Carb loading: real science for marathons. A pasta excuse for everyone else.
Filling your muscles with stored carbohydrate before a long race can keep you going for longer. That only matters if the race is longer than about 90 minutes. Here's how it works, and how athletes actually do it.
The short version
- What it is
- Eating a lot of carbohydrate, about 10–12 g per kg of body weight a day, for one to two days before a long endurance event, while training less.
- Good for
- Marathons, long triathlons, long cycling and ski races: anything over about 90 minutes.
- Bad at
- Short races, gym sessions, team sports, and everyday life.
- Evidence
- Strong, for long endurance events. No benefit for short ones.
- Our take
- Real sports nutrition. Not a lifestyle. Our plan isn't built for race week.
What carb loading actually is
Your muscles store carbohydrate as glycogen, a ready-to-burn fuel. In a long, hard effort, those stores run low, and when they do, you slow down dramatically. Runners call it hitting the wall. Cyclists call it bonking. Carb loading means filling the tanks above their normal level before the race.
The original 1960s method was brutal: a hard exhausting workout, three days of almost no carbs, then three days of loads of carbs. Later research showed you don't need the miserable depletion phase. A study in trained runners found a moderate approach raised glycogen almost as high as the classic method.5 Today's sports guidelines recommend 10–12 g of carbohydrate per kg of body weight a day for 36–48 hours before events longer than 90 minutes.3
How it works in your body
Muscle glycogen fuels hard endurance exercise. In efforts under an hour or so, you rarely run out, so extra stores don't help. In events lasting longer than about 90 minutes, running low on glycogen coincides with exhaustion, and higher starting stores push that moment back.1
Your muscles fill fast if you rest and eat a lot of carbs. In a study of trained athletes who stayed inactive and ate 10 g of carbohydrate per kg of body weight, glycogen reached its maximum after just one day and stayed there.4 That's the "one-day load" many athletes now use.
Glycogen is stored with water. So when you load, you'll weigh a kilo or two more on race morning.6 That's fuel, not fat. Don't panic.
What you eat, what you don't
Eat (in the 1–2 days before)
- White rice, pasta, potatoes without skin
- White bread, bagels, rice cakes
- Bananas, fruit juice, honey
- Low-fibre cereals, oats in moderation
- Sports drinks to top up
- Familiar foods you've tested in training
Forget it (until after the race)
- Huge bowls of beans and lentils (gas, cramps)
- Big salads and lots of raw vegetables
- Fatty, creamy or fried meals that fill you up without carbs
- Spicy food you're not used to
- Anything new on race week
- Alcohol
Yes, this is the one article where we recommend white bread and juice. For one or two days, for a specific job. Low fibre is the point: it gets carbs in without upsetting your gut on race day.
A loading day, in real food
For a 70 kg runner, 10 g per kg is about 700 g of carbohydrate in a day.3 That's a lot more than "a big plate of pasta the night before". The trick is to spread it out and keep fat and fibre low, so you're not stuffed:
- Breakfast: a bagel or white toast with honey or jam, a banana, a glass of juice.
- Mid-morning: rice cakes with jam, or a sports drink.
- Lunch: a large plate of white rice or pasta with a light tomato sauce and a little chicken or fish.
- Afternoon: a low-fibre cereal with milk, or rice pudding.
- Dinner: another big portion of rice, noodles or potatoes without skin, simple protein, few vegetables.
Drinks are your friend here: juice and sports drinks add carbs without filling your stomach. And do a dress rehearsal before a long training run, not for the first time before the race.
In Singapore: plain white rice, rice noodles, kway teow soup, chee cheong fun, white bread kaya toast (go easy on the butter) and bananas all load well. Skip the rich curries, deep-fried sides, and chilli you don't normally eat. In the heat, sports drinks pull double duty for fluid and salt.
In Austria, Germany and Switzerland: white rolls (Semmeln, Brötchen), plain pasta, potatoes without skin, rice pudding (Milchreis) and Germknödel without the butter flood all work. The classic trap is the "pasta party" with creamy sauces and the pre-race Weissbier.
