Most athletes carb load wrong. The pasta dinner the night before a marathon or Ironman is not carb loading — it is one meal that partially refills glycogen you have already been burning through race week travel, nerves, and short shakeout runs. Real carb loading takes three days and requires numbers most athletes find uncomfortable.
Done correctly, carb loading can add 2–3% to your performance and effectively push back the wall by 30–40 minutes in a marathon. Here is exactly how to do it.
What carb loading actually does
Your muscles and liver store glycogen — the fast-burning fuel that powers moderate-to-high intensity effort. At baseline, you hold about 400–600 grams. With full carb loading, you can push that to 700–900 grams. Each gram of glycogen is stored with roughly 3 grams of water, which is why you feel heavier and fuller after a proper carb load. That water is not dead weight — it contributes to hydration during the race and is metabolized alongside the glycogen.
The extra glycogen does not make you faster. It makes you last longer at the pace you have trained for. The wall is a depletion event; carb loading delays it.
Who should carb load
Carb loading is beneficial for events lasting more than 90 minutes at sustained moderate-to-high intensity. That means marathons, 70.3, Ironman, and ultra marathons all qualify. Half marathons in the 1.5–2 hour range benefit from optimized pre-race fueling but do not require a three-day protocol. If you are racing a 5K, carb loading is irrelevant.
The 3-day protocol
Day 3 before the race
Target 7–8 grams of carbohydrate per kilogram of body weight. For a 70 kg athlete, that is 490–560 grams of carbohydrate across the day. Reduce training to a very easy 20–30 minute run or rest completely. The idea is to stop depleting glycogen while starting to load it.
Good food choices: white rice, pasta, bread, bananas, oats, fruit juice, sports drinks. Keep fat low (fat slows gastric emptying and takes up calorie space you need for carbs), keep fibre low (you do not want GI trouble on race day), and avoid anything new.
Day 2 before the race
Push to 10–12 grams of carbohydrate per kilogram of body weight. This is the hardest day of the load — you are eating significantly more than your normal intake and you will feel full. For the 70 kg athlete, that is 700–840 grams of carbohydrate. Spread it across 4–5 meals and include liquid carbohydrates (fruit juice, sports drinks) to make volume easier to manage.
Training on day 2 should be minimal — a short shakeout at most. Your job is to eat and rest.
Race eve
Drop back to 8–10 grams per kilogram. Keep it familiar: whatever works for you. White pasta with minimal sauce, white rice with chicken, plain bread, banana. No fibre, no spice, no alcohol, no new restaurants. Eat your main meal by 6 pm so you have 12 hours to digest before a 6 am race start.
Avoid the temptation to over-eat at dinner. You did the work on days 2 and 3. Race eve is about maintaining, not pushing higher.
Race morning
Aim to eat 2–3 grams of carbohydrate per kilogram of body weight, 2–3 hours before the start. For the 70 kg athlete, that is 140–210 grams. White toast with honey, porridge with banana, white rice — again, familiar foods only. A small coffee is fine and benefits performance, but avoid anything with milk if your gut is sensitive.
If your race start is before 6 am, a liquid breakfast (maltodextrin powder in water, sports drink) may be easier to get down than solid food at 3:30 in the morning.
Common mistakes
Starting too late. One pasta dinner is not a carb load. Start three days out.
Adding fat with the carbs. Creamy pasta sauces, olive oil, cheese — these slow gastric emptying and compete for calorie space you need for carbohydrate. Keep meals simple.
Adding fibre. Salads, beans, lentils, whole grain bread during load days are asking for GI trouble. Stick to low-fibre sources.
Panicking at the scale. You will gain 1–3 kg during a proper carb load from glycogen and bound water. This is not fat. It will be gone by race finish, and it is working for you, not against you.
Trying something new. Race week is not the time to experiment with new foods, restaurants, or cuisines. Familiar foods only.
Timing it to your race calendar
If your race is on a Sunday, day 3 is Thursday, day 2 is Friday, and race eve is Saturday. That means Thursday through Saturday are load days. Build this into your travel plans — airport and hotel food is notoriously hard to carb load from. Bring your own supplies wherever possible.
A personalized fueling plan that calculates your specific carb load quantities based on your weight, event distance, and race start time removes the arithmetic. Athletes who hit their carb load correctly are not guessing at aid stations — they are executing a plan they already know works.
Once the load is done: read what to eat the night before the race, follow the race-morning breakfast timing to top up without GI risk, and check the full marathon fueling guide for the race itself.
How many carbs per day when carb loading
The formula is straightforward: multiply your body weight in kilograms by your target grams per kilogram.
