60–90 g of carbs per hour, enough sodium, and the right fluid intake over 4.5–7 hours — how to fuel your half-distance race safely and well.
"How much do I really need to eat and drink during the race?" At half distance, the answer is far more concrete than for shorter races: from about 2.5 hours of exercise onward — and half distance takes most people 4.5 to 7 hours — sports scientists recommend around 90 g of carbohydrates per hour from multiple sugar sources. A single carb source like pure glucose can only be processed by your gut at about 60 g per hour. Mix glucose and fructose, though, and your body uses two separate absorption pathways at once — like two checkout lanes instead of one — and the uptake rate rises noticeably.
In practice that usually means 60–90 g per hour for a half distance, depending on how trained your gut is and your race pace. Skip practicing this in training and you risk gut trouble — the most common cause of a run falling apart.
Just as important as carbs: sodium. For every liter of sweat you lose between 400 and 1,500 mg of sodium — over a multi-hour race in the heat, that adds up fast. Drink only water during long exertion and you risk dilutional hyponatremia — diluted sodium in the blood, a genuine medical emergency. In a well-known marathon study, 13% of finishers had low sodium levels after the race, and 0.6% were critically low. That's not a theoretical risk — it's real and avoidable.
Start around 60 g per hour if you have little experience with race nutrition, and build toward 80–90 g with training. Practice this amount in long sessions, not for the first time on race day — your gut has to learn absorption just like your legs learn running.
Begin taking in carbs in the first 15–20 minutes on the bike, not once you feel hungry. An energy deficit you only notice after an hour is nearly impossible to make up.
Over hours of exertion you can lose between 0.5 and 2.5 liters of sweat per hour depending on conditions. As a rough guideline, aim for 400–800 ml of fluid per hour in small sips, adjusted for heat and your own sweat rate.
In extended heat, deliberately add sodium — through electrolyte tablets or sodium-containing sports drinks — plain water alone isn't enough over hours of exertion in heat. This matters especially if you sweat heavily and salty (white salt rings on your clothing are a tell).
After dismounting the bike, tolerance for solid food often drops. Switch more to gels and drinks rather than bars while running, and ease the amount back slightly if your stomach protests — adapt rather than stick rigidly to the plan.
Gut trouble is the classic half-distance issue — usually triggered by too much carb intake, untested products, or too little fluid. Reduce the amount immediately if you feel nauseous, and keep sipping fluid instead of pausing altogether.
Take symptoms like severe headache, confusion or nausea despite adequate fluid seriously — these can be signs of hyponatremia. In that case, report to course marshals or medics immediately instead of continuing.
Test your complete race fueling at least twice in a long brick session that comes as close as possible to your target time — including heat, if your race is in summer. That's the only way to find out beforehand whether a product actually works for you.
A trick experienced athletes use: mix gels with an isotonic drink on the bike instead of relying on just one — it spreads carb uptake across two pathways and is easier on your stomach.
The usual target range is 60–90 g per hour from multiple sugar sources like glucose and fructose. Start conservatively and increase the amount as your gut gets more trained.
A rough guideline is 400–800 ml per hour, adjusted for temperature and your individual sweat rate — hours of exertion can mean losing between 0.5 and 2.5 liters of sweat per hour. Better to sip regularly in small amounts than drink large amounts rarely.
Because you lose 400–1,500 mg of sodium per liter of sweat. If you only replace fluid with water during long, heavy exertion, blood sodium can become diluted — hyponatremia, which occurred in around 13% of endurance athletes in one study and turned critical in 0.6%.
Immediately reduce your carb intake and keep sipping fluid instead of pausing entirely. Switch from solid bars to more liquid gels if needed — they're usually easier to digest under exertion.
Half-Distance Triathlon: The Half Marathon After 90 km on the Bike