Alcohol and carb loading
OK, now and then
- After the race: one beer or glass of wine with a real meal
- Alcohol-free beer the night before (carbs, no alcohol)
Not on race week
- "Carb loading" with beer
- Drinking the night before an event
- Celebrating before you've rehydrated
50 Club: one alcohol-free beer with the pasta, a real one after the finish line, with food.
Alcohol dehydrates you, disturbs sleep and adds nothing useful to your glycogen stores. All the details are in our alcohol guide.
What it's good for, with proof
Long races, later fatigue
A review of carb loading research found that higher starting glycogen postponed fatigue by about 20% in endurance exercise lasting more than 90 minutes, and could improve performance over a set distance by 2–3%.1 In a marathon, 2–3% can be several minutes.
It doesn't take a week
The one-day protocol filled muscle glycogen to maximum in trained athletes, as long as they rested.4 Less time eating mountains of pasta, same result.
Fuel during the race matters too
Sports scientists recommend 30–60 g of carbohydrate per hour during longer events, and up to 90 g per hour for events over 2.5 hours.2 Loading fills the tank. Fuelling during the race keeps it from running dry.
The uncomfortable truth
"Carb load before any race." For short efforts, there's little or no benefit.1 In one study of trained runners, carb loading made no difference to performance in a 21 km run.5 For a 5K, a gym session or a football match, normal eating does the job.
"I run, so I need to eat like a marathoner every day." Training needs depend on how much you actually train. An hour of jogging three times a week doesn't call for 10 g per kg. That's how runners gain weight while training for a marathon.
The risks
- Stomach trouble. Too much fibre, fat or new food before a race means bloating and toilet stops. Practise your loading before a long training run.
- Feeling heavy. The extra water weight can feel sluggish. It's normal and goes once you start burning the fuel.
- Diabetes. Huge carb loads with insulin or other diabetes drugs need a plan with your diabetes team.
- Doing it for nothing. Loading for short events is just overeating.
Allergies: watch the staples
| Staple | Allergen (EU list of 14)7 | Swap |
|---|---|---|
| Pasta, white bread, bagels | Cereals containing gluten, sometimes eggs | White rice, potatoes, rice noodles |
| Pancakes, waffles | Cereals containing gluten, eggs, milk | Rice porridge with honey |
| Rice pudding, milky cereals | Milk | Rice pudding with oat or soy drink |
| Energy bars and gels | Often nuts, peanuts, milk, soy | Check labels, test in training |
| Dried fruit | Often sulphur dioxide and sulphites | Bananas, sulphite-free dried fruit |
Don't do carb loading on your own if you…
- have type 1 or type 2 diabetes
- have irritable bowel syndrome or another gut condition
- have ever had an eating disorder
- aren't doing an event longer than about 90 minutes
Healthen me asks about all of these and gives you a different plan if any apply.
How we use carb loading in your plan
We don't. Carb loading is information only: our plans are for everyday life, not race week, and our everyday rules (low-carb, carbs last, a fasting window) are the opposite of a load.
If you have a marathon or long event coming up, pause the plan for those two days and follow your coach or a sports dietitian. If you train a lot and want a low-carb approach with a carb top-up around sessions, read about targeted keto.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
Sources
- Hawley JA et al. Carbohydrate-loading and exercise performance: an update. Sports Medicine 1997;24(2):73–81. doi.org/10.2165/00007256-199724020-00001
- Burke LM et al. Carbohydrates for training and competition. Journal of Sports Sciences 2011;29 Suppl 1:S17–S27. doi.org/10.1080/02640414.2011.585473
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine joint position statement: nutrition and athletic performance. Medicine & Science in Sports & Exercise 2016;48(3):543–568. doi.org/10.1249/MSS.0000000000000852
- Bussau VA et al. Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology 2002;87(3):290–295. doi.org/10.1007/s00421-002-0621-5
- Sherman WM et al. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine 1981;2(2):114–118. doi.org/10.1055/s-2008-1034594
- Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition 1992;56(1 Suppl):292S–293S. doi.org/10.1093/ajcn/56.1.292S
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj