Carb loading is one of the best-known nutrition strategies for a marathon, and one of the most misunderstood. It doesn't mean a mountain of pasta the night before the race. This guide explains what carb loading actually is, why it works, how many grams you need per kilogram of bodyweight, what to eat and what to avoid, with a full-day example menu. For everything else you do in the days before the race, see our guide on what to eat before a half marathon or marathon.
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The last 36 to 48 hours before a race lasting more than 90 minutes.
Around 8 to 12g of carbohydrate per kilogram of bodyweight per day.
Easily digested carbs, low in fat and fibre.
What is carb loading?
Carb loading, or carbo-loading, means deliberately eating a lot more carbohydrate than usual in the days before a long race, while training much less. The goal is to fill your glycogen stores as fully as possible. Glycogen is how your body stores carbohydrate, in your muscles and liver, and it's your main fuel at race pace.
Why does carb loading work?
Your glycogen stores are limited. At a hard pace they run low after roughly 90 minutes, and that's when your pace starts to drop: in a marathon, that's the infamous wall. Carb loading lets you build those stores well beyond what your normal diet provides. Research shows the benefit is clearest for efforts longer than 90 minutes, where it helps you hold your pace for longer.
Training less while you load matters as much as what you eat. Your muscles use very little glycogen, so what you eat goes into storage. The old idea of first draining your stores with several low-carb days, known as the Saltin method, is no longer needed. Current guidelines show that 36 to 48 hours of high carbs plus rest does the job.
Seeing the scales go up by 1 to 2kg is normal. Your body stores roughly 3g of water with every gram of glycogen. That's not fat, it's fuel and fluid you'll use during the race.
Carb loading before a half marathon or marathon: which distances need it?
- Marathon, long triathlon, long ride: yes, load for 36 to 48 hours.
- Half marathon: if you'll be running for more than about 90 minutes, which is true for most recreational runners, a shorter 24 to 36 hour carb load helps.
- 5K and 10K: not needed. A normal carb-rich dinner the night before and a good breakfast are enough.
How many carbs per kg when carb loading?
The carb loading guideline is 8 to 12g of carbohydrate per kilogram of bodyweight per day, over the last 36 to 48 hours. For most recreational runners, 8 to 10g per kilogram is a realistic and effective target. For example: if you weigh 60kg and aim for 10g per kilogram, that's 10 x 60 = 600g of carbs a day.
| Bodyweight | 8g/kg | 10g/kg | 12g/kg |
|---|---|---|---|
| 60kg | 480g | 600g | 720g |
| 70kg | 560g | 700g | 840g |
| 80kg | 640g | 800g | 960g |
| 90kg | 720g | 900g | 1080g |
For comparison, many runners eat around 4 to 5g per kilogram on a normal day, so carb loading means roughly doubling it. On race morning, add a breakfast with 1 to 4g of carbohydrate per kilogram, two to three hours before the start.
How to carb load, step by step
- Taper your training. In the final days, only do short, easy runs.
- Raise your carbs 36 to 48 hours before the start, or 24 to 36 hours for a half marathon.
- Spread it through the day. Eat something carb-rich every two to three hours rather than three huge meals.
- Cut back on fat and fibre to make room for carbs and keep your gut settled.
- Drink some of your carbs. Juice, squash or a sports drink help you hit your target without feeling stuffed.
- Test it first, before a long run or a tune-up race.
Carb loading foods: what to eat and what to avoid
Good carb sources for loading
- White rice, pasta and couscous. Our pasta is an easy base.
- White bread, bagels, crumpets and English muffins.
- Peeled potatoes, mash or gnocchi.
- Oats or Ultra Fine Oats for porridge or shakes.
- Bananas, fruit juice, apple purée and a little dried fruit.
- Honey, jam, syrup, rice cakes and malt loaf.
- Sports drink, like our Isotonic Sports Drink with 32g of carbohydrate per serving.
