Race prep · Fueling
How to Carb Load
To carb load, eat 10 to 12 grams of carbohydrate per kilogram of bodyweight per day for one to three days before a race lasting longer than 90 minutes, while reducing training to near zero. The depletion phase from the 1960s is obsolete. Tapering is what creates the glycogen capacity.
EB says
10-12 g/kg
daily carb target while tapering
Why carb loading works
Muscle glycogen is the rate-limiting fuel for sustained efforts above about 65 percent of VO2 max, and running out of it is what causes the marathon wall around mile 20. A normal glycogen store lasts roughly 90 to 120 minutes of hard exercise. Carb loading pushes muscle glycogen to 150 to 200 percent of its baseline level, giving you more time at race pace before you are forced to slow down.
This is also why carb loading is pointless for short races. A 5K or 10K finishes long before you deplete a normal glycogen store, so loading just adds weight without benefit. The break-even point is roughly 90 minutes of sustained effort at race intensity.
Glycogen is stored with water at about 3 grams of water per gram of glycogen. Expect to gain 1 to 2 kg during a full carb load. This is stored fuel and water (not fat) and it is metabolized alongside the glycogen during the race.
Carb loading protocols compared
The current evidence-based approach is to eat 10 to 12 grams of carbohydrate per kilogram of bodyweight per day for one to three days before the race while reducing training to near zero. Bussau and colleagues showed in 2002 that a single day at this dose with full rest achieves the same maximal glycogen as three-day protocols, making the one-day method the practical default for most athletes.
| Protocol | Depletion phase | Load window | Daily carb target | Best for |
|---|---|---|---|---|
| Classic (Bergstrom, 1967) | Yes: 3 days low-carb + hard training | 3 days | 8-10 g/kg | Outdated |
| Modified (Sherman, 1981) | No | 3 days, taper | 8-10 g/kg | Most marathoners |
| One-day (Bussau, 2002) | No | 24-36 hours, rest | 10-12 g/kg | Time-crunched, well-trained |
How much to eat when carb loading
Eat 10 to 12 grams of carbohydrate per kilogram of bodyweight per day during the loading window. For a 60 kg (132 lb) athlete that is 600 to 720 grams of carbohydrate per day; for a 75 kg (165 lb) athlete it is 750 to 900 grams. These amounts are dramatically higher than a typical diet and require displacing fat, protein, and fiber to hit the target.
Use the carb loading calculator to get your exact gram target based on your bodyweight and event type.
Sample day at 10 g/kg for a 70 kg (154 lb) runner (700 g carbs)
| Meal | Foods | Carbs (g) |
|---|---|---|
| Breakfast | 2 cups cooked white rice, 1 large banana, 2 tbsp honey | 160 g |
| Mid-morning snack | 2 plain bagels, 2 tbsp jam | 110 g |
| Lunch | 2 cups cooked white pasta, tomato sauce (no oil), 2 slices white bread | 175 g |
| Afternoon snack | 2 rice cakes, 1 large banana, 300 mL sports drink | 100 g |
| Dinner | 2 cups cooked white rice, grilled chicken breast, 1 cup fruit sorbet | 155 g |
| Total | 700 g |
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Best foods for carb loading
The best carb loading foods are low-fiber, easy-to-digest carbohydrates: white rice, white pasta, plain bagels, white bread, bananas, honey, fruit juice, rice cakes, and plain sports drinks. Avoid whole grains, vegetables, beans, legumes, and high-fat foods during the loading window.
Eat freely
- White rice, white pasta, white bread
- Plain bagels, rice cakes
- Bananas, melon, fruit juice
- Honey, jam, maple syrup
- Sports drinks, gels
- Plain crackers, pretzels
Avoid during the load
- Whole grains (oats, brown rice, whole wheat)
- Vegetables and salads
- Beans and legumes
- High-fat foods (cheese, nuts, oils)
- Alcohol
- High-fiber fruits (berries, apples with skin)
Gear up
Carb loading staples athletes actually buy
Low-fiber, easy-digesting carbs for the loading window. Test any new food in training first.
