Carb loading isn't about a giant pasta dinner the night before. Done right, it fills your glycogen tank to overflowing—fuel for marathon and beyond.

Here's how to load properly.

What Is Carb Loading?

The Science

Glycogen = stored carbohydrate in muscles and liver.

Normal glycogen stores: ~400-500g (1,600-2,000 calories)

After carb loading: ~600-900g (2,400-3,600 calories)

The benefit: More fuel before you tap into fat (slower) or bonk.

Why It Works

When you combine:

• Reduced training (taper)
• High carbohydrate intake
• Adequate time (2-3 days)

...muscles supercompensate, storing more glycogen than normal.

Who Needs It

Rule of thumb: If your race lasts over 90 minutes, carb loading helps.

The Modern Protocol

Forget the Old Way

Old protocol (1960s-1980s):

1. Deplete glycogen with hard training
2. Eat low-carb for 3-4 days
3. Then load heavily for 3-4 days

Problems: Miserable, risky, unnecessary.

The Simple Approach

Modern protocol:

1. Taper training normally (50-60% reduction)
2. Increase carbs to 8-12g/kg/day for 2-3 days
3. Race with full glycogen stores

No depletion phase needed. Same glycogen supercompensation.

How Much to Eat

The Target

8-12 grams of carbs per kilogram of bodyweight per day

What This Looks Like

For a 70kg runner targeting 700g carbs/day:

It's a lot. You'll feel full. That's normal.

Adjusting Calories

Should you eat more total calories?

Yes, somewhat. Carb loading naturally increases calories. But you don't need to massively overeat—you're also tapering, so total energy expenditure is lower.

Focus on hitting carb targets, not calorie targets.

Best Foods for Carb Loading

Prioritize Low-Fiber

High fiber can cause GI distress on race day. During carb loading, choose:

White, refined carbs:

• White rice
• White pasta
• White bread
• Bagels (plain, not seeded)
• Pancakes/waffles
• Pretzels
• Crackers

Sugary options (for additional carbs):

• Fruit juice
• Honey
• Maple syrup
• Jam/jelly
• Gummy candy
• Sports drinks

Fruits (lower fiber):

• Bananas
• Applesauce
• Melon
• Grapes

Foods to Avoid

High fiber:

• Whole grains
• Beans/legumes
• Raw vegetables
• High-fiber cereals
• Whole wheat anything

Heavy fats (slow digestion):

• Fried foods
• Creamy sauces
• Rich desserts
• Fatty meats

Unfamiliar foods:

• Anything new
• Exotic cuisines
• Foods you haven't tested

Sample Day

Day before marathon:

• 6:00 AM: 2 white bagels with honey, orange juice
• 9:00 AM: Sports drink, banana
• 12:00 PM: Large bowl white pasta with marinara, white bread, grape juice
• 3:00 PM: Rice cakes with jam, pretzels
• 6:00 PM: White rice, grilled chicken, white dinner roll, applesauce
• 8:00 PM: Pretzels, sports drink, small bowl of cereal with milk

The Loading Timeline

3 Days Out (Thursday for Sunday race)

• Begin increasing carbs
• Reduce training to short, easy runs
• Target 8-10g/kg carbs

2 Days Out (Friday)

• Continue high carb intake
• Very light or no running
• Target 10g/kg carbs
• Stay hydrated

1 Day Out (Saturday)

• Maintain high carbs
• No running or only light shakeout
• Target 8-10g/kg carbs
• Dinner not too late (allow digestion)

Race Morning

• Breakfast 2-4 hours before start
• 60-100g carbs (familiar foods)
• Light, easily digestible
• Example: Bagel with honey, banana, sports drink

Common Mistakes

1. Not Eating Enough

The problem: High-carb diet doesn't feel like high-carb diet.

The reality: 600-900g of carbs is A LOT. If you're not feeling stuffed, you're probably under-eating.

The fix: Count carbs, not just meals.

2. Too Much Fiber

The problem: Switching to "healthy" whole grains.

The reality: Fiber + race nerves = bathroom problems.

The fix: Go white and refined. This isn't the time for whole foods.

3. Too Much Fat

The problem: Adding cheese, creamy sauces, rich foods.

The reality: Fat slows digestion and displaces carb calories.

The fix: Keep fats moderate. Focus on carbs.

4. Waiting Until Night Before

The problem: Only one big pasta dinner.

The reality: One meal can't fully load glycogen.

The fix: Start 2-3 days out.

5. Worrying About Weight Gain

The problem: Scale goes up 2-4 pounds.

The reality: This is glycogen + water. It's GOOD.

The fix: Embrace the weight. It's fuel.

6. Trying New Foods

The problem: "I heard X is great for carb loading."

The reality: Unfamiliar foods can cause GI distress.

The fix: Stick to familiar, tested foods.

For Half Marathon

Do You Need to Carb Load?

Finishing under 90 minutes: Probably not necessary. Normal eating is fine.

Finishing 90+ minutes: Light carb loading can help.

Modified Protocol

• 1-2 days of increased carbs (not 3)
• Target 7-8g/kg (not 10-12)
• Less aggressive than full marathon protocol

Special Considerations

Vegetarian/Vegan

Carb loading is naturally easier plant-based. Plenty of options:

• Rice, pasta, bread
• Potatoes
• Fruit, juice
• Plant-based sports nutrition

Challenge: May need more volume to hit targets (plant foods often lower calorie density).

Gluten-Free

Options:

• Rice (white)
• Potatoes
• Gluten-free pasta
• Rice noodles
• Corn-based products
• Fruit

Challenge: Many convenient carb sources (bread, bagels, pasta) contain gluten. Plan ahead.

Diabetes

Carb loading requires careful blood sugar management. Work with your healthcare provider and adjust insulin as needed.

GI-Sensitive Runners

Start loading earlier (3-4 days out) with moderate carb increases rather than aggressive loading close to the race. Very low fiber is crucial.

Carb loading is simple in concept: eat a lot of carbs for 2-3 days before a long race. In practice, it requires planning—you need to eat more than feels natural, choose the right foods, and start early enough. Do it right, and you'll toe the line with a full tank of fuel.

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

Plan your race nutrition with our Race Nutrition Plan Template.