Bonking—hitting the wall—is largely preventable. The solution is simple: fuel during long runs.

This guide covers everything you need to know about in-run nutrition, from when to start fueling to advanced protocols for ultramarathons.

Quick Start: Fueling Essentials

Don't have time to read everything? Here's what you need to know:

The 5-Minute Fueling Protocol

1. Under 60-75 minutes? — No fuel needed. Water is sufficient.
2. Over 60-75 minutes? — Target 30-60g carbs per hour
3. Start early — First fuel at 30-45 minutes, not when you're tired
4. Choose your fuel — Gels, chews, or real food (whatever your gut tolerates)
5. Practice first — Never try new fuel on race day

Quick Reference: Fueling by Distance

Quick Reference: Common Fuel Options

Key principle: Fuel before you need it. If you wait until you're bonking, it's too late.

Who This Guide Is For

This guide helps runners at every level master in-run nutrition:

What You'll Achieve

After reading this guide and applying its principles:

• Know exactly when you need fuel and when you don't
• Choose the right fuel for your body and your event
• Calculate your needs precisely for any distance
• Train your gut to handle race-day nutrition
• Execute a race plan with confidence
• Troubleshoot any GI issues that arise

When You Need Fuel

The 60-75 Minute Threshold

This is the key decision point for in-run fueling:

Under 60-75 minutes: Your glycogen stores handle it. Water is sufficient. Don't complicate things.

Over 60-75 minutes: Fuel extends performance. Glycogen depletion becomes a limiter without it.

Exception: Very low-intensity runs may not deplete glycogen as quickly; very high-intensity runs may deplete it faster.

Why Fuel Matters: The Science

Your body stores carbohydrates as glycogen in muscles and liver:

• Glycogen stores: Roughly 1,500-2,000 calories
• Depletion timeline: 90-120 minutes of moderate running
• When depleted: Bonking, hitting the wall, sudden fatigue

With proper fueling:

• External carbs supplement glycogen
• Glycogen stores last longer
• Performance sustained

Fueling by Distance

Who DOESN'T Need to Fuel

• Runs under 60 minutes at any intensity
• Easy runs under 75-90 minutes (if well-fueled beforehand)
• Short races (5K, 10K) — glycogen is sufficient

Don't over-complicate short runs. Fuel is for long efforts.

The In-Run Fueling Framework

Successful race nutrition requires four components working together:

┌─────────────────────────────────────────────────────────────┐
│              IN-RUN FUELING FRAMEWORK                        │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  1. TIMING              2. QUANTITY                          │
│  ┌──────────────┐       ┌──────────────┐                    │
│  │ Start early  │       │ 30-60g/hour  │                    │
│  │ 30-45 min in │       │ (up to 90g   │                    │
│  │ Regular      │       │  for ultras) │                    │
│  │ intervals    │       │              │                    │
│  └──────────────┘       └──────────────┘                    │
│         │                      │                             │
│         └──────────┬───────────┘                            │
│                    │                                         │
│         ┌──────────▼───────────┐                            │
│         │    RACE DAY SUCCESS   │                            │
│         │                       │                            │
│         └──────────┬───────────┘                            │
│                    │                                         │
│         ┌──────────┴───────────┐                            │
│         │                      │                             │
│  3. GUT TRAINING        4. PRODUCT CHOICE                   │
│  ┌──────────────┐       ┌──────────────┐                    │
│  │ Practice in  │       │ Find what    │                    │
│  │ training     │       │ works for    │                    │
│  │ Build        │       │ YOUR gut     │                    │
│  │ tolerance    │       │              │                    │
│  └──────────────┘       └──────────────┘                    │
│                                                              │
└─────────────────────────────────────────────────────────────┘

Skip any component and the others are compromised.

What to Eat

You have multiple options for in-run fuel. The "best" choice is what your gut tolerates and you can execute consistently.

