Fueling & Hydration for Runners

Carbohydrate is the engine fuel

Your body stores only a limited amount of carbohydrate, and running off that store is what causes the marathon "wall." Taking carbs in during long efforts spares those stores and keeps your blood sugar up. The old guidance — about 60 g/hour from a single sugar, up to ~90 g/hour from a glucose-fructose mix for long events — still holds as a foundation¹.

But the ceiling has risen for trained athletes. In elite marathoners, taking 120 g/hour of glucose-fructose produced more carbohydrate burned and a *lower* oxygen cost of running than 60 or 90 g/hour². The real world has followed: the men's marathon world record (Sabastian Sawe's 1:59:30 at London 2026) was fueled at well over 100 g/hour³, and the Tour de France peloton now routinely rides at ~120 g/hour, up from far less a decade ago⁴. Higher intakes work — but only if your gut can handle them, which is a trainable skill, not a given.

Train your gut

The gut adapts to what you repeatedly ask of it. Practicing high-carb intake during training — "gut training" — measurably reduces stomach distress and improves how much fuel you absorb during long efforts⁵. The flip side: pushing very high intakes you *haven't* rehearsed tends to backfire with GI symptoms⁶. So rehearse race-day fueling in your long runs, with the exact products you'll use, and build the rate up gradually.

Carb-load before long races

For races around two hours or longer, topping off muscle glycogen beforehand pays off. You don't need the old week-long depletion ritual — a single day of very high carbohydrate intake while resting can nearly max out muscle glycogen⁷. In practice, that means leaning your last day or two before a long race heavily toward carbs (and easing training volume anyway during the taper).

Hydration and electrolytes

Drink to thirst rather than on a rigid schedule — both dehydration and over-drinking hurt performance and (in the case of over-drinking) can be dangerous. In longer or hotter efforts, include sodium, since you lose it in sweat and it helps you hold onto fluid⁸. Heat and altitude both raise your fluid needs, and a sports drink conveniently delivers carbs, fluid, and sodium together.

Don't forget daily fueling

In-run fueling sits on top of eating enough day to day. Endurance training raises your carbohydrate and overall energy needs, and chronically under-fueling undercuts adaptation, recovery, and health⁸. Match your intake to your training load — more carbohydrate around your hardest and longest days.

How much, by effort

A practical starting framework — then personalize it by rehearsing in training:

• Under ~60–75 minutes: usually no fueling needed; water to thirst.
• 1–2.5 hours (incl. the marathon): roughly 60–90 g carbs/hour, built up through gut training; well-trained athletes can push higher.
• Ultras (many hours): about 30–90 g carbs/hour, often mixing gels/drink with real food, plus deliberate sodium and fluid⁹.
• Always: practice it first. The number that works is the one your gut has rehearsed, not the highest one on a chart.