Glycogen loading before a marathon or long ride: a practical 48-hour plan

Who benefits from carbohydrate loading?

It is most relevant to events with continuous or repeated work lasting roughly 90 minutes or more: a marathon, long trail race, gran fondo, triathlon or multi-hour ski event. A short race or easy training session rarely needs a special loading phase.

If your usual diet is low in carbohydrate, a sudden large increase can cause fullness. A gradual rise and easy-to-digest sources are more useful than chasing a theoretical maximum.

How much: a practical rather than absolute target

Classic studies used high intakes, often around 7–10 g carbohydrate per kilogram of body mass per day. In a small 2026 study, 10 g/kg/day for 48 hours produced the largest glycogen rise compared with 6 and 8 g/kg, but only 11 trained athletes took part.

For a 70 kg athlete, 7 g/kg is 490 g carbohydrate—far more than most people imagine. You do not need to force the maximum laboratory dose. If it has not been rehearsed, choose a lower tolerable target and spread it over frequent meals.

A 48-hour example

Two days before

Use porridge, bread and banana at breakfast; rice or potatoes with a modest lean-protein serving at lunch; yoghurt, bread, fruit or a sports bar as snacks; and pasta or rice at dinner. Drink regularly without forcing fluid.

The day before

Keep carbohydrate in each meal but reduce very fatty, spicy and unfamiliar foods. For a sensitive gut, white rice, white bread, peeled potatoes, banana, drinks and small snacks may be easier.

Race morning

Eat a rehearsed breakfast 2–4 hours before the start. In the final hour, use only a small familiar top-up if it is already part of your training plan.

Common mistakes

• One huge dinner: loading requires time and several meals.
• More fat with more carbohydrate: total energy becomes excessive and digestion slower.
• Too much fibre: healthy every day is not always ideal immediately before a race for a sensitive gut.
• New products: race week is not a tasting session.
• Panicking about body mass: glycogen binds water, so a small temporary increase is expected.

A portion check without obsessive weighing

If you do not want to weigh every gram, start with a carbohydrate source in every main meal plus 2–3 snacks, while reducing very fatty extras. On one rehearsal weekend, estimate the total so you learn whether your idea of “high carbohydrate” actually approaches the target.

Liquid carbohydrate and sports foods can help when normal food volume becomes too large, but they must be familiar. People with diabetes, reactive hypoglycaemia or gastrointestinal disease should not build a high-carbohydrate protocol without medical or dietetic advice.

Related guides

• Energy gels and isotonic drinks during exercise: when and how to combine them
• Gut training: how to train your digestive system for long events
• Isotonic drinks and hydration: an electrolyte guide for marathon runners