Pre-race and race-morning fuelling
Evidence: strong
Eat 1–4 g/kg of carbohydrate 1–4 hours before the start, scaling the amount down the closer you are to it. Keep it low-fibre, low-fat and familiar. Rehearse the whole routine in training.
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 fills the tank in the days before a long race. The last few hours are a separate job: top up without upsetting the gut. Fuelling during the race itself is a third, separate decision.
The pre-event meal
The consensus pre-event meal supplies 1 to 4 g of carbohydrate per kg of body mass, eaten 1 to 4 hours before the start (Thomas et al. 2016; Burke et al. 2011). The amount scales with the time available: closer to 4 g/kg with a full four hours to digest, down towards 1 g/kg when the start is an hour away. For a 70 kg runner that is roughly 70 to 280 g of carbohydrate.
The point of the meal is to top up liver glycogen, which drains overnight even after a loading week, since the liver feeds blood glucose to the brain and body through the fast (Burke et al. 2011). Muscle glycogen, by contrast, is largely set by the loading already done and changes little over breakfast. So race morning is about the liver, not the muscles.
What you eat matters as much as how much. Choose low-fat, low-fibre, familiar foods, because fat and fibre slow gastric emptying and add gut bulk that can cause cramping, urgency or a stitch once you start running (Thomas et al. 2016). Porridge, white toast with jam or honey, a banana, a bagel, rice or a sports drink are typical choices. Race morning is the wrong time to try a new food.
The reactive-hypoglycaemia worry
Carbohydrate taken in the 30 to 60 minutes before the start raises insulin, and in some people that, combined with the start of exercise, drops blood glucose enough to cause a brief wobble early on, sometimes called rebound or reactive hypoglycaemia (Burke et al. 2011). This is real but minor and individual: most runners are unaffected, the dip is transient, and exercise itself suppresses insulin once you are moving, so it tends to resolve within the first 10 to 20 minutes of warming up (Thomas et al. 2016). It is a reason to know your own response, not a reason to skip pre-race carbohydrate. If you are one of the sensitive few, the simple fixes are to take the carbohydrate earlier, take it within a few minutes of the gun, or warm up before the last feed.
Hydration and caffeine
Start well hydrated rather than over-drinking on the morning. Drink to thirst through the run-up and have a measured amount with the meal; do not force fluid, since drinking far beyond thirst risks hyponatraemia and confers no benefit (see hydration and electrolytes). Pale-straw urine is a reasonable gauge.
If you use caffeine, the standard timing is about 60 minutes before the start, at 3 to 6 mg/kg, which is when blood levels peak from a normal dose (Guest et al. 2021). Caffeinated gum or gels absorb faster and can be taken closer to the gun or saved for late in a long race.
Rehearse it
Race-morning fuelling is a skill, not a fixed prescription, because tolerance for volume, timing, specific foods and caffeine varies widely between people. Rehearse the exact meal, timing and drinks before hard training sessions and tune-up races, so that nothing on the day is untested (Thomas et al. 2016). This is the same logic as gut training for in-race fuelling: practise it until it is boring.
A worked race morning
For a 70 kg runner with a marathon at 9 am, eat around 1.5 g/kg, roughly 100 g of carbohydrate, at about 6.30 am: porridge with honey and a banana, plus a sports drink, all things eaten before long runs. Sip water to thirst afterwards. Take roughly 300 mg of caffeine at about 8 am. Then move straight onto the in-race plan once running.