- Day 3 before race: body weight (kg) × 7–8 g = daily carbohydrate target
- Day 2 before race: body weight (kg) × 10–12 g = daily carbohydrate target
- Race eve: body weight (kg) × 8–10 g = daily carbohydrate target
For a 70 kg runner targeting 10–12 g/kg on day 2, that is 700–840 g of carbohydrate — roughly equivalent to 14–17 cups of cooked white rice. Spread across 4–5 meals with liquid carbohydrates filling the gaps, this is achievable. Use the carb-loading planner to calculate your exact gram targets based on your body weight.
Best foods for carb loading
Not all carbohydrate sources are equal during a carb load. You want high carb density, low fiber, and low fat. These are the best options:
- White rice — roughly 45 g carbohydrate per cooked cup, virtually no fiber, easy to eat in large quantities
- White pasta — similar density to rice, familiar for most athletes; choose plain tomato sauce over cream-based
- White bread and bagels — convenient, portable, easy to add honey or jam for extra carbs without fat
- Bananas — around 27 g carbohydrate each, easy to digest, also provide potassium
- Sports drinks — liquid carbohydrates that bypass fullness signals; useful when solid food becomes difficult
- Fruit juice — similar function to sports drinks; orange juice and apple juice are low-fiber and carbohydrate-dense
Avoid whole grain bread, brown rice, legumes, salads, and cruciferous vegetables during load days. These are good foods — but their fiber content causes GI distress when consumed in large volumes close to race day.
3-day carb loading meal plan
This is a sample plan for a 70 kg athlete targeting 10–12 g/kg on day 2. Scale portions up or down based on your weight and the formula above.
Day 1 (3 days out — 7–8 g/kg target):
- Breakfast: large bowl of oats with banana and honey, glass of juice
- Lunch: white rice bowl with grilled chicken and a small portion of plain vegetables
- Snack: bagel with jam, sports drink
- Dinner: pasta with plain tomato sauce, white bread roll
Day 2 (2 days out — 10–12 g/kg target):
- Breakfast: white toast with honey and jam, large glass of orange juice
- Snack: banana and sports drink
- Lunch: large white rice bowl with a small amount of plain protein
- Snack: bagel with jam, more juice or sports drink
- Dinner: large pasta portion with plain tomato sauce, white bread
Day 3 / Race eve (8–10 g/kg target):
- Breakfast: oats or white toast with banana, juice
- Lunch: white rice or pasta, small plain protein portion
- Dinner (by 6–7pm): familiar pasta or rice dish, no experiments
- Evening snack if needed: plain white bread, banana, or small sports drink
Carb loading for triathlon vs marathon
The same 3-day protocol applies to both events, but triathlon introduces additional variables.
For a marathon, carb loading is straightforward: fill glycogen stores for a single 2.5–5 hour effort. The protocol above is designed with marathon runners in mind.
For a 70.3 or Ironman triathlon, carb loading serves the same purpose but you will also be fueling aggressively during the event — especially on the bike. This means your carb load is the foundation, not the ceiling. A triathlete who carb loads correctly and then executes their in-race fueling plan will far outperform one who carb loads but under-fuels on the bike.
One triathlon-specific note: race morning timing is more complex when transition setup requires arriving 90 minutes before gun time. Build your race-morning meal schedule around your check-in time, not just the gun.
Frequently asked questions
How many carbs should I eat when carb loading?
10–12 grams per kilogram of body weight per day for 2–3 days before the race. A 70 kg runner targets 700–840 g of carbohydrate on peak load days.
Can you carb load in 1 day?
One day can partially refill glycogen stores but is less effective than a 2–3 day protocol. For best results, start three days before your race. A single elevated-carb day the day before is better than nothing, but you will leave performance on the table compared to the full protocol.
Does carb loading make you gain weight?
Yes — typically 1–3 lbs (0.5–1.5 kg) temporarily. This weight is water bound to stored glycogen, not fat. It is expected, desired, and will be metabolized during the race. Do not panic at the scale in race week.
What are the best foods for carb loading?
White rice, white pasta, white bread, bagels, bananas, and sports drinks. These are high in carbohydrates, low in fiber, and easy to digest. Avoid high-fiber foods like whole grains, legumes, and vegetables during load days.
Should I avoid fat and fiber during carb loading?
Yes. Both fat and fiber slow gastric emptying and compete for calorie space you need to hit your carbohydrate targets. High fiber intake during load days also increases the risk of GI distress on race day. Keep meals simple: plain carbohydrate sources with minimal additions.
Can you carb load for a half marathon?
Yes, though a 1-day protocol — elevated carbohydrates the day before — is sufficient for most half marathoners. A full 3-day carb load is designed for events lasting more than 2.5 hours. For a half marathon, focus on hitting 6–8 g/kg the day before and eating a solid race morning breakfast.