oxidation at given pace
  • Potential benefits for ultra-endurance at lower intensities

Confirmed drawbacks:

  • Impaired high-intensity performance: Fat-adapted athletes show reduced VO2max, lactate threshold, and sprint capacity
  • Reduced carbohydrate metabolism (lose the ability to burn carbs efficiently)
  • No performance advantage over high-carb athletes in races from 5K to marathon
  • Metabolic inflexibility: stuck in fat-burning mode

The better approach: Periodized "Train Low, Compete High"

Strategic low-carbohydrate availability for specific sessions:

  • Fasted easy runs (30-90 minutes) once or twice per week
  • "Sleep low" protocol: train hard in evening, restrict carbs before bed, train easy fasted next morning
  • Occasional back-to-back training with limited refueling between

Benefits:

  • Enhances fat oxidation capacity (metabolic flexibility)
  • Maintains ability to burn carbs when needed
  • Best of both worlds: fat-burning efficiency + high-intensity performance

Always fuel:

  • High-intensity workouts (intervals, tempo, threshold)
  • Long runs >90 minutes
  • Key race-simulation sessions
  • Races

Bottom line: Don't go full keto/low-carb if you want to race well. Do incorporate strategic low-carb training to enhance fat oxidation while maintaining carbohydrate metabolism. Flexibility beats rigidity.

Q5: Is fasted training beneficial?​

Short answer: Fasted easy training can enhance fat oxidation and metabolic adaptations, but should be used strategically—not for all training.

Benefits of occasional fasted training:

  • Increased fat oxidation during exercise
  • Enhanced mitochondrial biogenesis (more mitochondria)
  • Improved metabolic flexibility
  • Teaches body to be efficient with limited fuel
  • May improve insulin sensitivity

Appropriate use:

  • Easy aerobic runs (30-90 minutes, conversational pace)
  • Low-intensity cycling
  • Recovery sessions
  • Once or twice per week maximum
  • Only in base/build phases, not during peak training or taper

Do NOT train fasted for:

  • High-intensity workouts (intervals, tempo, threshold)
  • Long runs >90 minutes
  • Back-to-back hard training days
  • When recovering from illness or injury
  • If you have history of RED-S or eating disorders

Risks of excessive fasted training:

  • Impaired workout quality (can't hit prescribed intensities)
  • Increased muscle breakdown
  • Poor recovery
  • Compromised immune function
  • Low energy availability (RED-S risk)
  • Not sustainable during high-volume training

How to implement:

  • Start with 30-minute easy runs
  • Gradually extend to 60-90 minutes
  • Listen to your body—if feeling weak/dizzy, eat
  • Always fuel hard workouts and long runs
  • Maintain overall daily carbohydrate intake (just timing shift)

Who should avoid fasted training:

  • Anyone with history of disordered eating
  • Athletes with menstrual irregularities
  • During periods of high stress or inadequate sleep
  • When fighting illness
  • Beginners (focus on consistency first)

Recommendation: Fasted easy training is a tool, not a rule. Use it strategically to build metabolic flexibility, but don't sacrifice workout quality or overall fueling.

Q6: How do I know if I'm consuming enough during a race?​

Short answer: Track your carb intake, monitor performance and symptoms, and assess post-race recovery.

Calculating your intake:

Do the math during or after your race:

  • Count gels consumed: 25g each
  • Measure sports drink: ~15g carbs per 8oz
  • Add any food consumed

Example:

  • 4 gels (100g) + 40oz sports drink (75g) = 175g total
  • Over 3-hour marathon = 58g/hour
  • Verdict: Probably underfueled for marathon (target 60-90g/hour)

Performance indicators:

Signs you fueled well:

  • Even pacing throughout race
  • Maintained or increased pace in final third
  • Mental clarity, good focus
  • No sudden energy crashes
  • Minimal cramping
  • Good recovery in days following

Signs you underfueled:

  • "Bonking" or hitting the wall
  • Dramatic pace slowdown in final third
  • Brain fog, difficulty concentrating
  • Lightheadedness or dizziness
  • Seeing stars, tunnel vision
  • Legs felt "empty" or "dead"
  • Post-race extreme fatigue lasting days

Signs you overfueled or fueled poorly:

  • GI distress (nausea, cramping, diarrhea)
  • Bloating or sloshing feeling
  • Excessive bathroom stops
  • Difficulty consuming more fuel

Post-race assessment:

Good fueling results in:

  • Quick recovery (feeling decent next day)
  • Minimal muscle damage markers
  • Normal appetite returns within hours
  • No extreme fatigue or weakness

Testing in training:

  • Practice with different amounts: 40g/hour, 60g/hour, 80g/hour
  • Note how you feel during and after
  • Track performance (pace, perceived exertion)
  • Gradually increase tolerance over weeks/months

Target ranges:

Event DurationCarb Target
<60 min0-30g/hour (mouth rinse OK)
60-150 min30-60g/hour
150 min-3 hours60-90g/hour
3+ hours (ultra)90-120g/hour

Remember: Individual variability is huge. Some athletes thrive on 60g/hour, others need 100g/hour. Training your gut increases capacity over time.