- Instant white rice (microwave cups)The easiest low-residue staple. ~45 g carbs per cup with zero prep on race weekend.View on Amazon →
- Pure maple syrupFast, low-fiber liquid carbs. ~13 g per tablespoon to stir into oats or sip late.View on Amazon →
- Low-fiber sports drink mixLiquid carbs for the final hours when solids feel heavy. Easy on a nervous gut.View on Amazon →
- Digital food scaleHit your gram targets exactly instead of guessing portions during loading.View on Amazon →
As an Amazon Associate we earn from qualifying purchases.
When to start carb loading
Start your carb load 24 to 48 hours before the race. For a Sunday marathon, begin Friday night or Saturday morning. Longer loading windows (three days) are useful when weekly training volume is very high and glycogen was heavily depleted mid-week; for most well-tapered athletes, the one-day to two-day approach is sufficient.
The evening before the race, keep dinner familiar and low-risk: not a new restaurant and not an unusually large meal right before bed. Your last significant carb-loading meal should be lunch or dinner the day before, giving your GI tract time to process before race morning.
Race morning: eat 1 to 4 g/kg of easy carbohydrates 2 to 3 hours before the start to top off liver glycogen depleted overnight. See what to eat before a marathon for the full race morning protocol.
Frequently asked questions
What is carb loading?
Carb loading is eating a very high carbohydrate diet for one to three days before an endurance event to maximize glycogen stored in your muscles and liver. A trained athlete normally stores 400 to 500 grams of glycogen; loading can push muscle glycogen to 150 to 200 percent of its normal level, extending the time before you deplete and hit the wall.
How many carbs per day do you need to carb load?
The evidence-based target is 10 to 12 grams of carbohydrate per kilogram of bodyweight per day for one to three days. For a 70 kg (154 lb) runner, that is 700 to 840 grams of carbohydrates per day, substantially more than a normal diet. You must taper training simultaneously so the carbohydrate is stored rather than burned.
When should you start carb loading?
Start the loading phase 24 to 48 hours before the race. The one-day (Bussau) protocol has been shown to achieve the same maximal glycogen saturation as three-day protocols when training is reduced to near-zero during the load window. Begin no later than the morning of the day before race day.
Do you need to deplete glycogen before carb loading?
No. The depletion-and-deprivation phase from the original 1960s method is no longer recommended. Modern studies show you reach the same maximal glycogen without it. Tapering your training in the final one to three days before the race is what opens up glycogen capacity; the depletion phase is unnecessary and miserable.
Should you carb load for a half marathon?
Carb loading is most beneficial for events lasting longer than 90 minutes at race intensity. A half marathon is right on the edge: slower runners benefit clearly; faster runners who finish under 90 minutes get minimal benefit. If your half marathon goal time is under 1:45, a modest carb focus the day before (8 to 10 g/kg rather than a full load) is sufficient.
Why do you gain weight when carb loading?
Glycogen is stored with water at a ratio of approximately 3 grams of water per gram of glycogen. Storing an extra 200 to 400 grams of glycogen adds 600 g to 1.2 kg of water alongside it. Total weight gain of 1 to 2 kg during a full carb load is normal, expected, and not fat. That water is structural and is metabolized alongside the glycogen during the race.
What foods are best for carb loading?
Low-fiber, easy-digesting carbohydrates are best: white rice, white pasta, plain bagels, white bread, bananas, honey, fruit juice, rice cakes, and plain sports drinks. Avoid whole grains, vegetables, beans, legumes, and high-fat foods. Fiber increases GI transit time and can cause GI distress during the race if loading is done within 48 hours of the start.
Get your exact numbers
Carb Loading Calculator
Enter your bodyweight and race distance to get your exact daily carb target in grams.
On-course fueling
Carb Calculator
How many grams of carbs per hour to take on course for your race distance and intensity.
Race morning
What to Eat Before a Marathon
Race morning meal timing, portion size, and the 2 to 3 hour pre-race fueling window.