Energy Gels

What they are: Concentrated carbohydrate packets (20-25g per gel)

Pros:

• Quick absorption
• Easy to carry
• Designed for running
• Precise carb counting

Cons:

• Texture/taste can be off-putting
• Can cause GI issues for some
• Most require water to digest
• Cost adds up

Popular options:

• GU — 22g carbs, many flavors, caffeine options
• Maurten — 25g carbs, hydrogel technology, neutral taste
• Huma — 21g carbs, chia-based, real fruit ingredients
• Spring Energy — 20-45g carbs, real food based
• SiS — 22g carbs, isotonic (no water needed)

Energy Chews

What they are: Gummy-like pieces you chew while running

Pros:

• Easier to eat in small pieces
• More enjoyable texture for some
• Similar carb content to gels
• Good for portioning

Cons:

• Require chewing while running
• Sticky in cold weather
• Hard to eat at high intensity
• Can stick to teeth

Popular options:

• Clif Bloks — 24g per 3 pieces
• Gatorade Chews — 21g per 4 pieces
• Skratch Chews — 20g per 4 pieces

Real Food

Options that work well:

Pros:

• Natural, less processed
• Often easier on stomach
• Variety prevents flavor fatigue
• Cheaper

Cons:

• Bulkier to carry
• May require more chewing
• Can be messy

Sports Drinks

Can be used for:

• Carbs (instead of or alongside gels)
• Hydration
• Electrolytes

Example: Gatorade Endurance provides ~21g carbs per 12 oz.

Good for: Races with aid stations where you can rely on drink availability.

Comparison Chart

How Much to Eat

The General Guidelines

Standard protocol: 30-60 grams of carbs per hour

High-carb protocol: Up to 90 grams per hour for very long efforts (3+ hours), using multiple carb sources (glucose + fructose)

Why the Range?

30g/hour: Minimum effective dose, good starting point 45g/hour: Sweet spot for most runners 60g/hour: Upper limit for single carb source (glucose) 90g/hour: Maximum with multiple transporters (glucose + fructose)

Translating to Products

Frequency vs. Amount

You can take the same total carbs in different ways:

Option 1: Large amounts less frequently

• 1 gel every 45 minutes
• Simpler to remember
• Higher GI risk per serving

Option 2: Small amounts more frequently

• 1/3 gel every 15 minutes
• Steadier energy delivery
• Often easier to digest

Research suggests: More frequent, smaller amounts are easier to digest and may provide steadier energy.

Timing: Start Early

Key principle: Start fueling before you're depleted.

Common mistake: Waiting until you feel tired—by then you're already depleted and it's hard to recover.

What the Elites Do

Elite marathoners often consume 60-90g/hour using highly concentrated gels (Maurten) and practiced gut tolerance. They start fueling within the first 5K.

You don't need to match elite intake, but the principle applies: early and consistent.

The 90g+ Protocol

The traditional limit of 60g/hour has been expanded by modern research. Here's how high-carb fueling works for endurance events.

Why More Than 60g?

The old science: Glucose absorption maxes out at ~60g/hour due to intestinal transporter limits.

The new science: Using multiple transportable carbohydrates (glucose + fructose) bypasses this limit. Different sugars use different intestinal transporters.

The formula:

• Glucose alone: max ~60g/hour
• Glucose + fructose (2:1 ratio): up to 90-120g/hour

Who Should Use High-Carb Protocols

Ideal for:

• Ultramarathons (50K+)
• Ironman triathlons
• Very long marathons (4+ hours)
• Any event over 3 hours where maximizing carb delivery matters

Not necessary for:

• Marathons under 3:30 (standard 60g/hour is sufficient)
• Half marathons and shorter
• Events where intensity limits gut function

Products Designed for 90g+ Intake

Maurten Gel 100:

• 25g carbs per gel (hydrogel technology)
• Designed for high-volume intake
• Better tolerated than traditional gels at high doses

Maurten Drink Mix 320:

• 80g carbs per 500ml serving
• Enables liquid-based high-carb strategy
• Popular with elite marathoners and ultra runners

Spring Energy gels:

• Real food-based (rice, fruit)
• 20-45g carbs per gel depending on variety
• Often better tolerated for very long events

SiS Beta Fuel:

• 80g carbs per serving
• 1:0.8 maltodextrin to fructose ratio
• Purpose-built for 80g+ per hour protocols

Building to 90g+ Per Hour

This requires dedicated gut training:

Key principle: Increase gradually. Jumping straight to 90g/hour without training will cause GI disaster.

High-Carb Protocol Example (100-Mile Ultra)

The Risks

GI distress is more likely at high intake:

• Bloating, nausea, cramping
• Diarrhea in worst cases
• Can derail an entire race

Mitigation:

• Train your gut systematically
• Use products designed for high intake
• Back off if you feel distress building
• Have a "Plan B" with lower intake

Do You Need This?

For most recreational runners: No.

