Carb Loading
Carbohydrate Loading
Carb loading is the practice of maximizing glycogen stores before endurance events through increased carbohydrate intake. Learn how to carb load effectively for races.
Quick Answer
Carb Loading — is the practice of consuming extra carbohydrates before endurance events to maximize glycogen storage in muscles and liver. Done correctly, it can increase glycogen stores by 25-100% and delay fatigue during races lasting 90+ minutes.
What is Carb Loading?
Carb loading (carbohydrate loading) is a nutritional strategy to maximize the body's glycogen stores before an endurance event.
Why it works:
- Muscles use glycogen as primary fuel during exercise
- Normal glycogen stores last ~90-120 minutes at race pace
- Extra glycogen extends time to fatigue
When Carb Loading Helps
| Event Duration | Carb Load? | Benefit |
|---|---|---|
| < 60 minutes | Not necessary | Glycogen sufficient |
| 60-90 minutes | Optional | Minor benefit |
| 90+ minutes | Recommended | Significant benefit |
Best for: Marathon, half Ironman, Ironman, century rides, ultra events.
How Carb Loading Works
The Science
Normal glycogen stores: ~400-500g total
- Muscle glycogen: ~300-400g
- Liver glycogen: ~80-100g
After carb loading: ~600-900g total
- Up to 100% increase in glycogen storage
What Happens Physiologically
| Phase | Effect |
|---|---|
| Taper begins | Less glycogen used in training |
| Carb intake increases | Muscles fill with glycogen |
| Rest continues | Glycogen continues accumulating |
| Race day | Maximum fuel stored |
Classic Carb Loading Protocol
3-Day Method (Modern Approach)
| Day Before Race | Carb Target | Notes |
|---|---|---|
| Day 3 | 8-10g/kg | Begin increasing carbs |
| Day 2 | 10-12g/kg | Peak carb day |
| Day 1 | 8-10g/kg | Maintain high carbs |
| Race morning | 2-3g/kg | Pre-race meal |
Example (70kg athlete):
- Days 2-3: 560-840g carbs daily
- Race morning: 140-210g carbs (3-4 hours before)
Original 7-Day Method (Less Common Now)
| Days Out | Phase | Diet |
|---|---|---|
| 7-4 | Depletion | Low carb, hard training |
| 3-1 | Loading | High carb, taper |
This older method is more stressful and not necessary for most athletes.
Read our complete guide: Cycling Carb Loading Guide.
Best Carb Loading Foods
High-Carb, Low-Fiber Options
| Food | Carbs per serving |
|---|---|
| White rice (1 cup cooked) | 45g |
| Pasta (1 cup cooked) | 45g |
| Bread (2 slices) | 30g |
| Banana | 27g |
| Sports drink (500ml) | 30-35g |
| Honey (1 tbsp) | 17g |
| Pancakes (2) | 40g |
| Oatmeal (1 cup) | 27g |
Sample Carb Loading Day
| Meal | Foods | Carbs |
|---|---|---|
| Breakfast | Pancakes, honey, banana, juice | 120g |
| Snack | Bagel with jam | 60g |
| Lunch | Pasta with light sauce, bread | 150g |
| Snack | Sports drink, pretzels | 70g |
| Dinner | Rice, chicken, bread | 130g |
| Evening | Sports drink, crackers | 50g |
| Total | ~580g |
Carb Loading Mistakes
1. Not Eating Enough
Many athletes underestimate 8-10g/kg:
- 70kg athlete needs 560-700g carbs
- That's 2,200-2,800 calories from carbs alone
2. Fiber Overload
High-fiber foods cause GI issues:
- Avoid: Whole grains, beans, raw vegetables
- Choose: White bread, white rice, pasta
3. Too Much Fat
Fat fills you up before carbs:
- Avoid: Heavy sauces, butter, fried foods
- Choose: Low-fat preparations
4. New Foods
Race week isn't time to experiment:
- Stick to familiar foods
- Avoid trying new restaurants
5. Wrong Timing
Last-minute loading doesn't work:
- Start 2-3 days before race
- Race morning loading is different (pre-race fuel)
Carb Loading and Weight
Expect Weight Gain
| Cause | Typical Gain |
|---|---|
| Glycogen storage | 1-2 kg |
| Water retention | 2-3 kg |
| Total | 2-4 kg |
This is temporary and good—that water helps with hydration.
Don't Panic
The weight gain is:
- Fuel you'll use during the race
- Water for hydration
- NOT fat gain
Pre-Race Meal
Race Morning (3-4 hours before)
| Goal | Amount |
|---|---|
| Carbs | 2-3g/kg (150-200g for 70kg) |
| Fat | Low |
| Fiber | Low |
| Protein | Moderate |
Examples:
- Oatmeal with honey and banana
- Bagel with jam and sports drink
- Rice with eggs
- Pancakes with syrup
Carb Loading by Event
Marathon
| Day | Carbs |
|---|---|
| 3 days before | 8g/kg |
| 2 days before | 10g/kg |
| Day before | 8g/kg |
| Race morning | 2g/kg |
Ironman / Ultra
| Day | Carbs |
|---|---|
| 4 days before | 8g/kg |
| 3 days before | 10g/kg |
| 2 days before | 10g/kg |
| Day before | 8g/kg |
| Race morning | 2g/kg |
Read our Marathon Nutrition Guide.
Common Questions
Do I need to deplete glycogen first?
No—the old depletion phase isn't necessary. Modern protocols show equivalent glycogen loading without the depletion stress.
Will carb loading make me slower?
The extra weight is offset by the extra fuel. Studies show net performance improvement for events 90+ minutes.
What if I'm carb-intolerant?
Work with a sports dietitian. Some athletes use modified approaches with lower carb targets and extended loading periods.
Does carb loading work for fat-adapted athletes?
Fat-adapted athletes may need modified approaches. However, research shows even fat-adapted athletes benefit from some carb loading for high-intensity efforts.