Marathon carb load

Carb loading tops up the fuel in your muscles before a long race. It means eating much more carbohydrate than usual for a short time. Here is your number.

Your details

Carbs over the last 36 hours before the race

1,048 to 1,257 g

in total: 699 to 838 g a day at 10 to 12 g per kg

Your weight11 st 0 lb
Each day699 to 838 g (2,794 kcal to 3,353 kcal from carbs)
Split over 5 meals and snacks a dayabout 140 to 168 g each
What that looks like100 g dry pasta about 70 g; a bagel about 45 g; 500 ml sports drink about 30 g
36 or 48 hours?36 hours is enough for most people with a lighter taper
Race daypick your start time for when to begin and a breakfast plan

Carb loading is for races of 90 minutes or more. Eat less fibre and fat for those days so there is room, expect the scales to go up a kilo or two (it is stored water), and try it before a long training run first.

If you have diabetes, talk to your diabetes team before carb loading.

The working

10 to 12 g per kg

Sports guidance suggests 10 to 12 g of carbohydrate per kg of body weight a day for 36 to 48 hours before events lasting over 90 minutes. At 11 st (69.9 kg): 699 to 838 g a day, which is 2,800 to 3,350 kcal from carbs alone. Over 36 hours (one and a half days) that is 1,048 to 1,257 g in total; over 48 hours it is 1,397 to 1,676 g. Split into five meals and snacks a day, each one carries about 140 to 168 g.

On a plate

What 700 g looks like

Food (typical)	Carbs
Big bowl of pasta (100 g dry)	70 g
Bagel	45 g
Large banana	30 g
500 ml sports drink	30 g
Bowl of rice (75 g dry)	60 g
Two slices of white toast with jam	45 g

Many runners use lower fibre choices like white pasta and rice so there is room, and sports drinks or juice to top up.

Race morning

When to start and breakfast

Pick your start time and we count back. For a 09:00 start, a 36 hour load begins about 21:00 two days before; 48 hours begins at 09:00 two days before. Race breakfast guidance is 1 to 4 g of carbohydrate per kg, 1 to 4 hours before (Thomas, Erdman and Burke 2016). Three hours before at 69.9 kg is about 210 g at 06:00: a bagel with jam, a banana and a sports drink gets most of the way.

Tips

Make it easier

Practise before a long training run first
Cut back fat and fibre so you have space
Expect to gain a kilo or two: it is water stored with the carbs
Keep training light; this is taper time

Read with care

What this cannot tell you

Short racesFor a 5k or 10k, a normal diet is enough.
DiabetesTalk to your diabetes team before carb loading.
Eating difficultiesIf eating a lot feels stressful, a lighter approach is fine.

Questions

Common questions

How many carbs to load before a marathon?

About 10 to 12 g per kg of body weight a day for 36 to 48 hours.

When should I start carb loading?

One and a half to two days before the race.

Does carb loading make you gain weight?

You may weigh 1 to 2 kg more, mostly water stored with carbohydrate. It is fuel, not fat.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

If food feels hard

If eating, weight or food is on your mind a lot, you are not alone. Your GP can help, and Beat has a free helpline on 0808 801 0677 (England, weekdays 3pm to 8pm).