• Standard 30-60g/hour protocols work fine for marathons
• The extra complexity and GI risk may not be worth it
• Elite-level intake requires elite-level gut training

Consider it if:

• You're racing ultras competitively
• You've hit fueling limits with standard protocols
• You're willing to invest months in gut training
• GI issues haven't plagued you historically

Training Your Gut

Your gut is trainable. Don't skip this step.

Why Gut Training Matters

The gut can adapt to:

• Absorb more carbohydrates
• Tolerate fuel during running
• Improve gastric emptying

Untrained gut + race day fuel = GI disaster

The 8-Week Gut Training Protocol

Weeks 1-4: Introduction

• Practice fueling on long runs
• Start with small amounts (15-20g/hour)
• Use the products you'll race with
• Note any discomfort

Weeks 5-8: Building

• Increase to target race intake (30-45g/hour)
• Time fueling as you would in race
• Practice at various intensities
• Fine-tune timing and products

Weeks 9+: Race Simulation

• Match race-day fueling exactly
• Practice at race pace
• Build confidence
• No new products—only what's proven

Gut Training Key Principles

1. Consistency — Practice every long run
2. Progression — Gradually increase amounts
3. Specificity — Use race-day products
4. Timing — Practice race-day timing
5. Documentation — Track what works

Signs Your Gut Is Adapting

• Less bloating at same intake
• Faster stomach settling after fuel
• Higher tolerance at faster paces
• No issues at target intake level

Race Day Fueling Strategy

Pre-Race Nutrition

Night before:

• Carb-rich dinner (not excessive)
• Familiar foods only
• Adequate hydration

Morning of (2-4 hours before):

• Familiar breakfast
• 60-100g carbs
• Easy to digest

30 min before (optional):

• One gel (20-25g carbs)
• Tops off glycogen
• Not required if breakfast was adequate

During Race: Example Plans

Half Marathon (1:45 finish):

Marathon (3:30 finish, ~45g/hour):

Adjust based on:

• Your pace
• Your tolerance
• Aid station locations
• Course specifics

Taking Fuel at Aid Stations

Tips for smooth execution:

• Slow slightly (don't run hard and eat)
• Grab water to wash down gel
• Have backup fuel even if using aid stations
• Know what the race provides

Practice: Run through simulated aid stations in training.

Plan B: When Things Go Wrong

Things can go wrong. Have contingencies:

Hydration + Fueling Together

Option 1: Gel + water at aid stations (most common)

Option 2: Sports drink only (provides both carbs and fluid)

Option 3: Gel + sports drink (high carb—watch for GI issues)

Watch for: Over-fueling when combining multiple sources. 2 gels + sports drink = 65g+ carbs, may cause problems.

Electrolytes

Most gels contain sodium. For long, hot races:

• Additional electrolytes may help
• Salt tabs or electrolyte capsules
• High-sodium sports drinks

See Running in the Heat for more on electrolyte needs.

Fueling Decision Framework

Use this framework to build your fueling plan for any event.

Step 1: Determine If You Need Fuel

Duration > 60-75 minutes?
├── NO → No fuel needed, water only
└── YES → Continue to Step 2

Step 2: Calculate Carb Target

Target Duration:
├── 75-120 min → 30-45g/hour
├── 2-4 hours → 45-60g/hour
└── 4+ hours → 60-90g/hour (trained gut)

Step 3: Choose Your Fuel Type

GI sensitivity?
├── HIGH → Real food or hydrogel products (Maurten)
├── MEDIUM → Mix of gels and chews
└── LOW → Standard gels work fine

Convenience priority?
├── HIGH → Gels (easy to carry, precise)
└── LOW → Real food (may taste better)

Race has aid stations?
├── YES → Can supplement with on-course drinks/food
└── NO → Must carry everything

Step 4: Build Your Timeline

Race Duration: _____ hours
Carb Target: _____ g/hour
Total Carbs Needed: Duration × Target = _____g

Fuel Timing:
- First fuel: 30-45 minutes
- Subsequent: Every 20-30 minutes
- Number of servings: Total ÷ Carbs per serving

Step 5: Practice and Refine

□ Test in training (8+ weeks before race)
□ Simulate race conditions
□ Adjust based on GI response
□ Lock in plan 2-3 weeks before race
□ No new products race week

Common Mistakes

Mistake 1: Waiting Too Long to Start

The problem: Taking first fuel at mile 10 or hour 1.5

Why it fails: By then glycogen is significantly depleted. Playing catch-up doesn't work—your body can't absorb fast enough.