✅ Quick Reference​

At-a-Glance Guidelines

Daily Carbohydrate Targets by Training Volume​

Training Day TypeCarbs (g/kg)60kg Athlete70kg Athlete80kg Athlete
Rest/Easy3-5180-300g210-350g240-400g
Moderate training5-7300-420g350-490g400-560g
High volume/intensity7-10420-600g490-700g560-800g
Race day8-12480-720g560-840g640-960g

Protein Targets​

  • Daily: 1.4-1.8 g/kg body weight
  • Per meal: 25-40g
  • Post-workout: 20-30g within 60 minutes
  • Before bed: 20-40g slow-digesting (casein, Greek yogurt)

During-Exercise Fueling by Duration​

DurationCarbs/HourExample Products
<60 min0-30gMouth rinse or small amount
60-90 min30-60g1-2 gels OR 20oz sports drink
90-150 min60g2 gels + 16oz sports drink
150+ min60-90g3 gels + 16oz sports drink
Ultra (3+ hours)90-120gMix of gels, real food, drinks

Key principle: Start early (within 15-20 minutes), consume frequently (every 15-20 minutes), use multiple carb types (glucose + fructose) for >60g/hour.

Hydration Guidelines​

Sweat Rate Assessment:

  1. Weigh naked before 1-hour run (race conditions)
  2. Run 1 hour, noting fluid consumed
  3. Weigh naked after run
  4. Weight loss (kg) + fluids consumed (L) = sweat rate (L/hour)

During Exercise:

  • Target: Replace 50-80% of sweat losses
  • Range: 400-800ml/hour (highly individual)
  • Don't: Force excessive fluids or drink plain water exclusively
  • Do: Drink to thirst, use electrolyte beverages

Electrolyte (Sodium) Needs:

  • Minimum: 500-700mg sodium/hour
  • Heavy/salty sweaters: 1000mg+/hour
  • Sources: Sports drinks, salt tablets, salted foods

Race Day Checklist​

24-48 Hours Before:

  • Carb loading: 8-12g/kg/day
  • Reduce fiber, fat, gas-producing foods
  • Stay hydrated (not excessive)
  • All race nutrition gathered and organized
  • Nothing new or untested

Race Morning (3-4 hours before):

  • Pre-race meal: 1-4g/kg carbs (familiar foods)
  • Caffeine: 3-6mg/kg if practiced
  • Adequate fluids, not excessive
  • Bathroom visits

To Carry/Access During Race:

  • Planned number of gels/chews
  • Salt tablets if using
  • Knowledge of aid station locations and offerings
  • Fuel schedule written on hand/arm or in pocket
  • Backup gel in case one drops

Post-Race (within 30-60 min):

  • Recovery nutrition: carbs + protein
  • Rehydration with electrolytes
  • Continue fueling throughout day

Quick Carb Calculations​

Pre-Race Meal (3-4 hours before):

  • Marathon: 2-3g/kg (140-210g for 70kg athlete)
  • Half-marathon: 1-2g/kg (70-140g)

During Race:

  • Marathon goal time 3-4 hours: need 180-360g total carbs (60-90g/hour)
  • Half-marathon goal 1.5-2 hours: need 45-120g total carbs

Post-Race Refueling:

  • Immediate (0-60 min): 1.0-1.2g/kg carbs + 0.25-0.4g/kg protein
  • First 24 hours: 7-10g/kg carbs to maximize glycogen resynthesis

Troubleshooting Quick Reference​

ProblemQuick Solutions
BonkingMore carbs pre-race and during; start fueling earlier
GI distressDilute drinks, reduce carb rate, practice gut training, try different products
CrampingMore sodium (500-700+mg/hour), better pacing, adequate training
Flavor fatigueBring variety: alternate sweet/savory, different textures
NauseaSlow down temporarily, small sips, ginger, switch to bland foods (banana, bread)

Products to Test in Training​

Gels (25g carbs each):

  • GU Energy Gel (glucose/fructose blend)
  • Maurten Gel 100 (hydrogel technology)
  • Honey Stinger (honey-based)
  • SIS GO Isotonic (liquid gel)

Chews/Blocks:

  • Clif Shot Bloks
  • GU Energy Chews
  • Honey Stinger Chews
  • Skratch Energy Chews

Sports Drinks:

  • Gatorade Endurance (more sodium)
  • Maurten Drink Mix
  • Skratch Labs Sport Hydration
  • Tailwind Nutrition

Real Food Options:

  • Bananas
  • Rice cakes with honey/nut butter
  • Dates
  • Homemade energy bites
  • Boiled potatoes with salt

Always test before race day.

💡 Key Takeaways​

Essential Insights for Endurance Nutrition

  1. Carb Loading and Race Fueling Are Non-Negotiable for Performance

    • For events >90 minutes, carb loading (8-12g/kg for 24-48 hours) and during-exercise carb intake (60-90g/hour) dramatically improve performance. This isn't optional—it's physiological necessity. You only store ~2000 kcal of glycogen, enough for 90-120 minutes at race pace.

