Carbohydrate loading
Evidence: strong
Effective for events over about 90 minutes: roughly 7-12 g/kg/day (around 10 is typical) for 36-48 hours. No harsh depletion phase needed, and no benefit for shorter events.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Carbohydrate loading raises muscle glycogen stores before a long race, delaying the point at which depletion forces a slowdown. The classic 1967 protocol used a depletion phase followed by three days of high carbohydrate intake (Burke et al. 2011). Trained athletes no longer need the unpleasant depletion phase: 24 to 48 hours of high intake is enough, because their muscles supercompensate readily (Burke et al. 2011).
The consensus target is roughly 7 to 12 g of carbohydrate per kg of body mass per day for 36 to 48 hours, for events lasting more than about 90 minutes, with around 10 g/kg the commonly cited figure (Burke et al. 2011). A 2025 meta-analysis suggests the lower end, more than about 8 g/kg/day, may be enough (Solem et al. 2025). Loading roughly doubles muscle glycogen, though running supercompensates less than cycling and carries more gastrointestinal burden, so the glucose-fructose mix and gut training matter more for runners (Solem et al. 2025).
The benefit is specific to longer events. Higher starting glycogen extends time to exhaustion, and loading improves performance for races of about 30 km and longer, mainly by preserving back-half pace rather than raising top speed (Burke et al. 2011). It is the mechanism behind delaying “the wall”, the glycogen depletion that typically occurs around 32 km. There is no benefit for events under 90 minutes, and pushing glycogen to extremes brings diminishing returns because higher stores are also burned faster.
A worked example
Loading for a 70 kg runner
Around 10 g/kg/day is roughly 700 g of carbohydrate per day for the last 36 to 48 hours before a marathon, far more than most people eat without trying. Pushing to the top of the range adds gastrointestinal load for little extra glycogen, so most runners are better aiming near 8 to 10 g/kg than chasing the ceiling. In practice that means making carbohydrate the centre of every meal and snack (rice, pasta, bread, potatoes, fruit, juice, sports drink) while cutting back on fat, fibre and protein to make room and avoid gut bulk. Training is tapered at the same time, so the extra carbohydrate is stored rather than burned. Expect a kilogram or two of water weight, since glycogen is stored with water; that is the loading working, not a problem.