Carb loading calculator

How many carbs should you eat to carb load?

Carb loading fills your muscles with stored carbohydrate (glycogen) so it lasts longer in a long race. The joint position statement from the American College of Sports Medicine and dietitian bodies advises 10–12 g of carbohydrate per kg of bodyweight a day for the 36–48 hours before events longer than 90 minutes (Thomas et al., 2016). For a 70 kg runner, that is 700–840 g a day.

For races of 90 minutes or less, such as most 10k races, a full load is not needed. Normal fuelling of 7–12 g per kg in the 24 hours before is enough.

Is one day of carb loading enough?

Often, yes. Trained athletes who ate 10 g per kg for one day while resting reached high glycogen levels (Bussau et al., 2002). Two days gives more room for a normal appetite and for a day that does not go to plan.

What to eat when carb loading before a marathon

• White rice, pasta, bread, bagels, potatoes without skins, and breakfast cereals.
• Fruit juice, sports drinks, honey, jam and low-fibre fruit such as bananas.
• Smaller amounts of fat and fibre, so the volume of food stays manageable and your stomach stays settled.
• Six or more meals and snacks, instead of one huge pasta dinner the night before.

Read the full plan, with a sample day, in how to carb load for a marathon.

What to eat on race morning

The same statement advises 1–4 g of carbohydrate per kg eaten 1–4 hours before the start. Eat the smaller amount if you eat closer to the start. Use foods you have tried before long training runs (Burke et al., 2011).

Why your weight goes up when you carb load

Your body stores water with glycogen, so gaining around a kilo during a carb load is normal. It is fuel, not fat.

Scientific sources

1. Thomas D. T., Erdman K. A. & Burke L. M. (2016). Nutrition and athletic performance: joint position statement. Medicine & Science in Sports & Exercise, 48(3), 543–568.
2. Burke L. M. et al. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(Suppl 1), S17–S27.
3. Bussau V. A. et al. (2002). Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology, 87(3), 290–295.
4. Sherman W. M. et al. (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine, 2(2), 114–118.
5. Fairchild T. J. et al. (2002). Rapid carbohydrate loading after a short bout of near maximal-intensity exercise. Medicine & Science in Sports & Exercise, 34(6), 980–986.

More endurance tools and guides: Sports nutrition, including the race fuelling and hydration calculator.