With Boston on April 20 and London on April 26, tens of thousands of marathon runners are entering their final weeks of preparation. Training is largely done — the hay is in the barn, as coaches like to say — but one critical variable remains within your control: race day fuelling. Getting nutrition right can be the difference between a personal best and a painful final 10 kilometres, and the science on what works has never been clearer.
The headline number is carbohydrate intake. At marathon intensity, your body's glycogen stores can sustain roughly 90 to 120 minutes of running before they begin to decline, which is why in-race fuelling is not optional for anyone targeting a finish time beyond that window. Current research recommends consuming 60 to 90 grams of carbohydrate per hour during the race, delivered through a combination of gels, chews, or sports drinks depending on personal preference and gut tolerance. Studies have consistently shown that runners hitting the upper end of that range have higher odds of achieving their goal times, including sub-3:00 finishes.
Hydration is the second pillar. The general guideline is 400 to 800 millilitres of fluid per hour, adjusted for your individual sweat rate, the ambient temperature, and your pace. The key is to drink early and consistently rather than waiting until you feel thirsty, which is a lagging indicator of dehydration. Sodium replacement matters too, particularly for salty sweaters or races in warm conditions — a practical target is 300 to 600 milligrams of sodium per hour, which most electrolyte drinks and salt tablets will cover.
The most important rule is also the simplest: practice everything in training. Every gel brand, every fluid quantity, every timing strategy should be tested during long runs before race day. Your gut is a trainable organ, and runners who progressively build to their race-day carbohydrate target across training blocks report far fewer gastrointestinal issues on the day itself. Do not try anything new on race morning, no matter how promising it sounds. The marathon is not the place for experiments.