Marathon Fuel and Hydration
Carbohydrate, fluid and electrolyte basics for training and race day.
- Written by
- YourMarathonPace
- Published
- 9 November 2026
This guide is general information, not medical or coaching advice. It has not yet been reviewed by a qualified coach. Speak to a doctor before starting a new training programme, especially if you have a health condition or injury.
Carbohydrate loading
For races longer than about 90 minutes, sports-nutrition guidelines suggest eating more carbohydrate in the 36–48 hours beforehand. That's roughly 10–12 g per kg of body weight per day. Choose familiar, easy-to-digest foods and cut back on fibre if it upsets your stomach.
Fuelling during the race
Guidelines suggest about 30–60 g of carbohydrate per hour for long endurance events, and up to about 90 g for events lasting more than 2.5 hours, using mixed sugar types such as glucose and fructose. Most runners use gels, chews or sports drinks, starting early and taking small amounts regularly.
Fluids and electrolytes
Drink to avoid both large fluid losses and drinking too much. Drinking far more than you sweat can cause hyponatraemia (low blood sodium), which is dangerous. Drinking to thirst, or to a plan based on your sweat rate in training, is safer than drinking at every station. If you get a severe headache, confusion or vomiting, get medical help.
Practising in training
Use your long runs to practise exactly what you'll eat and drink on race day, including the race's own drink brand if you plan to use it. Your gut can get used to taking in fuel while running. Race day isn't the time to try something new. If you have diabetes or another medical condition, check your plan with a doctor or dietitian.
Sources
- Carbohydrates for training and competition — Journal of Sports Sciences (Burke et al., 2011)
- A step towards personalized sports nutrition: carbohydrate intake during exercise — Sports Medicine (Jeukendrup, 2014)
- Exercise and fluid replacement (position stand) — American College of Sports Medicine (2007)
- Nutrition and athletic performance (joint position statement) — American College of Sports Medicine (2016)
This guide is general information, not medical or coaching advice. It has not yet been reviewed by a qualified coach. Speak to a doctor before starting a new training programme, especially if you have a health condition or injury.