What to limit
- High-fibre foods: wholegrains, beans and lentils, bran and big portions of raw veg or cabbage.
- Fatty and fried food, creamy sauces and lots of cheese. Fat fills you up without topping up your glycogen.
- Spicy food and alcohol.
- Big portions of protein that fill your stomach and leave no room for carbs.
- Anything you've never eaten before. Race weekend isn't the time for a new restaurant or new sports nutrition.
Best carb loading meals: an example day
This menu provides around 650g of carbohydrate, roughly 10g per kilogram for a 65kg runner. Adjust the portions if you weigh more or less. Amounts are rounded.
| Meal | Example | Carbs |
|---|---|---|
| Breakfast | Porridge with 100g Ultra Fine Oats, a banana and 2 tbsp honey, plus a glass of orange juice | approx. 145g |
| Snack | Bagel with jam | approx. 65g |
| Lunch | 125g (dry weight) white rice with chicken and a mild sauce, plus a glass of juice | approx. 125g |
| Afternoon | 2 servings of Isotonic Sports Drink and 4 rice cakes with jam | approx. 105g |
| Dinner | 150g (dry weight) pasta with tomato sauce and lean mince, 2 slices of white bread | approx. 145g |
| Evening | A bowl of rice pudding and a banana | approx. 65g |
Protein still has a place, just in normal portions, like the chicken at lunch and the mince at dinner. After the race, protein becomes a priority again: protein contributes to a growth in and maintenance of muscle mass. How to recover after the finish is covered in our guide on what to eat before a half marathon or marathon.
Common carb loading mistakes
- Only loading the night before. One huge plate of pasta won't fill your stores and mostly leaves you feeling heavy. Spread it over one to two days.
- Eating more instead of eating differently. It's about the share of carbs, not extra fat and protein on top.
- Too much fibre. Wholegrains are normally a great choice, but in these days they can cause gut trouble.
- Training through it. Keep training hard and you'll burn what you store.
- Panicking about the scales. A kilo or two extra is exactly the point.
On race day itself, you top up on the move with fast carbs, like an Energy Gel or sports drink. How many gels you need per hour is covered in our energy gel guide.
FAQ: carb loading
When should I start carb loading for a marathon?
Start 36 to 48 hours before the race, so usually two days out. For a half marathon, 24 to 36 hours is enough.
How many carbs per kilogram should I eat when carb loading?
The guideline is 8 to 12g per kilogram per day. If you weigh 60kg and aim for 10g per kilogram, that's 600g of carbohydrate a day.
Do I need to carb load before a half marathon?
If you'll be running for more than about 90 minutes, it helps, and a shorter 24 to 36 hour load is enough. If you're quicker than that, a carb-rich dinner the night before will do.
What are the best carb loading foods?
Easily digested carbs like white rice, pasta, white bread, bagels, peeled potatoes, oats, bananas, juice and sports drink, with little fat and fibre.
Will carb loading make me gain weight?
Usually 1 to 2kg, from the water your body stores alongside glycogen. It's fuel for the race, not fat.
Is carb loading worth it for cycling?
For long rides or races over 90 minutes, yes. The principle is the same as for running, although on the bike it's often easier to eat and drink on the move.
Finally
Carb loading isn't magic, but it's one of the simplest ways to start a long race with a full tank. Rest, eat smart and test it first, and you'll have energy right to the final mile.
Sources
- Burke LM, Hawley JA, Wong SH, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29 (Suppl 1), S17-S27.
- Thomas DT, Erdman KA, Burke LM (2016). American College of Sports Medicine Joint Position Statement: Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise, 48(3), 543-568.
- Bussau VA et al. (2002). Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology, 87, 290-295.
- Bergström J et al. (1967). Diet, muscle glycogen and physical performance. Acta Physiologica Scandinavica, 71, 140-150.
- NHS: Eat well
- British Nutrition Foundation
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