How to carb-load for a marathon
Eat more than 8 g of carbohydrate per kilo of body weight a day for the last 36–48 hours before the race. Strong evidence from 63 trials shows this raises the carbohydrate stored in your muscles (grade A). The link from loading to a faster marathon rests on older observational data (grade C), so the overall grade is Mixed.
What to do
- On the two days before the race, aim for 8–10 g of carbohydrate per kilo of body weight a day. For a 70 kg runner, that is 560–700 g a day.
- Choose low-fibre, energy-dense foods so you can reach the target without feeling stuffed.
- Women and smaller runners: raise total calories, not just the share of carbohydrate.
- Expect the scale to show a higher weight on race morning. Don't cut back because of it.
- Eat a carbohydrate-rich breakfast about 3 hours before the start, around 2 g per kilo, and no solid food in the last 30 minutes.
Why load at all?
Your muscles store carbohydrate as glycogen, a ready-to-use fuel for running. Carb-loading means eating extra carbohydrate in the last days before a race to top those stores up. It sits alongside the other two fuel jobs on race day: breakfast, and taking carbohydrate during the race (see carbs per hour and hitting the wall).
What the research shows
Loading raises glycogen. A 2026 meta-analysis of 63 trials found that intakes above 6.5 g of carbohydrate per kilo of body weight a day raised muscle glycogen. It recommends more than 8 g per kilo a day for 36–48 hours before the event (Jones and colleagues, 2026). This part of the evidence is strong.
Most athletes fall short. In a survey of endurance athletes, only 10% reached the traditional loading target of 10–12 g per kilo (Sampson and colleagues, 2024). The newer meta-analysis suggests a slightly lower target can still work, which may be easier to reach, though that is our reading rather than a tested comparison.
Women need more total energy. In one study, women raised their glycogen only when they ate more total calories, not just a larger share of carbohydrate (Tarnopolsky and colleagues, 2001).
The link to marathon time is weaker. The evidence that loading leads to a faster marathon comes from older observational data (Atkinson and colleagues, 2011). That is not a trial. Hence the Mixed grade: strong for “fills the tank”, weaker for “makes you faster”.
A practical loading plan
The plan below follows the evidence on amounts and timing. The exact day split is a common convention.
- Days −2 and −1 (the two days before the race): 8–10 g of carbohydrate per kilo a day. Don’t go below about 7 g per kilo. Some runners go up to 10–12 g per kilo, but it is optional.
- Choose low-fibre, energy-dense foods. They make the numbers easier to hit without feeling overfull.
- Raise total energy, especially if you are a woman or a smaller runner. Don’t just replace other foods with carbohydrate.
- Expect your weight to rise. The scale will go up over the loading days. That is expected, so don’t react by eating less.
Loading fits naturally into the last days of a taper, when training is light.
Race morning
Eat breakfast. Eating before prolonged exercise improves performance (Aird and colleagues, 2018). A common target is about 2 g of carbohydrate per kilo, about 3 hours before the start. The workable range is 1–4 g per kilo, eaten 1–4 hours before. Keep it low in fat and fibre.
Stop solid food about 30 minutes before the start. Eating solid food in the last half hour increased bloating and the urge to go to the toilet (Zhao and colleagues, 2025). After that, rely on the planned pre-start gel or drink from your race fuelling plan.
Rehearse your race breakfast before at least two long runs so you know what your stomach accepts. That is coaching convention, not a tested rule.
Worked example: a 70 kg runner
This is an example only. Multiply your own weight by the same numbers.
| What | Per kilo | For 70 kg |
|---|---|---|
| Loading, days −2 and −1 | 8–10 g/kg a day | 560–700 g a day |
| Loading, minimum | 7 g/kg a day | 490 g a day |
| Loading, optional high end | 10–12 g/kg a day | 700–840 g a day |
| Race breakfast, about 3 h before | 2 g/kg | 140 g |
| Race breakfast, full range | 1–4 g/kg | 70–280 g |
560–700 g a day is a lot of food. Spread it over three meals and two or three snacks, and lean on low-fibre foods. That is our suggestion for making the target realistic.
What we don’t know
- No modern trial links a specific loading amount to marathon time. The time benefit rests on older observational data.
- The day-by-day split is convention. The research supports the amount and the 36–48 hour window, not a particular menu.
- Women are under-studied. The finding that women need extra total energy comes mainly from one older study.
- How slower runners benefit compared with faster runners has not been tested.
Sources
- Jones et al. (2026). Carbohydrate loading and muscle glycogen: meta-analysis of 63 trials.
- Sampson et al. (2024). Carbohydrate intake practices of endurance athletes.
- Tarnopolsky et al. (2001). Carbohydrate loading and energy intake in women.
- Atkinson et al. (2011). Carbohydrate loading and marathon performance.
- Aird et al. (2018). Pre-exercise feeding and endurance performance.
- Zhao et al. (2025). Timing of solid food before exercise and gut symptoms.
Last reviewed 13 November 2026.