  2. Your Gut is Trainable—Use It

    • The ability to consume and absorb 60-90g of carbs per hour during exercise is a skill that requires months of practice. Start with 30g/hour and progressively increase. Athletes who train their gut have fewer GI issues and better race-day fueling capacity. Practice in training what you'll do on race day.

  3. Periodize Everything: Training, Carbs, and Fueling

    • Match your nutrition to your training phase and daily training load. High-carb days for hard/long workouts (7-10g/kg), moderate carbs on easy days (3-5g/kg). Strategic low-carb easy sessions can enhance metabolic flexibility, but always fuel high-intensity work and races. Train low (sometimes), compete high (always).

  4. Metabolic Flexibility Beats Metabolic Rigidity

    • The goal isn't to be a "fat-burner" or "carb-dependent"—it's to be efficient at using both fuel sources appropriately. Fat-adapted athletes can oxidize more fat but sacrifice high-intensity performance. Metabolically flexible athletes efficiently burn fat at easy paces and carbs at race pace. This gives you resilience and performance.

  5. Early and Consistent Fueling Prevents the Bonk

    • Don't wait until you're tired to start fueling—by then it's too late. Begin consuming carbs within 15-20 minutes of starting your race, and fuel consistently every 15-20 minutes. Small, frequent doses work better than large boluses. The bonk isn't inevitable—it's preventable with proper fueling strategy.

🔗 Connections to Other Topics​

Related Wellness Science
Related Goals

📚 Sources​

Scientific References and Further Reading

Position Stands and Reviews​

  1. Thomas, D.T., Erdman, K.A., & Burke, L.M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501-528.

    • Comprehensive position stand covering all aspects of sports nutrition

  2. Burke, L.M., Hawley, J.A., Wong, S.H.S., & Jeukendrup, A.E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(sup1), S17-S27.

    • Detailed review of carbohydrate needs for endurance athletes

  3. Jeukendrup, A.E. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1), S25-S33.

    • Evidence-based recommendations for during-exercise carbohydrate intake

Carbohydrate Metabolism and Fueling​

  1. Stellingwerff, T., & Cox, G.R. (2014). Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition, and Metabolism, 39(9), 998-1011.

  2. Jeukendrup, A.E. (2017). Training the Gut for Athletes. Sports Medicine, 47(Suppl 1), 101-110.

    • How to train gastrointestinal tolerance for carbohydrate intake during exercise

  3. Currell, K., & Jeukendrup, A.E. (2008). Superior endurance performance with ingestion of multiple transportable carbohydrates. Medicine & Science in Sports & Exercise, 40(2), 275-281.

    • Research on glucose-fructose combinations increasing absorption rates

Carbohydrate Periodization and Fat Adaptation​

  1. Marquet, L.A., et al. (2016). Enhanced Endurance Performance by Periodization of Carbohydrate Intake: "Sleep Low" Strategy. Medicine & Science in Sports & Exercise, 48(4), 663-672.

    • Strategic carb periodization enhances training adaptations

  2. Burke, L.M., et al. (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of Physiology, 595(9), 2785-2807.

    • Landmark study showing performance impairment with ketogenic diet despite adaptation

  3. Impey, S.G., et al. (2018). Fuel for the work required: a theoretical framework for carbohydrate periodization and the glycogen threshold hypothesis. Sports Medicine, 48(5), 1031-1048.

Hydration and Electrolytes​

  1. Sawka, M.N., et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377-390.

  2. Baker, L.B. (2017). Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Medicine, 47(Suppl 1), 111-128.

RED-S and Low Energy Availability​

  1. Mountjoy, M., et al. (2018). International Olympic Committee (IOC) Consensus Statement on Relative Energy Deficiency in Sport (RED-S): 2018 Update. British Journal of Sports Medicine, 52(11), 687-697.
  • Comprehensive review of RED-S causes, consequences, and treatment
  1. Logue, D.M., et al. (2020). Low Energy Availability in Athletes 2020: An Updated Narrative Review of Prevalence, Risk, Within-Day Energy Balance, Knowledge, and Impact on Sports Performance. Nutrients, 12(3), 835.

Practical Resources​

  1. Jeukendrup, A.E. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition & Metabolic Care, 13(4), 452-457.

  2. Pfeiffer, B., et al. (2012). Nutritional intake and gastrointestinal problems during competitive endurance events. Medicine & Science in Sports & Exercise, 44(2), 344-351.

  • Survey of nutrition practices and GI issues in endurance athletes
  • Burke, L., & Deakin, V. (2015). Clinical Sports Nutrition (5th ed.). McGraw-Hill Education.
  • Fitzgerald, M. (2012). Racing Weight: How to Get Lean for Peak Performance. VeloPress.
  • Jeukendrup, A., & Gleeson, M. (2018). Sport Nutrition (3rd ed.). Human Kinetics.

Online Resources​