The fix: First fuel at 30-45 minutes, while you still feel good.

Mistake 2: Not Practicing in Training

The problem: First time using gels is race day

Why it fails: Your gut isn't trained. Unfamiliar products cause GI distress. You don't know what works.

The fix: Practice fueling on every long run for 8+ weeks before race.

Mistake 3: Taking Too Much at Once

The problem: Downing 2-3 gels when you finally remember to fuel

Why it fails: Gut can't absorb 50-75g at once. Result: nausea, cramping, bloating.

The fix: Smaller amounts more frequently. One gel every 20-30 minutes.

Mistake 4: Using New Products on Race Day

The problem: "The race has X brand at aid stations, I'll use that"

Why it fails: Even similar products can affect you differently. GI distress is race-ruining.

The fix: Train with what you'll race with. Carry your own if aid stations have different products.

Mistake 5: Ignoring GI Warning Signs

The problem: Pushing through building nausea or bloating

Why it fails: GI problems compound. What starts as mild discomfort becomes race-ending distress.

The fix: Back off at first signs. Switch to sips of sports drink. Let stomach settle before trying more.

Mistake 6: Fueling Short Runs

The problem: Bringing gels on a 45-minute easy run

Why it fails: Wastes money, unnecessary GI stress, creates dependency on fuel you don't need.

The fix: Only fuel runs over 60-75 minutes. Shorter runs don't need it.

Troubleshooting GI Issues

Nausea

Likely causes:

• Taking too much at once
• Not enough water with gels
• Running too hard to digest

Solutions:

1. Smaller amounts, more frequent
2. Always take gel with 4-6 oz water
3. Slow pace slightly when fueling

Cramping/Bloating

Likely causes:

• Too much fructose
• High fiber in fuel
• Dehydration or overhydration

Solutions:

1. Switch to glucose-dominant products
2. Avoid fiber during runs
3. Balance fluid intake

Diarrhea/Urgency

Likely causes:

• Gut not trained
• Too much sugar alcohol (sorbitol)
• Anxiety or race-day stress

Solutions:

1. More gut training in practice
2. Check gel ingredients for sugar alcohols
3. Stick to familiar products

"Nothing Sits Well"

Likely causes:

• Genuinely sensitive gut
• Anxiety reducing gut function
• Running too intensely to digest

Solutions:

1. Try real food instead of gels
2. Try liquid calories (sports drink)
3. Try hydrogel products (Maurten)
4. Reduce race pace at fueling points

When to Seek Help

If GI issues persist despite:

• Thorough gut training
• Multiple product types tried
• Proper timing and hydration

Consider consulting a sports dietitian. Some runners have underlying conditions affecting gut function during exercise.

Tools and Templates

Recommended Tools

• Race Nutrition Plan Template — Build your complete race day fueling strategy
• Hydration Calculator — Balance fluids with fueling
• Marathon Pacing Template — Integrate fueling into your race plan
• Weekly Training Log — Track fueling practice in training

Race Day Fueling Checklist

Week before:

• All race fuel purchased and tested
• Know what's available on course
• Backup fuel ready
• Race morning meal planned

Night before:

• Fuel laid out with race gear
• Morning meal ingredients ready
• Timing worked out (when to eat, when to leave)

Race morning:

• Breakfast eaten 2-4 hours before
• Pre-race gel (optional, 30 min before)
• All fuel on body/accessible

During race:

• First fuel at 30-45 minutes
• Fuel every 20-30 minutes after
• Water with each gel
• Adjust if GI issues arise

Training Fuel Log

Track every long run:

Related Guides

Training & Racing

• Marathon Training Guide — Complete marathon preparation including nutrition timing
• Picking a Training Plan — Match your plan to your fueling needs
• Analyzing Race Results — Including nutrition performance review

Nutrition & Hydration

• Caffeine and Running — Using caffeine strategically with fuel
• Running in the Heat — Fueling when it's hot (electrolyte considerations)
• Hydration for Runners — Balancing fluids with fuel

Endurance Events

• Ultramarathon Basics — High-volume fueling for ultras

Fueling during runs is a skill. It requires practice—both the logistics and the gut adaptation. Start fueling early, take smaller amounts more frequently, and train your gut in training. Never try new fuel on race day.

Master this, and you'll never bonk again.

For the complete guide to nutrition for runners, see the Running Nutrition Complete Guide.